Telecommunications Handbook 

for Transportation Professionals 

The Basics of Telecommunications 

Final Report 

September, 2004 
Notice 

This document is disseminated under the sponsorship 

of the Department of Transportation in the interest of 

information exchange. 

The United States Government assumes no liability for its contents or use thereof.
Technical Report Documentation Page

1. Report No. 

FHWA-HOP-04-034 

2. Government Accession No. 3. Recipient's Catalog No. 

5. Report Date 

August, 2004 

4. Title and Subtitle 

Telecommunications Handbook for Transportation Professionals 

The Basics of Telecommunications 

6. Performing Organization Code 

7. Author(s) 

Sheldon Leader 

8. Performing Organization Report No. 

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) 

11. Contract or Grant No. 

12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered 

14. Sponsoring Agency Code 

15. Supplementary Notes 

16. Abstract 

This handbook was created to provide individuals responsible for managing and implementing Traffic 

Signal, and Freeway Management programs with an understand of the basic technologies of 

telecommunications. The handbook provides a brief look at the history of telecommunications so that 

its readers may gain an understanding of why various processes exist, and how the technologies 

evolved. The handbook is not designed to be used as a specification for telecommunication systems. 

The technologies associated with telecommunications are in a constant state of change. This handbook 

was written over a two year period between August, 2002 and June 2004. During this time, a number of 

emerging technologies began to reach maturity. The most significant of these, wireless internet access, 

and voice over IP have caused the major carriers (telephone companies) to announce the construction of 

new facilities to provide “Internet Telephony” services. 

Readers of this handbook should gain an understanding of the basic technologies underlying most 

telecommunications systems designed to transmit both voice and data information. 

17. Key Word 

Telecommunications 

18. Distribution Statement 

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 

287 

22. Price 
 

This Page Intentionally Blank
5

FOREWORD

This handbook was created to provide individuals responsible for 

managing and implementing Traffic Signal, and Freeway 

Management programs with an understanding of the basic 

technologies of telecommunications. The handbook provides a 

brief look at the history of telecommunications so that its 

readers may gain an understanding of why various processes 

exist, and how the technologies evolved. The handbook is not 

designed to be used as a specification for telecommunication 

systems. 

The technologies associated with telecommunications are in a 

constant state of change. This handbook was written over a two 

year period between August, 2002 and June 2004. During this 

time, a number of emerging technologies began to reach maturity. 

The most significant of these, wireless internet access, and voice 

over IP have caused the major carriers (telephone companies) to 

announce the construction of new facilities to provide “Internet 

Telephony” services. This construction is to start in 2004. 

Welcome to the future! 
6

ACKNOWLEDGEMENTS

The author would like to acknowledge the invaluable contributions 

of the following individuals for volunteering their time to review 

this document: 

• Karen Jehanian, KMJ Consulting, Haverford, PA 

• Jambala (Jay) Ruit, Edwards and Kelcey, Inc., West Chester, 

PA 

• Jeffery Purdy, Edwards and Kelcey, Inc., West Chester, PA 

• Richard Easley, E2 Engineering, Ashburn, VA 

• Ray Cauduro, GDI Systems, LLC, Newport, OR 

The following individuals supported the overall development of 

this document: 

• Paul Olson, FHWA, San Francisco, CA 

• Bill Jones, FHWA, Washington, D.C. 

• Lou Neudorf, Siemens ITS, New York, NY 

• Robert Reiss, Dunn Engineering Associates, Westhampton 

Beach, NY 

• Robert Gordon, Dunn Engineering Associates, Westhampton 

Beach, NY 

• Warren Tighe, Siemens ITS, Concord, CA 
7

TABLE OF CONTENTS

1. Chapter One - Telecommunication Basics....................................................................................................15 

Introduction..............................................................................................................................................................15 

Purpose .......................................................................................................................................................................15 

Relationship to National Architecture..............................................................................................................16 

Open System Interconnection Model (OSI) ...................................................................................................16 

Telecommunications History ................................................................................................................................18 

Handbook Organization.........................................................................................................................................20 

2. Chapter Two – Fundamentals of telecommunications..............................................................................23 

Introduction.............................................................................................................................................................23 

Transmission Media................................................................................................................................................25 

Media Consideration Factors .........................................................................................................................26 

Wireline Media ...................................................................................................................................................28 

Transmission Signaling Interfaces....................................................................................................................52 

Data & Voice Signaling - Basics .....................................................................................................................53 

Electro-Mechanical Signal Interfaces ........................................................................................................54 

Video Transmission............................................................................................................................................55 

Video Compression.............................................................................................................................................57 

Video CODECS....................................................................................................................................................57 

Video Compression.............................................................................................................................................58 

Streaming Video.................................................................................................................................................60 

Basic Telephone Service........................................................................................................................................61 

Multiplexing..............................................................................................................................................................63 

Time Division Multiplexing ..............................................................................................................................64 

Packet Division Multiplexing...........................................................................................................................65 

T-1 Communication Systems...........................................................................................................................66 

Transporting Digital Communications via an Analog Network...............................................................68 

High Capacity Broadband Transmission ...........................................................................................................69 

T-1/DS-1 & T-3/DS-3 ......................................................................................................................................70 

DSL .........................................................................................................................................................................71 

SONET..................................................................................................................................................................72 

ATM.......................................................................................................................................................................73 

FDM .......................................................................................................................................................................75 

WDM – CWDM & DWDM.................................................................................................................................75 

Ethernet...............................................................................................................................................................76 

Conclusions.................................................................................................................................................................81 

3. Chapter Three – Telecommunications & The National ITS Architecture ........................................83 

Introduction.............................................................................................................................................................83 

Overview – The National ITS Architecture...................................................................................................84 

Vehicle-to-Vehicle (VtV) .................................................................................................................................85 

National ITS Architecture Flows & Telecommunications...........................................................................89 

Market Packages................................................................................................................................................90 

Example Illustration .........................................................................................................................................92 

Application of Telecommunications Using the National Architecture Flows........................................94 
8

Comparison of Rural and Urban Telecommunications Requirements Using the National 

Architecture Flows ................................................................................................................................................97 

Rural Systems.....................................................................................................................................................98 

National Transportation Communication for Intelligent Transportation Systems Protocol (NTCIP)

................................................................................................................................................................................... 100 

Conclusion................................................................................................................................................................ 105 

4. Chapter Four – Developing the Telecommunication System................................................................ 106 

Introduction........................................................................................................................................................... 106 

Selecting the Consultant.................................................................................................................................... 106 

There’s no substitute for experience........................................................................................................ 107 

Different Telecommunication Design Specialties.................................................................................. 108 

Types of Telecommunications Experience................................................................................................ 108 

Knowledge of Telecommunications Systems Relationships.................................................................. 109 

Educational Qualifications .............................................................................................................................110 

Requirements Analysis .........................................................................................................................................113 

The “Gee-Whiz” Factor ..................................................................................................................................115 

Keep expectations realistic – ask questions .............................................................................................115 

A Systematic Engineering Approach to the Requirements Analysis ......................................................116 

Key points to consider:....................................................................................................................................117 

Ask The Questions...........................................................................................................................................117 

Creating The Requirements Document............................................................................................................121 

Three Basic Systems Types: ........................................................................................................................ 122 

Developing a Budget........................................................................................................................................ 122 

Conclusion................................................................................................................................................................ 123 

A few simple guidelines to follow: .............................................................................................................. 123 

5. Chapter Five – Telecommunications for Field Devices ......................................................................... 124 

Basic Communication Circuits for Field Devices.......................................................................................... 126 

Basic Circuit Types.......................................................................................................................................... 126 

The Design Process.............................................................................................................................................. 128 

Traffic Control Device Circuits................................................................................................................... 134 

Traffic Control System ................................................................................................................................. 135 

Basic Data Circuit Types .................................................................................................................................... 136 

Basic Traffic Device Type Communication Circuits............................................................................... 138 

Basic Video Communication Circuits............................................................................................................141 

Video-over-IP (VIP) ........................................................................................................................................ 147 

Basic Traffic and Freeway Management Networks.....................................................................................151 

Basic Device Networks....................................................................................................................................151 

Complex Communication Networks .................................................................................................................. 152 

Summary............................................................................................................................................................. 160 

Network Topology ................................................................................................................................................ 162 

Point-To-Point Networks............................................................................................................................... 163 

Star Networks.................................................................................................................................................. 163 

Ring Networks .................................................................................................................................................. 164 

Mesh Networks ................................................................................................................................................ 165 

Network Redundancy...................................................................................................................................... 167 

Conclusion................................................................................................................................................................ 167 

6. Chapter Six – Maintenance & Warranties................................................................................................ 168 
9

Introduction........................................................................................................................................................... 168 

Why create a Maintenance Budget? ............................................................................................................... 169 

Creating the Maintenance Budget ................................................................................................................... 172 

Warranties, Extended Warranties & Service Plans................................................................................... 177 

Warranties ........................................................................................................................................................ 178 

Extended Warranties..................................................................................................................................... 179 

Relationship of Warranties to System Specifications..........................................................................181 

Service Plans......................................................................................................................................................181 

Conclusions.............................................................................................................................................................. 184 

7. Chapter Seven – System Examples............................................................................................................. 185 

Introduction........................................................................................................................................................... 185 

Utah DOT System................................................................................................................................................ 186 

Background ........................................................................................................................................................ 186 

The System - Existing.................................................................................................................................... 188 

The System - New............................................................................................................................................191 

City of Irving Texas ............................................................................................................................................ 193 

Background ........................................................................................................................................................ 193 

Proposed Update.............................................................................................................................................. 194 

5.8 GHz Attributes......................................................................................................................................... 196 

Theory of Operation....................................................................................................................................... 197 

The Irving Proposal......................................................................................................................................... 198 

Tie-in To Main Communication Network....................................................................................................202 

Conclusion................................................................................................................................................................203 

8. Chapter Eight – Construction.......................................................................................................................204 

Introduction...........................................................................................................................................................204 

Handling and Installation of Fiber Optic (and Copper) Communications Cable ..................................205 

Receiving and inspecting fiber optic cable...............................................................................................206 

Unloading, moving and storing cable...........................................................................................................207 

Testing the cables...........................................................................................................................................208 

Documentation and record maintenance................................................................................................... 210 

General Cable, Installation and Design Guidelines.......................................................................................211 

Cable Pull-box/Splice-box Placement .........................................................................................................211 

Cable Installation and Pulling Guidelines................................................................................................... 212 

General Cable Construction Guidelines........................................................................................................... 214 

Aerial Construction ......................................................................................................................................... 215 

Direct Burial Construction............................................................................................................................ 218 

Conduit Construction ...................................................................................................................................... 219 

Wireless Systems Construction.......................................................................................................................220 

Planning for Wireless Systems.................................................................................................................... 221 

A Word About Antennas ...............................................................................................................................224 

Guidelines for Handling & Installation of Wireless Antenna and Transmission Cable ................224 

Conclusion................................................................................................................................................................226 

Resources:..........................................................................................................................................................226 

9. Chapter Nine – The internet ........................................................................................................................227 

Introduction...........................................................................................................................................................227 

What is the Internet? ...................................................................................................................................227 

History of the Internet ................................................................................................................................228 
10

The Internet and the World-Wide-Web ......................................................................................................229 

How Does the Internet Work?.........................................................................................................................233 

Addressing – Formats.....................................................................................................................................235 

Types of Internet Networks .......................................................................................................................237 

Role of the Internet for Traffic, ITS, Freeway Management & Traveler Information.................239 

Use of the Internet for Center-to-Center Communications.............................................................. 241 

Conclusions..............................................................................................................................................................246 

10. Chapter Ten – The Future........................................................................................................................247 

Introduction...........................................................................................................................................................247 

Circuit Switched Vs. Packet Switched ......................................................................................................247 

Trends for Transportation ................................................................................................................................249 

High Speed Ethernet......................................................................................................................................249 

Resilient Packet Ring (RPR)........................................................................................................................... 251 

Broadband Wireless........................................................................................................................................252 

Radio Frequency Identification (RFID) ....................................................................................................253 

Conclusions..............................................................................................................................................................254 

11. Appendix........................................................................................................................................................256 

IEEE 802 Standards & Working Groups........................................................................................................256 

Comparison Analog Voice & VoIP......................................................................................................................257 

Calculating Fiber Optic Loss Budget...............................................................................................................258 

Criteria & Calculation Factors......................................................................................................................258 

Calculating a “Loss Budget”...........................................................................................................................259 

Rural Telecommunications Requirements Testimony..................................................................................262 

Steve Albert – Senate hearing....................................................................................................................262 

About the Author......................................................................................................................................................268 

Glossary........................................................................................................................................................................269 
11

LIST OF TABLES

Table 1-1: OSI Protocol Stack ................................................................................................................................................... 17

Table 2-1: Twisted-Pair Communication Cable Category Ratings....................................................................................... 31

Table 2-2: Fiber Optic Cable Classifications..........................................................................................................................35

Table 2-3: Fiber Cable Color Identification Chart ...............................................................................................................36

Table 2-4: Fiber Optic Cable Buffer Types............................................................................................................................39

Table 2-5: Comparison Single Mode Fiber & Multimode Fiber...........................................................................................43

Table 2-6: Frequencies for Unlicensed Radio Systems .......................................................................................................49

Table 2-7: CEA Estimates of the Number of Low Power Radio Devices .........................................................................50

Table 2-8: Comparison of TDM & PDM.....................................................................................................................................66

Table 3-1: DSRC Vehicle-Roadside Relationships..................................................................................................................87

Table 3-2: Communication Needs & Requirements................................................................................................................94

Table 3-3: NTCIP Device Management Protocol List .........................................................................................................104

Table 3-4: NTCIP List of Systems Management Protocols..............................................................................................104

Table 5-1: Location of Field Controllers ................................................................................................................................129

Table 5-2: Location & Data Requirements Table ..................................................................................................................131

Table 5-3: DB-25 Connector Cable..........................................................................................................................................133

Table 5-4: Voice, Video & Text Transmission Requirements............................................................................................143

Table 5-5: Field Device Location .............................................................................................................................................158

Table 6-1: Example Communication Device Inventory List.................................................................................................171

Table 6-2: Technician Experience Classification.................................................................................................................173

Table 7-1: Deployment Cost Estimates ...................................................................................................................................191

Table 8-1: Example of Manufacturer Recommended Span Lengths for Areial Cable Segments.............................216

Table 9-1: Internet Communication Elements ..................................................................................................................... 242

Table 10-1: Comparison Traditional CCTV vs. VIP Systems Requirements .................................................................. 250

Table 11-1: IEEE 802 Standards List .................................................................................................................................... 256

Table 11-2: Fiber Loss Budget Calculation............................................................................................................................ 259
12

LIST OF FIGURES

Figure 1-1: Diagram - NTCIP Standards Framework............................................................................................................ 17

Figure 1-2: Telecommunication Timeline..................................................................................................................................20

Figure 2-1: RJ45 Connector ........................................................................................................................................................29

Figure 2-2: Twisted Pair Cable...................................................................................................................................................30

Figure 2-3: Co-Axial Cable Illustration....................................................................................................................................32

Figure 2-4: Basic Fiber Optic Strand Construction..............................................................................................................33

Figure 2-5: Fiber Optic Cable Illustration..............................................................................................................................36

Figure 2-6: Diagram of Basic Connector Wiring....................................................................................................................54

Figure 2-7: Illustration of Basic Telephone Call Process....................................................................................................62

Figure 2-8: TDM Process Flow Chart........................................................................................................................................64

Figure 2-9: Flow Chart - PDM Process .....................................................................................................................................65

Figure 2-10: Diagram of Computer Digital Output Converted to Analog using a MODEM..........................................67

Figure 2-11: Diagram of Analog Inputs to T-1 Mux...............................................................................................................69

Figure 2-13: DWDM Channels.....................................................................................................................................................75

Figure 2-14: Diagram - Typical Office LAN............................................................................................................................80

Figure 2-15: Diagram - Metro Area Network (MAN)........................................................................................................... 81

Figure 3-1: National ITS Architecture Communications Sausage Diagram....................................................................83

Figure 3-2: Diagram - Mobile 2-Way Radio Network...........................................................................................................86

Figure 3-3: National Architecture EM-4 Market Package..................................................................................................90

Figure 3-4: EM-4 Market Package with Telecommunications Flows.................................................................................92

Figure 3-5: EM-4 Market Package with "Sausage Diagram" Elements ............................................................................93

Figure 3-6: TMC Area of Responsibility ..................................................................................................................................94

Figure 3-7: Diagram - TMC to EMA Link .................................................................................................................................95

Figure 3-8: Diagram - TMC to EMA with Fiber Communication Link................................................................................96

Figure 3-9: Diagram - TMC to EMA Comm Link Rural Setting...........................................................................................97

Figure 3-10: Diagram - TMC to EMA Rural using Leased Telephone Lines .....................................................................98

Figure 3-11: NTCIP Standards Framework...........................................................................................................................100

Figure 4-1: Field Devices Communication Link Requirements ............................................................................................113

Figure 4-2: Chart Relationship Communication to Overall System ..................................................................................114

Figure 5-1: Diagram - Technology Flow ..................................................................................................................................124

Figure 5-2: Diagram - 3 Types of Communication Circuits................................................................................................127

Figure 5-3: Napkin Sketch of Communication System.......................................................................................................129

Figure 5-4: Location Map...........................................................................................................................................................130

Figure 5-5: System Schematic.................................................................................................................................................132

Figure 5-6: DB-25 Connector....................................................................................................................................................134

Figure 5-7: DB-9 Connector......................................................................................................................................................134

Figure 5-8: Modem Block Diagram...........................................................................................................................................136

Figure 5-9: CCTV Circuit Diagram ...........................................................................................................................................137

Figure 5-11: Diagram Field Controller to Host Computer..................................................................................................138

Figure 5-12: Diagram - Point-to-Multipoint...........................................................................................................................139

Figure 5-13: Diagram - Multidrop System.............................................................................................................................140

Figure 5-14: Diagram - FDM Hub Circuit...............................................................................................................................144

Figure 5-15: Diagram - CCTV with CODEC ............................................................................................................................145

Figure 5-16: Diagram - Typical CODEC Communication Circuit - 1990's Deployment................................................147

Figure 5-17: VIP Basic Camera System..................................................................................................................................149

Figure 5-18: Diagram - Add-on Conversion to VIP ..............................................................................................................150

Figure 5-19: Diagram - Basic Traffic Device Communication Circuit ..............................................................................151

Figure 5-20: Diagram of described system ..........................................................................................................................153

Figure 5-21: Diagram STSS Communication System ..........................................................................................................154

Figure 5-22: Diagram UTSS Communication System .........................................................................................................156
13

Figure 5-23: Straight Line Diagram........................................................................................................................................156

Figure 5-24: Diagram - Site Equipment .................................................................................................................................159

Figure 5-25: System Block Diagram .......................................................................................................................................160

Figure 5-26: Diagram - Point-to-Point Network ..................................................................................................................163

Figure 5-27: Diagram - Star Network....................................................................................................................................164

Figure 5-28: Diagram - Ring Network ....................................................................................................................................164

Figure 5-29: Diagram - Mesh Network ..................................................................................................................................166

Figure 6-1: Photograph of a Fiber Optic Modem.................................................................................................................170

Figure 7-1: Diagram UDOT Current System.........................................................................................................................190

Figure 7-2: Graph - Comparison of Savings Realized by UDOT Converting to an IP Architecture.........................191

Figure 7-3: Diagram - Comparison Multi-Drop VS. Ethernet ...........................................................................................192

Figure 7-4: Diagram - Wireless Channel Alignment for 360 Degree Coverage ...........................................................195

Figure 7-5: Diagram - Channel Re-use Plan for Wide Area Coverage ............................................................................197

Figure 7-6: Diagram - Proposed Channel Re-use Plan .........................................................................................................198

Figure 7-7: Drawing - Typical CCTV Site...............................................................................................................................199

Figure 7-8: Typical CCTV Site Schematic............................................................................................................................ 200

Figure 7-9: Map of Proposed Irving Texas System............................................................................................................201

Figure 7-10: Schematic - Microwave Backbone Configuration........................................................................................ 202

Figure 7-11: Diagram - Microwave Backbone ....................................................................................................................... 203

Figure 8-1: Fiber Cable Route Construction – Photograph Courtesy Adesta, LLC...................................................... 204

Figure 8-2: Fiber Cable Route Construction – Photograph Courtesy Adesta, LLC..................................................... 204

Figure 8-3: Fusion Splicing Fiber Strands - Photograph Courtesy Adesta, LLC ........................................................ 209

Figure 8-4: Aerial Fiber Optic Cable Splice Box - Photograph Courtesy Adesta, LLC..............................................212

Figure 8-5: Typical Telephone Pole .........................................................................................................................................217

Figure 8-6: Installation of Wireless System - Photograph Courtesy GDI Systems, LLC........................................ 220

Figure 8-7: Example of Antenna Coverage Pattern - Antenna Specialists Products................................................. 224

Figure 9-1: Actual Sketch of the Original Internet Concept.......................................................................................... 228

Figure 9-2: Map - Location of Major MCI Internet Nodes in United States............................................................. 229

Figure 9-3: Diagram General Internet Architecture........................................................................................................ 232

Figure 9-4: Diagram - Traveler Information Provided via the Internet...................................................................... 234

Figure 9-5: National ITS Architecture Sausage Diagram with Internet added ....................................................... 240

Figure 9-6: Internet Elements Schematic........................................................................................................................... 243

Figure 9-7: Schematic - Multiple Agency Center-to-Center Links via the Internet ................................................ 244

Figure 9-8:ITS Center-to-Center Communication Diagram............................................................................................. 245
14

 

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Chapter 1 

15

1. CHAPTER ONE - TELECOMMUNICATION 

BASICS

Introduction 

The “Telecommunications Handbook for Transportation 

Professionals” was originally published in 1987 as the 

“Communications Handbook for Traffic Control Systems”. The 

first (and only) update was initiated in 1991, and published in 

1993. Given the significant advances in the technology of 

telecommunications, and the complexities of Traffic and ITS 

systems deployment its is necessary to create a new (rather than 

a revision) handbook providing a broader view of 

telecommunications technology as applied for traffic and 

transportation purposes. This handbook provides a broad overview 

of telecommunications technology and history. 

Purpose 

The “Telecommunications Handbook for Transportation 

Professionals” is intended to provide an introduction to 

telecommunication technology and process for transportation 

engineers and project managers involved in the design and 

deployment of traffic signal and freeway management systems. 

The handbook can be used as a resource that provides an overview 

of the various technical issues associated with the planning, 

design, operation, and management of a communications system. It 

is intended to provide the user with a better understanding of 

applied communications technology and the considerations for use 

in freeway and surface street networks. 

The intended audience is transportation professionals who may be 

involved with, or responsible for any phase in the life cycle of a 

traffic signal or freeway management control network. This 

includes all public or private “practitioners” (e.g., managers, 

supervisors, engineers, planners, or technicians) involved with any 

issue or decision (e.g., policy, program, funding, or system 

implementation) and who may directly or indirectly influence the 

performance of traffic on local arteries or freeway facilities. 

These activities may include, but not be limited to, planning and 

design, operational strategies, programs, and services that 

support continuous management of travel and control of traffic, 

and the technology infrastructure to provide these capabilities. 
Telecommunications Handbook for Transportation Professionals 

Chapter 1 

16

Relationship to National Architecture 

Telecommunications systems as part of the National ITS 

Architecture are the connecting pathways that bind the various 

elements of traffic signal, freeway management, and 

transportation systems together. The National ITS Architecture 

“sausage diagram” indicates how these elements are bound 

together, but does not specify the telecommunication system. The 

developers of the National ITS Architecture understood that 

each telecommunication system would be uniquely designed to 

meet the needs of each project. 

The significant diversity of communications technologies and the 

overall complexity of traffic signal, freeway management, and 

transportation systems have created a need for traffic and 

transportation professionals to implement the Systems 

Engineering Process (SEP). This handbook provides a summary 

(Chapter 4) of how to apply an SEP to the development of a 

telecommunications system, for traffic signal and freeway 

management systems development. 

Open System Interconnection Model (OSI) 

The OSI model is an International Standards Organization (ISO) 

standard that defines a framework for implementing 

telecommunication and software protocols. The OSI model is 

organized into seven hierarchal layers. Control is passed from one 

layer to the next starting at the application layer and proceeding 

down to each successive layer and back as required for any given 

process. Most of the functionality of the OSI model exists in all 

communications systems - however, two or three layers may be 

combined into one. The most significant role of the OSI model is 

to serve as a reference for the development of other protocol 

stacks. A detailed explanation of the OSI Model is provided in 

the Addendum section of this handbook. Table 1-1, provides a list 

of the OSI Model Protocol Stack. 
Telecommunications Handbook for Transportation Professionals 

Chapter 1 

17

Table 1-1: OSI Protocol Stack 

OSI Protocol Stack 

Layer # Protocol 

7 Application 

6 Presentation 

5 Session 

4 Transport 

3 Network 

2 D at a Lin k 

1 Physical 

Telecommunications hardware generally utilizes layers one and 

two of the protocol stack. Modems, multiplexers, bridges, 

routers, switches, media converters, codecs, etc. are examples of 

the types of devices that exist at the physical and data link 

layers of the protocol stack. All media and most of the protocol 

converters are considered as layer one items. Some 

communication hardware devices are designed to operate at 

higher layers. A network router is often referred to as a “layer 3 

router” . This is one of the few examples of communication 

hardware that is designed to function above layer two. Most 

communication systems are not designed using the OSI protocol 

stack. This is because the hardware vendors have already taken 

the OSI model into consideration for the design of their 

products. The RS232 and RJ45 connectors built into the 2070 

traffic controller are already layer one compliant. Serving as a 

protocol stack model, OSI is used as the reference for the 

development of most other communications protocols. The 

National Transportation Control Interface Protocol (NTCIP) 1 has 

a specially developed protocol stack based on the OSI model. 

 

1 http://www.ntcip.org
Telecommunications Handbook for Transportation Professionals 

Chapter 1 

18

Notice (figure 1-1) that the NTCIP protocol stack is modeled on 

the OSI stack, and has embedded telecommunication standards. 

Communication system designers would simply use the pre-defined 

telecommunication standards. However, developers of software 

control systems must be acutely aware of the NTCIP protocol 

stack. NTCIP and its role in the development of a communication 

system is explained in Chapter 3.

Telecommunications History 

The history of modern-day communications technology can be said 

to have started when Samuel Morse invented the wireline 

telegraph in 1832. However, it was Alexander Graham Bell’s 

invention of the telephone, in 1874, that led to the development 

of our present day communications technology. Morse had simply 

created a way for humans to extend their ability to transfer 

information – instantly – over great distances. Bell gave us the 

ability to have the most intimate form of communication over 

distances – the use of our voices. 

The concept of the telephone instrument – and the system that 

allows it to work – was so strong that most communication 

Figure 1-1: Diagram - NTCIP Standards Framework
Telecommunications Handbook for Transportation Professionals 

Chapter 1 

19

technology during the past 125 years was developed to support an 

efficient voice communication network. It wasn’t until 2004 that 

major telecommunication carriers announced the need to develop, 

and support, a network designed for the purpose of transporting 

digital data. 

The wireless telegraph (now referred to as radio) was invented by 

Guillermo Marconi in 18962

. When wireless communication was 

finally able to be used for voice transmission, it emulated the 

telephone system. 

From 1874 to 1980, communication networks around the world 

were constructed to facilitate the efficient and economical 

transmission of voice conversations. Multiplexing and digital 

transmission systems were developed to “cram” more voice 

conversations into the existing copper wire communication 

facilities. 

The Internet, first developed in 1973 as a project for the U.S. 

Department of Defense Advanced Research Projects Agency 

(ARPA), initiated a profound change in the future development of 

communications networks and technologies. Originally called the 

Arpanet – linking several Universities and research laboratories – 

it evolved into the world wide web (WWW). During this period, 

there were a number of significant technology advances and 

government enforced corporate reorganizations that helped to 

change the direction of communications systems development: 

1. Computing and communications technologies were provided a 

big boost by the invention of the integrated circuit (IC) in 

1959. The IC permitted development and manufacture of 

smaller and more automated communication devices at a very 

low cost. 

2. The Carterphone Decision, by the U.S. Supreme Court, in 

1968, made it possible for the connection of non-telephone 

company owned devices (until this point, only devices owned 

and operated by the telephone companies were permitted). 

3. In the 1970s, fiber strands were first used as a 

communication medium. 

4. In 1983, the U.S. Supreme Court mandated reorganization 

of AT&T was enforced. 

 

2 Historically, Marconi is credited with the invention of the wireless telegraph, however, a landmark June 21, 1943 supreme court decision stated 

that Marconi had violated Nikola Tesla's patents for wireless communications. See "United States Reports; Cases Adjudged in the Supreme 

Court of the United States," Vol. 320; Marconi Wireless Telegraph Co. of America v. United States, pp. 1-80. 
Telecommunications Handbook for Transportation Professionals 

Chapter 1 

20

New inventions coupled with increasing business and consumer 

demand for computer and data communication services forced a 

change in the nature of the development of communications 

networks. By 1995, most installation of communications networks 

was devoted to the efficient transmission of data generated by 

computers. However, these networks were still based on a voice 

communication design. 

The development and introduction of broadband data 

communications standards (IEEE 802 Series 3

) helped to create a 

demand for communications networks designed to support data 

communications. 

By 2003, wireless (cellular telephone) networks were available to 

almost every location of the United States (remote wilderness 

areas still lack coverage). According to the Cellular 

Telecommunications & Internet Association (CTIA), there were 

more than 148 million wireless subscribers, and 92% were using 

digital service. 

A timeline of the support for traditional voice transmission 

services versus data transmission services might appear as 

follows: 

By 2003, 63% of Americans use the internet, and 31% of home 

users have broadband access 4

. In early 2004, Verizon, announced 

a major upgrade of its basic telephone network to support 

“Internet Telephony” or Voice over Internet Protocol (VoIP) 5

. 

Southern Bell Corporation (SBC) also announced similar upgrades 

for its networks. 

Handbook Organization 

The Telecommunications Handbook for Transportation 

Professionals is organized to provide the reader with a logical 

flow of information with a description of various communication 

 

3 http://www.ieee.org

4

 Pew Trust – “Internet & American Life”, December 2003. - http://www.pewtrusts.org 5

 Ivan Seidenberg, CEO Verizon, at the Consumer Electronics Show, Jan 2004. 

1876 1995 Present

Telephone

Invented

Voice

Network

Dominance

Data

Network

Dominance

Starts

Figure 1-2: Telecommunication Timeline 
Telecommunications Handbook for Transportation Professionals 

Chapter 1 

21

terms and technologies that are commonly used (or considered) 

for the deployment of Freeway Management and Traffic Signal 

systems. Technical descriptions are kept at a minimum 

engineering level to provide non-communication professionals with 

a basic understanding of the technologies. 

Chapter Two – Telecommunications Fundamentals. Communication 

technology is provided in a “basic to complex” order. The chapter 

starts with copper based transmission media and steps the reader 

through a progression of terminology that includes: fiber optics, 

wireless, video multiplexing and Ethernet systems. 

Chapter Three – Telecommunications & The National Architecture. 

The chapter is a general look at the relationship of 

telecommunications systems design and the National ITS 

Architecture and NTCIP. The reader will be made aware of the 

fact that NTCIP is not a standard, but a protocol that defines 

the relationship of the many current (and developing) 

communications standards for use in a traffic signal, freeway 

management, or transportation system. 

Chapter Four – Developing the Telecommunication System. This 

chapter provides the reader with a system engineering approach 

to the design of a communications system that supports traffic 

and transportation requirements. The chapter provides a step-bystep process that should result in a communication system 

requirements analysis and preliminary design. The primary axiom 

that drives the design of a communications system is - “there are 

no absolutes!” For most communication systems there are usually 

several ways to achieve the desired results. A qualified 

communications system designer will generally present several 

different approaches and ask the project manager to make a 

decision. 

Chapter Five - Communications for Field Devices. The chapter 

provides an in-depth look at basic system configurations for field 

devices used in traffic signal and freeway management systems. 

Each field device has a specific set of communications 

requirements. 

Chapter Six – Communication System Maintenance. Maintenance of 

a telecommunication system is essential. Operators of these 

systems must provide for the care and feeding of the networks 

that connect all field devices and operational centers. The 

chapter discusses the need to create a budget for maintenance, 

the relationship of manufacturer warrantees to maintenance, and 

technician qualifications. 
Telecommunications Handbook for Transportation Professionals 

Chapter 1 

22

Chapter Seven – System Examples. This chapter presents a look 

at “real-world” systems deployed by departments of 

transportation. Two systems are described to show how similar 

problems use different approaches to a solution. 

Chapter Eight – Installation and Testing. A major cost element in 

the deployment of a communications system is installation 

(construction). Very often, project managers assume that proper 

installation procedures are being used by contractors. This 

chapter provides guidelines for proper handling and installation 

of communications media. Wireline and wireless media are 

discussed. 

Chapter Nine - The Internet. First conceived and implemented 

nearly thirty years ago, has had a profound effect on the way 

individuals, private companies and public organizations 

communicate on a day-to-day basis. The chapter in this document 

will provide the reader with a basic understanding of the 

composition of the Internet, the World Wide Web (WWW), how it 

works, and how it can be used as part of an overall 

communications and operational strategy for Traffic Signal, FMS, 

and ITS systems. 

Chapter Ten - The Future. An attempt to provide some insight on 

the general future of communications systems and the possible 

implications for the deployment of telecommunications systems to 

support Freeway Management and Traffic Signal systems. 

Appendix A – Contains additional information that readers of this 

handbook can use for investigation of additional resources. The 

following items are included in this appendix: 

• List of IEEE 802 standards and working groups 

• Comparison of analog voice and voice-over-IP (VoIP) 

• How to calculate a fiber optic loss budget 

• A discussion of rural telecommunications requirements 

Glossary – Definitions – will provide a listing of all terminology 

used in this handbook. 
Chapter 2 

23

2. CHAPTER TWO – FUNDAMENTALS OF 

TELECOMMUNICATIONS

Introduction 

Transmitter, receiver, transmission medium - these are the basic 

elements that make up a communication system. Every human 

being is equipped with a basic communication system. The mouth 

(and vocal cords) is the transmitter, ears are the receivers, and 

air is the transmission medium over which sound travels between 

mouth and ear. The transmitter and receiver elements of a data 

modem (such as the type used in a traffic signal system 

controller box) may not be readily visible. However, look at a 

schematic of its components, and you will see elements labeled as 

“XMTR” and “RCVR”. The modem’s transmission medium is typically 

copper wire, fiber, or radio. 

Almost all communications networks have as their basis the same 

set of Telephony (Telepho–Ny) standards and practices. “Ma Bell” 

(the Bell Telephone System and 

American Telephone & 

Telegraph, and others) spent 

years and billions of dollars 

creating, perfecting and 

maintaining a 

telecommunications network 

dedicated to providing the 

most reliable voice 

communication service in the 

world. All other communication 

technology and process evolved based on that communications 

network. Engineers and scientists involved in the development of 

new communication technologies and processes had to make 

certain that their “product” could be used within the existing 

telephone networks. And, the telephone company required 

backward compatibility. Telephones manufactured in 1950 still 

work in today’s network. Modems manufactured in 1980 still work 

in the current system. 

As you read through this chapter, and the rest of the handbook, 

please keep in mind that telecommunication standards, practices, 

and protocols were developed for the communication industry. All 

Some communication transmission 

protocols were developed to work 

independently of the Telephone System. 

Ethernet, for example was created to 

facilitate data communication within a 

closed system that was contained within 

an office building. The Internet was 

created as a closed communication 

network. 
Telecommunications Handbook for Transportation Professionals 

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24

of these systems must be adapted for use in a traffic signal or 

freeway management system. 

Today, in North America, Mexico, most of Europe and the Pacific 

Rim, voice services are in fact sent as digital signals and 

converted to analog just before leaving (and arriving at) the 

serving central office, at the end-user points. The reader might 

ask: “If voice is converted to digital isn’t that the same as 

data?” The answer is no - “digital transmission” does not 

automatically infer data communications compatibility. Analog 

transmission systems can, and do, carry data. In 

telecommunications, digital and analog are distinct forms of 

communication transmission. This chapter provides information 

about the basics of telecommunications - the transmission media 

and transmission systems, as well as an explanation of the 

differences between analog and digital transmission. Transmission 

media are those elements that provide communication systems 

with a path on which to travel. Transmission systems are those 

elements (hardware and software) that provide management of 

the communication process and 

the use of the transmission path. 

The telecommunications world 

would be very simple if the 

distinction between transmission 

media and systems (protocols) 

were easily defined. Often, a 

specific transmission system will 

only work within a specific 

medium. Spread Spectrum Radio 

is one example. Radio (RF) is the 

transmission medium, and spread 

spectrum is the transmission system (protocol). Although it is 

possible to create a spread spectrum communications signal over 

wireline, the process is not typically used because there are 

other more efficient methods of transmission signaling. 

Therefore, spread spectrum transmission signaling is almost 

always associated with RF. There is always a point at which the 

Spread Spectrum Radio system must interface with another 

transmission medium, and/or system. This is accomplished by 

converting from RF to a wireline signaling protocol. The 

telecommunications process can be viewed as an excellent example 

of multi-modalism. 

For purposes of this discussion, 

voice is any transmission that 

can be switched through the 

Carrier networks in an analog 

format. This includes data 

transmitted within a voice 

channel using a modem. Data is 

any digital transmission that 

cannot be switched through the 

Carrier networks. 
Telecommunications Handbook for Transportation Professionals 

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25

The chapter is divided into sections that cover 

• Transmission Media 

• Transmission Signaling 

• Basic Telephone Service 

• Multiplexing 

• High Capacity and Broadband Transmission 

Sub-topics in the sections look at: 

• Media Consideration Factors (why use one over another) 

• Differences between voice and data signaling 

• Video Transmission (CODECS & Compression) 

• T-1 Communication 

• SONET, WDM & Ethernet 

• Wireless 

Transmission Media 

Transmission media are the highways and arteries that provide a 

path for telecommunications devices. There is a general tendency 

to say that one transmission medium is better than another. In 

fact, each transmission medium 

has its place in the design of 

any communication system. Each 

has characteristics which will 

make it the ideal medium to use 

based on a particular set of 

circumstances. It is important 

to recognize the advantages of each and develop a system 

accordingly. 

Transmission efficiency is generally viewed as the amount of 

signal degradation created by the use of a particular transmission 

medium. The transmission medium presents a “barrier” to the 

communication signal. The “barrier” can be measured by many 

different factors. However, one common question is asked about 

all communication media. How far will the communication signal 

energy travel before it becomes too weak (or distorted) to be 

considered unsable? There is equipment available to extend the 

distance for transmitting a signal, but that adds to the overall 

cost and complexity of deployment. 

Factors to consider when 

choosing transmission media 

include: cost, ease of installation 

and maintenance, availability, and 

most important, efficiency of 

transmission. 
Telecommunications Handbook for Transportation Professionals 

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26

MEDIA CONSIDERATION FACTORS

Ease of installation of the communication medium is relatively 

simple to define. Generally, all communication media require care 

when being installed. The installation should be accomplished by 

trained and knowledgeable technicians and managers. For 

purposes of this discussion, consider the relative degree of 

difficulty for the placement of the transmission medium. Cables 

(fiber or copper) require a supporting infrastructure, as does 

radio or infrared. Consider the following: 

If you are planning to use fiber optic (or copper cable) and the 

system plan calls for crossing the Delaware River, there will be 

significant installation (construction) challenges. The 

construction may require a bore under the river, or finding a 

suitable bridge. Either of these methods may add significantly to 

your budget. Wireless might seem like a good option. It 

eliminates the need to find a suitable crossing location for your 

cable. However, you will need to place the antenna at sufficient 

height to clear trees buildings and other objects, and account for 

terrain differences on both sides of the river. Local residents of 

the nearby Yacht Club condominiums may complain about the radio 

tower spoiling their view of the sunset. Don’t forget to add in the 

cost of hiring a graphic artist to create a drawing that shows how 

lovely the rays of the setting sun are when reflected off the 

radio tower. 

Some products may be more 

readily available than others. 

For example, the most 

common type of fiber cable 

available is outside plant 

with armor shielding, 96 

strands of single mode fiber 

arrayed in loose buffer tubes, on 15,000 foot reels. Make certain 

that you allow enough time for product to be manufactured, 

especially if a special cable or hardware configuration is 

required. Availability of product due to manufacturing delays will 

impact on overall project schedule and may impact on overall 

project costs. 

Cables that contain combinations of different types of fiber 

strands such as single mode and multimode fibers, or mixtures of 

copper and fiber, or odd (different from standard put-ups) 

“Put-ups” – the term cable 

manufacturers use to describe the 

configuration of a cable. The 

expression is often used in the 

following manner: “The cable is 

available in 5000 foot “put-ups”. 
Telecommunications Handbook for Transportation Professionals 

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27

numbers of fiber strands will require more time to produce and 

could add several months to the delivery cycle. 

Fiber, copper, radio, infrared all have different transmission 

characteristics. Fiber is considered to have the best overall 

characteristics for transmission efficiency. That is, the 

effective loss of signal strength over distance. Cable is rated by 

the manufacturer for signal loss. Signal loss factors are stated in 

terms of dB per 1000 meters. Typical single mode fiber may have 

a signal attenuation factor of between 0.25 dB/km and 0.5 dB/km. 

The cable manufacturer will provide a specification description 

for each product they offer. In theory, you can send a signal 

further on fiber than via most other transmission media. 

However, consider that radio signals at very low frequencies 

(below 500 kilohertz) can travel for thousands of miles. This type 

of radio signal can be used to carry data, but very impractical for 

use in traffic signal and freeway management systems. VLF radio 

signals are only capable of efficiently carrying data at very low 

bit rates. This type of system was used by the Associated Press 

organization to transmit news articles between Europe and North 

America, and is also used by the Military for very long distance 

data communications. 

Maintenance and operational costs are two other factors that 

should be considered when comparing transmission media for any 

given application. Fiber optic cable can be installed in conduit six 

feet below grade, and never touched for decades. Maintenance of 

the fiber cable is minimal. Microwave systems may be constructed 

in less time and at a lower cost than fiber cable placed in 

conduit, but the tower sites require significantly more 

maintenance, including re-painting the tower, and annual 

inspections for rust. 

In summary, take all of the attributes of the potential media 

that could be used for a specific application and determine which 

will provide the most “bang for the buck”. This does not always 

mean most bandwidth, highest transmission speed, easiest to 

install, or lowest cost - all factors that may influence your choice 

of transmission media. The best media are the ones that will 

support as many of the system requirements as possible and help 

to assure satisfaction with overall performance. 
Telecommunications Handbook for Transportation Professionals 

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28

WIRELINE MEDIA

We begin with basic information about the most common types of 

transmission media used today: 

• Copper Wire 

• Fiber Optics 

• Radio Frequency (Wireless) 

• Free Space Optics 

Many engineers will argue that one transmission medium is the 

best, or better than some of the others. The reader should keep 

in mind that each medium has advantages and disadvantages. 

Which medium is best depends upon the purpose of the 

communications system and the desired end results. In fact, most 

systems are a hybrid. That is, two or more media are combined to 

effect the most efficient communication network infrastructure. 

There are many traffic signal systems that combine a twisted 

copper pair infrastructure with wireless links to serve part of 

the system. The decision to create this type of system may have 

been based on economics, but that is certainly one of the reasons 

to choose one medium over another, or to combine the use of 

several. 

Copper Media 

The electrical properties of copper wire create resistance and 

interference. The further communication signals travel the more 

they are weakened by the electrical properties associated with 

the copper cable. Electrical, resistance within the copper medium 

slows down the signal or flow of current. The electrical 

properties of copper wire are the key factors that limit 

communication transmission speed, and distance. However, it was 

those same properties together with cost, ease of manufacture, 

ability to be drawn into very thin strands, and others that made 

copper a logical choice for its selection as a communication 

transmission medium, and a conductor of electricity. Aluminum 

and gold are also used for communication purposes, but gold (the 

most efficient) is too expensive to use for this purpose and 

aluminum is not an efficient conductor for communication 

purposes. 

There are two primary types of cables containing copper wire 

used for communication: 
Telecommunications Handbook for Transportation Professionals 

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29

• Twisted Pair 

• Coaxial 

Twisted Pair 

Communication signals sent over copper wire are primarily direct 

electrical current (DC) which is modulated to represent a 

frequency. Any other electrical current near the communication 

wire (including other communication signals) can introduce 

interference and noise. Multiple communication wires within a 

cable bundle can induce interfering electro-magnetic currents, or 

“cross-talk”. This happens when one signal within the cable is so 

strong that it introduces a magnetic field into an adjacent wire, 

or communication pair. Energy sources such as power transmission 

lines, or fluorescent lighting fixtures can cause electromagnetic 

interference. This interference can be minimized by twisting a 

pair of wires around a common axis, or by the use of metallic 

shielding, or both. The twisting effectively creates a magnetic 

shield that helps to minimize “crosstalk”. 

Twisted pair is the ordinary copper wire that provides basic 

telephone services to the home and many businesses. In fact, it is 

referred to as “Plain Old Telephone Service” (POTS). The twisted 

pair is composed of two insulated copper wires twisted around one 

another. The twisting is done to prevent opposing electrical 

currents traveling along the individual wires from interfering 

with each other. 

Twisted copper pair, is what Alexander Bell used to make the 

first telephone system work and is generally the most common 

transmission medium used today. 

A broad generalization is that 

twisted copper pair is in fact 

the basis for all 

telecommunication technology 

and services today. Ethernet – 

originally developed to work over 

coaxial cable - is now a 

standard based on twisted pair. 

By comparison, a basic voice 

telephone conversation uses one 

(1) twisted pair, where as an 

Ethernet session uses at least 

two (2) twisted pair (more about 

Figure 2-1: RJ-45 Connector
Telecommunications Handbook for Transportation Professionals 

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30

Ethernet later in this chapter). 

Each connection on twisted pair requires both wires. Since some

telephone sets or desktop locations require multiple connections, 

twisted pair is sometimes installed in two or more pairs, all 

within a single cable. For some business locations, twisted pair is 

enclosed in a shield that functions as a ground. This is known as 

shielded twisted pair (STP). Ordinary wire to the home is 

unshielded twisted pair (UTP). Twisted pair is now frequently 

installed with two pairs to the home, with the extra pair making 

it possible to add another line - perhaps for modem use. 

Twisted pair comes with 

each pair uniquely color 

coded when it is packaged 

in multiple pairs. 

Different uses such as 

analog, digital, and 

Ethernet require 

different pair multiples. There is an EIA/TIA standard for color 

coding of wires, wire pairs, and wire bundles. The color coding 

allows technicians to install system wiring in a standard manner. 

A basic single telephone line in a home will use the red and green 

wire. If a second phone line is provided, it will use the yellow and 

black wire. The most common 

cause of telecommunication 

system problems is incorrect 

wiring. This wiring protocol is 

for standard telephone set 

jack connections. Data systems 

use different arrangements 

and color codes. The most common is the EIA/TIA standard. 

Please note that NEMA and ICEA have color codes for electrical 

wire. Do not confuse these with telecommunication wire color 

coding standards. 

Twisted pair is categorized by the 

number of twists per meter. A greater 

number of twists provides more 

protection against crosstalk, and other 

forms of interference and results in a 

better quality of transmission. For data 

transmission, better quality equates to 

fewer transmission errors. Later in this chapter, we’ll look at the 

Cat 3 cable is considered to be 

the standard for basic telephone 

and Ethernet services. However, 

CAT 5 is being deployed as a 

replacement and in all new 

installations. 

EIA/TIA provides a color code and wiring 

standard for RJ-45 Connectors. The 

standard is EIA/TIA 568A/568B. These 

standards utilize 4 twisted pair, because 

the RJ-45 connector has 8 terminals. 

Figure 2-2: Twisted Pair Cable
Telecommunications Handbook for Transportation Professionals 

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31

effects of transmission errors as they impact on throughput and 

delay times. 

There are two types of twisted pair cables used for most inbuilding situations today - Category 3 UTP (CAT 3) and Category 

5 UTP (CAT 5). However, as of the writing of this handbook, all 

new and replacement installations use CAT 5. These cables have 

been developed based on a set of standards issued by the 

EIA/TIA (Electronic Industry Association/Telecommunications 

Industry Association). CAT 3 is used primarily for telephone 

cabling and 10Base-T installations, while CAT 5 is used to support 

10/100Base-T installations. CAT 5 wiring can also be used for 

telephone systems. Therefore, most new installations use CAT 5 

instead of CAT 3. The CAT 5 cable is pulled to a cubicle or office 

and connected to a universal wall plate that allows for 

installation of data and voice communication systems. Category 5E 

(CAT 5E) has been developed to accommodate GigE installations. 

CAT 5E is manufactured and tested under stricter guidelines than 

CAT 3 or CAT 5. Two new standards – CAT 6 and CAT 7 - have 

been adopted to meet criteria for 10GigE (and higher) 

transmission speeds. 

Table 2-1: Twisted-Pair Communication Cable Category Ratings 

Category Maximum Data Rate Usual Application 

CAT 1 Less than 1 Mbps Analog Voice (POTS), Basic 

Rate ISDN, Doorbell wiring 

CAT 2 4 Mbps Primarily used for Token Ring 

Networks 

CAT 3 16 Mbps 

Voice and Data, and 10Base-T 

Ethernet. Basic telephone 

service 

CAT 4 20 Mbps Used for 16 Mbps Token Ring 

CAT 5 100 Mbps up to 1 

Gbps 

10Base-T, 100Base-T (fast 

Ethernet), GigE, FDDI, 155 

Mbps ATM 

Cat 5E 100 Mbps FDDI, ATM 
Telecommunications Handbook for Transportation Professionals 

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32

CAT 6 Greater than 100 

Mbps 

Broadband Applications 

CAT 7 Emerging Standard GigE plus 

Coaxial Cable 

Coaxial cable is a primary type of copper cable used by cable TV 

companies for signal distribution between the community antenna 

and user homes and businesses. It was once the primary medium 

for Ethernet and 

other types of local 

area networks. With 

the development of 

standards for 

Ethernet over 

twisted-pair, new 

installations of 

coaxial cable for 

this purpose have 

all but disappeared. 

Coaxial cable is 

called "coaxial" 

because it includes 

one physical channel 

(the copper core) that carries the signal surrounded (after a 

layer of insulation) by another concentric physical channel (a 

metallic foil or braid), and an outer cover or sheath, all running 

along the same axis. The outer channel serves as a shield (or 

ground). Many of these cables or pairs of coaxial tubes can be 

placed in a single conduit and, with repeaters, can carry 

information for a great distance. In fact, this type of cable was 

used for high bandwidth and video service by the telephone 

companies prior to the introduction of fiber in the 1980’s. 

There are several variations. Triaxial (Triax) is a form of cable 

that uses a single center conductor with two shields. This 

composition affords a greater transmission distance with less 

loss due to interference from outside electrical signals. Twinaxial 

(Twinax) is two coaxial systems packaged within a single cable. 

Insulation

Metallic Shield (can 

be foil or braided)

Outer 

Sheath

Copper 

Core

Figure 2-3: Co-Axial Cable Illustration
Telecommunications Handbook for Transportation Professionals 

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33

Coaxial cable was invented in 1929 and first used commercially in 

1941. AT&T established its first cross-continental coaxial 

transmission system in 1940. Depending on the carrier technology 

used and other factors, twisted pair copper wire and optical fiber 

are alternatives to coaxial cable. 

Coaxial cable was originally used by some traffic departments to 

provide communications between field controllers and the central 

controller in an automated traffic signal system. It was also the 

medium of choice for early implementation of video incident 

management systems used in ITS. However, with the introduction 

of fiber optics, the use of coaxial cable has all but been 

abandoned for this purpose. 

Coaxial cable is still used for connecting CCTV cameras to 

monitors and video switchers. As the cost of using fiber optics 

has begun to drop, camera manufacturers are installing fiber 

optic transceivers in the camera. This is especially useful for 

preventing interference from electrical systems, or creating a 

secure video transmission network. 

Fiber Optics & Fiber Optic Cable 

Fiber optic (or "optical fiber") refers to the medium and the 

technology associated with the transmission of information as 

light impulses along a strand of glass. A fiber optic strand 

carries much more 

information than 

conventional copper wire 

and is far less subject to 

electromagnetic 

interference (EMI). 

Almost all telephone 

long-distance (cross 

country) lines are now 

fiber optic. 

Transmission over fiber optic strands requires repeating (or 

regeneration) at varying intervals. The spacing between these 

intervals is greater (potentially more than 100 km, or 50 miles) 

than copper based systems. By comparison, a high speed electrical 

signal such as a T-1 signal carried over twisted-pair must be 

repeated every 1.8 kilometers or 6000 feet. 

Core

Cladding 

(Refractive 

Coating)

Cover

Figure 2-4: Basic Fiber Optic Strand Construction
Telecommunications Handbook for Transportation Professionals 

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34

Fiber optic cable loss is calculated in dB per kilometer (dB/KM), 

and copper cables are rated in dB per meter (dB/M). Note: The 

Appendix of this handbook includes an explanation of how to 

calculate a fiber optic loss budget.

The fiber optic strand is constructed (see graphic) in several 

layers. The core is the actual glass, or fiber, conductor. This is 

covered with a refractive coating – called cladding - that causes 

the light to travel in a controlled path along the entire length of 

the glass core. The next layer is a protective covering that keeps 

the core and coating from sustaining damage. It also prevents 

light from escaping the assembly, and has a color coding for 

identification purposes. The core, coating and covering are 

collectively referred to as a “strand”. Fiber strand sizes are 

always referred to in terms of the diameter of the core. 

Fiber Optic Cable 

Fiber strands are typically bundled within a cable. The strands 

can be placed in a “tight” or 

“loose” buffer tube array. The 

loose buffer tube array is the 

most commonly deployed for 

outside plant applications. 

Tight buffered cable is 

generally used within a building 

for riser and horizontal cable. Tight buffer cable is also used for 

an “indoor/outdoor” application. This cable is constructed with a 

weather/moisture resistant cable sheath, and is generally used to 

get from a splice box located within several hundred feet of a 

building utility entrance, and must be run several hundred feet 

within a building to the main fiber distribution point. If the main 

fiber distribution point is less than 100 feet from the building 

entrance, there may be no advantage to using the indoor/outdoor 

cable. 

Fiber strands are placed in a large (relatively) diameter tube and 

allowed to “float” with considerable movement. As the fiber cable 

is pulled into place (in conduit, directly buried, or placed on a 

pole) the strands are not subjected to the forces of the pulling 

tension. The strands therefore sustain minimal damage or 

distortion from stretching. 

Inside plant cable is constructed 

to be flexible and lightweight. The 

cable may be coated to meet fire 

protection codes. 
Telecommunications Handbook for Transportation Professionals 

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35

Fiber cables are (as are all communications cables) manufactured 

based on their intended use. Each cable will have a standard set 

of markings indicating its 

primary use, the name of the 

manufacturer a National 

Electrical Code rating and a UL 

approval code, the number of 

fibers contained within the 

cable, the outside diameter of 

the cable, and the 

manufacturer’s product 

nomenclature. All of these items should be checked when the 

cable is delivered to a storage area and then at the job-site 

before the cable is installed. Generally, fiber cables fall into one 

of the following classifications: 

Table 2-2: Fiber Optic Cable Classifications 

Fiber Cable 

Classification 

General Purpose 

Inside Plant Device to device wiring 

Horizontal, or Intraoffice Run on a single floor and between rooms 

Riser or intra-building Run between floors in a building, usually 

in an elevator shaft or conduit 

Plenum Specially coated cable to meet fire 

codes for cable run within an air space. 

Aer i a l C ab le Us u a l ly s tr un g on U ti li ty po l es an d 

designed to be either self-supporting or 

lashed to a supporting cable. Cables are 

usually constructed with materials that 

are resistant to aging from exposure to 

sunlight. 

Direct-burial Cables that are designed to be directly 

buried in a trench. 

Duct Cable Cables that are designed to be installed 

Outside plant cable is 

constructed to withstand 

immersion in water, will resist 

exposure to ultraviolet rays, and 

is protected from rodents and 

birds. 
Telecommunications Handbook for Transportation Professionals 

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36

in a conduit 

S ub m ar in e C a b le C ab l es t ha t ar e de sig n ed to be 

submerged. 

Inside-Outside Cables that are used to transition 

between outside plant and inside plant. 

Some cables are manufactured with a metallic armored sheath to 

provide added strength and protection against rodents. Fiber 

cable that is placed in underground conduit, is normally filled 

with a waterproof gel compound. Outside plant cables are 

generally manufactured with a gel filling in the buffer tubes and 

a water blocking tape between the inner and outer jackets. Both 

outer and inner jackets are made of materials designed to 

withstand immersion and resist corrosion. 

Fiber strands and cables are manufactured with a standard color 

coding. This permits effective management of cables because of 

the normally high strand counts contained within a cable. There 

are 24 color combinations used. A loose buffer tube cable with 

576 strands would have 24 tubes colored as indicated in the 

chart below. Within each buffer tube would be 24 fiber strands 

using the same 

color scheme. 

Therefore, 

strand number 47 

would be in an 

orange buffer 

tube and have a 

rose with a 

black tracer 

colored 

protective 

coating. 

Table 2-3: Fiber 

Cable Color 

Identification Chart 

Fiber Cable Identification Color Chart 

Inner 

Jacket

Central Strength Member

Outer 

Jacket

Armor

(Corregated Steel, 

or Aramid Fiber)

Buffer 

Tubes

Filler 

Material

Figure 2-5: Fiber Optic Cable Illustration
Telecommunications Handbook for Transportation Professionals 

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Buffer Tube / Fiber Strand 

Number 

Color 

1 Blue 

2 Orange 

3 Green 

4 Brown 

5 Slate 

6 White 

7 Red 

8 Black 

9 Yellow 

10 Violet 

11 Rose 

12 Aqua 

13 Bl u e/ B la ck Tr a cer 

14 Or a n g e/ B la ck Tr ac er 

15 Gr e en /B l ack Tr a cer 

16 Br ow n /B l a ck Tr a cer 

17 Sl a te /B l ack T r a cer 

18 W hit e/ B la ck Tr a cer 

19 R ed/B l ack T r a cer 

20 Bl a ck /Y e l l ow Tr a c er 

21 Y el low /B l a ck Tr a c er 
Telecommunications Handbook for Transportation Professionals 

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22 Vio le t /B la ck Tr a cer 

23 R ose/ Bl a ck Tr ac er 

24 Aq u a /B l ack Tr a cer 

Another aspect of fiber construction is the actual size of the 

fiber strand. Most fiber is produced in a diameter of 125μm - 

a combination of the fiber core and its cladding. Most multimode 

cable used today has a core diameter of 62.5μm and most single 

mode fiber has a core diameter of 9μm. Therefore, the fiber 

strand size will normally be listed as 62.5μm/125μm for 

multimode and 9μm/125μm for single mode fiber. 

The strand diameter is kept consistent to help with the 

manufacturing and installation processes. The core diameter 

varies because of differences in some of the transmission 

characteristics of the fibers. When purchasing fiber cable to be 

added to an existing system, make certain that strand diameter 

and the core diameters match. Fusion splicing (see chapter 8 for 

an explanation of splicing) fibers with different core diameters 

is possible. However, there will probably be a misalignment that 

is the cause of poor system performance. If you must use fibers 

with different core diameters it is best to use a mechanical 

splice to assure proper alignment. Never splice multimode fiber 

to single mode fiber. If you must place single mode and multimode 

in the same system use a “mode converter” to facilitate the 

transition. 

Fiber Cable Types 

Fiber cables are produced in two basic forms: 

• Loose Tube Buffered Cable 

• Tight Buffered Cable 
Telecommunications Handbook for Transportation Professionals 

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39

Loose tube cables are primarily used in outside plant applications. 

They are designed to protect the fibers from damage (stretching 

and kinking) that might result 

from an overly aggressive cable 

puller. The tube arrangement 

also allows for easier 

transition to fiber drops at 

buildings or communication 

cabinets. The fiber strands 

float within the buffer tubes 

and are not part of the cable 

structure. Loose tube cables 

are ideal for metropolitan and 

long distance cable installations. 

Tight buffer cables are specified for inside plant use. These 

types of cables are designed for use within a controlled 

environment such as a building or inside plant equipment cabinets. 

Because the cable is used within a building the cable it requires 

less physical protection and has greater flexibility. The fibers 

within the cable are susceptible to damage from aggressive cable 

pulls because the fiber strands are part of the cable structure. 

The strands are tightly bound in a central bundle within the outer 

cable sheath. 

Fibers are assembled into either stranded or ribbon cables. 

Stranded cables are individual fibers that are bundled together. 

Ribbon cable is constructed by grouping up to 12 fibers and 

coating them with plastic to form a multi fiber ribbon. Stranded 

and ribbon fiber bundles can be packaged together into either 

loose or tight buffering cable. 

Table 2-4: Fiber Optic Cable Buffer Types 

Cable Buffer Types 

Loose Buffered Cable Tight Buffered Cable 

Individual fibers move freely within 

a buffer tube 

Fibers are tightly bound into a 

bundle 

Large cable diameter to Smaller cable diameter 

Note: Many manufacturers will 

provide both loose tube and tight 

buffered cable. Some only provide 

one type. Specify and purchase 

the type of cable that best meets 

y our needs. Remember, “in 

telecommunications, there is no 

single solution for all 

r e q uirements!!!” 
Telecommunications Handbook for Transportation Professionals 

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40

accommodate buffer tubes 

Fibers protected from cable pulling 

forces 

Fibers sensitive to pulling forces 

Used primarily for outside plant Used for inside plant and 

distribution 

Fiber Strand Types: 

Fiber strands are produced in two basic varieties: Multimode and 

Single mode. Each variety is used to facilitate specific 

requirements of the communication system. 

Multimode is optical fiber that is designed to carry multiple light 

rays or modes concurrently, each at a slightly different 

reflection angle within the optical fiber core. Multimode fiber 

transmission is used for relatively short distances because the 

modes tend to disperse over longer lengths (this is called modal 

dispersion). Multimode fibers have a core diameter of between 50 

& 200 microns. Multimode fiber is used for requirements of less 

than 15,000 feet. Multimode fiber became available during the 

early 1980’s and is still being used in many older systems. With 

the advances in fiber technology and the number of product 

choices available, multimode fiber is almost never deployed for 

new systems. There are mechanical devices available that 

accommodate a transition from multimode fiber to single mode 

fiber. Multimode fiber is generally “lit” with LED (Light Emitting 

Diodes) which are less expensive than LASER transmitters. 

Multimode fiber is generally manufactured in two sizes 50μm and 

62.5μm. 

Single mode is optical fiber that is designed for the transmission 

of a single ray or mode of light as a carrier. Single mode fiber 

has a much smaller core than multimode fiber. Single mode fiber 

is produced in several variations. The variations are designed to 

facilitate very long distances, and the transmission of multiple 

light frequencies within a single light ray. Following chapters will 

discuss transmission system capabilities – See: Ethernet, SONET 

and DWDM. Single mode fiber is generally manufactured with 

core diameters between 7 and 9 microns. 
Telecommunications Handbook for Transportation Professionals 

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41

During the past 10 years, a number of variants of single mode 

fiber have been developed. Some of the fibers are used for long 

distance systems, and others are used for metropolitan systems. 

Each of these has been developed with special characteristics 

designed to enhance 

performance for a 

specific purpose. The 

most widely used all 

purpose single mode fiber 

is SMF-28 which can be 

used for all purposes, 

except long reach DWDM 

systems. 

Freeway Management and 

Traffic Signal Control 

would be considered – 

from a communications 

perspective – as general 

purpose systems. 

Designers of 

Transportation Management Systems using fiber should strongly 

consider specifying SMF-28 type single mode fiber. This fiber is 

very available and normally is lowest in price. 

Fiber optic cable is priced on the basis of strand feet. A 5,000 

foot cable with two fiber strands is 10,000 fiber strand feet. A 

5,000 foot cable with 24 fibers is 120,000 strand feet. The cost 

of the first cable might be $5,000, or 50 cents per strand foot. 

The cost of the second cable might be $24,000, but the cost per 

strand foot is only 20 cents. Therefore, when purchasing fiber 

optic cable, it is always best to consider potential system 

additions in order to incur a lower overall materials cost. 

Remember, price per fiber strand foot is not the only factor to 

consider in overall system costs. Digging a four (4) foot deep 

trench, placing conduit in the trench, and repairing the street 

carries the same cost regardless of the strand count, and that’s 

about 90% of the total cost of deploying fiber optic cable. If 

construction costs $100 per linear foot, then the overall cost per 

strand foot is $50.50 per foot for two (2) strands and $4.37 for 

twenty-four (24) strands. Items not included in this calculation 

are the costs associated with splicing, optimization and 

engineering. Those are 10% of the total cost. 

Note: SMF-28 is a trademarked 

nomenclature of Corning Cable, that 

has become a generic term used to 

describe an all purpose single mode 

fiber. Nearly all traffic signal and 

freeway management systems will use 

an all purpose single mode fiber. Fiber 

optic product characteristics are in a 

constant state of change. Investigate 

before finalizing system 

specifications. The Resource Section 

of this handbook contains a list of 

fiber optic cable manufacturers and 

their web sites. 
Telecommunications Handbook for Transportation Professionals 

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42

Single Mode vs. Multimode Fiber 

Following is a general comparison of Single Mode and Multimode 

fibers: 

Single mode fiber has a very small core causing light to travel in 

a straight line and typically has a core size of 8 to 10 microns. It 

has (theoretically) unlimited bandwidth capacity, that can be 

transmitted for very long distances (40 to 60 miles). Multimode 

fiber supports multiple paths of light and has a much larger core 

- 50 or 62.5 microns. Because multimode fibers are five to six 

times the diameter of single mode, transmitted light will travel 

along multiple paths, or modes within the fiber. Multimode fiber 

can be manufactured in two ways: step-index or graded index. 

Step-index fiber has an abrupt change or step between the index 

of refraction of the core and the index of refraction of the 

cladding. Multimode step-index fibers have lower bandwidth 

capacity than graded index fibers. 

Graded index fiber was designed to reduce modal dispersion 

inherent in step index fiber. Modal dispersion occurs as light 

pulses travel through the core along higher and lower order 

modes. Graded index fiber is made up of multiple layers with the 

highest index of refraction at the core. Each succeeding layer 

has a gradually decreasing index of refraction as the layers move 

away from the center. High order modes enter the outer layers 

of the cladding and are reflected back towards the core. 

Multimode graded index fibers have less attenuation (loss) of the 

output pulse and have higher bandwidth than multimode stepindex fibers. 

Single mode fibers are not affected by modal dispersion because 

light travels a single path. Single mode step-index fibers 

experience light pulse stretching and shrinking via chromatic 

dispersion. Chromatic dispersion happens when a pulse of light 

contains more than one wavelength. Wavelengths travel at 

different speeds, causing the pulse to spread. Dispersion can also 

occur when the optical signal gets out of the core and into the 

cladding, causing shrinking of the total pulse. 

Single mode shifted fiber uses multiple layers of core and 

cladding to reduce dispersion. Dispersion shifted fibers have low 
Telecommunications Handbook for Transportation Professionals 

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43

attenuation (loss), longer transmission distances, and higher 

bandwidth. 

Table 2-5: Comparison Single Mode Fiber & Multimode Fiber 

Comparison Single Mode Fiber – Multimode Fiber 

C h a r a c t e r i s t i c S i n g l e M o d e M u l t i m o d e 

Bandwidth Virtually Unlimited Less than virtually unlimited 

Sig n a l Q ua l ity E xc e l len t ov er l on g 

distances 

Excellent over short 

distances 

Primary 

Attenuation 

Chromatic 

Dispersion 

Modal Dispersion 

Fib er Ty p es St ep I n de x & 

Dispersion Shifted 

Step & Graded Index 

Typical Application Almost anything 

(including Ethernet)

Analog Video; Ethernet; 

Short Range Communications 

Wireless Media 

Since the invention of the Wireless Telegraph in 1896 

communication system designers have sought to use wireless 

because of the reduced infrastructure cost and complexity, when 

compared to wireline communication systems. There is no need to 

construct miles of telephone line poles or cable trenches. Simply 

put in a few strategically positioned radio towers and transmit 

around the world. Today, wireless systems are significantly more 

complex because we want to allow millions of users to make 

telephone calls or receive feature length movies via wireless 

systems. There are four general types of wireless (radio) 

communication systems: 

• Cellular Telephone 

• Basic 2-Way Radio 

• Point-to-point 

• Wi-Fi (Wireless Fidelity), and recently, Wi-Max 

Traffic signal and freeway management systems use three of the 

variants to support operations, and are considering the use of 
Telecommunications Handbook for Transportation Professionals 

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44

Wi-Fi. The Wi-Fi/Wi-Max systems are becoming increasingly 

ubiquitous in their deployment, and a part of most 

telecommunication deployment strategies. Chapter 7 provides a 

description of a proposed use of Wi-Max for the Irving, Texas 

traffic signal system. Wi-Fi/Wi-Max systems are Ethernet based 

and allow for a seamless transition from wireless to wireline. 

Cellular Systems 

Cellular wireless telephone networks provide users with a mobile 

extension of their wireline voice networks. During the past 10 

years, cellular telephone systems moved from a luxury that only 

wealthy individuals or corporations could afford to a commodity 

service that is affordable, and used by majority of adults (also 

large numbers of children and teenagers) in North America 

Europe and the Pacific Rim countries. Many third world countries 

are expanding their telephone networks via the creation of an 

extensive wireless system that eliminates the cost of 

constructing the “wired” systems. 

Cellular telephone systems come in two basic varieties: Analog or 

Digital. Analog uses two standards – AMPS (advanced mobile 

phone system), and GSM (global system for mobile 

communication). AMPS was deployed in North America and GSM 

was deployed in most of the rest of the world. The two systems 

are not compatible. Different telephone handsets are required, or 

at least a hand set that will incorporate both systems. 

Many digital variants are in the process of being deployed. 

Because the cost of deployment is so high cellular carriers have 

been building the required infrastructure in several stages. The 

first stage is called 2nd generation. Carriers took the existing 

analog service with one user per radio channel and added a system 

that would allow several users per radio channel. These are 

multiplexing schemes called TDMA (time division multiple access) 

- an analog service, and CDMA (code division multiple access) – a 

digital service. The basic plan was to move from 2nd to 3rd 

generation within a short period of time. The upgrade would 

provide users with voice and data services. The data services 

would provide significantly higher throughput – greater than 56 

Kbps – for internet and e-mail access. However, the cost of the 

upgrade was so high that carriers decided to take an 

intermediate step – 2.5G – to provide improved voice and low 

bandwidth data services. Carriers were hoping that the internet 
Telecommunications Handbook for Transportation Professionals 

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45

boom of the late 1990’s would create a consumer demand for 

wireless internet services. However, this demand did not 

materialize, and the carriers slowed their deployment of 3G 

systems. With the advent of inexpensive Wi-Fi/Wi-Max systems, 

general consumer and commercial demand, and laptop computers 

that can run for 5 hours on battery, wireless carriers are 

deploying “overlay systems” that can provide broadband internet 

access and general networking services. Wi-Fi/Wi-Max will be 

discussed later in this chapter, and an example of a Wi-Fi/WiMax system used for traffic signal control will be discussed in 

Chapter 7. 

CDPD 

CDPD (cellular digital 

packet data) is an analog 

data overlay that has been 

in operation since 1993. 

This service provides data 

throughput at 9.6 Kbps (in 

theory up to 19.2 Kbps), 

and is an overlay to the 

analog cellular telephone 

system. CDPD is being used by a number of communities as a 

wireless communication link to control traffic signal systems. As 

the analog cell systems are converted to digital, CDPD is being 

phased out. The wireless carriers are not providing a substitute. 

If you have an existing system that relies on CDPD service, you 

will need to change to a new service. 

Point-to-Point Radio Systems 

These are radio systems that communicate between fixed 

locations. Generally, they are used as a replacement for wireline 

systems. Point-to-Point systems can be established using almost 

any radio frequency. However, most systems are developed using 

frequencies in the microwave spectrum of 800 MHz to 30 GHz. 

The Federal Communications Commission has designated groups of 

frequencies throughout the usable radio spectrum for “fixed 

service” use. 

Microwave 

Microwave is a fixed point-to-point service that provides 

connectivity between major communication nodes. Telephone and 

An “overlay system” is one that is 

built upon and existing infrastructure. 

Because there is a basic cellular 

transmitter site infrastructure in 

place, wireless carriers can deploy WiFi systems for substantially less 

mone y than u p g radin g to 3G.
Telecommunications Handbook for Transportation Professionals 

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46

long distance companies use the service to provide backup for 

their cabled (wireline) infrastructure and to reach remote 

locations. Public Safety agencies use microwave to connect 2-way 

radio transmitter sites to a central location. Businesses also use 

these systems for the same purposes. 

The frequencies allocated for this service are in the 6 and 11 

gigahertz ranges. All users are required to obtain a license for 

use from the FCC (Federal Communications Commission). 

Frequency licenses are granted on a non-interfering (with other 

users) basis. Systems can be designed to operate over distances 

of about 20 miles between any two points. Other frequencies 

available in the 900 megahertz, 2 and 23 gigahertz range do not 

require a license. Because these frequencies do not require a 

license it is up to users to resolve any interference problems 

without support from the FCC. As with all microwave, the FCC 

permits only point-to-point uses. Many DOTs are using spread 

spectrum systems in the 900 MHz and 2 GHz bands. 

Spread Spectrum Radio 

Spread spectrum radio is a technology that “spreads” the 

transmission over a group of radio frequencies. Two techniques 

are used. The most common is called “frequency hopping” The 

radio uses one frequency at a time but at pre-determined 

intervals jumps to another frequency to help provide a “secure” 

transmission. The second system actually spreads the 

transmission over several frequencies at the same time. The 

method helps to prevent interference from other users. These 

systems are generally used for distances of less than 2 air miles. 

Spread spectrum technology for telecommunication systems was 

originally developed during World War II 6

. Most notably, the 

technology has inherent features that provide for a very secure 

means of communicating even in “unfriendly” RF environments. 

Despite widespread military use, the technology was not made 

available for commercial use until l995 when the U.S. Federal 

Communications Commission (FCC) issued ruling 15.247 permitting 

the use of spread spectrum technology for commercial 

applications in the 900, 2400 and 5800 MHz frequency bands. 

 

6

 Hedy Lamarr, once considered as the most beautiful woman in Hollywood was a co-inventor of the frequency 

hopping technique for spread spectrum radio. Hedy and her co-inventor George Antiel, a musician) created the 

technique as part of a guidance system for torpedoes during WWII. 
Telecommunications Handbook for Transportation Professionals 

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47

The basic concept of spread spectrum refers to an RF modulation 

technique that spreads the transmit signal over a wide spectrum 

(or bandwidth).Contrary to conventional narrow band modulation 

techniques that are evaluated by their ability to concentrate a 

signal in a narrow bandwidth, spread spectrum modulation 

techniques use a much wider bandwidth. 

A typical spread spectrum transmitter will integrate the actual 

signal with a sequence of bits that codes (referred to as pseudorandom code) and spreads the signal over a bandwidth usually 

from 20 to 30 MHz. 

The spreading is actually accomplished using one of two different 

methods - direct sequence or frequency hopping. Direct sequence 

spread spectrum uses the pseudo-random code, integrated with 

the signal, to generate a binary signal that can be duplicated and 

synchronized at both the transmitter and receiver. The resulting 

signal evenly distributes the power over a wider frequency 

spectrum. Direct sequence spread spectrum is usually used to 

transmit higher speed digital data for T1, or high-speed wireless 

data networks. 

The second popular type of spread spectrum modulation is 

frequency hopping. This technique is similar to a conventional 

narrow band carrier with a narrow transmit bandwidth. The 

difference from the former is a random hopping sequence within 

the total channel bandwidth. Spread spectrum modulation 

techniques have a principal advantage over other radio 

techniques: the transmitted signal is diluted over a wide 

bandwidth, which minimizes the amount of power present at any 

given frequency. The net result is a signal that is below the noise 

floor of conventional narrow band receivers, but is still within 

the minimum receiver threshold for a spread spectrum receiver. 

While the receiver is able to detect very low signal powers, the 

receivers are also designed to reject unwanted carriers, including 

signals which are considerably higher in power than the desired 

spread spectrum signal. Each transmitter and receiver is 

programmed with unique spreading sequences which are used to 

de-spread the desired signal and spread the undesired signal, 

effectively canceling the noise. 
Telecommunications Handbook for Transportation Professionals 

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48

Two-way Radio 

Two-way radio systems 

have been in common use 

since the 1930’s. 

Originally used by the 

military, various federal 

agencies, police, fire and ambulance, and local governments, its 

use has expanded to include almost every aspect of our social 

infrastructure, including individual citizens using “Ham Radio” 

systems. Most commonly used frequencies are in the 30, 150, 450 

– 512 and 800 megahertz ranges. Coverage is usually expressed in 

terms of “air mile radius”. Systems in the 150 MHz band can 

typically cover 15 to 30 air miles in radius from a single 

transmitter location. 

The FCC has been encouraging the use of regional systems that 

incorporate all state, county and municipal agencies into a single 

group of radio channels. The available radio spectrum is being reallocated to accommodate these systems. At the same time, the 

FCC is restricting transmitter power outputs and antenna height. 

Many of the early (1970s & 1980s) system designs sought to use 

maximum transmitter power outputs of more than 100 watts and 

very high antenna sites. This usually created interference 

problems with other users on the same radio frequency. 

Today, many Departments of Transportation are joining forces 

with public safety agencies to create a common radio 

communication system. This allows for easier coordination of 

resources to resolve traffic incidents. 

Wi-Fi 

Wi-Fi Systems is a term that is applied to a generic point-tomultipoint data communication service. The Federal 

Communications Commission (FCC) has set aside radio spectrum in 

the 900 MHz, 2GHz and 5 GHz frequency range. The frequencies 

are available for use by the general population and commercial 

enterprise. No licenses are required, and the only restrictions 

are that systems not exceed power or antenna height 

requirements. Complete rules governing the use of Wi-Fi systems 

are listed under FCC rules: Title 47 CFR Part 15. 

In its 1989 revision of the Part 15 rules, the Commission 

established new general emission limits in order to create more 

flexible opportunities for the development of new unlicensed 

Coverage for all radio systems is 

expressed in terms of “air miles”, 

because radio waves tend to travel in 

straight lines. 
Telecommunications Handbook for Transportation Professionals 

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49

transmitting devices. These more general rules allow the 

operation of unlicensed devices for any application provided that 

the device complies with specified emission limits. This revision 

also established new “restricted bands” to protect certain 

sensitive radio operations, such as satellite downlink bands, and 

federal government operations, and prohibited transmissions by 

unlicensed devices in those bands. The rules have been further 

modified to add spectrum and encourage the growth of Wi-Fi 

systems. The FCC Spectrum Policy Task Force issued a report 

from its Unlicensed Devices and Experimental Licenses Working 

Group in November 2002. 

The full report is available at the following web site: 

http://www.fcc.gov/sptf/files/E&UWGFinalReport.doc. The report 

takes note of the significant growth of Wireless ISPs and the 

increasing use of this service to provide broadband internet 

access in rural areas. The report makes recommendations for 

consideration of increasing authorized power output in rural 

areas as well as making additional spectrum available. 

Table 2-6: Frequencies for Unlicensed Radio Systems 

Bands Available for Unlicensed Spectrum 

B a n d A ut h o ri z ed F r e q u e n ci es (MH z ) 

ISM/ Spread 

Spectrum 1985 902-928, 2400-2483.5 & 5725-5850 

Unlicensed PCS 1993 1910-1930 & 2390-2400 

Millimeterwave 1995 59,000-64,000 

U-NII 1998 5150-5350 & 5725-5825 

Millimeterwave 

(Expansion) 2001 57,000-59,000 

Many traffic signal and freeway management systems are 

currently using spread spectrum radio systems in the ISM bands. 

The following table provides some estimates of the number of 

devices used in the unlicensed spectrum - this information was 

provided by the Consumer Electronics Association (CEA) to the 

FCC in September, 2002: 
Telecommunications Handbook for Transportation Professionals 

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50

Table 2-7: CEA Estimates of the Number of Low Power Radio Devices 

CEA Estimates of Low Power Device Usage 

P r o d u c t P e n et r a ti o n N um b er p er 

Household 

Total 

Installed 

Base 

(millions) 

Cordless Phones 81.0% 1.50 130.01 

Garage Door Openers 40.8% 1.29 56.26 

Wireless Routers NA NA 1.14 

Remote Control Toys 19.5% 2.61 54.47 

Toy Walkie-talkies 15.1% 1.85 29.81 

Baby Monitors 10.5% 1.38 15.52 

Home Security Systems 18.0% 1.10 21.21 

Keyless Entry Systems 

for Cars 

26.5% 1.40 39.71 

The IEEE is working on developing and improving a number of 

wireless transmission standards for Wi-Fi. The most widely used 

are the 802.11 series. The reader should check the IEEE web site 

for the latest standards being issued, and consult with equipment 

vendors and systems engineers to determine which are applicable 

for their specific requirements. A continuing theme throughout 

this handbook is that no single system or standard is a solution 

for all problems. 
Telecommunications Handbook for Transportation Professionals 

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WLAN 

A wireless LAN lets users roam around a building with a computer 

(equipped with a wireless LAN card) and stay connected to their 

network without being connected to a wire. The standard for 

WLANs put out by the Institute of Electrical and Electronics 

Engineers (IEEE) called “802.11B” or “Wi-Fi” is making WLAN use 

faster and easier. A WLAN can reach 150 m radius indoors and 

300 m outdoors. WLANs require a wired access point that 

connects all the wireless devices into the wired network. 

802.11A, is supposed to transfer data at even higher speeds of up 

to 54 Mbps in the 5 GHz band. 

802.11B transfers data at speeds of up to 11 Mbps in the 2.4 GHz 

radio band (a license is not required for this band). 

802.11G, offers up to 54 Mbps data rates, functions in the 2.4 

GHz range, and is compatible with 802.11B. Equipment using the 

802.11B standard will work in an 802.11G system. 

WLANs are used on college campuses, in office buildings, and 

homes, allowing multiple users access to one Internet connection. 

WLAN hubs are also deployed in many airports, and popular 

commercial establishments such as coffee shops and restaurants. 

These hubs allow laptop users to connect to the Internet. 

A major drawback of WLANs is the lack of security. Research has 

found flaws in the 802.11 systems. Transmissions can be 

intercepted making it easy for hackers to interfere with 

communications. Another problem is overcrowding of the 

bandwidth. Too many people or businesses using WLANs in the 

same area, can overcrowd the frequency band. Problems with 

signal interference can occur and there are fears that the 

airwaves may become overloaded. Despite these drawbacks, 

WLANs are a successful and popular technology, which are 

widespread and being incorporated into most new laptop and 

personal digital assistant (PDA) computers. 

Note: two good sources of information on these types of systems 

are the Wi-Max organization at http://www.wimaxforum.com , and the 

Wi-Fi organization at http://www.wi-fi.org . 

Wi-MAX 

Based on the IEEE 802.16 series of standards, Wi-MAX is a wide 

area wireless system with a coverage area stated in terms of 
Telecommunications Handbook for Transportation Professionals 

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52

miles rather than feet. The standard was developed to provide 

for fixed point-to-multipoint coverage with broadband 

capabilities. For the latest information on the evolving 802.16 

standards, check the IEEE web site: 

http://grouper.ieee.org/groups/802/16/index.html

“802.16 is a group of broadband wireless communications standards for 

metropolitan area networks (MANs) developed by a working group of the 

Institute of Electrical and Electronics Engineers (IEEE). The original 802.16 

standard, published in December 2001, specified fixed point-to-multipoint 

broadband wireless systems operating in the 10-66 GHz licensed spectrum. An 

amendment, 802.16a, approved in January 2003, specified non-line-of-sight 

extensions in the 2-11 GHz spectrum, delivering up to 70 Mbps at distances up 

to 31 miles. Officially called the WirelessMANTM specification, 802.16 

standards are expected to enable multimedia applications with wireless 

connection and, with a range of up to 30 miles, provide a viable last mile 

technology.” 7

Chapter seven provides a presentation of how the City of Irving 

Texas is using an 802.16 based system to reduce the overall cost 

of deploying a new centrally controlled traffic signal system. 

Free Space Optics (FSO) 

(FSO) Free Space Optics is another wireless system being used 

today. Instead of using radio frequencies, this system uses a 

LASER transmitted through the air between two points. The 

LASER can be used for transmission of broadcast quality video. 

These systems are limited to an effective range of 3 air miles. 

Transmission Signaling Interfaces 

All Freeway Management and Traffic Signal systems rely on a 

communications process to support their operations. Some use a 

very simple process with “low speed” data transmitted between a 

single device and a central computer. The basic transmission of 

the data, accomplished by transmi tting bit by bit over a single 

path (wire or some other transmission medium) between two 

communication points, is called “serial”. Other systems use a more 

complex process with multiple bits transmitted simultaneously 

over multiple paths between two points, or “parallel”. This section 

looks at the transmission of voice, data, and video and the 

various types of physical and logical interfaces used for this 

purpose. 

 

7

 IEEE 802.16 web site – description of 802.16 service. 
Telecommunications Handbook for Transportation Professionals 

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53

DATA & VOICE SIGNALING - BASICS

Carrier (the telephone company) operated communication 

networks are primarily designed to facilitate the transmission of 

voice in either analog or digital formats. During the 1990s, many 

new telecommunication companies were formed dedicated to 

providing efficient transmission of data. Some of these 

companies attempted to build their own communications networks, 

but ran out of financial resources because of the enormous 

expense for construction, operation and maintenance. Many of 

their customers wanted to use one network for both voice and 

data, and only wanted to deal with one communications provider. 

Voice signaling interfaces are very simple. They are either 2 or 4 

wire, and pass frequencies in the 0 to 4,000 Hz range. This same 

frequency range is used by modems to interface with the 

telephone networks. The modem converts the output of a 

computer to voice frequencies. Traffic signal controllers have 

used modems to communicate over voice based telephone networks 

for many years. They use a combination of dial-up and private line 

services. The digital output of the traffic signal field controller 

is converted to an analog format by the modem. 

In the early 1960s, the Telephone Companies (Carriers) 

recognized that customers would want to transmit data via the 

existing networks. The Carriers began to add equipment and 

processes to their networks that 

would support the need. They 

started with the use of private 

fixed point-to-point services and 

then added switched data 

communication services via the 

PSTN (Public Switched Telephone Network). 

Data can be transmitted in either an analog or digital format and, 

transmitted via 2 or 4 wire circuit. In an analog system, most 

data is transmitted using a dial-up modem via the PSTN. Private 

line systems (leased from a Carrier) normally use a 4 wire 

communication circuit. Some carriers do offer 2 wire private line 

services. Private line service is provided as either analog, or 

digital. Private-line circuits are always point-to-point and never 

run through a switch. 

Analog Private-line circuits are normally referred to as 3002 or 

3004. The 3000 designation refers to available bandwidth. The 2 

Data is information content. 

Analog and digital are formats 

for transmitting information. 
Telecommunications Handbook for Transportation Professionals 

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54

and 4 refer to the number of wires in the circuit. Digital Privateline services are: DDS (Digital Data Service – 56 Kbps or less); 

T-1/T-3; DS-1/DS-3; Fractional T-1; SONET; Ethernet (a recent 

addition to the types of available services). 

Very often, the terms T-1/T-3 and DS-1/DS-3 are used 

interchangeably. However, there is a fundamental difference 

between the service offerings. T-1/T-3 circuits are formatted by 

the Carrier into voice channel equivalents. All multiplexing 

equipment with maintenance and operation is provided by the 

Carrier. Pricing for these services is usually regulated by state 

public utility commissions (called a tariff). DS-1/DS-3 circuits 

are provided without format. The end-user is responsible for 

supplying the multiplexing equipment to format the circuit. 

Maintenance and operation is the responsibility of the end-user. 

The Carrier is only responsible for making certain that the 

circuit is always available for use. Fees for DS-1/DS-3 circuits 

are typically not regulated, and are based on market competition. 

ELECTRO-MECHANICAL SIGNAL INTERFACES

Electro-mechanical interfaces for data transmission and signaling 

normally fall under the following standards: RS-232; RS-422; RS423; RS-449; RS-485. Each of these standards provides for the 

connector wiring diagrams and electrical signaling values for 

communications purposes. These standards were developed by the 

EIA (Electronic Industries Alliance) and the TIA 

(Telecommunications Industry Association). More information can 

be found at the EIA web site - http://www.eia.org , and the TIA web 

site – http://www.tiaonline.org . Notice in the following diagram that 

all 25 pins of a 25 pin connector have an assigned function. This 

S hield S hield

XMTR

RCVR

XMTR

RCVR

Figure 2-6: Diagram of Basic Connector Wiring
Telecommunications Handbook for Transportation Professionals 

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is due to the fact that the connector standard was developed 

prior to the development of software that would control most of 

the functions. Most personal computers (PC) use a 9 pin variation. 

There are also variations that use 3 or 5 pins. Please check the 

equipment manufacturer’s recommendations. Many communication 

system problems occur because the connectors are not properly 

wired. Following is a listing of 

some of the connector 

standards that use a d-sub 

miniature type connector: 

• RS 449 (EIA-449) 

• RS 530 (EIA 530) 

• RS-232D 

• RS232 

• RS366 

• RS422 37pin 

• RS422 9pin 

• Serial (PC25) 

• Serial (PC9) 

All of the above are based on a similar standard and there is 

latitude for manufacturers to use some of the leads in these 

connectors for a special function. 

If your system is connected via a carrier network the 

transmitter-receiver cross over is done in the network. In a 

private network the crossover is accounted for in the basic 

network design. Double check to make certain that the design 

accounts for transmitter to receiver connections. 

VIDEO TRANSMISSION

During the past 15 years, traffic and freeway management 

agencies have been integrating the use of CCTV cameras into 

their operational programs. The heavy use of this technology has 

created a need to deploy very high bandwidth communication 

networks. The transmission of video is not very different from 

voice or data. Video is transmitted in either an analog or digital 

format. Video transmitted in an analog format must travel over 

If you are encountering a communication 

problem – check the connectors and their 

wiring pattern. Remember the basic 

elements of all communications systems: 

transmitter; receiver; medium. If the 

transmitter wire is connected to the same 

numbered pin at both ends, the receivers 

can’t hear.
Telecommunications Handbook for Transportation Professionals 

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coaxial cable or fiber optic cable. The bandwidth requirements 

cannot be easily handled by twisted pair configurations. 

Video can be transmitted in a digital format via twisted pair. It 

can be transmitted in a broadband arrangement as full quality and 

full motion, or as a compressed signal offering lower image or 

motion qualities. Via twisted pair, video is either transmitted in a 

compressed format, or sent frame-by-frame. The frame-by-frame 

process is usually called “slow-scan video”. 

Full color broadcast analog video requires a substantial amount of 

bandwidth that far exceeds the capacity of the typical twisted 

pair analog voice communication circuit of 4 KHz. Early 

commercial television networks were connected via Coaxial cable 

systems provided by AT&T Long Distance. These networks were 

very costly to operate and maintain, and had a limited capability. 

Transmission of analog video requires large amounts of 

bandwidth, and power. The most common use of analog video 

(outside of commercial broadcast TV) is for closed circuit 

surveillance systems. The cameras used in these systems use less 

bandwidth than traditional broadcast quality cameras, and are 

only required to send a signal for several hundred feet. For 

transmission distances (of analog video) of more than 500 feet, 

the system designer must resort to the use of triaxial cable, or 

fiber optics. Depending upon other requirements, the system 

designer can convert the video to another signal format. The 

video can be converted to a radio (or light) frequency, digitized, 

or compressed. 

Cable companies have traditionally converted television broadcast 

signals to a radio frequency. With this technique, they can 

provide from 8 to 40 analog channels in a cable system using 

coaxial cable (more about multiplexing later in this chapter). 

Cable company operators wanting to provide hundreds of program 

channels will convert the video to a radio frequency, and then 

digitize. The cable company is able to take advantage of using 

both fiber and coaxial cable. These are called HFC (hybrid fiber 

coax) systems. Fiber is used to get the signal from the cable 

company main broadcast center to a group of houses. The existing 

coaxial cable is used to supply the signal to individual houses. 

Early freeway management systems used analog video converted 

to RF and transmitted over coaxial cable. Later systems used 
Telecommunications Handbook for Transportation Professionals 

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fiber optic cable with either RF signal conversion, or frequency 

division multiplexing (see Multiplexing in this chapter). 

With the introduction high bandwidth microprocessors and 

efficient video compression algorithms, there has been a shift 

from analog video transmission systems to digital systems. New 

processes such as Video over IP (Internet Protocol) and 

streaming video allow for the broadcast of video incident images 

to many user agencies via low (relatively) cost communication 

networks. Before looking at the systems, let’s take a look at the 

various types of video compression schemes. 

VIDEO COMPRESSION

Compressed Video - Since the mid-1990s, FMS system designers 

have turned to digital compression of video to maximize 

resources, and reduce overall communication systems costs. The 

digital compression of video allows system operators to move 

video between operation centers using standard communication 

networks technologies. 

Video compression systems can be divided into two categories – 

hardware compression and software compression. All video 

compression systems use a Codec. The term Codec is an 

abbreviation for coder/decoder. A codec can be either a software 

application or a piece of hardware that processes video through 

complex algorithms, which compress the file and then decompress 

it for playback. Unlike other kinds of file-compression packages 

that require you to compress/decompress a file before viewing, 

video codecs decompress the video on the fly, allowing immediate 

viewing. This discussion will focus on hardware compression 

technologies. 

VIDEO CODECS 

Codecs work in two ways - using temporal and spatial compression. 

Both schemes generally work with "lossy" compression, which 

means information that is redundant or unnoticeable to the 

viewer gets discarded (and hence is not retrievable). 

Temporal compression is a method of compression which looks for 

information that is not necessary for continuity to the human eye 

It looks at the video information on a frame-by-frame basis for 

changes between frames. For example, if you're working with 

video of a section of freeway, there's a lot of redundant 
Telecommunications Handbook for Transportation Professionals 

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information in the image. The background rarely changes and most 

of the motion involved is from vehicles passing through the scene. 

The compression algorithm compares the first frame (known as a 

key frame) with the next (called a delta frame) to find anything 

that changes. After the key frame, it only keeps the information 

that does change, thus deleting a large portion of image. It does 

this for each frame. If there is a scene change, it tags the first 

frame of the new scene as the next key frame and continues 

comparing the following frames with this new key frame. As the 

number of key frames increases, so does the amount of motion 

delay. This will happen if an operator is panning a camera from 

left to right. 

Spatial compression uses a different method to delete 

information that is common to the entire file or an entire 

sequence within the file. It also looks for redundant information, 

but instead of specifying each pixel in an area, it defines that 

area using coordinates. 

Both of these compression methods reduce the overall 

transmission bandwidth requirements. If this is not sufficient, 

one can make a larger reduction by reducing the frame rate (that 

is, how many frames of video go by in a given second). Depending 

on the degree of changes one makes in each of these areas, the 

final output can vary greatly in quality. 

Hardware codecs are an efficient way to compress and 

decompress video files. Hardware codecs are expensive, but 

deliver high-quality results. Using a hardware-compression device 

will deliver high-quality source video, but requires viewers to 

have the same decompression device in order to watch it. 

Hardware codecs are used often in video conferencing, where the 

equipment of the audience and the broadcaster are configured in 

the same way. A number of standards have been developed for 

video compression – MPEG, JPEG, and video conferencing. 

VIDEO COMPRESSION

MPEG stands for the Moving Picture Experts Group. MPEG is an 

ISO/IEC working group, established in 1988 to develop standards 

for digital audio and video formats. There are five MPEG 

standards being used or in development. Each compression 

standard was designed with a specific application and bit rate in 
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mind, although MPEG compression scales well with increased bit 

rates. 

Following is a list of video compression standards: 

• MPEG-1 - designed for transmission rates of up to 1.5 

Mbit/sec – is a standard for the compression of moving 

pictures and audio. This was based on CD-ROM video 

applications, and is a popular standard for video on the 

Internet, transmitted as .mpg files. In addition, level 3 of 

MPEG-1 is the most popular standard for digital compression 

of audio--known as MP3. This standard is available in most 

of the video codec units supplied for FMS and traffic 

management systems. 

• MPEG-2 - designed for transmission rates between 1.5 and 

15 Mbit/sec – is a standard on which Digital Television set 

top boxes and DVD compression is based. It is based on 

MPEG-1, but designed for the compression and transmission 

of digital broadcast television. The most significant 

enhancement from MPEG-1 is its ability to efficiently 

compress interlaced video. MPEG-2 scales well to HDTV 

resolution and bit rates, obviating the need for an MPEG-3. 

This standard is also provided in many of the video codecs 

supplied for FMS. 

• MPEG-4 – a standard for multimedia and Web compression - 

MPEG-4 is an object-based compression, similar in nature to 

the Virtual Reality Modeling Language (VRML). Individual 

objects within a scene are tracked separately and 

compressed together to create an MPEG4 file. The files are 

sent as data packages and assembled at the viewer end. The 

result is a high quality motion picture. The more image data 

that is sent the greater the lag-time (or latency) before the 

video begins to play. Currently, this compression standard is 

not suited for real-time traffic observation systems that 

require pan-tilt-zoom capability. The “forward and store” 

scheme used in this system inhibits eye-hand coordination. 

However, this is an evolving standard. The latency factor 

between image capture and image viewing is being reduced. 

The latency factor can be reduced to a minimum if the image 

and motion quality do not have to meet commercial video 

production standards. Most surveillance systems can 
Telecommunications Handbook for Transportation Professionals 

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60

function without this quality and can use pan-tilt-zoom 

functions. 

• MPEG-7 - this standard, currently under development, is also 

called the Multimedia Content Description Interface. When 

released, it is hoped that this standard will provide a 

framework for multimedia content that will include 

information on content manipulation, filtering and 

personalization, as well as the integrity and security of the 

content. Contrary to the previous MPEG standards, which 

described actual content, MPEG-7 will represent information 

about the content. 

• MPEG-21 - work on this standard, also called the Multimedia 

Framework, has just begun. MPEG-21 will attempt to 

describe the elements needed to build an infrastructure for 

the delivery and consumption of multimedia content, and how 

they will relate to each other. 

• JPEG - stands for Joint Photographic Experts Group. It is 

also an ISO/IEC working group, but works to build standards 

for continuous tone image coding. JPEG is a lossy 

compression technique used for full-color or gray-scale 

images, by exploiting the fact that the human eye will not 

notice small color changes. Motion JPEG is a standard that is 

used for compression of images transmitted from CCTV 

cameras. It provides compressed motion in the same manner 

as MPEG, but is based on the JPEG standard. 

• H.261 - is an ITU standard designed for two-way 

communication over ISDN lines (video conferencing) and 

supports data rates which are multiples of 64Kbit/s. 

• H.263 - is based on H.261 with enhancements that improve 

video quality over modems. 

STREAMING VIDEO

Streaming video relies on the video compression standards listed 

above, and primarily on the MPEG-4 video CODEC. Streaming video 

is not a transmission technique. Streaming video is a protocol for 

the efficient movement of entertainment (or news broadcasts) to 

individual users via the internet. 

A streaming video system requires the use of a video server to 

store content that is downloaded to the end user via a 
Telecommunications Handbook for Transportation Professionals 

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communications network. The first few seconds of the program 

are forwarded to the viewer, with the additional information 

downloaded as the first images are being viewed. This provides 

the end user with a continuous program, or “stream’ of 

information – hence, the term streaming video. 

Streaming video can be used to provide travelers with delayed (by 

five to ten seconds) images from traffic intersections, or live 

reports from transportation management centers. This technique 

can also be used to connect public safety agencies to direct video 

feeds from traffic incident locations via the internet, or an 

intranet. The video codecs used to support streaming are 

software based, not hardware based. Several common video codec 

applications are in use throughout the world. Your desktop PC 

probably has two (or more) of these applications. Microsoft’s 

“Windows Media Player” and Apple’s “Quicktime” are two of the 

most popular. Real Networks has a very popular media player. 

These media players are designed to play multiple types of media 

files. Almost all PC manufacturers include media player software 

as part of their package. A discussion of Video over IP and 

Ethernet will be presented in chapters 7 and 9. 

Basic Telephone Service 

This section will look at the various aspects of basic voice and 

analog telephone services including dial-up and special service 

voice and data circuits. The primary reason for existence of 

traditional telephone (including cellular) carriers is to provide 

person-to-person voice communications. This fact will continue to 

remain true as long as our present system of telecommunications 

endures. Certainly, the methods and processes used to provide 

that communication have gone through tremendous change in the 

past 25 years, however, we can count on the basic process to 

continue to be used into the foreseeable future. Voice over IP 

(VoIP) is beginning to emerge as a replacement for traditional 

switched analog voice services. During the writing of this 

handbook, most of the major communication carriers announced 

that construction investments would be shifted to “Internet 

Telephony” systems (the carrier term for VoIP).
Telecommunications Handbook for Transportation Professionals 

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P.O.T.S., or dial-up, is the term for the primary 

telecommunication service that we all use today. The service is 

always analog (to the end user), is always switched, and is always 

2-wire. The call process involves a protocol that keeps telephone 

sets in an “idle” status until a user wants to make a call. It is 

important to understand this protocol, because the dial-up 

modems used on a 170, 2070, or NEMA traffic signal controller, 

or an ITS device such as a Variable Message Sign, must follow 

the same process. The process involves using a telephone number 

to identify the other end of the communication circuit. When 

making a normal voice telephone call this may not seem like a very 

lengthy process. However, use this protocol in a system that 

Lift Handset

Request For DialTone

Acknowledged

Call

Initiation

Dialed Number

Received &

Forwarded

Call

Initiation

PSTN

Called Number

Processed

Serving C.O.

Lift Handset Called Number

Received

Call

Acknowledged

Ring Current

Sent to Called

Party

Call

Initiation

Called Number

Processed

Serving C.O.

Figure 2-7: Illustration of Basic Telephone Call Process
Telecommunications Handbook for Transportation Professionals 

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requires polling with fast turn-around times, and the process 

won’t work. The reader should note that P.O.T.S. is a shared 

system and that connections between any two points are not 

guaranteed. Also, a dial-up connection presents the possibility of 

a security breach that can be used to corrupt the system. 

Special service or fixed point-to-point telephone circuits are 

used to directly connect field devices to a control point, or one 

traffic control center to another, or in any process where 

immediate and guaranteed communication is required. These 

circuits are specifically designed and constructed for the use of 

a single customer. They are never routed through a switch. 

Customers pay an initial fee for installation of the service (this 

is called a non-recurring charge), and a monthly (recurring 

charge) use, distance, and maintenance fee. 

Several types of special service circuits are available. The most 

common are 2 and 4 wire – generally referred to as 3002 and 

3004. Others provide for special signaling such as E&M (Ear & 

Mouth), FXO/FXS (Foreign Exchange Office/Station), ARD 

(Automatic Ring-down). 

Traffic Signal, Freeway Management and ITS systems requiring 

the use of analog special service generally use 3002 and/or 3004 

telephone circuits. In circumstances where a direct voice link is 

required between a TOC and a field office, or Public Safety 

Dispatch Point, an ARD circuit can be used. 

Multiplexing 

Multiplexing is the process of combining two or more information 

channels into a single transmission medium. There are a number of 

different standards that can be applied to the process. Many 

standards are common and are applied by manufacturers and 

carriers on a world-wide basis. This assures that a multiplexing 

protocol used in Japan can also be used in Brazil, Kansas, New 

York, or Tulsa. 

This section will focus on two of the most common types of 

multiplexing – TDM (time division multiplexing), and PDM (packet 

division multiplexing. Additionally, this section will describe the 

primary multiplexing protocol in use in North America: T-1. 

T-1 was the basic type of multiplexing scheme selected by Bell 

Labs for high capacity communication links. It is so pervasive in 

the world wide telephone network, that replacement protocols are 
Telecommunications Handbook for Transportation Professionals 

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just being introduced. A second type of multiplexing – Packet - 

will also be discussed, because this is now being used to support 

the conversion of the telephone networks from analog to digital. 

Packet multiplexing is used to support IP and Ethernet. 

TIME DIVISION MULTIPLEXING

Time Division Multiplexing is a method of putting multiple data 

streams in a single communication channel, by separating it into 

many segments. Each segment is of a very short duration and 

always occurs at the same point in time within the main signal. In 

TDM, there is a direct relationship between the connections 

(ports) on the multiplexing hardware and the multiplexing 

protocol. The data for port number one of the multiplexer always 

falls within the same time period (time frame #1) - because the 

originating end multiplexer always places the data for each 

communication port at the same place. 

In time, the receiving end multiplexer is able to funnel data to 

the correct port. There is no data added to the bit stream to 

identify the data. With TDM, the general rule is “time slot 

(frame) one = communication port one”. A T-1 multiplexer has 24 

ports (one for each time slot). Therefore, time slot one = port 

one; time slot two = port two; etc. In a TDM transmission, each 

time slot is always present even if only one time slot actually has 

data. The bandwidth is always used. 

A nalog to S erial 

D igital B it S tream

B it S tream 

D ivided into E qual 

Groups

G roups of B its 

placed into 

Fram es

Fram es are 

placed into 

Transm ission 

S ignal

Transm ission 

S ignal C ontains 

S pecific N um ber 

of Fram es

Figure 2-8: TDM Process Flow Chart
Telecommunications Handbook for Transportation Professionals 

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PACKET DIVISION MULTIPLEXING

Packet Division Multiplexing (PDM) is a method of breaking the 

data into multiple groups. Each group is given an identity at the 

origination so that the multiplexer at the receiving end can 

assemble groups of data to re-create the information as it was 

originated. In theory, many information sources can be funneled 

through a single communication port on both ends. In some packet 

multiplexing schemes, the size of the packet – the amount of data 

included – can vary to provide greater throughput of information. 

With packet multiplexing, the bandwidth used never exceeds the 

total amount of data in all packets being transmitted. The PDM 

scheme is important because it is the basis for the new 

generation of broadband communication processes. Ethernet is an 

example of a transmission protocol that relies on packet division 

multiplexing. 

TDM is excellent for supporting voice communications and 

broadcast quality video, because each service gets the amount of 

bandwidth required. PDM is excellent for data transmission 

because it only uses the bandwidth required and requires less 

hardware. The technologies of TDM and PDM have both been 

available for many years. TDM was more broadly deployed because 

it suited the requirement of the telephone companies to provide 

high quality voice communications. However, with recent advances 

in communication technology this is changing. 

Analog to S erial 

D igital Bit Stream

Bit Stream 

D ivided into 

P ackets

Identification 

added to Packets

Packets are 

placed into 

Transm ission 

Signal

Transm ission 

S ignal C ontains 

as m any Packets 

as Necessary

Figure 2-9: Flow Chart - PDM Process
Telecommunications Handbook for Transportation Professionals 

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The following table provides a comparison of packet and time 

division multiplexing: 

Table 2-8: Comparison of TDM & PDM 

Time Division Multiplexing Packet Multiplexing 

Fixed Bandwidth Bandwidth Varies Based on Need 

Data Placed in Time Frames Data Placed in Packets 

Data for individual channels always 

in same place 

Data for individual channels 

identified within packets 

Ideal for transporting voice & 

video 

Ideal for transporting data 

T-1 COMMUNICATION SYSTEMS

The T-1 based digital network has been under development for 

more than 40 years. During this time, a hierarchy of transmission 

levels has been implemented through a wide variety of equipment. 

The primary device is 

a channel bank which 

can be arranged to 

carry many different 

voice, analog data, or 

digital data signals. 

Port cards in the 

channel bank are used 

to support the type 

of inputs into the T-1. 

The most common are 

voice (POTS), and 

digital data (DDS). 

A T-1 contains 24 

signals (or channels). Each channel is represented by 8 bits, for a 

total of 192 bits within a single frame. A bit is added for 

management (synchronization, error checking, etc), and the result 

is a T-1 frame. Because the sampling rate of each channel is 8000 

times per second, a T-1 contains 8000 frames, or 1,544,000 bits. 

In a TDM system, each channel is recognized within each frame at 

T-1 Analog to Digital Conversion 

Process A voice signal is changed from 

analog to digital within a channel bank 

by two processes. First, the analog 

signal is sampled 8000 times each 

second. Each sample is converted to a 

discrete voltage level. Second, each 

voltage is converted to a binary code 

represented by an 8 bit word. 

Therefore, 8000 samples times 8 bits 

is 64,000 bits – a DS-0 communication 

channel. 
Telecommunications Handbook for Transportation Professionals 

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exactly the same point in time. That is - for example - channel 

one never appears in a channel five time slot. 

This most common form of multiplexing is used primarily for voice 

channel services. In fact almost all P.O.T.S. and Special Service 

communication circuits are multiplexed for transport between 

Telephone Company Central Offices. Multiplexing (from the 

telephone company perspective) was developed to obtain 

efficiency in the use of the available communication cable plant. 

The telephone companies were able to provide services to more 

customers without the expensive installation of new 

communication cables. 

There were a number of early attempts at providing an efficient 

multiplexing protocol; for voice based services, but the carriers 

had to consider the overall quality of the voice communication. 

Ultimately, the standard for “toll-grade” voice was set as the 

transmission of frequencies between 0 Hz and 4000 Hz. 

The voice frequencies are digitized for multiplexing via a process 

that samples the frequencies at 8000 points in one cycle (Hz) in a 

period of one second. Each digital sample point is produced as an 

8 bit character. Therefore, each voice channel uses 64,000 bits 

per second. Twenty-four voice channels are combined into a single 

multiplexed communication channel referred to as a T-1. 

Because the telephone company needs to monitor and manage the 

T-1 circuit, it “steals” 8000 bits. A few bits are taken from each 

sample point, and the caller never notices a reduction in quality. 

Most data transmission is accomplished using a dial-up modem. 

The modem converts the data output of a computer (or other 

device – traffic signal field controller, dynamic message sign, 

etc.) to a VF (voice frequency) signal. This signal is treated as if 

it were a P.O.T.S telephone call. The modem dials a telephone 

number associated with another modem and a connection is made 

via the switched voice network. The telephone network does not 

PC MODEM

Computer – Digital 

Output

Modem – Voice 

Frequency Output

Figure 2-10: Diagram of Computer Digital Output Converted to Analog using a MODEM
Telecommunications Handbook for Transportation Professionals 

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treat the call as if it were something special. In terms of T-1 

multiplexing, it is treated as if it were a normal telephone call. 

Multiplexing does reduce some of the overall quality of the 

transmission, but does not affect its usability. Unfortunately, 

each step in the process of getting data transmitted from one 

location to another can introduce a problem. Therefore, when 

troubleshooting, it is important to check every segment of the 

transmission path and all attached equipment – especially if the 

trouble cannot be found at either of the termination points. T-1 

multiplexers are designed to convert analog signals to digital, 

therefore, data output by a computer must be converted to 

analog before being multiplexed. 

In addition to dial-up data transmission, the telephone companies 

offer two additional services: 2/4 wire analog circuits (as 

mentioned above) and DDS (Digital Data Service). The 2/4 wire 

services are generally used for transmission rates of 9600 bits 

per second, or slower. DDS (originally offered for data rates 

from 2400 bits per second and higher) is used primarily for data 

transmitted at 56,000 bits per second. A DSU/CSU is required to 

condition a digital output from a computer to a format that will 

travel over telephone lines. Because the signal is no longer 

analog, a special interface card must be installed in the T-1 

multiplexer (see below). 

TRANSPORTING DIGITAL COMMUNICATIONS VIA AN ANALOG NETWORK

Whenever a digital signal is be transported via the public 

telephone network it must be “conditioned” for travel. This is 

because the basic wiring infrastructure was designed to 

transport an analog communication signal. Analog communication is 

accomplished by providing a variable electrical signal which varies 

as the frequency of a human speaking. Changes in volume and 

pitch are represented by a smooth flowing electrical current with 

positive and negative values. A dial-up modem converts your 

computer output to a series of analog tones which can be 

transported via the network in the same manner as a voice 

telephone call. 
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Digital signals are different. Data is represented by the 

presence, or absence of an electrical signal – “on or off”. “On” 

represents 1, “off” represents 0. Electrical signals can have 

either a positive, or a negative value. The digital output of your 

computer must be converted to something that is compatible with 

the existing telephone network. A Data Service Unit (DSU) is 

used to convert the on/off electrical signal to something that 

looks like an analog signal. Electrical voltages representing 1 are 

given alternating positive and negative values. The momentary 

absence of an electrical signal is assigned a zero value. The DSU 

is normally used in conjunction with a Channel Service Unit (CSU). 

The CSU is used as a management tool to make certain that the 

communications link is performing to specification. 

High Capacity Broadband Transmission 

This section describes various high capacity and broadband 

transmission systems. When the telephone companies first 

deployed T-1 services, they called this “High Capacity” digital 

services. Video transmission for broadcast or conferencing used 

multiple T-1s, or multiple T-3 circuits. With the deregulation of 

telephone companies and the rise in demand for very high 

capacity, a new type of service was developed – broadband. As 

explained, T-1’s are formatted by the telephone carriers, but 

large corporate users, government entities, and even the home 

user want un-formatted bandwidth to be available for a large 

number of services. 

#1

#24

#17

#8 T-1 M ultiplexer

(up to 24 COM Ports)

1 7

2 4

8

1

Analog – Voice 

Frequency

T-1 Signal

Figure 2-11: Diagram of Analog Inputs to T-1 Mux
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T-1/DS-1 & T-3/DS-3 

T-1 and DS-1 services are fixed point-to-point systems, and 

dedicated to a single customer. These types of services are most 

often used to connect Traffic Operations Centers. They may also 

be used to bring the data and video images from a section of 

freeway back to a TOC. 

DDS are digital voice channel equivalents as described previously 

and are used as a fixed point-to-point service. T-1 service is 

channelized to accommodate 24 DDS circuits. 

The terms T-1 and DS-1 are often used interchangeably, but each 

is a distinctly different service provided by telephone companies 

and carriers. T-1 service is channelized with the carrier providing 

all multiplexing (channel banks) equipment. The customer is 

provided with 24 DS-0 interfaces. Each DS-0 interface has a 

maximum data capacity of 56 kbps (or can accommodate one voice 

circuit). The customer tells the carrier how to configure the 

local channel bank (multiplexer). 

DS-1 service allows the customer to configure the high speed 

circuit. The customer provides (and is responsible for 

maintaining) all local equipment – multiplexer, and DSU/CSU. The 

carrier provides (and maintains) the transmission path. The 

customers can channelize the DS-1 to their own specifications as 

long as the bandwidth required does not exceed 1.536 mbps, and 

the DS-1 signal meets applicable AT&T, Bellcor (Telcordia) and 

ANSI standards (these standards are now maintained and 

available through Telcordia). 

Customers may purchase fractional service to save money. In this 

case, they don’t pay for a full T-1 or DS-1. However, the 

economies for this type of service are only realized for longer 

distances. The local loop (link) for Fractional T-1 is still charged 

at the full service rate. 

T-3 and DS-3 services are essentially higher bandwidth variants 

of T-1 and DS-1. The T-3 provides either 28 T-1s or 28 DS-1s, 

and the DS-3 provides about 44 mbps of contiguous bandwidth. 

DS-3s are used for Distance Learning and broadcast quality 

video. They are also used in enterprise networks to connect major 

office centers. 

T-1, DS-1, T-3, and DS-3 have the following characteristics: 

• They are all private line services 
Telecommunications Handbook for Transportation Professionals 

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• They are all provided on a fixed point-to-point basis 

• Most users pay for the installation of the service 

• Users pay a monthly fee based on distance – very large 

corporate customers are able to negotiate favorable rates 

for DS-1 and DS-3 services. 

• Users pay a fixed monthly connection and maintenance fee 

DSL 

DSL (Digital Subscriber Loop) services are DS-1 and Fractional 

DS-1 variants that use existing P.O.T.S. service telephone lines 

to provide broadband services at a substantially lower cost. Local 

DS-1 service starts at $500 per month. Basic DSL service starts 

at less than $50 per month. The primary difference between the 

services is that DS-1 is setup as a private line system with fixed 

communication points. DSL service is typically used to provide 

broadband internet connectivity. Some carriers will create a 

“quasi” private circuit by linking two customer locations to a 

common Central Office. The primary advantage of DSL for the 

homeowner or small business is that it shares the existing 

telephone lines and it keeps the cost of installation at a much 

lower level. 

DSL service has the following characteristics: 

• Typically provided in an ADSL (Asymmetrical DSL) format 

with the link toward the customer (download) at a higher 

rate than the link toward the Internet (upload). 

• DSL can be provided as SDSL (Symmetrical DSL) when the 

user needs to have equal bandwidth bi-directionally. 

• DSL is a shared service. At peak use times, the available 

bandwidth is reduced. Many users have complained that they 

get better service via dial-up. 

• DSL offerings start at 384 kbps/128 kbps and can rise to 

6.0 mbps/6.0 mbps. (the monthly rates start at $30 and rise 

to $400). 

• DSL can only be used when the customer is no more than 

18,000 “wire feet” from the Serving Central Office. Best 

service is available when the customer is less than 12,000 

“wire feet” distant. 

• DSL is most often used to provide internet access. 
Telecommunications Handbook for Transportation Professionals 

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SONET 

SONET (Synchronous Optical Network) is the first fiber optic 

based digital transmission protocol/standard. The SONET format 

allows different types of transmission signal formats to be 

carried on one line as a uniform payload with network 

management. A single SONET channel will carry a mixture of 

basic voice, high and low speed data, video, and Ethernet. All of 

these signals will be unaffected by the fact that they are being 

transported as part of a SONET payload. 

The SONET standard starts at the optical equivalent of DS-3. 

This is referred to as an OC-1 (Optical Carrier 1). The optical 

carrier includes all of the DS-3 data and network management 

overhead, plus a SONET network management overhead. In North 

America, the following SONET hierarchy is used: OC-3; OC-12; 

OC-48; OC-96; OC-192. The number indicates the total of DS-3 

channel equivalents in the payload. 

Within the payload, SONET network management allows for the 

shifting of DS-1 circuits. SONET is a point-to-point TDM system, 

but it has the ability to allow users to set up a multipoint 

distribution of DS-1s and DS-3s. Therefore, it is possible to 

direct a DS-1 from one location to many locations within the 

SONET network. The reader should note that SONET does not 

provide “bandwidth-on-demand”. The routing of portions of the 

SONET payload to multiple points must be planned and built into a 

routing table. 

A SONET network management program provides the ability to 

set up multiple routing plans. These plans can be executed as part 

of a program to restore service in the event of an outage in a 

portion of the network. Some early adopters of SONET 

attempted to use this feature to provide for “time-of-day” 

routing changes. Often users were disappointed with the results. 

Normally, SONET is transmitted in groups of DS-3s (OC-3, OC12, OC-48, etc). In this mode, the SONET payload is segmented 

within the DS-3. However, it is possible to combine DS-3s into a 

single channel. An OC-3C (concatenated) is a group of DS-3s 

combined into a single payload to allow for the total use of the 

OC-3 as a single data stream. 
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ATM 

Asynchronous Transfer Mode (ATM) is a widely deployed 

communications backbone technology based on Packet 

Multiplexing. ATM is a data-link layer protocol that permits the 

integration of voice and data, and provides quality of service 

(QoS) capabilities. This standards-based transport medium is 

widely used for access to a wide-area (WAN) data communications 

networks. ATM nodes are sometimes called “Edge Devices”. These 

Edge Devices facilitate telecommunications systems to send data, 

video and voice at high speeds. 

ATM uses sophisticated network management features to allow 

carriers to guarantee quality of service. Sometimes referred to 

as cell relay, ATM uses short, fixed-length packets called cells 

for transport. Information is divided among these cells, 

transmitted and then re-assembled at their final destination. 

Carriers also offer “Frame Relay” service for general data 

requirements that can accept a variable packet or frame size. 

Frame Relay systems use variable cell (packets) based on the 

amount of data to be transmitted. This allows for a more 

efficient use of a data communications network. 

ATM services are offered by most carriers. A number of DOTs 

are using this type of service – especially in metropolitan areas – 

to connect CCTV cameras (using compressed video), traffic signal 

systems, and dynamic message signs to Traffic Operations 

Centers. The stable packet size is well suited for video 

transmission. ATM is generally not used by telephone companies 

for toll grade voice, although its stable packet size was 

developed to meet requirements for voice service, 
Telecommunications Handbook for Transportation Professionals 

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In a WAN (wide area network), ATM is most often used as an 

“edge” transport protocol. ATM devices typically have ports that 

allow for easy connectivity of legacy systems and the newer 

communications systems. In a private (or enterprise) network, as 

shown in figure 2-12, ATM is effectively used for voice and video 

transport as well as data. 

ATM has fixed-length “cells” of 53 bytes in length in contrast to 

Frame Relay and Ethernet’s variable-length “frames.” The size of 

cell that represents a compromise between the large frame 

requirements of data transmission and the relatively small needs 

of voice calls. By catering to both forms of network traffic, ATM 

can be used to handle an end user’s entire networking needs, 

removing the need for separate data and voice networks. The 

performance, however, can also be compromised, and the network 

may not be as efficient as dedicated networks for each service. 

ATM systems usually require DS-1 circuits, but can be made to 

work in a lower speed environment. 

ATM does have a reputation for being difficult to interface to an 

existing network. However, competent network technicians can 

usually overcome most difficulties. Missouri DOT is using an ATM 

based network for its ATMS. 

Ethernet

Router

Telephone

PBX

ATM

Edge D evice

100 MBps

DS-1

SONET

Hub O C-3

SONET

Hub

SONET

Hub

OC-12

OC-12

OC-12

ATM

Edge D evice

ATM

Edge D evice O C-3

O C-3

Typical A TM over SO N ET C om m unication N etw ork

SONET

R ing

Figure 2-12: Diagram - ATM over SONET Network
Telecommunications Handbook for Transportation Professionals 

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FDM 

Frequency Division Multiplexing (FDM) is used when large groups 

of analog (voice or video) channels are required. The available 

frequency bandwidth on an individual communications link is 

simply divided into a number of sub-channels, each carrying a 

different communication session. A typical voice channel requires 

at least 3 kHz of bandwidth. If the basic communication link is 

capable of carrying 3 megahertz of bandwidth, approximately 

1000 voice channels could be carried between two points. 

Frequency Division Multiplexing was used to carry several low 

speed (less than 2400 bits per second) data channels between two 

points, but was abandoned in favor of TDM which has an ability to 

carry more data channels with more capacity over greater 

distances with fewer engineering problems. 

Many older Cable TV systems use FDM to carry multiple channels 

to customers. This type of system was used by Freeway 

Management Systems to carry video over coaxial cable. However, 

most coaxial systems have been replaced by fiber optic systems. 

Fiber has a greater bandwidth capability than coaxial cable, or 

twisted pair. The FDM scheme allows for multiple broadband 

video channels to be carried over a single strand of fiber. 

WDM – CWDM & DWDM 

Wave Division Multiplexing (WDM) is an optical variant of FDM. A 

beam of light is divided into segments called lambdas. The Greek 

letter Lambda ( λ ) is used to represent the wave channels. These 

lambdas are actually different colors of light. Because a 

wavelength is inversely proportional to frequency WDM is 

logically equivalent to FDM. 

Light transmitted over a fiber is 

normally a group of frequencies 

that can be used to create a 

single communication channel, or 

multiple channels. The frequency 

group can be broken into several 

sub groups. The LASER output of 

a multiplexer is “tuned” to a 

specific set of frequencies to form a single communication 

channel. These channels are then transmitted with other 

Optical 

LASER 

Transmitter 

Up to 

64 Lambdas 

OC-48

GigE

GigE

Figure 2-13: DWDM Channels
Telecommunications Handbook for Transportation Professionals 

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frequency groups via a wave division multiplexer. Unlike FDM, the 

information sent via the frequency groups is digital. 

Two variables of WDM are used, CWDM (coarse wave division 

multiplexing) and DWDM (dense wave division multiplexing). 

DWDM systems can carry as many as 64 channels at 2.5 gigabits 

per second per channel over a pair of fibers. Each DWDM lambda 

is equal to one OC-48 (48 DS-3s), or one Gigabit Ethernet 

channel (future systems will allow 2 GigE channels per lambda). 

ETHERNET

Ethernet is a packet based network protocol, invented by the 

Xerox Corporation, in 1973, to provide connectivity between many 

computers and one printer. Ethernet was designed to work over a 

coaxial cable that was daisy-chained (shared) among many 

devices. The original Xerox design has evolved into an IEEE 

series of standards (802.XXX) with many variations that include 

10Base-T, Fast-Ethernet (100Base-T), and GigE (Gigabit 

Ethernet). 

The Ethernet system consists of three basic elements: 

1. The physical medium used to carry Ethernet signals between 

computers, 

2. A set of medium access control (MAC) rules embedded in 

each Ethernet interface that allows multiple computers to 

fairly arbitrate access to the shared Ethernet channel, 

3. An Ethernet frame that consists of a standardized set of 

bits used to carry data over the system. 

The most current configurations use twisted pair with devices 

networked in a star configuration. Each device has a direct 

connection to an Ethernet hub, or router, or switch. This system 

then provides each user with a connection to a printer, file 

server, another user computer (peer), or any other device on the 

network. 

Ethernet works by setting up a very broadband connection to 

allow packets of data to move at high speed through a network. 

This assures that many users can communicate with devices in a 

timely manner. The Ethernet is shared, and under normal 

circumstances, no one user has exclusivity. 
Telecommunications Handbook for Transportation Professionals 

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Traditional Ethernet networks of the 1990s used a protocol 

called CSMA/CD (carrier sense multiple access/collision 

detection). In this arrangement, the transmitting device looks at 

the network to determine if other devices are transmitting. The 

device “senses” 

the presence of a 

carrier. If no 

carrier is present, 

it proceeds with 

the transmission. 

The CSMA 

protocol is not 

perfect, hence the 

need for Collision 

Detection. 

Occasionally, more 

than one device 

transmits 

simultaneously and 

creates a “call 

collision”. If the originating device does not receive an 

acknowledgement from the receiving device, it simply retransmits 

the information (not as part of the Ethernet protocol, but part 

of an application protocol). In an office environment, where users 

are trying to access a printer, or a file-server, this is normally 

not a problem. Most users are not aware of any significant delays. 

In this arrangement all devices are wired to the network through 

a “hub”. The hub provides a central meeting point for all devices 

and users on the network, but has very little intelligence for 

managing activity on the network. In fact all communications on 

the network are sent to all devices on the network. 

Each Ethernet-equipped computer, also known as a station, 

operates independently of all other stations on the network: 

there is no central controller. All stations attached to an 

Ethernet are connected to a shared signaling system, also called 

the medium. Ethernet signals are transmitted serially, one bit at 

a time, over the shared signal channel to every attached station. 

To send data, a station first listens to the channel, and when the 

channel is idle the station transmits its data in the form of an 

Ethernet frame, or packet. 

Note: When Ethernet is used to connect only two 

devices via a common communication channel CSMA 

is not used. This is because the two devices can 

coordinate communication so that one does not 

interfere with the other. This type of system can 

be used to transmit broadband video over long 

distances to take advantage of the bandwidth and 

economics of using Ethernet. 

Freeway Management Systems using incident 

detection CCTV cameras may use this type of 

arrangement to facilitate Video over IP. This 

allows video from the field to be transported to 

the TCC for further distribution. 
Telecommunications Handbook for Transportation Professionals 

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After each frame transmission, all stations on the network must 

contend equally for the next frame transmission opportunity. This 

ensures that access to the network channel is fair, and that no 

single station can lock out the other stations. Access to the 

shared channel is determined by the medium access control (MAC) 

mechanism embedded in the Ethernet interface located in each 

station. The medium access control mechanism is based on a 

system called Carrier Sense Multiple Access with Collision 

Detection (CSMA/CD). 

Modern networks still use CSMA/CD, but are managed by routers 

and switches. Routers are not actually Ethernet devices - they 

operate at layer 3 of the OSI protocol stack. The router is able 

to manage the flow of data between devices and has the 

intelligence to route information between specific devices. A 

request to view a file from an individual computer is routed to 

the specific file server storing the information. None of the 

other computers on the network see the data request. However, 

the router will simply route the request, it won’t manage several 

users trying to access the same file server simultaneously. 

Management of users in a network is accomplished by a Switch. 

The Switch has the intelligence and computing “horsepower” to 

manage users and allocate bandwidth. A Switch can be set to 

block some users from the system based on various factors, such 

as priority and time-of-day requirements. 

Following is a description of the most commonly used Ethernet 

protocols: 

• 10Base-T was (as this handbook was being developed, 

100Base-T was most common, with GigE catching on fast). 

This is typically run over twisted pair copper and is 

adequate for most small office data communication 

requirements. 

• Fast Ethernet or 100Base-T can be run over the same 

twisted pair infrastructure. The 10Base-T protocol allows 

for a maximum throughput of 10 megabits of data and the 

100Base-T allows 100 megabits of data throughput. However, 

various factors keep these systems from exceeding more 

than 70 percent of stated capacity. Chief among these 

problems is overloading of the number of users and the 

condition of the wired infrastructure. 
Telecommunications Handbook for Transportation Professionals 

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• 100Base-TX is a two twisted copper pair (4 wire) 

transmission standard. Identical to 10Base-T, it is also 

referred to as “fast Ethernet”, and provides 100 Mbps 

throughput. 

• 100Base-FX is a fiber optic transmission standard for Local 

Area Networks. 

• GigE (gigabit Ethernet) is a very high bandwidth service 

(One gigabit per second) and is being deployed in many large 

office networks. In addition to allowing more users onto the 

network, GigE is capable of facilitating video between 

desktops, and desktop to desktop conferencing between 

users. GigE is also the preferred communications protocol 

for linking one office building to another. Metropolitan 

Networks (MAN) using DWDM facilitate a “real-time” GigE 

link. IT departments can create a storage area network 

(SAN) to link together many databases. Large financial 

institutions connect locations in a region to facilitate 

electronic commerce using DWDM and GigE. Many telephone 

carriers are beginning to add GigE services to their network 

offerings. 

• 10GigE protocols and standards are being developed by IEEE 

under 802.3ae and 802.3AK. The 10GigE standards are being 

developed to use the protocol for broadband metropolitan 

area network (MAN) connectivity. At this time, there is no 

intention to use the standard to support desktop 

applications, however, all things change. 10GigE systems will 

be deployed using fiber optic transmission networks. 

Following is an example of a 10GigE Network. 
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Because most of these networks are deployed in office buildings, 

the twisted pair cables tend to be run close to interferencecausing electrical fixtures. The drawing shows a typical LAN for 

a small office. Notice that most of the office computers are 

connected via a hub, and that the printers, and communications 

services are connected via dedicated servers. This is simply one 

type of network that can be established using Ethernet. In very 

small offices, every device can be directly connected to a router. 

Large corporations will network several routers. The actual 

network configuration is based on completing a requirements 

document (see chapter 4). In this system every computer has 

access to every device, but the router can be programmed to 

restrict access based on the unique identity of each computer 

work station. 

Figure 2-15 provides a look at how multiple building networks are 

connected via a metropolitan area network (MAN) Notice that 

The Internet

Ethernet

Fax

Color Printer

Plotter

Print Server

Router Ethernet

File Server File Server File Server

Hub

`

`

`

`

`

Communication 

Server

Fire Wall

Figure 2-14: Diagram - Typical Office LAN
Telecommunications Handbook for Transportation Professionals 

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81

there is one primary router in each building connected to a 

10GigE network - each building is a node on the network. The 

common basis of Ethernet protocols provides an easy expansion 

path. The system shown is actually a network of networks. 

Conclusions 

The design of telecommunications systems is an iterative process. 

Each piece of a system is dependent upon the others. A simple 

example of this dependency can be found in the use of a modem. 

Basic modems rely on the cables that connect them to a computer 

(a serial cable) and the twisted-pair cable that connects them to 

a telephone network. Each of these elements is dependent upon 

the other to provide a working system. These types of 

dependencies can be found in all telecommunication systems. This 

chapter was organized to provide basic information about 

Internet

10GigE

10GigE

10GigE

10GigE

10GigE

Router

Building 1

Router

Building 3

Router

Building 4 LAN

LAN

LAN

LAN

LAN

Router

Building 2

Router

Building 2

LAN

SAN

SAN

Figure 2-15: Diagram - Metro Area Network (MAN)
Telecommunications Handbook for Transportation Professionals 

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individual elements and their relationships. Recognition of these 

relationships will help to provide an effective design of a 

telecommunications network. 
Chapter 3 

83

3. CHAPTER THREE – TELECOMMUNICATIONS &

THE NATIONAL ITS ARCHITECTURE

Introduction 

During the past 20 years, a number of technology based systems 

have evolved to support transportation operations, traffic 

management, traveler information, fleet management, and incident 

control. These include: 

• Automated Traffic Signal Systems 

• Commercial Vehicle Operations (CVO) 

• Freeway Management 

• Traveler Information 

• Remote Weather Information Systems (RWIS) 

• Incident Management 

• Special Events 

Figure 3-1: National ITS Architecture Communications Sausage Diagram 
Telecommunications Handbook for Transportation Professionals 

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• Ramp Metering 

• Electronic Toll Collection. 

Automated traffic signal systems have been in use for over 50 

years, while traveler information systems are still in the process 

of developing – especially since the FCC allocated 511 as a 

universal traveler information telephone number for the U.S. In 

fact, all systems are in a continuous evolutionary process because 

technologies supporting the systems are always changing. As a 

direct result of the change, telecommunications systems that 

support transportation operations are also evolving. 

Chapter 3 will look at the relationship of the National ITS 

Architecture to the process of engineering and specifying 

communication links and services for a transportation management 

system. This chapter will also provide information on the 

developing standards within NTCIP and how they will impact on 

the design of communications systems supporting transportation. 

Overview – The National ITS Architecture 

The National ITS Architecture is a flexible framework for the 

interrelationship of operational transportation systems. Various 

telecommunications strategies can be used within the context of 

the National Architecture. These include urban and rural system 

deployments, for local and regional transportation management 

systems. Functionally, there are very few differences between 

urban and rural systems. Vehicle speed and volume detectors 

function the same in both situations, as do CCTV cameras, 

changeable message signs, and almost any other device used in 

transportation management systems. However, telecommunications 

strategies do vary based on location. A telecommunications 

architecture that supports urban deployments may not be suitable 

for a rural system. The key factors to consider when creating a 

design are distance of field devices to a control center, 

availability of electrical power resources, and availability of 

public telephone infrastructure. 

The National ITS Architecture provides system developers with a 

detailed view of the relationships between travelers and 

associated transportation organizations. Each of the 

relationships has a communications requirement. Communications 

can be thought of as the glue that binds required operational 

functions. The National Architecture can be viewed in several 
Telecommunications Handbook for Transportation Professionals 

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different ways: Logical Relationship; Physical Relationship; 

Market Package Relationship; and Functional Relationship. The one 

constant in each type of relationship is communications. The 

Architecture makes no distinction in the type of communications 

systems that can be used. The system designer is free to use any 

telecommunications systems and devices that will support overall 

requirements. 

The National Architecture provides a diagram of the general 

relationships (“Sausage Diagram) listing four (4) generic types of 

telecommunications systems: 

• Vehicle-to-Vehicle 

• Dedicated Short Range Communications (DSRC) 

• Wide Area Wireless 

• Wireline 

Wireline and Wireless are the two primary types of 

telecommunications architectures shown in the diagram, with 

Vehicle-to-Vehicle (VtV) and DSRC being two applications of 

wireless. There is no distinct requirement to use RF, Copper, or 

Fiber Optics as a transmission medium. Nor is there any 

suggestion as to the network topology: point-to-point, star, ring, 

mesh, etc. 

VEHICLE-TO-VEHICLE (VTV) 

These are wireless systems and use radio frequencies (RF) as the 

medium. There are some systems that use light or sound for 

communication, but the systems used in traffic and 

transportation management are predominantly RF. VtV systems 

can use one, or a combination of radio systems for communication. 
Telecommunications Handbook for Transportation Professionals 

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Mobile 2-Way Radio 

Generally used between vehicles for wide area communication in a 

Private Land Mobile Radio Service (PLMRS) on frequencies set 

aside by the Federal Communications Commission (FCC) for that 

purpose. The system is used by DOT maintenance groups to 

facilitate operations between work crews and a central (or 

regional) dispatch center. Under the definition of the National 

Architecture, this is a wide-area mobile communication system. 

These same systems can also be used to coordinate joint 

operations between Police Departments and the DOT. These 

systems can also provide for an exchange of digital data 

information. 

Cellular Telephone Service 

Can be used for communication between the occupants of two (or 

more) vehicles. This system can be utilized to provide secure 

personalized travel and transportation information to individual 

Records

Database

Router

Ethernet

Records

Management

System

Dispatcher

Work Station

Dispatcher

Work Station

Application

Server

Mobile

Computer

Base Station

Radio

2-Way Radio

T-1

Communication

Link

Figure 3-12: Diagram - Mobile 2-Way Radio Network
Telecommunications Handbook for Transportation Professionals 

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87

travelers. The FCC requires that all wireless carriers provide 

location information when a request for emergency services is 

requested (the caller dials 9-1-1). The system may also be used to 

provide traffic management centers with general congestion 

information (not a requirement under FCC regulations). 

DSRC 

The sausage diagram shows this as a vehicle to roadside 

architecture, however, this is also considered as a very low 

power, very short range communication system between vehicles. 

DSRC generally refers to radio systems that operate on 

frequencies set aside by the FCC (in the US) between 5.8 and 5.9 

GHz. However, toll collection and vehicle identifications systems 

currently operating in the 900 MHz range are considered – by the 

transportation industry – as DSRC. Automobile manufacturers 

have developed VtV systems using radar in the 35 GHz and 70 

GHz frequency bands, and are looking at the possibility of using 

5.8 GHz. 

Dedicated Short Range Communication Systems (DSRC) are 

wireless systems used to communicate over distances of less than 

1000 feet (300 meters). They can be used for vehicle-to-roadside 

(VtR ) or VtV. The systems are primarily deployed using RF, but 

can be deployed using infra-red (IR), or low power LASER as the 

communication medium. The National Architecture diagram shows 

DSRC in a relationship between the categories of Automotive 

Vehicles and Roadside Services: 

Table 3-1: DSRC Vehicle-Roadside Relationships 

Vehicles Roadside 

Passenger Car Traveler Information 

Emergency Vehicle Toll Collection 

Commercial Vehicle Parking Management 

Transit Commercial Vehicle Check 

Maintenance & Construction 
Telecommunications Handbook for Transportation Professionals 

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These relationships are not fixed. Any vehicle using DSRC should 

be able to access a suite of services which include passing 

information between vehicles and the roadside. Standards for 

DSRC are being developed and tested by ASTM using IEEE 

802.11a, as a basis. A major difference between the DSRC 

standard and 802.11a is the frequency range being used. DSRC 

will operate within a frequency spectrum set aside for this 

purpose, and requires licensing. 802.11a systems operate in a 

frequency spectrum that is set aside for general use and requires 

no license. Detailed information about DSRC is available at the 

following web site: 

http://www.leearmstrong.com/DSRC/DSRCHomeset.htm . 

Wide Area Wireless Systems (WAWS) 

WAWS are RF communication systems that can cover several 

square miles to thousands of square miles. They generally include 

Cellular and standard 2-Way Radio systems. Most of these 

systems are designed to provide full voice service and some data 

services. The National Architecture shows WAWS as providing 

VtV and vehicle to center communications (VtC). DOT 

Maintenance, Mass Transit, and Public Safety use WAWS as a tool 

for field to center communications. Additionally, Police and Fire 

agencies use these systems to enhance field unit communications. 

All WAWS have a similar architecture - a central base station 

that can communicate with mobile and handheld radios. The base 

station is a high powered transmitter and receiver combination 

placed in the center of the required coverage area. The base 

station utilizes an antenna placed at a relatively high (above 

ground) location (normally on top of a tower or building rooftop). 

Cellular systems are very similar in design except that there are 

many base stations interconnected by a wireline network designed 

to provide continuous service to callers using handheld radios 

(handsets). The overall system is interconnected to the PSTN to 

facilitate voice communication. 

WAWS systems can also be used for field operational control of 

Freeway Management systems in rural settings. Oil and gas 

transmission companies use these types of systems for monitoring 

pipelines. These systems are called SCADA (system control and 

data acquisition). All incident and traffic flow detection systems 
Telecommunications Handbook for Transportation Professionals 

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are, in fact, SCADA systems in that they use various types of 

sensors to detect a change of state (vehicle speeds and lane 

occupancy) to alert TMC operators that a specific section of 

roadway may have a congested condition. 

Wireline Systems 

A generic reference to any type of system that uses a physical 

connection of copper wire or fiber optic cable as the 

communication link. Generally, wireline systems can be divided 

into three categories: Wide Area Network (WAN); Metropolitan 

Network (MAN); Local Area Network (LAN). 

National ITS Architecture Flows & Telecommunications 

This section will provide an examination of how market packages 

and flow models, as presented by the National ITS Architecture, 

can be used to create requirements for telecommunications 

systems and services. The NA is very large and has many 

components. The creators of the NA have developed “Market 

Packages” to help users work with the document. The Market 

Packages provide a graphical representation for easy visualization 

and can be a valuable tool in the design of a telecommunications 

system. 
Telecommunications Handbook for Transportation Professionals 

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90

MARKET PACKAGES

The market packages contained within the NA provide a good 

reference to how individual items (control center operators, 

roadway devices, data, and control systems) are positioned within 

a system, and their linked relationships. The system engineer 

must start at a very high level to produce an overview 

telecommunications architecture. As individual items within a 

market package are examined, their requirements will be added to 

the overall system. Modifications to the initial overview are made 

until a working telecommunications architecture is established. 

This is a “top-down” approach to help the engineer gain an 

understanding of the system that will be needed. In fact, the 

system is designed using a “bottoms-up” approach, because the 

system must provide communications services for every device in 

the market package. Let’s take a look at a typical market package, 

and apply a telecommunications system. 

The Roadway Service Patrol Market Package (EM-4) describes a 

service that assists motorists with vehicle problems (flat tire, 

EM4 - Roadway Service Patrols

incident information

vehicle

location

emergency

operations

status

Emergency

System Operator

Information 

Service Provider

Emergency

Management

Service Patrol

Management

Emergency 

Vehicle

On-Board EV En 

Route Support

On-Board EV

Incident Management

Communication

Traffic 

Management

Vehicle

incident information

incident status

emergency vehicle

tracking data

emergency dispatch

response

emergency dispatch

requests

Maintenance and 

Construction 

Management

incident information

emergency

operations

request

Figure 3-3: National Architecture EM-4 Market Package
Telecommunications Handbook for Transportation Professionals 

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out of gas,) and is part of the incident clearance solution to help 

minimize congestion. Note that the selected market package is 

part of an overall “center-to-center” architecture. Ultimately, 

the solution for the situation described by this market package 

will have to become part of a larger communication system. In 

chapter Four, the process of breaking the overall communication 

system design problem into its basic elements is discussed. The 

graphic 8

 shown is presented in the NA. 

The above graphic represents only a small portion of the overall 

system that provides traffic management, incident detection, and 

incident response and clearance. The arrows indicate how 

information flows between the responsible agencies. These same 

arrows also provide an indication of the required communication 

links. Looking at the sausage diagram, it is easy to see that this 

system will utilize a combination of wireline and wide area 

wireless telecommunications systems. The NA does not specify 

the actual type of communications systems to be used. This is up 

to the individual developers of a system. The NA recognizes that 

the type of communication will be standard (and conform to 

FHWA requirements), but that each individual system will have 

different deployment variables. These include: 

• Location – urban or rural 

• Scope of services offered by the agency operating the TMC 

• Budget – extensive or limited 

• Regional or Local – system is “stand-alone” or part of a 

larger operation 

• Coordination – level of cooperation between service 

providers. 

• Legacy 

 

8

 Source: http://itsarch.iteris.com/itsarch/html/mp/gatms08.htm 
Telecommunications Handbook for Transportation Professionals 

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EXAMPLE ILLUSTRATION

For purposes of illustration of the telecommunication system: 

• The TMC is part of a regional operation with roadway 

service patrols offered by commercial contract 

organizations. 

• The service patrols are dispatched by local Police 

Departments. 

• The EM4 diagram shows several active boxes (purple and 

yellow). 

• The Traffic Management box is grayed, but we’ll change it 

to active (blue) for this discussion. 

• Add several communication arrows not shown in this diagram. 

Take a second look at the EM4 diagram (Figure 3-4): 

Notice that incident detection and incident response request 

flows have been added. 

EM4 - Roadway Service Patrols

incident information

vehicle

location

emergency

operations

status

Emergency

System Operator

Information

Service Provider

Emergency

Management

Service Patrol

Management

Emergency

Vehicle

On-Board EV En

Route Support

On-Board EV

Incident Management

Communication

Traffic

Management

Vehicle

incident information

incident status

emergency vehicle

tracking data

emergency dispatch

response

emergency dispatch

requests

Maintenance and

Construction

Management

incident information

emergency

operations

request

Incident

Detection

Incident Response

Request

Figure 3-4 EM-4 Market Package with Telecommunications Flows
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Next, assume the following: 

• Traffic Management is a function of the DOT Transportation 

Management Center. 

• Emergency Management is the responsibility of a County 

Emergency Management/ 911 Center. 

• The dispatching is accomplished by a local Police Department 

(Emergency System Operator), 

• The Emergency Response Vehicle is operated by a private 

contractor. 

• Add the telecommunications sausage diagram elements 

(green) to complete the diagram (Figure 3-5): 

The NA does not provide any details on telecommunication 

requirements or specifications. However, it does provide a good 

starting point via the Market Package Diagrams. Taking the 

diagrams and adding the telecommunications function is a good 

way to visualize the requirements. Program managers are provided 

a concept of the elements that must be detailed in the overall 

EM4 - Roadway Service Patrols

incident information

vehicle

location emergency

operations

status

Emergency

System Operator

Information

Service Provider

Emergency

Management

Service Patrol

Management

Emergency

Vehicle

On-Board EV En

Route Support

On-Board EV

Incident Management

Communication

Traffic

Management

Vehicle

incident information

incident status

emergency vehicle

tracking data

emergency dispatch

response

emergency dispatch

requests

Maintenance and

Construction

Management

incident information

emergency

operations

request

Incident

Detection

Incident Response

Request

Wireline

Wireline

Wireline

Wide Area Wireless

Wide Area Wireless

Wireline

Figure 3-5: EM-4 Market Package with "Sausage Diagram" Elements
Telecommunications Handbook for Transportation Professionals 

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project. The importance of this is discussed in chapter Four. In 

the next section, we’ll apply the telecommunication elements to 

the diagram. 

Application of Telecommunications Using the National Architecture 

Flows 

A good way to go from the market package concept to a 

telecommunication requirements document is to create a table 

based on the above diagram. The table will contain the “points-ofcommunication”, and a brief description of needs. The developer 

of the table should also note that the Market Package describes 

information flows. These flows are not descriptive of the 

communication links, but can be used to help define the 

telecommunication links. The definition will include bandwidth 

requirements and the type of communication – voice or data or 

both. The following is an example of the table: 

Table 3-2: Communication Needs & Requirements 

Communication Points Needs Requirements 

Incident Detection to 

TMC 

In place (existing 

system) None (uses existing) 

TMC to EM Wireline Comm Link Voice & Low Speed 

Items Not Under Control of TMC

EM4 - Roadway Service Patrols

incident information

Traffic

Management

Incident

Detection

Incident Response

Request

Wireline

Wireline

Wireline

vehicle

location emergency

operations

status

Emergency

System Operator

Information

Service Provider

Emergency

Management

Service Patrol

Management

Emergency

Vehicle

On-Board EV En

Route Support

On-Board EV

Incident Management

Communication

Vehicle

incident information

incident status

emergency vehicle

tracking data

emergency dispatch

response

emergency dispatch

requests

Maintenance and

Construction

Management

incident information

emergency

operations

request

Wide Area Wireless

Wide Area Wireless

Wireline

Figure 3-6: TMC Area of Responsibility
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Data (unless video is 

part of the package) 

EM to Maintenance Wireline Comm Link Low Speed Data 

The items listed in the above table are the responsibility of the 

DOT, because the emergency management function is being 

provided by another agency. It is helpful for the system designer 

to have a complete understanding (for purposes of coordination) 

of the entire system, but it is only necessary to focus on the 

elements which must be provided by the DOT. 

The TMC is responsible for creating the incident detection 

information, initiating a request to the EM and providing 

necessary information, plus coordination of support from the 

DOT. There is also the connection between the incoming incident 

detection information and the outgoing request for EM assistance 

to clear the incident. The system designer must provide for a 

communications link between the “in-house” TMC systems. 

Notice that a dedicated communication port on the router is 

assigned to the link between the TMC and the EMA. This assures 

that the “incident response request” and “incident information” 

links are always available. Also, the use of a dedicated leased 56 

Kbps digital circuit from a local carrier and the Frame Relay 

network assure secure transfer of information. The NA defines 

the requirements for each link as individual one way flows, but 

TMC to EMA Communication Link

FRAD FRAD

100BaseT

Carrier Based Frame Relay

Network

56k Local Loop

Operator

Work

Station

56k Local Loop

DOT

Transportation

Management Center

County

Emergency Management

Agency

Router

56K Dedicated Port

Operator

Work

Station

Router 100BaseT

56K Dedicated Port

Figure 3-7: Diagram - TMC to EMA Link
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the telecommunications system design provides for a single bidirectional flow. The difference is that the NA is showing how 

information flows and the communication diagram is detailing a 

physical link. Also note that the above diagram represents one of 

several possible solutions. It essentially assumes that only text 

and database information are transferred between the TMC and 

the EMA. A system that provides for the transfer of “real-time” 

video from the TMC to the EMA would use a broadband 

communication solution. 

In the diagram, the Carrier based solution has been replaced with 

a direct private fiber communication link. This could also be a 

link leased from a carrier. 

Looking at the EM4 Market Packages, you will notice that a link is 

provided between the EMA and the Maintenance and Construction 

Management organizations. In a “real world” scenario, the link 

could be via the TMC. The NA is showing this link as a reminder 

that more than one transportation organization needs 

information. The overall design needs to account for each 

communication link. 

Based on the NA, the Maintenance and Construction group 

receives information from the EMA, but does not send 

information back. We have to assume that construction and 

maintenance information is submitted to the EMA via another 

channel. This information is probably routine traveler information 

about lane and road closings and general repair work. For this 

case, the EM4 Market Package is a good model, but does not show 

all of the potential communication links. There may be a number 

TMC to EMA Communication Link

100BaseT Direct Fiber Link

Operator

Work Station

with Video

Player

Application

DOT

Transportation

Management Center

County

Emergency Management

Agency

Router Router 100BaseT

Video

Switch

Streaming

Video

Processor

Analog

Video

GigE

Operator

Work Station

with Video

Player

Application

Figure 3-8: Diagram - TMC to EMA with Fiber Communication Link
Telecommunications Handbook for Transportation Professionals 

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of internal links that are not shown in the Market Packages. Do a 

thorough search of all of the requirements for communication. 

Comparison of Rural and Urban Telecommunications Requirements 

Using the National Architecture Flows 

In this section we will examine how the National Architecture 

works for both Rural and Urban telecommunication systems 

scenarios. The market packages and architecture flows are 

designed to remain unaffected by the location of the system. The 

variables are accounted for by making the market package and 

the architecture flows work in a particular situation – that is, 

meeting the needs of a rural or an urban/suburban location, 

and/or a local or regional system. 

Using the EM4 Market Package, let’s examine alternatives based 

on location. The Department of Transportation (for this scenario) 

is responsible for the Traffic Management function, and the 

County (for this scenario) is responsible for the Emergency 

Management function. The TMC and the County EMA are 

separated by several blocks or several miles. In an urban 

situation they are probably in separate buildings in the rural 

setting they may be in the same building, or separated by 20 

miles. Let’s look at the urban and rural separate building scenario 

and develop a communication link. 

TMC to EMA Communication Link

Rural Application

Operator

Work

Station

Private

DS1

Operator

Work

Station

Private

DS1

DOT

Transportation

Management Center

County

Emergency Management

Agency

Comm. Tower

100BaseT Router

Router 100BaseT

Figure 3-9: Diagram - TMC to EMA Comm Link Rural Setting
Telecommunications Handbook for Transportation Professionals 

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The diagram in the figures above are designed to facilitate the 

urban/suburban deployment. This single link will provide a 

physical path for the “incident response request” and the 

“incident information response” data flows. Please note that this 

information can be transferred in the form of voice or data. The 

final system requirements document will provide the details. For 

purposes of this illustration we will assume that the 

communication is a data transaction using a specific software 

application. 

RURAL SYSTEMS

The rural setting is characterized by a lack of available 

electrical power and telephone company infrastructure. This 

places a greater financial burden on the development of a 

telecommunications system. The rural communication links can use 

the same type of wireline system (as the urban example). 

However, a portion of the leased DS-1 link monthly fees are 

based on distance. In the urban system, the TMC and the EMA 

may only be separated by several city blocks. A rural situation 

could have the TMC and the EMA separated by 10 to 15 miles. The 

monthly cost of the leased line becomes a major consideration – a 

56 KBps leased line may cost more in the rural setting than the 

DS-1 in the urban setting because leased telephone line services 

have a mileage based price component. Although the monthly fees 

TMC to EMA Communication Link

Rural Application

(Leased telephone Lines)

Operator

Work

Station

Leased

DS-1

Operator

Work

Station

Leased

DS-1

DOT

Transportation

Management Center

County

Emergency Management

Agency

100BaseT Router

Router 100BaseT

CSU

CSU

CSU

CSU

Figure 3-10: Diagram - TMC to EMA Rural using Leased Telephone Lines
Telecommunications Handbook for Transportation Professionals 

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are primarily based on bandwidth, a one mile DS-1 may have a 

lower overall cost than a 20 mile 56 Kbps leased line. 

Several alternatives can be considered to help lower the overall 

cost of the communication link. Voice communication via a 

telephone is one way to keep costs down. A dial-up modem could 

be used for low bandwidth data communication. If a microwave 

system is available, a hybrid wireline-microwave system could be 

created. Many states have microwave backbones that can be 

accessed by multiple agencies. The key concept to understand is 

that the National Architecture flows are not affected by the 

telecommunications infrastructure. The following is an example of 

a hybrid block diagram 

The above diagram assumes that the TMC and EMA are located 

within 1000 feet of a microwave site. A privately constructed 

communications link to the tower sites would be very cost 

efficient. If the buildings are several miles from the sites, it 

may be more cost efficient to lease a DS-1 between the buildings 

and the tower sites. A comparison of communications systems 

used in rural and urban settings will show that rural systems are 

more expensive to construct. The variance in cost is accounted 

for on a distance basis. One of the primary engineering problems 

for telecommunications systems is that of overcoming distance. 

By comparison, rural systems must overcome significantly longer 

distances than urban systems. There are a number of other 

problems which must be overcome. Additional material about 

telecommunication problems associated with rural ITS 

deployments can be found in the addendum chapter 9

. 

 

9 Written Testimony of Stephen Albert, Director Western Transportation Institute, Montana State University to 

United States Senate Committee on Environment and Public Works Subcommittee on Transportation, Infrastructure 

and Nuclear Safety. 
Telecommunications Handbook for Transportation Professionals 

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National Transportation Communication for Intelligent Transportation 

Systems Protocol (NTCIP) 

The following statement is provided on the NTCIP introductory 

web page10: “The NTCIP is a family of standards that provides 

both the rules for communicating (called protocols) and the 

vocabulary (called objects) necessary to allow electronic traffic 

control equipment from different manufacturers to operate with 

each other as a system. NTCIP standards reduce the need for 

reliance on specific equipment vendors and customized one-of-akind software. To assure both manufacturer and user community 

support, NTCIP is a joint product of the National Electronics 

Manufacturers Association (NEMA), the American Association of 

State Highway and Transportation Officials (AASHTO), and the 

Institute of Transportation Engineers (ITE).” 

For telecommunication purposes, the NTCIP User Guide provides a 

further definition: “NTCIP is a family of communication 

 

10 http://www.ntcip.org 

Figure 3-11: NTCIP Standards Framework
Telecommunications Handbook for Transportation Professionals 

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standards for transmitting data and control information between 

microcomputer controlled devices used in Intelligent 

Transportation Systems”. These standards are specific to 

transportation, and build upon existing (and developing) 

telecommunication standards and protocols. 

A traffic signal control system using twisted pair (see chapter 2) 

communication links and an RS 232 interface before the 

implementation of NTCIP will continue to use the same wiring 

protocol after the implementation of NTCIP. This will also be 

true for an incident management system using CCTV transmitted 

via fiber optic cable. The physical interface for the transmission 

of data and their associated standards and protocols do not 

change. 

Implementing NTCIP as part of 

the telecommunications 

infrastructure requires careful 

calculation of bandwidth. NTCIP 

protocols add “overhead” to the 

communication process. Some 

systems that exist today can 

handle this added overhead 

without re-configuration. Others 

will require changes. 

A traffic signal system that has 

15 controllers sharing a single 9.6 Kbps multi-drop communication 

circuit may, (depending upon the specific NTCIP protocol) need to 

be reconfigured. The re-configuration may require the use of 

more bandwidth, or a reduction of the number of controllers on 

the circuit. The NTCIP User Guide provides a careful examination 

of the issues related to bandwidth calculation and the 

implementation of NTCIP. The NTCIP User Guide can be found at 

the following web address: http://www.ntcip.org/library/guide.asp

The material contained in this section was developed from 

information available from the National Transportation 

Communication ITS Protocol (NTCIP) web site. The reader is 

referred to http://www.ntcip.org for specific information and 

resources. 

The National Transportation Communications for ITS Protocol 

(NTCIP) is a group of communications protocols developed for 

traffic and transportation systems. The transportation 

Overhead is any information 

that is added to a 

communication transmission and 

is not part of the original 

message. This information is 

used to identify transmission 

origin and destination, assist 

with network management, look 

for transmission errors, etc. 
Telecommunications Handbook for Transportation Professionals 

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community has long needed a mechanism whereby 

interchangeability and interoperability for the various 

components of transportation systems could be achieved. It is 

for this reason that NTCIP is being widely embraced and is being 

specified for new system deployments. 

NTCIP protocols allow for the interchange of devices of similar 

purpose and different manufacture to be placed in systems. The 

protocols allow for many different devices to share a common 

communication channel. 

Interchangeability is defined as the capability to exchange 

devices of the same type (e.g., a signal controller from different 

vendors) without changing the software. Interoperability is 

defined as the capability to operate devices from different 

manufacturers, or different device types (e.g., signal controllers 

and dynamic message signs) on the same communication channel. 

NTCIP is a suite of communications protocols and data definitions 

that have been designed to accommodate the diverse needs of 

various subsystems and user services of the National ITS 

Architecture. It is intended principally to handle these needs in 

two areas: communications between a management center and 

field devices, and communications between two or more 

management centers. Examples of the first application include 

transfer of command and configuration data between a 

transportation management center and field devices such as 

traffic signal controllers, dynamic message signs, environmental 

sensor stations, ramp meters, etc. Examples of the second 

application include transfer of data between multiple management 

centers within one agency, as well as transfer of data between 

management centers operated by different agencies. 

NTCIP differs from past practice in defining communications 

protocols for management systems in that it is not a single 

communications protocol designed for one purpose. Rather it 

consists of a whole suite of protocols covering the spectrum from 

simple point-to-point command/response protocols to quite 

sophisticated object oriented techniques. This is because of the 

diversity of the applications into which NTCIP is being deployed, 

and the resulting diversity of application specific characteristics 

such as type and quantity of data to be transferred, criticality 

of data transfer times, acceptable cost of communications 

infrastructure, criticality of data security and integrity issues, 
Telecommunications Handbook for Transportation Professionals 

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to name a few. Insofar as data definitions are concerned, NTCIP 

does not completely define the functionality of the central or 

field devices to which it applies. It only specifies the data 

objects to be transferred and limited functionality directly 

related to these objects. For example, NTCIP does not define the 

details of how a traffic controller operates, e.g., it does not 

define that a green must be terminated by a yellow and that a 

red must be displayed after a yellow. However, it precisely 

defines the data that may be communicated between traffic 

controllers and traffic management centers, and thereby defines 

the aspects of functionality (e.g., it requires that the length of 

the yellow clearance interval must be as indicated by the phase 

Yellow Change object). 

NTCIP standards and protocols are not designed to replace the 

general suite of communication standards and protocols developed 

by other standards organizations (e.g.: IEEE; ASHTO; etc.). In 

fact, it incorporates many of those standards. 

The introduction to this chapter indicated that the use of 

protocols adds the “cost of bandwidth”. The primary rule that 

needs to be followed in the design of a communication system is – 

“nothing is free!” Every communication protocol adds to the total 

amount of data being transported. The requirement for additional 

bandwidth to accommodate “overhead” protocols should not be 

considered in negative light. But, it must be considered! 

“Overhead” is anything that adds to the communication 

requirement. Any protocol for network management, any 

information that identifies a device, any information that is used 

for command and control, and routing information is considered as 

overhead. If the information is not part of the message – it’s 

overhead! Note: The actual amount of overhead required by the 

use of NTCIP, or any other OSI layer support is dependant upon 

the actual configuration of the NTCIP, or OSI Model, layer 

protocol. 

NTCIP is used for device management and systems message 

management. The following tables provide examples of NTCIP 

protocols: 
Telecommunications Handbook for Transportation Professionals 

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Table 3-3: NTCIP Device Management Protocol List 

Device Management 

1 Traffic signal management system communicating with 

traffic signal controllers at intersections.

2 

Transit management system communicating with monitoring 

devices and passenger information signs on transit vehicles 

and at transit stations and stops. 

3 Freeway management system communicating with detectors 

and ramp meters on freeways. 

4 

Traffic management system controlling CCTV cameras, 

dynamic message signs, advi sory radio transmitters, 

environmental sensors, and traffic count stations on 

roadways. 

5 Provide a synchronized time source for all devices 

(especially traffic signal controllers) in a single system. 

Table 3-4: NTCIP List of Systems Management Protocols 

Systems Message Management

1 

Two or more traffic signal management systems exchanging 

information (including second-by-second status changes) to 

achieve coordinated operation of traffic signals managed by 

the different systems and to enable personnel at one center 

to monitor the status of signals operated from another 

center.

2 

A transit system reporting schedule adherence exceptions 

to kiosks, to a transit customer information system, and to 

a regional traveler information system, while also asking a 

traffic signal management system to instruct its signals to 

give priority to a behind-schedule transit vehicle. 

3 

An emergency management system reporting an incident to a 

freeway management system, to a traffic signal management 

system, to two transit management systems, and to a 
Telecommunications Handbook for Transportation Professionals 

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traveler information system. 

4 

A freeway management system informing an emergency 

management system of a warning message just posted on a 

dynamic message sign on the freeway in response to its 

notification of an incident. 

5 Center – to – Center Communications 

6 Center – to – Field Device Communications 

As of the date of this handbook, individual NTCIP system 

packages are still under development. The reader should check at 

the web site for the latest information. 

Conclusion 

From a telecommunications perspective, neither the National ITS 

Architecture, nor NTCIP provides answers to design problems. 

NTCIP is a recommended set of communication protocols based on 

existing (telecommunication) standards. The National ITS 

Architecture provides significant detail on communication flows, 

but does not provide a design of the telecommunications system. 

The developers of the architecture understood that the design of 

a communication system would be unique for each ITS system. 
Chapter 4 

106

4. CHAPTER FOUR – DEVELOPING THE 

TELECOMMUNICATION SYSTEM

Introduction 

Telecommunication systems can be very complex and difficult to 

design because there is usually more than one way to meet 

requirements. Often, several communication protocols must be 

used in the final design. This chapter attempts to provide the 

traffic engineer, and traffic system project manager, with a 

suggested process for developing the design and specification for 

a communications network to support traffic signal and freeway 

management systems. A theme that is repeated throughout this 

handbook is that the design of a communications network to 

support roadway and transportation functions is not a stand-alone 

process. The determination of functionality and selection of 

options must be done as an integrated part of the overall traffic 

management system design. Personnel responsible for the 

development of the communications system should be full 

members of the overall project team. 

Central to the development of the communication system is the 

fact that it is there to serve the requirements of the overall 

project. Communication project personnel should attend general 

project planning meetings. If new roadway construction, or 

roadway modification, is part of the overall project, 

communication engineers should be included. 

This chapter is organized into six primary sections. First, a 

recommendation of qualifications for a telecommunications 

consultant, including types of experience and education. The next 

three sections are devoted to the Requirements Document. The 

development of a complete requirements document is essential to 

the proper implementation of a telecommunications system. The 

final section concludes this chapter with some basic 

recommendations for managing the communication project. 

Selecting the Consultant 

This section provides guidelines for selecting an engineering / 

communications consultant with the right qualifications. Three 

basic qualification areas must be considered when selecting a 

qualified communication consultant: experience, education, 
Telecommunications Handbook for Transportation Professionals 

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project background. And, these four (4) basic rules apply in 

making the selection: 

THERE’S NO SUBSTITUTE FOR EXPERIENCE. 

Qualified applicants need to demonstrate a good understanding of 

how each element of a communication system will impact on the 

viability of a whole system. There are only a few engineering 

schools offering degree programs in telecommunications. 

Technology changes faster than the professors can write new 

text books. 

Communication Engineers don’t design traffic (or freeway 

management) systems don’t use a traffic engineer to design a 

communication network. 

There’s no substitute for experience. Consulting firms (or 

individuals) should have at least 10 years (as individuals or 

combined with other team members) of experience in analysis, 

design and implementation of communications systems. Ten years 

may seem like a very heavy requirement, but will assure that the 

engineer (or firm) will have a broad range and depth of 

experiences. Most communication system engineers are used to 

the idea of wearing many hats. And, as technology changes, there 

is a greater need to have a broad application experience than a 

specific focus. There is also a need to understand legacy 

technologies. In many circumstances, the communication engineer 

must design a system that allows for the use of legacy 

technologgy, adds current technologies, and provides for 

implementation of future technologies. 

During the course of writing this handbook, more than a dozen 

new IEEE standards relating to Ethernet and the application of 

Ethernet to wireless and broadband wireless were either 

published, or sent to committees for final acceptance, and there 

are about a dozen more in development. Since the early-1990s 

there has been a focus – by the telecommunication carriers – to 

move from primary support of analog voice based services to data 

transmission services. During that same period, Transportation 

agencies – on a broad scale - embraced the use of technology to 

support their operations. Their use of telecommunication 

technologies has very rapidly evolved from analog systems to 

digital data systems and the use of wireless. There is a general 

convergence of voice based and data based telecommunications 

services. This creates a greater need for communication 
Telecommunications Handbook for Transportation Professionals 

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108

engineers to develop a broad based background. During the 

transition period, it is important for telecommunication system 

designers to have an understanding of both analog and digital 

communication systems. 

DIFFERENT TELECOMMUNICATION DESIGN SPECIALTIES

Many specialties have engineers that primarily do design and 

others that focus on construction or manufacturing. The same is 

true for telecommunications. There are engineers that only do 

design and those that work on the construction of the systems. 

For most ITS projects it’s a good idea to have at least one 

member of the design team that has experience in both the 

design and implementation of communication systems. Most 

communication system designers have learned valuable lessons by 

actually having to make their design work. Larger firms may have 

significant breadth of experience in developing traffic signal and 

freeway management systems. However, you’ll want to look closely 

at their experience with communications systems design and 

deployment. If you are making a choice between two or more 

qualified firms, take a hard look at both corporate and individual 

personnel experience. 

Many IT personnel have significant experience with the 

deployment of Local Area Networks, but the may lack a 

background with the types of systems required for freeway 

management and traffic signals. Local area networks are generally 

deployed within a building. The personnel designing those systems 

don’t have to worry about location of the media infrastructure, 

or bringing power to a communications cabinet, or using equipment 

that can survive extremes of temperature and moisture. On the 

other hand, make certain that an experienced IT person is 

involved in design of the control center. 

TYPES OF TELECOMMUNICATIONS EXPERIENCE

Communication system engineers should have the following 

experience (this can be defined as either direct experience or 

the management of individuals and firms doing the work): 

• Construction: Direct burial; conduit design; pole mounting of 

cable; towers and roof mounting of antennas for radio 

systems. 
Telecommunications Handbook for Transportation Professionals 

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• Equipment installation: multiplexers (analog, digital, and 

fiber optic); modems; DSU/CSU; routers; switches. 

• System Design: VF (voice frequency); Digital (T-1/T-3, 

Compressed Video); Fiber Optic (SONET, ATM, Video); 

Wireless; Ethernet, Video Over IP (VIP); Voice over IP 

(VoIP). 

• Experience in creating alternatives analysis to provide 

several options for meeting requirements. 

• Design and deployment of communications systems for 

traffic and transportation purposes. Very important – a 

communication engineer with no concept of traffic and 

transportation systems won’t understand what the 

communication system has to support. 

• The project background of a communication consulting 

engineer is important. Projects denote experience. 

• Overall project experience should be a combination of 

general communications systems design and deployment as 

well as specific. 

• Look for projects that relate to the objectives of the 

current project. 

• Any other relevant experience that directly relates to the 

specific project. 

KNOWLEDGE OF TELECOMMUNICATIONS SYSTEMS RELATIONSHIPS

Seek out engineering talent with a good understanding of how 

each element of the communication system will impact on the 

viability of the whole system. The following should be applied in 

the search for qualified firms and personnel: 

• There is almost never a situation in which one type of 

communication system (or element) will provide a solution 

for all system requirements. Very few communications 

systems use only one type of technology – look for personnel 

with a variety of system design and deployment experience. 

• Most systems use combinations of technologies. An existing 

large traffic signal control system may use twisted copper 

pair connections between local controllers and field masters, 

and a fiber connection between the field masters and the 

central computer. The local DOT may have decided to 
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upgrade the system by adding intersections and using 

wireless for the new communication links. The new 

communication system may also have to be capable of adding 

CCTV and traveler information signs. The communication 

engineer responsible for completing the design should have 

experience with all of the proposed equipment, the legacy 

equipment, and the necessary communication protocols. 

• An experienced communication system engineer will 

understand how all of the elements can be made to work 

together. Traffic engineers may have significant experience 

with the legacy portion of the system, but won’t understand 

how to integrate with the fiber and possibly Ethernet and 

broadband wireless systems. System designers lacking 

sufficient experience and education in only one piece of the 

communication requirements for the above system will 

probably make a mistake and there will be a need to spend 

additional money to correct the problem. 

• An experienced communications engineer will ask questions. 

They will want to know how the traffic signal or freeway 

management system is supposed to work and the 

communication needs of each element of the system before 

creating a design. When working with a communications 

engineer, tell them what you want the communication system 

to provide, not the type of technology required. 

EDUCATIONAL QUALIFICATIONS

Education is important, however, there are only a few 

Universities offering degree programs for communication system 

design and/or engineering. Most engineering schools offer 

courses in communication technology. However, the courses are 

designed to provide the student with a fundamental understanding 

of how the technologies work. Additional points: 

• Universities can’t make curriculum changes that keep 

pacewith the changes in communications technology. The 

implementation of new technologies is occurring within a 

short time frame after their invention Coincidently, 

universities are at the forefront of both the development of 

new communication technologies and their immediate 

implementation. 
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• Universities offer courses in communication technologies to 

provide students with knowledge that will assist in the 

design of communication hardware. These courses are 

normally associated with the Electrical Engineering program. 

• Many universities offer management level course work in 

telecommunications technology, but these are generally 

focused on the economic aspects, and strategies for their 

use. The Rochester Institute of Technology, Rochester, New 

York, offers Undergraduate and Graduate degree programs 

in the field of Telecommunications. The school also offers 

several certificate programs. More information is available 

at http://www.rit.edu . 

• There are no Professional Engineering licenses for 

Communication Engineers. The Electrical P.E. license exams 

don’t cover telecommunications. 

• An individual with an Electrical Engineering Degree and a PE 

is not necessarily a communications engineer. However, an 

individual with a Civil Engineering Degree, a PE and 5 to 10 

years of experience in the construction of communication 

networks should be heavily involved in both the design and 

deployment of communications infrastructure. 

• Many qualified communication engineers have a Bachelors, or 

Masters Degree, in a non-engineering field. However, their 

qualification for communication system design was learned 

on the job. Many have attended technical courses provided 

by equipment manufacturers or professional development 

companies. Taking these professional courses or seminars is 

a good way to keep “current” on new communication 

technologies. 

• Many Community Colleges offer Associate Degree Programs 

in communication and technology engineering. These 

programs generally focus on the construction of 

telecommunication infrastructure, the installation of media 

and use of test equipment. 

• The Armed Forces offer excellent training programs and an 

opportunity to design and implement telecommunication 

systems. Many individuals working in telecommunications 

have been through these programs. There’s a lot of good 

experience gained by installing, operating and maintaining a 

telecommunications network in a combat area. 
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Requirements Analysis 

The communication system requirements document is based on the 

overall concept of operations for the traffic/transportation 

system. Keep in mind that the communication system is a 

supporting element of the overall system. It is important for the 

project team to make certain that the communication engineer is 

fully aware of the concept of operations for the main project. 

The requirements analysis sets the tone for the whole project. 

Organizing the requirements analysis into primary elements will 

help the project team visualize the interactive relationships. The 

organization chart (figure 4-1) is a suggested representation of 

one method of creating the visualization. The reader may have 

another preferred way to show the relationships. There is no 

“right” or “wrong” way to present the information. Simply be 

aware that creating a requirements analysis for the 

communications system starts with the overall program 

requirements analysis. 

Figure 4-2, shows the relationships of the major functional 

elements of a proposed system and the general communication link 

required. In chapter 3 we looked at how the National 

Architecture is used to structure a relationship between various 

elements of a freeway management system. The requirements 

Figure 4-1: Field Devices Communication Link Requirements
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analysis is the process for telling systems designers what system 

functionality is needed. If the whole project was laid out in a 

block diagram , the figure 4-3 would represent one portion of the 

overall diagram. This diagram represents the communication links 

for the field equipment. 

Once the role of the communication system – in terms of the 

overall program – is established, the communication engineer 

should focus on developing this aspect of the requirements 

document. Following is an example of a communications system 

centric requirements relationship diagram: 

The chart is generic. There is no attempt to specify technology 

only general requirements. Communication technology strategy is 

determined by examination of the specific system requirements. 

The communication system is one of the operational elements of 

the Incident Management System. The chart shows the 

relationship of communications systems to the whole project and 

individual elements. The design engineer will be forced to explain 

all of the links and not overlook any requirements. 

Figure 4-2: Chart Relationship Communication to Overall System
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THE “GEE-WHIZ” FACTOR

It is important to approach the communications system design 

with the right attitude. There is a tendency to look at the “geewhiz” of communications technologies and assume they will 

support project requirements. Project managers and engineers 

should get past this phase of the requirements analysis as quickly 

as possible. Streaming Video over an IP Multi-cast network is not 

the only solution to provide for the distribution of video. The 

communications systems are designed, and implemented, in 

support of the traffic management system – not vice-versa! 

However, there is a valid reason for using the “gee-whiz” factor. 

Properly employed, it can lead to some innovative uses of 

technology. An example of the innovative use (within the 

transportation environment) is presented in Chapter 7. The 

project team should look at the “if anything is possible” scenario. 

It is perfectly acceptable to ask the communication engineer to 

look at system options using leading (sometimes called “bleeding”) 

edge technology. The communication engineer gains an 

understanding of project team expectations. In return, the 

project team is provided with enough information to make the 

right decisions. 

Completing the requirements analysis will provide the project 

development team with a clear understanding of the viable 

alternatives, the role of the communication system as part of the 

overall project and a potential budget for the communication 

system. 

The communication requirements analysis should be completed as 

a part of the overall project concept of operations and 

requirements analysis. When practical, wait until the project 

requirements analysis is almost complete. The communication 

system is there to serve the needs of the overall 

traffic/transportation system. 

KEEP EXPECTATIONS REALISTIC – ASK QUESTIONS

• Does the system have to be up and running 99.999% (“five 

nines”) of the time? Does the added cost and complexity 

make sense considering that a “five nines” tolerance is the 

equivalent of 315.36 seconds (or 5.256 minutes) per year of 

outage? 
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• Is QoS (Quality of Service) really an issue or is that just 

the Ethernet/ATM/SONET account manager talking? 

Constant monitoring of all system elements is more 

expensive to implement than a simple ability to locate 

problems. 

• Are there different requirements for each link and each 

device in the system? Don’t let one element of the system 

create problems for all of the other elements. Compromise 

will be necessary. 

• Is specification of end to end system latency of 1ms 

realistic? Consider a video system with PTZ. For the PTZ 

control a specification of 1ms latency may seem reasonable. 

However, a codec that delays the image by 2 seconds will 

make PTZ control unusable. 

• Traffic signal systems have typically operated on a point to 

multipoint poll/response protocol that requires a response 

within 50ms or less. Is it realistic to expect wireless or 

internet based systems to meet the polling latency 

requirements of a traffic signal system? 

Recognize that system reliability and quality are necessary and 

desirable. But, also recognize that many features and benefits 

have a cost. Use the “KISS” (keep it simple stupid) principle of 

system design whenever practical. The requirements document 

should help answer the following: 

• Are there viable alternatives that can help to lower the 

overall cost? 

• Can you obtain better functionality and greater value using 

an alternative even though it adds cost? 

• Will the use of alternatives add to, or reduce, overall 

system complexity? 

• Can the system allow for future growth or technology 

changes? 

A Systematic Engineering Approach to the Requirements Analysis 

There is no magic formula, just the tried and true “five Ws and 

H” question and answer technique – what, where, when, who, why, 

and how. The questions are not complex, but the individual 

answers may point to a series of complex design and 

implementation issues for the required communications system. 
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KEY POINTS TO CONSIDER: 

• View the communication system as a part of the overall 

traffic/transportation project. There are many examples of 

adding the communications network as an afterthought. This 

eventually causes dissatisfaction with the communications 

system. The end result is a requirement to spend additional 

money to correct problems. 

• Look at the whole system, not just the immediate 

construction project. Many ITS programs are developed as 

part of a roadway construction project. DOTs have been able 

to build long lengths of highway by breaking the 

construction into a series of small projects. However, those 

project sections are in fact part of a larger plan. The 

communications system should be part of the larger plan. 

There are too many examples of DOTs adding a different 

type of communication system to each construction project. 

• The communications network must be analyzed and designed 

to serve the long-term traffic management needs (e.g., what 

will the ultimate system provide in terms of geographic 

coverage and functionality). The potential communication 

needs of other government entities should also be 

considered in the analysis and design. Don’t design a 

communications system for a highway section project that 

will be expected to serve as part of a larger network that 

has not been planned. 

• Answer the questions. Take note that most of the answers 

are provided in the context of traffic and transportation 

terminology. This is recognition of the purpose of the 

system – to provide communications capabilities for a 

traffic/transportation system. 

• Each of the six primary questions will lead to secondary 

questions. 

• Follow the process through to a logical conclusion. 

ASK THE QUESTIONS

What is the purpose of the proposed traffic/transportation 

system? Look at the original project statement of purpose for 

this answer. Relate the communication requirements to the reason 

for the project’s existence. Most projects require bi-directional 
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information flow. Many require bandwidth to support video from 

CCTV cameras. 

• Will the communications network need to support multiple 

functions? Each function (traffic volume, traveler 

information, toll collection, congestion management) will 

have its own set of communication requirements. 

• What is the impact of the “Market Packages” as expressed 

in the National Architecture to the overall project? 

• What National Architecture Standards are envisioned for 

the system? 

• What is the role of communications in the overall 

traffic/transportation system? 

Where will it be located? Location of the project has an impact 

on overall design of the physical infrastructure and the cost of 

construction of a communication network. If the project is to be 

constructed in a narrow mountain pass, it will create challenges 

that won’t be encountered on a local city street. Where is the 

TMC to be located in relation to the field equipment? 

• If the TMC is located on the western edge of a city and the 

field equipment is located on the eastern edge, how will a 

communication link be created? Which will be more cost 

effective – lease, or construct the communications link? 

• Location may also impact on the type of communication 

media. During the “Gee Whiz” discussions, the project team 

may assume that Free Space Optics (see technology 

description in chapter 2) would be a good system, but this 

may be negated by the actual location of the intended 

system. 

When (over what period of time) will it be deployed? This is a 

question that is directed to the communication network. Does the 

project plan call for implementation over a relatively short period 

– one to two years – or a long period – five to eight years? 

• During a relatively short deployment time frame, project 

planners can assume that communication technology will 

remain stable. The communication system design team can 

propose a system without concern that communication 

technology and process will change. 
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• Taking into consideration the total duration of 

traffic/transportation projects, one could expect that 

proposed equipment and actually delivered equipment will 

have changed. Example: a system was specified that required 

a DS-1 Multiplexer and a separate CSU/DSU. By the time 

the system was deployed (1.5 years later), most 

manufacturers were offering a combined DS-1 Mux and 

CSU/DSU. This lowered overall cost, saved space, and 

reduced power requirements. The end user – a DOT – 

required three months of meetings, and substantial 

paperwork before allowing the change - including the saving 

of money. 

• Given the pace of change and innovation of communication 

technology and process, managers of long term projects 

should anticipate changes to equipment specifications. Under 

these circumstances, it might be wise to allow for a second 

look at communications technology before the final 

specifications are published. However, don’t make changes 

that will require a total re-write of the specifications. Look 

for improvements (or enhancements) that create an overall 

cost/benefit for the project. 

Who will operate and maintain the system? Consider wheter the 

communication system will require that operational personnel 

activate various functions of the communication equipment. All of 

the following may have an impact on the overall design of the 

communication system: 

• Will they need to know how to trouble-shoot for 

communication problems? 

• Will they need to be able to effect minor repairs? 

• Will they need to configure the operational functions of the 

communication system? 

• Do I have internal staff capable of maintaining the 

communication system? 

• What type of experience and educational qualifications are 

desirable? 

Answering the question of who will operate and maintain the 

system will lead to operator and maintenance staff qualification 

requirements. DOTs have personnel regulations and guidelines 

that have to be met in order to provide staffing. Private 
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contractors supplying operational and maintenance personnel may 

have to meet other criteria. Outsourcing might be a reasonable 

consideration. 

Why is the traffic system being deployed? This may seem 

redundant to the question of “what” is being deployed, but at this 

point the project team will focus on the specific type of traffic 

system. “Why” might be answered with a look at the research 

that was used to justify the deployment of the 

traffic/transportation system. The communication engineers 

responsible for analyzing and designing the communications 

system need to be provided with a good understanding of how 

various types of traffic/transportation systems work. This will 

lead to a design of the communication system based on the 

functions of the traffic/transportation equipment. Examples of 

various systems that should be explained: 

• Enforcement controls (Traffic Signal, Speed, etc.) 

• Toll Collection 

• Traveler Information 

• Incident Management 

• Traffic Signals 

• Ramp Management 

• General Traffic Information Collection 

• Regional Integration 

There are a number of “How” questions to be answered and most 

are interrelated. 

• How many devices will be deployed? A simple question that 

will have a tremendous impact on the overall design. A large 

number of devices will increase the bandwidth requirements 

and may strategically alter the initial communication system 

concept. 

• How many operators at the control center? Another very 

simple question that may have a significant impact on the 

design. Related to this is a question that deals with diverse 

operator (or system control) locations. The number of 

operators will impact on the communications network within 

the TCC. Diverse operator locations (different buildings) 
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will have an impact on the entire communication network – in 

terms of both complexity and cost. 

• How much redundancy is required? Redundancy can be viewed 

from several aspects. Redundant and diverse communication 

paths will add significantly to the overall cost of the 

project. It is probable that the total cost will increase by 

more than double. Redundant communication hardware will 

impact on the total by the factors of the hardware and 

installation costs. 

• How will regional requirements be met? 

• How much will it cost? 

• How will it be funded? The reader might wonder - “what’s 

the difference!” Each potential funding source will make 

payments under specific circumstances. Some may only pay 

for capital expenditures, while others may pay for capital 

and operational costs. The communications engineers will 

want to consider these aspects when making 

recommendations for the communication system 

architecture. If 50 percent of the communication system 

cost is for leased telephone line services, and the primary 

funding source will only provide for the capital 

expenditures, the project will lose 50% of its potential 

funding for communications systems. A public/private 

resource agreement may only provide for certain types of 

communication systems and equipment. Joint system 

development with a portion of the funding being provided by 

one, or more, additional agencies may add some requirements 

for the type of system or equipment used. The 

communication engineer will need to know if the funding 

arrangements will have an impact on the system design. In 

later stages of the requirements and design process, the 

engineer will need a good understanding of the amount of 

funding allocated for communications systems. 

Creating The Requirements Document 

Once the basic questions have been asked and answered the 

communications engineer will present a preliminary communication 

systems requirements document. The project design team should 

review the proposed requirements document, and consider the 

following: 
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1. Merging Expectations with Reality - At this point, it is time 

to look at the requirements for the communications system 

and reconcile original expectations with the realities of 

what is possible. Compare expectations with the preliminary 

communication systems design. Ask the communication 

engineer to fully explain how technical and financial barriers 

impact on expectations. Challenge the requirements 

document. 

2. What Type of Communications System Should I Build? Now 

that the requirements document has been presented, the 

project team needs to determine if it should follow all of 

the suggestions made in the requirements document. There 

may be new information that was not available when the 

communications design team started to work on the 

requirements document. 

THREE BASIC SYSTEMS TYPES: 

• Private System – the DOT builds its own system and is 

totally responsible for the construction, operation and 

maintenance. 

• Public Network Based – the entire system is leased from 

local telecommunication carriers or other types of 

communication service providers. 

• Hybrid – Public/Private – a combination of the above systems 

types. In most instances, the DOT will take responsibility 

for field communication devices and circuits and use leased 

telecommunication facilities for transport back to the TCC. 

DEVELOPING A BUDGET

Once the requirements have been reviewed against expectations, 

it’s time to develop a “real” communication system budget. 

• Price out the “ideal” system – have the communications 

engineers do a comparison between the system described by 

the requirements document, and the expected system. 

• Determine if there are alternatives that will help the 

project get closer to the expected system without degrading 

performance criteria suggested in the requirements 

document. 
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• Are there viable alternatives that can help to lower the 

overall cost? The Utah DOT system described in chapter 7 

provides a good alternatives example. 

• Can you obtain better functionality? What’s the marginal 

cost adjustment for a significant increase in additional 

functions? Will the additional functions increase the overall 

cost of maintenance and operation? 

• Can the system provide for future growth? Not just amount 

of capacity, but the ability to handle (accept) technology 

changes. 

Conclusion 

A FEW SIMPLE GUIDELINES TO FOLLOW: 

• There’s no magic formula 

• Make certain that the communications engineering team is 

part of the overall project team. 

• Don’t let the communications engineering team act as an 

independent agent without direction. 

• Assure that they receive significant input from the overall 

project team. 

• Don’t let the “techno-speak” (language of the 

communications engineers) be a creative engineering barrier. 

• Investigate, and make certain that you have selected the 

right communication engineering team partner. 

• Don’t be afraid to ask questions and seek explanations. It’s 

your system, you have a right to know! 
Chapter 5 

5. CHAPTER FIVE – TELECOMMUNICATIONS FOR 

FIELD DEVICES

Previous chapters provided a look at the terminology, technology 

and history of telecommunications as well as the need to create a 

viable requirements document. This theme is continued with a 

look at the primary building block of telecommunications systems 

– the communication circuit. Telecommunication technology, its 

use and deployment, is an iterative process with new building upon 

the old. This is the industry’s (telecommunication) way of 

assuring backward compatibility, and the continuing deployment 

of available new technology. The diagram is a representation of 

the merging of voice and data over copper. Analog voice 

communications evolved to digital voice communications. One voice 

channel carried over a pair of copper wires evolved to hundreds 

of conversations over the same pair of wires. The use of copper 

as a communication medium evolved into the use of fiber. The 

change of technology was revolutionary, but the implementation 

of the change was evolutionary. No sudden and dramatic change 

from one technology or process to the next. 

In the 1980s, that process changed. The convergence of events, 

technology developments, and action by the U.S. Department of 

Justice and the Courts precipitated a change in the corporate 

structure of the monopoly afforded to AT&T. The “telephone 

company” agreed to divide into several competing businesses. This 

created a competitive and open environment for the development 

of communications services and hardware that exists today. The 

basic developments and events: 

Basic Voice 

via Copper

Basic Data 

via Copper

Multiple 

Voice 

Channels

Multiple 

Data 

Channels

Combined 

Voice & 

Data

High 

Capacity Boradband

Figure 5-1: Diagram - Technology Flow
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• The “Carterphone” Decision of 1968 allowed end users to 

purchase and install telephone equipment from companies 

other than AT&T 

• The microprocessor was invented in 1971 

• Field trials by AT&T in 1977 proved that fiber could be used 

with transmission loss factors no greater than copper. 

• The ARPANET – precursor to the Internet – was activated in 

1969 

• AT&T implemented a plan to break into 7 regional and 

independent telephone companies, plus a manufacturing 

company – in 1983. 

These events, plus an overwhelming pent-up corporate and 

individual demand, converged to forge a new direction in 

telecommunications services and technology. However, corporate 

change and inventions did not minimize the desire to provide full 

backward compatibility with existing systems. 

Telecommunication technology is a major element of the 

application of traffic signal and freeway management and 

Advanced Transportation Management Systems. The use of 

telecommunication technology as a part of traffic management 

systems has followed an evolutionary process. Early traffic signal 

systems – deployed 50 years ago – used available 

telecommunication technology. Systems being deployed today take 

advantage of new technologies while accommodating existing – or 

legacy – systems. 

This chapter is devoted to a look at the specific communication 

circuit designs for traffic signal and freeway management 

systems. Much of the communication equipment used for both 

types of systems is very similar. There are application 

differences, but most of it is hierarchal and building block in 

nature. A common theme for all of the circuits is that they 

involve the use of a media or protocol converter. The flow is 

essentially from simple modem based systems using twisted pair, 

to fiber optics, and wireless, from analog transmission to digital 

transmission systems. From voice based communication protocols 

to Ethernet and Wireless Application (WAP) protocols. The 

examples provided in this chapter are the application of the 

technologies discussed in chapter Two. 
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Before discussing actual communication circuit types it is 

necessary to look at some of the basic elements of circuits, 

andthen understand their use as part of a traffic signal or 

freeway management system. 

Basic Communication Circuits for Field Devices 

We start with basic twisted pair copper and progress through 

fiber optics and 

wireless communication 

technologies. 

A key factor in the 

deployment of traffic 

and transportation 

control devices is the use of NTCIP (National Transportation 

Communication Interface Protocol) communication protocols. The 

use of NTCIP protocols does have an impact on the overall design 

of a communication network. Two rules that must always be 

followed in the design of a communication network: 

• All communication elements cost money 

• All communication protocols cost bandwidth 

Every item attached to a communication circuit has a monetary 

value. Therefore, complex is inherently more expensive. Always 

attempt to keep circuit designs simple. Recognize the total cost 

is not just for the initial hardware. There is an added cost of 

installation, optimization, maintenance and operation. Avoid using 

complex telecommunication technologies simply because they are 

the newest. The “latest and greatest” won’t always provide a 

solution to the communication challenges presented by a new 

traffic system. Let a properly developed communication system 

requirements document be your guide. 

BASIC CIRCUIT TYPES

This section provides a definition of the basic communication 

circuit types and a concept of where communication engineers 

start the process of system design. Chapter Two, presented a 

reference to directly connected and switched communication 

circuits. In fact, whether direct or switched, all communication 

circuits fall into one of three categories: 

NTCIP is actually a suite of 

protocols providing support for many 

different aspects of transportation 

communication system requirements.
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• Point-to-Point (see diagram) – the communication connection 

between two devices, or a device and a controller. 

• Point-to-Multipoint (see diagram) – a communication circuit 

connecting multiple devices to a controller. This can also be 

referred to as Multipoint-to-Point – depending on your 

starting point. 

• Multipoint-to-Multipoint (see diagram) – a communication 

circuit allowing many devices to connect to many devices; 

this type of system always involves a switch or router. 

 Figure 5-2, represents the three basic circuit types usin g 

modems as the end devices connected to private line 

communication links. There are many variations, especially when 

using dial-up networks, or intelligent switches and routers. For 

example, the internet is an example of a Multipoint-to-Multipoint 

circuit. Many individual home computers can connect to one, or 

many web sites via the PSTN. The same type of service is also 

Comm unication

Link

Com m unication Link

C om m unication Link

Modem Modem

Modem

Modem

Modem

Modem

Modem

Modem

Modem

Modem

Modem

Modem

Modem

Modem

Modem

Switch Switch

Point-to-Point

Point-to-M ultipoint

M ultipoint-to-M ultipoint

Figure 5-2: Diagram - 3 Types of Communication Circuits
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provided via Cable TV networks using a combination of routers 

and broadband multiplexers. 

The Design Process 

The development of a communication system design is very simple 

and not very complex – especially if a good requirements 

document is available. Let’s take a look at the process and the 

steps to creating the design. Assume that a requirements 

document has been created for a signalized intersection project. 

The document lists the following communication system 

requirements: 

• Seven 2070 controllers placed as indicated in table 

• Traffic signals at intersections automatically adjusted for 

timing parameters by host computer 

• Traffic Signals receive commands via field controllers 

• Host computer will poll 2070 controllers once every second 

with query for data & time hack. 

• 2070 controllers will store data from signalized 

intersections until requested by host computer 

• 2070 controllers must respond to host query within 20 

milliseconds 

• Notice that there is no discussion of the type of technology 

to be used. 
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This allows the communication engineer to make hardware 

recommendations based 

on the requirements. 

Communication engineers 

will generally visualize 

the basic communication 

circuit design as a block 

diagram rather than a 

mechanical design. This 

helps to simplify the 

overall design process. 

During the initial 

meeting to review the 

project concept, 

communications 

engineers will usually 

create a “back-of-theenvelope”, or “table 

napkin”, sketch. This 

helps to facilitate the 

discussion and provide 

the system designer and 

“client” (the DOT) with 

general points of agreement. 

Communications systems are designed from the ground up. First 

step is to lay out the points of communication - generally 

identified by location. Street addresses are preferred, however 

traffic management systems are deployed at intersections or 

points on a highway. Exact locations will be determined during a 

site walk through. A device location table for a traffic signal 

system may appear as follows: 

Table 5-1: Location of Field Controllers 

Host Computer Field Controller 

7th & East Napa East 2nd & East Spain 

 East Napa & East Spain 

 East 2nd & Patten 

Figure 5-3: Napkin Sketch of Communication System
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 East 4th & Dovall 

 East 4th & East Napa 

 East 4th & France 

 East 4th & Patten 

 East 4th & East 

MacArthur 

The table is then laid out on a map to help identify exact 

locations and to provide 

distance measurements. 

The distance 

measurements between 

devices are required in 

order to determine “link 

loss”. The communication 

engineer must know if 

the communication signal 

will need to be amplified 

to overcome excessive 

link loss. Distance 

measurements will also assist in the development of the 

construction budget. 

Next, a device and bandwidth 

table is created. The table 

shows the amount of data per 

transmission by site. For this 

type of system, the host 

computer normally sends a 

“time hack” and requests that 

the field units send available 

data. The table becomes a database for the system configuration. 

The communication engineer needs to determine the maximum 

amount of data traveling in any single direction. Based on the 

information in the table, the maximum amount of data flows from 

the field units to the host computer. The total is 6400 bits. 

Figure 5-4: Location Map

Note: This is a “fictitious” example 

of a traffic signal control system 

for the purpose of demonstrating 

how to calculate data 

communication circuit 

requirements. 
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Therefore, a 9600 Bps (9.6kbps) communication circuit can be 

used successfully. 

Table 5-2: Location & Data Requirements Table 

Item Host Computer Field Controller Maximum Data Per 

Transmission 

1 7t h & East 

Napa 

 200 bi ts 

2 E as t 2 n d & East Spain 800 bits 

3 East Napa & East Spain 800 bits 

4 E as t 2 n d & Patten 800 bits 

5 E as t 4 t h & Dovall 800 bits 

6 E as t 4 t h & East Napa 800 bits 

7 E as t 4 t h & France 800 bits 

8 E as t 4 t h & Patten 800 bits 

9 E as t 4t h & East 

MacArthur 

800 bits 
Telecommunications Handbook for Transportation Professionals 

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From this information, a schematic diagram is created. The 

schematic helps the communication engineer visualize the 

relationship of all points of communication. Overall design of a 

communication network includes all devices and communication 

cable routes. Figure 5-5, might be considered as a cover page for 

a set of schematics showing greater detail. One of the drawings 

that should be included is a cable detail with a chart showing the 

connector pins. Very often manufacturers make their devices with 

Controller

Controller

Controller

Controller

Controller

Controller

Controller

RS232

Host Computer

RS232

RS232

RS232

RS232

RS232

RS232

RS232

4W

9.6 M odem -FSK

9.6 Modem -FSK

9.6 Modem -FSK

9.6 Modem -FSK

9.6 Modem -FSK

9.6 Modem -FSK

9.6 Modem -FSK

9.6 Modem -FSK

1 2

3

4

5

6

7

8

Controller

RS232

9.6 Modem -FSK

9

Item Host Data Rate

123456789

7th & E Napa

E 2nd & E Spain

E Napa & E Spain

E 2nd & Patten

E 4th & Dovall

E 4th & France

E 4th & Patten

E 4th & E MacArthur

E 4th & E Napa

Contorller

200 Bps800 Bps800 Bps800 Bps800 Bps800 Bps800 Bps800 Bps800 Bps

Figure 5-5: System Schematic
Telecommunications Handbook for Transportation Professionals 

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a variety of cable connectors. Most computers use DB-9 

connectors and modems tend to have either DB-25, or RJ45 

connectors. If custom cables are needed, the cable connector and 

“pin-out” chart will save time and reduce confusion. If the Signal 

controller uses a DB-25 connector, and the modem has a DB-9 

connector you should include a table that provides the following 

detail: 

Table 5-3: DB-25 Connector Cable 

DB-9 to DB-25 Modem to Controller Cable 

Controller 25 Pin Connector Modem 9 Pin 

Connector 

RS232 Signal 

Pin # Pin # Function 

1 n /a Fr a me Gr o un d 

2 3 T X 

3 2 R X 

4 7 R TS 

5 8 C T S 

6 6 D SR 

7 5 Sig n a l Gr o u n d 

8 1 DC D 

9 n /a + T X 

11 n /a - T X 

18 n /a + R X 

20 4 D TR 

22 9 R I 

23 n /a D SR D 
Telecommunications Handbook for Transportation Professionals 

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25 n /a - R X 

This chart is based on EIA/TIA standards for RS232 serial 

cables. Double check the standards for final reference and ask 

the device manufacturers to supply pin-out diagrams. Standards 

change, but a manufacturer may not have incorporated the 

changes. 

This is a starting point in the overall design. As the process 

continues, the communication engineer will continue to refine the 

design until a reasonable conclusion is reached about solutions 

that will best support overall goals of the main project. A series 

of schematics are developed, and the design rules established in 

chapter Four are used to create a final design. 

TRAFFIC CONTROL DEVICE CIRCUITS

Following is a description of communications circuits commonly 

used in traffic and transportation systems. At the conclusion of 

chapter Five we will provide an example of a complex 

communication system that incorporates a number of varying 

traffic and transportation system devices. Chapter Seven will 

present examples of actual systems that have been deployed (or 

are in the process of being deployed). 

Earlier, communication circuits were described as having three 

(3) basic elements – transmitter, receiver, and transmission 

medium. That description was given to provide a basic 

understanding of communication circuits. Communication circuits 

have another element in common – protocol conversion. The most 

elementary system – two (2) tin cans and a string - has this 

element. The tin cans convert sound to a vibration which is 

transferred to the string. A basic telephone converts the human 

voice (sound) to an electrical signal (protocol conversion). The 

electrical signal is transmitted via copper wire (media). The 

Figure 5-6: DB-25 Connector

Figure 5-7: DB-9 Connector
Telecommunications Handbook for Transportation Professionals 

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135

electrical signal is received by another telephone and converted 

to sound. A modem converts the data protocol from a computer to 

a protocol that can be carried over a media11. Modem is a 

contraction of the phrase modulator/demodulator. The modem 

converts the binary one/zero data protocol of a computer (or 

other data device) to a protocol that can be carried via a specific 

medium. Modems have been developed for twisted pair, radio, and 

fiber optic. 

TRAFFIC CONTROL SYSTEM

Traffic controllers require a reasonably simple communication 

system. They are generally 

arrayed in a point-to-point, or 

point-to-multipoint serial 

network using low bandwidth, 

analog modems and twisted 

pair copper voice grade 

circuits. The greatest problem 

faced by a communication 

engineer in the design of 

these circuits is the polling 

requirements. Traffic signal 

systems are traditionally 

designed with system wide 

device polling every second. That is, every controller is polled 

once every second for information, and supplied with a clocking 

signal. 

Consider a traffic signal system that uses a 9600 bps data 

transfer speed. If each device transmits 1200 bits of data per 

poll, then – theoretically - a maximum of eight devices can be 

connected on a single multipoint communication circuit. Allowing 

for round-trip delay or potential line problems, a communication 

engineer would only connect seven devices to each circuit. In 

theory, a signal system with 50 controllers would require eight 

individual multi-drop communication circuits. 

If the traffic signal system uses a 10 bit message to provide all 

necessary information, a 9600 bps communication link could 

support a theoretical maximum of 960 field devices. The 

following formula is used: 9600 bits divided by 10 bits (each 

 

11 The plural term media is used because a modem can be used with many different types of media. It is the 

generic functionality of a modem that is being discussed in this section. 

Remember – software and data 

protocols are stated in bytes, but 

communication transmission is 

stated in bits. 1200 bits of data is 

150 bytes. One byte is equal to one 

character. Some traffic signal 

systems use a bit oriented 

message. The host computer is 

reading individual bits within a 

single byte to look for device 

status indications. 
Telecommunications Handbook for Transportation Professionals 

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136

message) = 960. However, this figure is further reduced by the 

total time (round trip communication time) it takes to poll each 

device, signal attenuation based on distance, type and makeup of 

communication media, and the signal-to-noise ratio of the 

communication link. Additionally, there is the latency induced by 

a device to properly format and send a response. 

If the system were using a byte oriented message, the maximum 

number of devices would be substantially less. A system that uses 

a message of 150 bytes would be limited to a maximum of 8 

devices on a 9600 bps link - 9600 bits divided by 8 (one byte) 

divided by 150 bytes (each message) = 8. Make certain that the 

communication engineer and the software manufacturer 

coordinate these details. This will save time when the system is 

being optimized. 

Basic Data Circuit Types 

The following diagram illustrates the basic elements of a modem. 

In fact, DSU/CSUs, Network Interface Cards (NIC), Video 

CODECs, and many other transmission devices have these same 

elements. Key differences are based on the type of data 

interface and the transmission medium. 

All communication circuits use some type of media – protocol 

converter so that device input/output can be transported via a 

specific media, or through a communication network. Examples 

are: 

• Traffic Signal Control 

XMTR

RCVR

Data I/O Port

Transmission 

Protocol 

Converter

XMTR

RCVR

Media I/O Port

Basic Modem Block Diagram

Figure 5-8: Modem Block Diagram
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137

• Communication Cabinet for Traffic Devices 

• Variable Message Sign 

• CCTV Camera 

• PTZ Control 

• RWIS Station 

• High Water Monitor 

When an engineer uses a modem they consider the device as an 

intermediary between the data equipment and the communication 

network. The computer (or 

other data device) is called the 

data termination equipment 

(DTE) and the modem is 

considered the data 

communication equipment 

(DCE). DTE and DCE are terms 

which help a communication 

engineer visualize a communication system in a technology 

neutral manner. The DCE device has two sides – DTE and Network. 

Using these terms, an engineer is able to visualize the orientation 

of the equipment to the network. 

A CCTV camera is considered as a DTE device because it provides 

data in the form of an image. The camera is actually converting 

the image to and electrical signal which must be transported via a 

DCE device. The DCE device could be a modem that converts the 

video electrical signal to a T-1 signal for transmission via twisted 

pair copper wire. In this case, the DCE modem device is called a 

CODEC. 

The terms are also used in 

maintenance and installation 

manuals. Technicians are able to 

easily identify which side of the 

device is connected to the data 

equipment and which is connected 

to the network. 

Transmission Network

Medium Transmission

Medium DCE

DTE

Figure 5-9: CCTV Circuit Diagram
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138

The communication system designer may prefer to create a 

system layout that is very generic. The designer can choose the 

technologies later in the process, but still has a working idea of 

how the system will be developed. 

When finalized, the above circuit may appear as follows: 

BASIC TRAFFIC DEVICE TYPE COMMUNICATION CIRCUITS

Communication links for Type 170/2070 and NEMA controllers are 

fairly simple. Under normal operation, a 1200 bit per second twowire half duplex circuit is used. Most systems are connected 

using an FSK communication protocol between the field controller 

modem and the master controller modem. A basic direct link 

between a single 170/2070 and a Master Control Computer would 

look as figure 5-11. Note that the private twisted pair cable installed by 

RG-59 Network

Coaxial T-1

Circuit Video

CODEC

CCTV

Figure 5-10: CCTV Circuit Diagram

DOT

Communication

Cable

Network

RS232

Cable

2/4 Wire

Private Line

Modem 170

Central

Control

RS232

Cable

2/4 Wire

Private Line

Modem

Figure 5-11: Diagram Field Controller to Host Computer
Telecommunications Handbook for Transportation Professionals 

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139

the DOT is described as a network.

Modems use a specific 

modulation protocol to 

convert the digital output of 

a computer (or traffic signal 

controller) to analog for 

transport via a telephone line 

or twisted pair. The protocol 

used by modems for 

connecting traffic signal 

controllers to central control 

computers is FSK (frequency 

shift keying). Frequency shift 

keying accommodates low 

speed (below 9.6 KBps) data 

transfer. For higher data 

rates, other Modem protocols 

are used – PSK (Phase Shift Keying) and QAM (Quadrature 

Amplitude Modulation). If you want to learn more about these 

transmission protocols, consult any good telecommunications text 

book – there are several listed in the reference section of this 

handbook. 

This basic communication system could be applied to almost any 

Frequency-shift keying (FSK) is a 

method of transmitting digital 

signals. The two binary states, “0” 

(Low) and “1” (high), are each 

represented by an analog waveform. 

“0” is represented by a specific 

frequency, and “1” is represented by 

a different frequency. A modem 

converts the binary data from a 

computer to FSK for transmission 

over telephone lines, cables, optical 

fiber, or wireless media. The modem 

also converts incoming FSK signals 

to digital low and high states, which 

the computer can "understand." 

DOT

Communication

Cable

Network

RS232

Cable

2/4 Wire

Private Line

Modem 170

Central

Control

RS232

Cable

2/4 Wire

Private Line

Modem

RS232

Cable

2/4 Wire

Private Line

Modem

RS232

Cable

2/4 Wire

Private Line

Modem

RS232

Cable

2/4 Wire

Private Line

Modem 170

RS232

Cable

2/4 Wire

Private Line

Modem 170

Point-to-Multipoint Network

w/ Multiple Comm Circuits

Figure 5-12: Diagram - Point-to-Multipoint
Telecommunications Handbook for Transportation Professionals 

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140

configuration. Substitute the 2/4 wire private line twisted pair 

with fiber and the basic network configuration does not change. 

The RS232 communication protocol used by the 170 controller 

would have to be converted to a light wave signal for transmission 

for transmission via the fiber. Decided to change to a newer 

2070 type controller, but want to keep the existing twisted pair 

communication links? Just replace the controller, because the 

modems and transmission line remain the same. Note: This is 

assuming that there are no changes to the software protocols in 

the overall traffic signal system.

This arrangement (figure 5-13) can be used for multiple locations 

that require multiple point-to-point communication circuits. Each 

controller would have a direct link to the central computer and a 

dedicated communication port. Engineers would refer to this as a 

point-to-multipoint communication network. The use of many 

communication circuits, modems, and communication ports on a 

central computer can be expensive. Traffic signal systems tend to 

use a variant of the point-to-multipoint. This arrangement is 

DOT

Communication

Cable

Network

Central

Control

RS232

Cable

2/4 Wire

Private Line

Modem

RS232

Cable

170

Multidrop Comm Circuit

RS232

Cable

170

RS232

Cable

170

RS232

Cable

170

2/4 Wire Multidrop Circuit

Modem Modem Modem Modem

Figure 5-13: Diagram - Multidrop System
Telecommunications Handbook for Transportation Professionals 

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141

called a multi-drop communication circuit. One modem at the 

central computer site serves many field modems. This scheme is 

especially cost efficient when leasing private line circuits from a 

carrier. The DOT pays for one communication circuit not the 

eight or more that it replaces. 

The central computer is controlling all of the communications 

process. It polls the field controllers for information, using a 

point-to-multipoint arrangement that allows all field units to 

respond individually. They have a virtual communication circuit to 

the central computer. Using the multidrop configuration allows 

the central computer to poll all of the field units attached to a 

single circuit, but each field unit must respond in sequence and 

cannot use the circuit while another unit is transmitting. Use of a 

multidrop arrangement 

requires close coordination 

between the communication 

system and the central 

computer software system. 

Make certain the 

communication engineer is 

fully aware of software 

communication delay requirements. If a field unit modem is 

sufficiently distant from the central computer, the software may 

have to be instructed to wait an additional one or two 

milliseconds for a response. 

The DB-25 to DB-9 diagram table – shown earlier in this chapter 

– indicates a pin labeled “CTS”. These initials stand for “Clearto-Send”. The field unit modem will wait for a Clear-to-Send 

indication before transmitting information to the central 

computer. If too much time has elapsed the central computer will 

complete another poll sequence. If there is too much delay, or 

the central has sent out too many requests for information, the 

central may assume that one or more field controllers have 

malfunctioned and issue an error report. 

BASIC VIDEO COMMUNICATION CIRCUITS

“Delay” – for this purpose – is 

defined as the amount of time 

elapsed from central computer 

request for information until it 

receives information from a field 

unit.
Telecommunications Handbook for Transportation Professionals 

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142

Most FMS and a few traffic signal control systems use CCTV 

cameras to support incident detection. The communications 

systems used for video transport are very similar to the basic 

communication links discussed previously. That is, they use a 

communication transmission device to convert the video signal to 

one that is compatible with the selected media. There are several 

different methods used to prepare a video signal for transmission 

over a communication 

link. The most common 

is to convert it to an 

analog electrical signal 

and transmit via 

coaxial cable. Most 

video originating from 

the type of cameras 

used in an FMS can 

travel about 100 to 

300 feet without 

degradation (depending 

upon the specifications 

of the cable). To 

travel longer distances 

the system must 

include amplifiers. Triaxial cable can usually provide distances of 

up to 1000 feet without an amplifier. All CCTV cameras used in 

North America provide an electrical video signal that meets 

standards developed by the National Television System Committee 

(NTSC). This standard is used by many other countries, including 

Japan, South Korea and Mexico. The NTSC standard is in part 

based on the 60 Hz AC electrical power provided in the United 

States, and was developed to provide a standard for broadcast 

television. The standard was adopted for use in CCTV systems. 

Two other standards exist – PAL and SECAM – based on the 

electrical standards in other parts of the world. 

Analog Video 

NTSC video can be transmitted via 

twisted pair, but not very far (a few 

feet). A standard telephone voice 

call (including low speed analog data used by traffic control 

devices) can be transmitted almost 20,000 feet. The difference 

NTSC stands for National Television System Committee, 

which devised the NTSC television broadcast system in 

1953. NTSC is also commonly used to refer to one type of 

television signal that can be recorded on various tape 

formats such as VHS, 3/4" U-matic and Betacam. 

The NTSC standard has a fixed vertical resolution of 525 

horizontal lines stacked on top of each other, with varying 

amounts of "lines" making up the horizontal resolution, 

depending on the electronics and formats involved. There 

are 60 fields displayed per second. A field is a set of even 

lines, or odd lines. The odd and even fields are displayed 

sequentially, thus interlacing the full frame. One full 

frame, therefore, is made of two interlaced fields, and is 

displayed every 1/30 of a second (30 frames per second).

Note: “Hertz” is a unit of time to 

describe the frequency of 

occurrence. “Bit” and “Byte” are 

units of data. 
Telecommunications Handbook for Transportation Professionals 

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143

is the amount of bandwidth used by the two signals. NTSC video 

requires between 3 MHz and 6 MHz, and a voice call requires less 

than 4 KHz of bandwidth. The following table provides a 

comparison of voice, video and text transmission requirements: 

Table 5-4: Voice, Video & Text Transmission Requirements 

Comparison of Voice, Video and Text Transmission Requirements 

Transmission Analog Digital Compressed 

NTSC Analog 

Video 

6.3 MHz 100 Mbit/s 1.5 - 10 Mbit/s 

HDTV 100 MHz 1.2 Gbit/s 20 Mbit/s 

Voice Telephone 4 KHz 56 Kbit/s 4 Kbit/s 

One Video Frame 3.3 Mbit/s 

One HDTV Video 

Frame 

 20 M bit s 

1000 Spoken 

Words 

 20 M bit s 

1000 Word Text 

File 

 60 Kbi ts 

CCTV cameras used for security and traffic incident detection do 

not output full broadcast quality signals and therefore do not 

require as much bandwidth. However, it is still greater than 4 

MHz. 

Most of the CCTV camera systems deployed in the 1990s used 

analog transmission systems with either coaxial cable or fiber 

optic cable. They were generally deployed in a configuration that 

used one communication link for each camera. As system 

operators gained knowledge of the video systems, they 

recognized that video signals could be multiplexed, allowing four 

(4) to sixteen (16) cameras to share a common communication link. 

Each camera could send a full video signal using a common coaxial 

cable (or fiber optic cable), and each could be displayed on 

individual monitors at the TMC. One of the drawbacks to this 

arrangement was that each video signal had to be brought to a 
Telecommunications Handbook for Transportation Professionals 

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144

communications hub for multiplexing. However, there was a 

significant savings for the total cost of the communications 

infrastructure. Figure 5-14, is a block diagram representing the 

basic elements of a frequency division multiplexing system. 

Video signals can also be converted to a digital signal in the same 

manner as voice is converted. A voice signal is digitized into a 64 

Kbit/s signal and can easily be transmitted via two twisted pair 

for up to 6,000 feet. However, a full NTSC video signal requires 

a 100 Mbit/s signal and will not travel more than a few feet over 

the same two twisted pair cable. In fact twisted pair is not used 

for DS-3; carriers use coaxial cable, or fiber. Full bandwidth 

video signals don’t travel very far (100 to 1000 feet) over coaxial 

cable. Transmitting video for any significant distance requires 

the use of a Video CODEC (coder/decoder). This type of CODEC is 

designed to use a DS-3 communication circuit. The DS-3 circuit is 

the equivalent of almost 45 Mbit/s. The reduction of the 

bandwidth to less than half of what is normally required is barely 

noticeable and in fact is used by broadcasters to send 

programming between television stations. DOTs have traditionally 

not used DS-3 CODECs because the cost of deployment was 

significantly greater than using the FDM type systems described 

above. DS-3 video CODECs have been in use for many years for 

“Distance Learning” programs and video conferencing. Many DOTs 

have deployed video systems using T-1/DS-1 communication links. 

Figure 5-15 is an example of a typical Video CODEC system using 

a T-1. 

Comm Hub

FDM

Hub

Four cameras deployed at 3000 foot intervals are hubed at a 

convenient location. Their video signals are multiplexed onto a 

single coaxial cable fro transmission to the TMC.

Figure 5-14: Diagram - FDM Hub Circuit
Telecommunications Handbook for Transportation Professionals 

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145

Digital Video CODECS 

In the 1990s, DOTs began to deploy video CODECs that could use 

DS-1 communication circuits (see figure 5-15). Telephone 

companies provided lower cost (than DS-3) services and the DOT 

could install twisted pair infrastructure within their own rightsof-way. 

Several different types of video CODECs are available to serve a 

wide variety of communication needs. The CODEC provides two 

functions. First, it converts the analog video to a digital code. 

Second, it “compresses” the digital information to reduce the 

amount of bandwidth required for transmission. In the process of 

converting from analog to digital and back to analog, the video 

image loses some quality. The compression process also adds a 

small loss of video quality. Each of the following CODECs are used 

in DS-1 systems and has its own set of video image quality loss 

characteristics. 

• H.261 CODECs are used primarily for PSTN based video 

conferencing. The A to D process sacrifices motion for video 

and audio quality. They typically use POTS (or DDS) services 

to reduce total cost of operation and are designed to 

provide simultaneous multiple connections for group 

conferencing. However, they can use DS-1 and “fractional 

DS-1” circuits for better image quality. 

Network RG-59

Coaxial T-1

Video Circuit

CODEC

Encoder

CCTV

T-1

Circuit

Monitor

RG-59

Coaxial

Video

CODEC

Decoder

Figure 5-15: Diagram - CCTV with CODEC
Telecommunications Handbook for Transportation Professionals 

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146

• JPEG (Joint Photographic Experts Group) and Motion JPEG 

are some of the most widely used CODECs for video 

surveillance purposes. However, they were primarily 

developed for the purpose of storing images electronically. 

Each still image is converted to an electronic data image and 

transmitted. The still images are assembled at a receive 

decoder and displayed at a rapid rate to provide motion. 

They can be used with POTS communication circuits, fixed 

low speed data circuits, or broadband copper and fiber optic 

communication links. They are also used in wireless 

applications such as spread spectrum radio. 

• MPEG (Moving Picture Experts Group) CODECs were 

developed to provide a better quality motion image 

compression. There is less image quality lost in the 

conversion and compression processes. However, the primary 

purpose of MPEG CODECs is to provide “real-time like” 

motion pictures via the internet (also called Streaming 

Video). The overall process creates a storage buffer so that 

there is always a slight delay between the request to view 

and the start of the motion picture. For the average user of 

the internet, this is not a problem. CODEC manufacturers 

using the MPEG-2 standard for traffic surveillance purposes 

have adapted this standard to create a real-time video 

transmission. However, this does have a minimal impact on 

final image quality. The MPEG-4 standard was developed for 

internet streaming video, but is also being adapted for 

“real-time” surveillance purposes. 

Pan-Tilt-Zoom Issues 

The use of pan-tilt-zoom (PTZ) created another problem. These 

devices use either a direct electrical signal with variable 

voltages, or special coding to activate one of the functions. The 

manufacturers of the PTZ devices developed special modems that 

convert the PTZ signal to an RS232 data stream so that it can be 

transmitted via standard communication circuits. This requires a 

separate communication path. Incident management systems built 

during the 1990s generally required separate communications 

equipment for both the video and the PTZ control. Originally, 

CCTV camera manufacturers offered an external converter. One 

was required at the camera end and the other with the video 

switcher at the TMC. Today, manufacturers offer products that 
Telecommunications Handbook for Transportation Professionals 

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147

combine both in one system using a single communication path. 

Most video CODECs and Fiber Video modems have a PTZ data port 

as part of the package, and cameras and switchers have the 

control signal conversions devices embedded. The video signal and 

the PTZ signal travel in opposite directions allowing full 

bandwidth to be provided for the video signal. 

VIDEO-OVER-IP (VIP) 

The video systems described previously were developed to work 

over communication networks that existed to process voice 

communications. All data and video transmissions have to be 

adapted for transport over large point-to-point communication 

networks. This requires a significant investment in transmission 

hardware and software systems and media infrastructure. 

Ethernet and VIP help to reduce the overall complexity of the 

communications networks and significantly lower the cost of 

hardware and infrastructure required to support the system. One 

of the major benefits is the relative ease with which video can be 

distributed to desktop computer workstations. Before discussing 

VIP, a quick look at how TV cameras function. 

Distributed computing and the explosion of the Internet have 

driven the use of internetworking for over 30 years. Practically 

F ie ld S ite

CCTV

C am era

P a n -T ilt-Z o o m

U n it

V id e o

CODEC

P a n -T ilt-Z o o m

C o n tro l B o x

T -1

M u ltip le x e r

NTSC

V id e o

COAX

PTZ

C o n tro l C a b le

R S 4 4 9 C a b le

R S 2 3 2 C a b le

V id e o

M o n ito r

V id e o S w itc h e r

P T Z C o n tro l

V id e o

CODEC

PTZ

M odem

T -1

M u ltip le x e r

NTSC

V id e o

COAX

PTZ

C o n tro l C a b le

R S 4 4 9 C a b le

R S 2 3 2 C a b le

Leased

T-1

C irc u it

T ra ffic M an ag e m e n t C en te r

NTSC

V id e o

COAX

Figure 5-16: Diagram - Typical CODEC Communication Circuit - 1990's Deployment
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every network in place today was engineered based on standards 

and technology optimized for handling the single data type, 

character data, that was prevalent as recently as 10 years ago. 

Today’s sophisticated applications often require networks to 

handle video, storage and IP/Telephony. The speed and bandwidth 

requirements for applications using these data types are so high 

that most network technology is simply not up to the task. DOTs 

implementing new Advanced Transportation Management Systems 

(ATMS) are looking to new data communication technologies to 

help simplify their networks, and reduce the overall costs of 

deployment and maintenance. Ethernet for general data 

communication and video-over-IP are logical choices. The next 

few pages will look at the deployment of Video-over-IP. 

TV cameras were first designed using an image pick-up tube. The 

face of the tube was coated with a light sensitive film that 

captured the image. The film created an electrical charge which 

was captured as an analog electrical signal. The electrical 

representation of the image was transmitted to a monitor. The 

output of the camera was an analog video signal. All of the 

equipment described above was needed to convert the video image 

to something that could be transported via the existing network 

infrastructure. 

In the early 1990s, the “Charged Coupled Device” (CCD) was 

perfected. A CCD is an electrical device that is used to create 

images of objects, store information (analogous to the way a 

computer stores information), or transfer electrical charge (as 

part of larger device). It receives as input light from an object. 

The CCD takes this optical input and converts it into an 

electronic signal - the output. The electronic signal is then 

processed by some other equipment and/or software to produce 

an image. The camera must convert the digital image to an analog 

TV signal. 

Initially, video transmitted via the Internet, was required to be 

converted from analog to digital, and then compressed for 

efficient transmission. VIP was created as a protocol for the 

efficient transmission of video via the internet (more about video 

over the internet and streaming video in Chapter 9). Some 

enterprising engineer recognized that cameras with CCDs were 

already capable of providing a digital image signal that was 

compatible with the digital display output of a typical desktop 

computer. CCTV cameras are manufactured today with a direct IP 
Telecommunications Handbook for Transportation Professionals 

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149

output. They can be directly connected to a communication circuit 

capable of carrying IP traffic. The image data from the camera 

can be directly routed to a desktop computer. 

Two types of basic VIP circuits can be used for video surveillance 

and incident detection in an FMS or traffic signal control system: 

• Direct VIP CCTV camera to Desktop Work Station 

• Analog CCTV camera to Desktop Work Station. 

The first is very simple (as shown in figure 5-17), and the second 

does not have a high degree of difficulty. The direct system uses 

a camera that is designed to provide a direct output to an 

Ethernet. The digital video signal is compressed using an MPEG 

software encoder, and then wrapped in an IP packet for 

transmission. The second system (as shown in figure 5-18) 

requires a video CODEC that is designed to take the analog 

output of an existing CCTV camera, convert it to digital, encode 

the signal, and wrap it in an IP packet for transmission. There is 

no need to convert the video signal back to analog. Just use any 

media viewer application with a compatible MPEG software 

decoder. 

CCTV Camera

Digital Video 

Image

MPEG

Software

Encoder

IP

Packet

WrapVIP to Network

Ethernet Switch

W ork Station

Video Over IP

Digital Image Transmission Process

Figure 5-17: VIP Basic Camera System
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Converting an existing system to VIP is relatively simple. Replace 

existing Video CODECs (or FDM modems) with a VIP CODEC. In 

most cases (note: replacement of an FDM system requires 

additional consideration of communication equipment), the 

existing communications cable infrastructure can be kept in 

place. Chapter Seven provides a description of the process used 

by Utah DOT to update its ATMS system to VIP. In the process, 

they were able to eliminate an expensive analog video switcher, 

and conveniently distribute video to multiple traffic, 

transportation and public safety agencies. 

Analog

to

Digital

MPEG

Software

Encoder

IP

Packet

Wrap

VIP to Network

Ethernet Switch

Work Station

Video Over IP

Analog Image to Digital Image

Transmission Process

Figure 5-18: Diagram - Add-on Conversion to VIP
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Basic Traffic and Freeway Management Networks 

BASIC DEVICE NETWORKS

The following systems all require the same type of communication 

circuit – low speed (9600 Bps or less). Some devices are 

connected via dial-up and others via private leased-line. RWIS 

systems normally communicate via a wide area radio link – a 

typical communication circuit diagram is provided below. 

• Dynamic Message Signs 

• Loop detectors 

• Radar detectors 

• Video detectors 

• Remote Weather 

Information Systems 

(RWIS) 

• Ramp Metering 

• Pavement Condition Sensors 

These devices all send or receive short (a few bytes) messages 

Network RS232

Cable Comm

Modem Link

Comm

Link

RS232

Cable

Modem

Controller

Radar

Detector

Central

Control

Traffic Device

Typical Communication Circuit

Comm Link is any analog data circuit 

9.6 Kbit/s or less. The link can be 

twisted pair, fiber optic, or wireless.

Figure 5-19: Diagram - Basic Traffic Device Communication Circuit

Note: Figure 5-19, is a basic network 

diagram for the listed devices. However, 

each device is unique and requires a 

specific set-up. 
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(e.g.: status, condition measurements, temperature, volume and 

speed, etc.). Most communication links are similar to those used 

by traffic signal controllers. One significant note is that RWIS 

sensors, very often, are located in remote areas without easy 

access to power and communication utilities. The preferred 

communication link is wide area radio. Wide area radio uses 

frequencies in the same range as Police, Fire, or Highway 

Maintenance vehicles. The systems use a fixed low power radio 

with a very directional antenna. The FCC has specific rules for 

using these types of radio systems on a secondary and noninterfering basis. The radio frequency availability and the rules 

for use are listed under “Title 47 CFR 90.20”. 

A communication engineer must be aware of all of the devices 

that will be deployed in the system. Each type of device has a set 

of communication requirements. The key differences are the 

frequency of communication, and the amount of data to be 

transferred. These factors are multiplied by the total number of 

devices to help determine the amount of required bandwidth. 

This section dealt with basic communication circuits for traffic 

signal control, video incident detection, and generic traffic 

devices. The next section will provide a look at how all of the 

circuits are integrated into a single communication network. The 

principles of multiplexing described in Chapter 2 will be 

applicable. 

Complex Communication Networks 

Let’s take a look at communication networks that support a 

complex traffic management system (an ATMS) combining traffic 

signals, CCTV cameras, dynamic message signs and radar 

detectors used for traffic volume and speed monitoring. A series 

of basic system design criteria and block diagrams will be 

created. Each will eventually become part of the requirements 

and specification documentation that is presented to potential 

engineering services, systems integrators and construction 

services vendors. Following is a typical scenario: 

The basic system is planned for a major arterial that connects a 

suburban community to a major urban center. The overall route is 

10 miles with a traffic signal system at both ends of the arterial, 
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some low points that flood during frequent heavy rain storms and 

a total of six travel lanes throughout the arterial system. 

The local DOT wants to optimize the traffic signal operation in 

both the suburban and urban areas adjacent to the arterial. They 

will utilize information collected from the arterial traffic flow 

radar speed and volume detectors at various points along the 

arterial. Additionally, the DOT will monitor for traffic incidents 

using radar detectors and CCTV cameras, and be notified of 

flooding conditions during rain storms via RWIS sensors. 

The DOT has specified that it does not want to construct a 

private communication network. There is easy access to 

communication facilities adjacent to the arterial that can be 

leased from “LocalTel”. 

The engineer developing the communication network will create 

several diagrams to assist in overall system design. One of those 

diagrams should be a private system alternative to provide cost 

comparisons. 

First, the engineer will create an overview block diagram to help 

visualize the relationship of the primary connection points. The 

communications engineer will also draft a narrative of the overall 

system - actually a statement of understanding, or concept of 

operations (from a communication perspective): 

“The proposed network will provide communication links to 

connect four (4) primary elements: existing suburban traffic 

Proposed Arterial Traffic Control System (ATCS )

Suburban Traffic 

Control System

(STSS)

Urban Traffic 

Control System 

(UTSS)

Traffic Control Center

STSS 

Computer

UTSS 

Computer

Proposed 

ATCS 

Computer

Existing

4W Leased

Communication Links

Existing

4W Leased

Communication Links

Proposed

Communication Links

Figure 5-20: Diagram of Proposed System
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signal system; existing urban traffic signal system; proposed 

arterial traffic control system; proposed central traffic control 

center. In addition to existing 170 type traffic signal 

controllers, the D.O.T. is proposing to add CCTV, changeable 

message signs, speed and volume detection equipment, deer 

crossing sensors, RWIS sensors, connectivity to the internet, and 

communication links to a regional traffic advisory network. The 

proposed system will replace existing copper communication links 

with fiber and make use of spread spectrum radio to link remote 

devices. New traffic signal control computers will be placed in 

the proposed TCC. The existing traffic signal control computers 

will remain in place as backup servers.”

This paragraph is reviewed by the project team for concurrence 

or changes. A block diagram representing the statement is 

created as a visual aid. 

Next in the process is the creation of an overview of the major 

systems. The overviews include simple block diagrams and a brief 

written description of the system. 

Suburban Traffic Signal System (figure 5-21): “The town of 

Nowheresville has an existing traffic signal system with a total 

of twenty-one 170 Type signal controllers. ” The system is 

deployed using two 4-wire 9.6 Kb/s multi-drop circuits leased 

from the Nowheresville Community Telephone Company. Modems 

Modem

Central

Control

Circuit 2

Modem Modem Modem Modem Modem Modem Modem Modem Modem

Modem

ModemModemModemModemModemModemModemModemModemModemModemModem

STSS Comm Diagram

Notes:

Y 2 Comm Links @9.6

Y 4W Private Lined Leased from Local Telephone Company

Y No circuit problems

Y Circuit #1 = 12 Drops

Y Circuit #2 = 9 Drops

Circuit 1

Figure 5-21: Diagram STSS Communication System
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used in the systems operate in a half-duplex mode. The traffic 

signal controllers are deployed in a 10 square block area of the 

community with the controlling computer located at 5th & Arch 

Streets.

Urban Traffic Signal System (figure 5-22): “The city of 

Wearegreat has an existing traffic signal system with a total of 

one hundred twenty (120) 170 Type signal controllers. The system 

is deployed using fifteen (15) 4-wire 9.6 multi-drop circuits 

leased from the Verybig Telephone Company. Modems used in the 

systems operate in a half-duplex mode. The traffic signal 

controllers are deployed in throughout the city with the 

controlling computer located at Broad & Main Streets.” 

Central

Control

C1

Modem

UTSS Comm Diagram

Notes:

Þ 14 Comm Links @9.6

Þ 4W Private Lined Leased from Local Telephone Company

Þ No circuit problems

Þ Circuit #1 : # 15 = 8 Drops

Modem

Modem

Modem

Modem

Modem

Modem

#41

Modem

#48 Modem

Modem

#49

Modem

#56 Modem

Modem

#57

Modem

#64 Modem

Modem

Modem

#1

Modem

#8

Modem

#9

Modem

#16

Modem

#17

Modem

#24

Modem

#25

Modem

#32

Modem

#33

Modem

#40

Modem

Modem

#81

Modem

#88 Modem

Modem

#89

Modem

#96 Modem

Modem

#97

Modem

#104 Modem

Modem

#105

Modem

#112

C15

Modem

Modem

#113

Modem

#120

Modem

#65

Modem

#72

Modem

#73

Modem

#80

Figure 5-22: Diagram UTSS Communication System
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The next set of schematics is for proposed systems. There is less 

detail because the systems that are represented do not exist. 

The engineer may put in some information about the 

communication circuits, but realizes that they will change as the 

development process continues. The following schematic (figure 

5-23) shows the proposed connecting arterial management system. 

The objective in the “first pass” at the system design should be 

generic making very few assumptions about the technologies that 

will be deployed. A database is developed using mile marker 

indicators as a reference for where equipment will be located. 

The requirements document should indicate the type of devices 

that will be deployed with approximate distances. The project 

team (including the communications engineer) should complete a 

field survey to pinpoint device locations. This will be critical for 

the communications system. The communication system designer 

will have to assure that there is enough signal strength. In 

addition to the device location, the table should also list 

approximate data bandwidth requirements. 

MM 82.7

Traffic 

Management 

Center

STSS UTSS

MM 84.0MM 85.9MM 88.9MM 91.5

MM 91.5MM 90.7MM 88.9MM 87.9MM 86.2MM 85.6MM 84.9MM 83.7MM 82.9

Figure 5-23: Straight Line Diagram
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Field Devices 

Device Field Unit Location Max Data Transaction/Sec

MM 82.9 1.536 Mbit/s 

MM 83.7 1.536 Mbit/s 

MM 84.9 1.536 Mbit/s 

MM 85.6 1.536 Mbit/s 

MM 86.2 1.536 Mbit/s 

MM 87.9 1.536 Mbit/s 

MM 88.9 1.536 Mbit/s 

MM 90.7 1.536 Mbit/s 

CCTV – PTZ Control 

MM 91.5 1.536 Mbit/s 

MM 85.6 2400 Bit/s 

RWIS 

MM 86.2 2400 Bit/s 

MM 82.9 1200 Bit/s 

MM 85.6 1200 Bit/s 

MM 86.2 1200 Bit/s 

MM 87.9 1200 Bit/s 

Radar Detector 

MM 88.9 1200 Bit/s 

MM 82.7 2400 Bit/s 

MM 85.9 2400 Bit/s 

MM 88.5 2400 Bit/s 

Dynamic Message Sign 

MM 91.5 2400 Bit/s 

Traffic Management Center MM 84.0 TBD 
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 Table 5-5: Field Device Location 

A straight line communication diagram (figure 5-23) is created 

from this information. The table and the straight line diagram 

help to provide the communication engineer with a better 

understanding of where devices will be placed. 

The communication system engineer creates a block diagram for 

each site to show how each device will be connected to the TMC. 

The diagram contains all necessary information and details the 

communication links and the type of connections for each device. 

A written description of the site details is also provided. Here’s 

an example based on MM 85.6: 

“The site at MM 85.6 will contain one CCTV Camera with PTZ side 

mounted at the 20 foot level of a 30 foot pole, an RWIS system 

will be placed on the top of the pole, and a radar detector will be 

side mounted at the 15 foot level. All of the communications 

equipment will be placed in a cabinet at the base of the pole. The 

communications cabinet will contain a Video CODEC which will 

have an RS 232 port for the PTZ. The cabinet will house a 

CSU/DSU multiplexer with four data ports. The primary 

communication link to the TMC will be a leased DS-1. A utility 

demarcation point will be placed within 50 feet of the site. The 

DOT will run necessary communication cable and power cable from 

the site to the utility demarcation.” 
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The written description of the site helps to clarify what is 

needed, and prevents a misinterpretation of the schematic 

diagram. 

Notice that the site at 85.6 has multiple devices and takes 

advantage of hardware that can provide multiple communication 

ports via the single DS-1. Also, a 170/2070 controller is not 

included. Some traffic control software may require the use of a 

controller. This system is however, incident based. That is, the 

radar detector provides data that indicates the speed of traffic 

at a specific point. The central computer reads the data and 

alerts operators to take action. For locations with a single 

device, a specific type of circuit can be leased. Another 

alternative can be used. Multidrop circuits for each type of 

device can be run to each site, and DS-1 circuits can be run to 

the CCTV sites. This will add equipment and complicate some of 

the communication systems. However, if one type of 

communication circuit has a problem, the others keep functioning. 

PTZ

Cable

RS232

Cable

Coaxial

Cable

RS232

Cable

Radar

Detector

UPS

Power 

Strip

Video 

CODEC

DSU/CSU 

Mux

Note: RS422 Cable 

connects CODEC to Mux

115 VAC Utility Telco Utility

(DS-1)

MM 85.6 Schematic

Figure 5-24: Diagram - Site Equipment
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Following is a block diagram (figure 5-25) for an entire system 

using device based communication circuits: 

SUMMARY

Traditionally, transportation and construction engineering 

documentation is a series of technical drawings with material and 

construction specifications incorporated as part of the PS&E 

information. A plan set for a lighting pole (for example) will 

contain all of the information required for the contractor to 

provide and install. The dimensions, weight, wind-loading and 

mounting information can be specifically quantified and shown in 

the plan set. Minor deviations from standards can also be shown. 

Actual written instructions and other requirements are kept to a 

minimum. There’s no instruction manual provided by the 

manufacturer that explains how to install and maintain the 

lighting pole. 

Notes:

Ö All Comm links leased from Localtel

Ö Video use DS-1 Links

Ö RD use 9.6 4W circuits with max. 5 drops ea.

Ö RWIS use 9.6 4W circuits

Ö DMS use 9.6 4W circuits with max 5 drops ea

ATCS Comm Block Diagram

Arterial Traffic Control System 

(ATCS)

M

CCTV Control

DMS Control

Radar Detector Control

CODEC

Video Switcher

PTZ Control

CSU/

DSU RS-449 Link

RS-232 Link

Video Link CSU/

CODEC RS-449 Link DSU

DS-1

Coax

M M M M M M

9.6 4W Multidrop

M RWIS Control

RD RD RD RD RD RD

M M

RW RW

9.6 4W Multidrop

M

M M M M M M

9.6 4W Multidrop

DM DM DM DM DM DM

Figure 5-25: System Block Diagram
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Telecommunications systems have the same type of requirements 

for documentation. However, remembering that 

telecommunications equipment is primarily designed for Carriers, 

there is additional documentation that is supplied, and necessary 

for installation and optimization. Hardware manufacturers 

provide a complete installation and maintenance manual with every 

device (or every 10 devices if ordered in large quantities). Make 

certain that the documentation manuals are kept, and that there 

is a set (in a weatherproof pouch) at every equipment cabinet, 

plus a master set at the TMC. 

A typical modem can be set to run at a fixed data rate, or allowed 

to adjust the data rate based on communication link conditions. 

If you don’t specify this in writing, there’s a fifty percent 

chance that the installer will be wrong. This will delay the overall 

project and cost money to correct. 

SONET multiplexers, Ethernet routers, spread spectrum radios, 

modems, etc. are manufactured to fulfill a number of different 

requirements. Make certain that your communication engineer 

provides enough information for installation personnel to properly 

setup and optimize the equipment in your freeway management 

and traffic signal control systems. 
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Network Topology 

A network can be defined as a link between any two points (or 

more) that mutually relies on the presence of the other. 

Communication points are normally referred to as nodes or hubs. 

Simple networks are developed to establish a temporary 

communication path, such as a basic telephone call. Complex 

networks are designed to provide a permanent communication link 

and have alternate links to protect the viability of the network. 

Freeway management systems typically use a complex 

communications network. 

Many types of networks can be defined for telecommunications, 

each with a different purpose. Understanding the different types 

of networks is important. Each type of network has advantages 

and drawbacks. There is no “ideal” network solution that fits all 

situations. Consideration should be given to the ultimate 

requirements of the system that a communication network will 

support. 

A “mesh” network may provide the ultimate solution for assuring 

that communication links will always be available. However, it is 

the most expensive network topology that can be established. Not 

assuring that communication links will be available when needed 

can also be expensive. Networks that support financial 

transactions require a high degree of reliability. The operators 

of financial networks will tend to require a highly redundant 

communication system. The telephone companies and long distance 

carriers have developed highly redundant networks to make 

certain that communication links are always available. 

Four basic network topologies with many variations can be 

described to meet requirements. 

• Point-to-Point 

• Star 

• Ring 

• Mesh 
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POINT-TO-POINT NETWORKS

Point-to-point is the simplest. Start at node 1 and connect to 

node 2, then 3, and continue. Communication is serial and passes 

through each node. Lose any one node or link, and communication 

can be disrupted. 

STAR NETWORKS

A Star network is simply a multipoint communication system that 

allows one node to communicate with many nodes (or many to one). 

This is also referred to as a “one-to-many” system. 10Base-T 

Ethernet is an example of star network. The LAN in your office 

has a router hub that connects all desktop computers to file 

servers and printers. 

The star network allows any point to communicate with any other 

point in the network. However, if the central hub is taken out of 

service, then the entire network is out of service. 

Hub 1 Hub 2 Hub 3

Figure 5-26: Diagram - Point-to-Point Network
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RING NETWORKS

Ring networks are designed to overcome the weakness of the 

point-to-point system. Placing the nodes so that they can always 

communicate with an adjacent node helps to assure an available 

communication path. Fiber Optic systems are generally deployed 

using a ring network topology. SONET multiplexer hardware is 

designed to facilitate various types of ring networks. Two basic 

ring architectures are available with many variations and 

combinations that can be developed. 

Uni-directional – the communication signal always travels in one 

direction around the ring. If any single node or path link is 

disrupted, communication between the other nodes continues in a 

serial path around the ring. A single strand of fiber can be used 

to for this type of network. 

Hub 1 Hub 3

Hub 4

Hub 3

Hub 5

Hub 2

Figure 5-27: Diagram - Star Network
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Bi-directional – the communication signal can travel in either 

direction. This allows the system to manage signal flow and 

determine the most efficient path. Two strands of fiber are 

used. One strand is the transmit, and the other is used for 

receive. Add more pairs of fiber strands, and the system will 

support dedicated hub-to-hub data flows. 

MESH NETWORKS

Hub 5

Hub 3

Hub 2

Hub 1

Hub 4 2 Fiber Strands

2 Fiber Strands 2 Fiber Strands

2 Fiber Strands 2 Fiber Strands

Ring Architecture

Bi-directional Data Flow

Figure 5-28: Diagram - Ring Network
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Mesh networks are a combination of the star and ring topologies. 

They can provide multiple communication paths for all nodes in 

the system. A ring network basically provides for one or two 

communication paths for each node. A mesh network can be 

designed to provide three, four, five, or more communication links 

for each node. How many is dependent upon the amount of money 

available and the willingness to manage and maintain a very 

complex communication system. 

Note that these network topologies are independent of the media 

being used for transmission. Most of the more complex network 

topologies are used with fiber. However, microwave systems are 

also arrayed in star, and ring topologies, and basic Ethernet local 

area networks use a star configuration. New generations of 

wireless networks are being developed using a mesh topology in 

order to assure connectivity. That is, wireless customers will be 

able to access a network via more than one wireless base site. 

Hub 6

Hub 5

Hub 3

Hub 4

Hub 1 Hub 2

Figure 5-29: Diagram - Mesh Network
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NETWORK REDUNDANCY

How much redundancy is needed in a communications network? 

There is no simple answer or magic formula. One answer may be to 

ask how long your system can be down before operations are 

affected. Another answer might hinge on whether parts of your 

system can be out of service and not effect operations. 

The mesh network shown above has multiple communication paths 

to each hub. If full redundancy is required one set of 

communications hardware for each communication link at each hub 

is required, and don’t forget to add redundant power supplies. 

This arrangement can be very expensive especially when you 

consider that mesh networks weren’t developed to provide 

communication path redundancy. Mesh networks were developed to 

support the needs of the internet. Communication paths have 

bandwidth limitations and communications hardware has functional 

limitations. To assure that most users of the internet will have a 

high availability of service, mesh networks are used. Mesh 

networks help to share communication path loading. This assures 

that no single communication path will become a bottle-neck. 

Using Mesh Networks for communication path redundancy also 

requires a very complicated “alternate routes table”. You have to 

provide each Hub with the routes to use if the primary is out of 

service. This can create problems with data intensive 

applications. 

Ring Networks were created to provide communication path 

redundancy. They are simple (compared to Mesh) to set up. There 

are no complicated routing tables. The hardware operating system 

is told to switch to the alternate path if communication is lost on 

the primary. The amount of hardware required to implement a 

Ring Network is less than a Mesh Network. 

Conclusion 

Development and design of a telecommunications system is an 

iterative processes. Each element is built upon a very specific set 

of standards and requirements. The use of any type of 

communications circuit to support a traffic or freeway 

management system should be based on a clear understanding of 

the requirements for such a system. The creation of a thorough 

set of system requirements is key to the design and construction 

of an efficient communications system. 
Chapter 6 

6. CHAPTER SIX – MAINTENANCE &

WARRANTIES

Introduction 

A basic truth of nature is that all things change. Until this point, 

the Telecommunication Handbook for Transportation 

Professionals, has looked at the planning and development of the 

communication system. Chapter 6 will discuss maintenance of 

telecommunication systems and look at issues that should be 

addressed by the operator of a system. The chapter provides 

information on the reasons for maintenance, technician 

qualifications, explanation 

of warranties, and typical 

cost of maintenance 

agreements. 

Communication systems are 

made of physical things 

that wear out (or change) 

over time. It is difficult 

to see the change, because 

there are very few moving parts. However, the components 

(transistors, capacitors, microprocessors, etc.) that make up 

devices that are part of a communication system do change, and 

lose their performance tolerances. When enough components 

operate at less than specification, the overall system (or device) 

will not perform as required. Operationally speaking, there is not 

a huge difference between a freeway system and a communication 

network. Both wear out from use and require maintenance and 

revitalization. 

Communication networks should be treated as any other element 

of a modern transportation system. DOTs need to provide an 

adequate budget for maintenance, and training for personnel to 

become familiar with the elements of the communication 

equipment. The DOT technicians don’t have to be capable of 

repairing the communications equipment. They simply have to be 

able to determine when the communication hardware is not 

functioning, and in many cases replace the device with a spare. 

Most manufacturers provide a detailed manual of installation, 

testing and maintenance recommendations. Many provide on-site 

Note: This chapter provides a focus on 

telecommunications equipment. The reader is 

referred to FHWA Handbook: “Guidelines for 

Transportation Management Systems Maintenance 

Concepts and Plans” for more information about the 

development of equipment maintenance programs. 

See:http://www.ops.fhwa.dot.gov/Docs/TMSMaintC

ptandPlans/index.htm
Telecommunications Handbook for Transportation Professionals 

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and factory depot service plans. The use of these plans may be a 

critical part of your overall maintenance program. 

This chapter will: 

• Review the need to create a budget for operations, 

maintenance and system upgrades. 

• Review the differences between product warranties, 

guarantees of performance, and service and maintenance 

plans. 

• Consider the relationship between D.O.T. product 

specifications and manufacturer warranties. 

• Provide recommendations to assist in setting a budget and 

creating a staff function to support maintenance. 

Systems maintenance and upgrade is crucial to efficient 

operations. All communication equipment does eventually wear out, 

or reach the end of useful operational life. The communication 

system is the glue that unites the elements of a traffic signal, 

FMS, or ITS system, keep it operating with an efficient 

maintenance and upgrade program. 

Why create a Maintenance Budget? 

Fifty years ago, communication equipment needed constant 

attention. The “state-of-the-art” used components that were 

highly sensitive to environmental variables (heat, cold, moisture, 

dust, etc.). Communication systems required significant 

adjustments by operations and maintenance personnel. All 

equipment was manufactured with external controls that were 

used to adjust the device back to specified parameters. Current 

equipment is less affected by its environment, and most 

manufacturers have eliminated the external adjustment controls. 

The use of fixed value components minimizes the need for 

adjustments. Communication devices either perform as specified, 

or must be replaced. Manufacturers have created “board level” 

systems with all necessary components placed on a single card. 

Some manufacturers will make significant claims about the 

reliability of their products. Many will claim MTBFs (mean-timebetween-failures) that make it seem as though failures occur 

once in a million years. But, nothing lasts forever. 
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Communication hardware normally fails either during, or just 

after, installation. These failures are the direct result of 

manufacturing “birth defects” - that is, the manufacturing 

testing process fails to identify a manufacturing error, or 

substandard component. 

However, the leading cause 

of near term failures is the 

result of improper 

installation or operation. 

Hardware manufacturers 

have standard component 

testing procedures to help 

assure that virtually all 

equipment leaving the 

production facility meets 

specifications (more on this 

subject later in the 

chapter). 

Installation failures are caused when technicians fail to 

familiarize themselves with the manufacturer’s recommendations. 

Many technicians will try to use shortcuts to reduce the 

installation time, or because they have installed similar equipment 

Most communication system component hardware is 

constructed on a single printed circuit board that 

can easily be replaced by a qualified technician. The 

components are so small that they can’t be repaired, 

or replaced. Simply replacing the board with the 

failing component saves time and money. 

Don’t confuse the “feature option” switches, or 

option setting software for maintenance controls. 

The feature setting switches and software are only 

provided to allow users to optimize a device for a 

specific operational requirement. 

Figure 6-1: Photograph of a Fiber Optic Modem - Courtesy GDI Communications, LLC
Telecommunications Handbook for Transportation Professionals 

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171

and believe that there are no differences between devices 

manufactured by different companies. Another common error is 

to assume that there won’t be differences between old and new 

versions of the same device. 

On a long term basis, most failures are the result of electronic 

component aging (through constant heating and cooling 

components will fail to meet original specifications). Systems will 

either fail, or develop substandard functional characteristics. 

Don’t forget that equipment also fails because of lightning 

strikes, electrical power surges, and connection of electrical 

power to a communications port. 

Most communications equipment is built with internal monitoring 

capabilities. Diagnostics are displayed in one of two general ways: 

external display on the equipment, or via diagnostics terminal (or 

as a program on a PC). Most modems have L.E.D. indicator lamps to 

show that the device is functioning in a proper manner. A 

multiplexer or router will provide diagnostics via directly 

connected terminal, or through a device setup and management 

program on a PC. 

Keeping track of all communication devices is part of any 

maintenance program. A simple equipment list table is best. The 

following is an example: 

Table 6-1: Example Communication Device Inventory List 

Communication Device Inventory 

Item I.D. Serial # Date 

Installed 

Warranty 

Term 

Device 

Location 

 

An individual should be assigned to keep track of all equipment, 

and maintain relationships with manufacturers, installation 

companies, and system integrators. This person should have 

experience (or training) for completing simple repair and 

installation of communications equipment. If there is not enough 

equipment to require a full-time staff maintenance specialist, the 

agency should consider part-time personnel, or an outsource 

contractor. A field verification inventory should be conducted at 
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least once per year. Whenever a new system is installed, an 

information table should be completed and added to the database. 

If communication systems are very reliable and don’t require 

constant attention, why budget for maintenance? 

• Communication systems are generally composed of items 

from many different manufacturers. 

• Most hardware and firmware (the hardware internal 

operation instructions) is revised on a regular basis to 

account for field use problems and changes in performance 

standards. 

• On rare occasion, the equipment does break down 

• External forces cause equipment failure 

1. Power fluctuations 

2. Cable cuts 

3. HVAC failure 

• Need for qualified personnel (or services) to provide for 

repair and restoration 

• Need to provide funding for emergency repair and 

restoration. When a problem does occur, there’s no rush to 

pull money away from some other budget. 

Creating the Maintenance Budget 

Creating a budget to provide for maintenance requires that 

several factors be considered: 

• Level of experience and training of communications 

equipment maintenance personnel? 

• Complexity of the communication equipment in the system. 

• Number of individual communication equipment devices. 

• The type of network being used – leased or owned. 

• Potential for emergency repairs. 

One of the first items to consider when creating a maintenance 

budget is “who” will do the maintenance work, and what type of 

services will they be required to provide? This is in some way a 

“chicken or the egg” question. If full maintenance services are 

provided (testing, using diagnostic equipment, and full repairs), 
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you will need highly qualified and trained technicians. If 

maintenance is viewed as a matter of blowing the dust out of the 

cabinet, and making a call to an out-sourced repair and 

maintenance service, a semi-skilled individual with minimal 

experience and training will suffice. 

Most DOTs have been using some type of communications system 

to support traffic management and department operations for 

many years. A few have created an internal staff function to 

support maintenance and upgrade functions, others outsource the 

required services. Following is a suggested maintenance 

technician experience level table: 

Table 6-2: Technician Experience Classification 

Technician Experience & Qualification Levels 

Level Yrs 

Experience 

Type of Experience Amount of Training 

Entry 0 – 2 years PC Skills, Technical 

Ability 

Vocational education 

from an accredited 

High School, or 

Technical School. 

Mid 2 – 6 years Military Experience with 

communication systems, 

or, Above + Working 

Knowledge of the 

Communication equipment 

in the system + Ability to 

replace module boards. 

Military Training, or 

above + 

Communication 

Theory Courses + 

Manufacturer 

Equipment Courses 

High 6-10 years Above + Additional 

Knowledge of 

communication systems + 

provide presentations at 

professional meetings + 

ability to trouble-shoot, 

and resolve system 

problems. 

Above + advanced 

communication theory 

courses 
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Senior 10+ years Above + participation in 

communication standards 

efforts + review of 

technical papers 

Above + additional 

technical training as 

required + extensive 

reading of technical 

books on 

communication 

process and theory. 

These levels of experience should be applied to both department 

personnel and/or outsourced personnel responsible for the 

maintenance of telecommunication equipment. These levels are 

directly related to experience with telecommunication and other 

technology based systems, not general work experience. An 

individual with 10 years of experience as a project manager would 

not be considered as having the qualifications to be a 

maintenance technician for telecommunication equipment. There 

are a number of good High School Vocational education programs, 

and Technical School programs that provide individuals with the 

proper knowledge and skills for an entry level maintenance 

technician position. The U.S. military provides well grounded 

maintenance technician training and experience for at least a 

mid-level position. 

The type of equipment will often help determine the experience 

level of personnel required to support a maintenance function. If 

everything is leased from a communication carrier, entry level 

personnel can be used. Their primary job description will be to 

manage the services supplied by the communication carrier, and 

call for support when necessary. 

A system comprised of a large number of communication devices 

with a mix of new (less than 2 years old) and legacy (more than 5 

years old) equipment will require support from more experienced 

personnel. With this type of system, the maintenance personnel 

will need to know when to call in outside support to effect 

repairs. 

If the system consists of a few CCTV cameras, several 

changeable message signs and traffic flow detectors, with 

required communication equipment, it’s probably best to arrange 

for outsourced services. Consider that special tools and test 

equipment may be needed to help troubleshoot communication 
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problems, with highly compensated experienced maintenance 

technicians. 

A communication equipment maintenance contract will typically 

cost between 10 and 20 percent (per year) of the original 

equipment cost. If the total system cost was $300,000, 

maintenance will average 

no more than $15,000 per 

year – significantly less 

than the cost of hiring a 

qualified individual. 

A system with several 

thousand devices spread 

over a large area that 

cost $20,000,000 to 

deploy will require a 

significant investment in 

maintenance and upgrade 

services. Outsourcing the needed services will most likely cost 

$4,000,000 per year (using the 10% to 20% rule). The cost of 

hiring five qualified personnel and supporting them with 

necessary tools, transportation, spare parts and training might be 

about $2,000,000 per year. Make certain that at least one of the 

technicians has a significant background for maintaining 

telecommunication systems. 

A simple single function system (traffic signal control) will 

require personnel with fewer skill sets. Training will be limited to 

knowledge of upgrades to cover new equipment. Systems will have 

minimum complexity. Complex systems supporting multiple types 

of communications equipment and systems will require a larger 

staff with more skill sets and continuous training for changes in 

systems and upgrades. 

One important aspect of 

the budget development 

process is completion of a 

risk assessment. This 

should have been done for 

the overall system design 

during consideration of redundancy, and will have a direct impact 

on the maintenance budget. The communication system is, in most 

respects, the least failure prone element of an overall system, 

The components of a $4 million maintenance budget 

would include: 

• Personnel 

• Maintenance Shop Facilities 

• Test Equipment 

• Spare parts inventory & consumable repair 

supplies. 

• Tools 

• Technician Training 

• Service Vehicles 

• Etc. 

Basic traffic signal systems use modems and wireline 

transmission media. Technicians will only have to be 

able to do general troubleshooting and item 

replacement. Traffic signal repair personnel can be 

trained to this level of repair. 
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but potentially has a high risk of being disrupted by outside 

forces. 

The risk assessment is not done to create the maintenance 

budget. Elements of the assessment will provide an indication of 

how much money will be required to accomplish repairs in the 

event of a problem. In this case, risk does not refer to 

intentional disruption – although, that certainly is a factor - but 

the potential for power failures, “Backhoe Fade” (cable cuts from 

construction), lightning strikes, HVAC failures, etc. The risk 

assessment should consider the following: 

• Assess which portions of the communications network are 

crucial to overall operations. 

• Which communication resources are needed to keep the 

operation functioning at a reasonable level? 

• What elements can you live without? 

• How long can you function without critical elements? 

• How much system degradation is acceptable? 

• Make an assessment that recognizes which elements must be 

kept in service and which can be removed from service 

during the repair and restoration cycle. 

Knowing which elements of your communication system can be out 

of service and awaiting repairs will help provide effective 

management of resources. The cost to effect repairs during a 

holiday period will always be more than repairs completed during 

normal business hours. Even during holiday periods there are 

portions of the system that can be out of service without 

effecting operations. 

Communication devices will require some type of upgrade during 

their life cycle. Most communication equipment will operate for 

10, or more, years without a problem. Equipment manufacturers 

will offer firmware updates, and occasionally revise the physical 

design of the equipment. Very often, these updates are not 

critical to existing operations and systems. However, you should 

budget for occasional updates, especially if the manufacturer 

offers a major firmware update. 

The firmware updates are normally free (some vendors do 

charge), but the end-user is required to cover the cost of 

installation. Installation of most firmware is usually only a 
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matter of uploading the update via the system manager program 

and can be accomplished by the operation staff. Occasionally the 

operation is more complex and will require the services of a 

qualified technician for a few days. Legacy systems may require 

significant replacements of components to accomplish the update. 

Consider the overall cost of updating older equipment and 

compare with replacement by new equipment. 

Upgrades to existing equipment, due to addition of new sections, 

can be accomplished via a budget provided by the contractor 

adding the new section - however, there may be unforeseen 

consequences as a result of the additions which were not 

considered as part of the new section budget. Consider 

availability of older equipment. The contractor may not be able to 

purchase exact duplicates of equipment used in older sections of 

highway. Make certain that the contractor gets new price 

estimates for the desired equipment. Older equipment becomes 

difficult to find and may cost more than the original. 

Warranties, Extended Warranties & Service Plans 

This section takes a look at various aspects of product 

warranties and their relationship to maintenance programs. There 

is a tendency to assume that a warranty will take the place of a 

maintenance program. Often, as consumers, we have become 

accustomed to relying on product warranties to help protect us 

against failure of a product. These warranties are very specific 

about the coverage, the rights of the company, and the rights of 

the consumer. “Note: The author suggests that you read a 

complete product warranty for any consumer electronics item you 

may have recently purchased. All of the examples considered for 

publication here had an express prohibition of reproducing 

without written permission”. All warranties reviewed had one 

thing in common - the very last sentence: “Specifications and 

availability subject to change without notice” . 

This last sentence is important, because manufacturers do change 

specifications on a regular basis. A key reason for changes is 

product updates. Products are updated based on feature demands 

from customers, or product problems discovered during warranty 

repairs. Standards also cause changes in product specifications. 

Often, manufacturers will release a product using a preliminary 

standard, and make changes when a standard is finalized. 
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Consumer based telecommunication products have a life cycle of 

18 to 24 months with new variants being released every 4 months. 

Wireless handsets are a good example. Commercial products have 

a longer life cycle, usually based on market demand. If the 

demand is strong, a manufacturer will keep producing a product 

for 5 to 10 years. However, that doesn’t keep the product from 

changing. Manufacturers do make changes for the reasons stated 

above. 

Some telecommunication products are manufactured to serve both 

consumer and commercial demand. Wireless routers based on the 

802.11 series of standards are an example. Their life cycle and 

new product introduction cycle follow the consumer market. If 

you are using these types of products in your system (most likely 

within a TMC) be prepared to have several different versions, and 

possibly units from different manufacturers. 

WARRANTIES

Following are a few key facts about warranties: 

• Most hardware manufacturers provide a warranty for their 

products. 

• There are no state or federal laws requiring that a warranty 

be provided. Several states have special regulations that 

may govern provisions of warranties, but those are primarily 

directed at protection for individual consumers, not 

commercial (or government) enterprise. 

• Warranties are offered as part of a marketing program. 

• Equipment manufacturers create a budget line item to 

provide for fulfillment of warranty programs. 

• Warranties normally provide for the repair, or replacement, 

of a product due to manufacturing defects. 

• Warranties are actually one of the cost components of a 

product. 

• Warranties are not maintenance programs! 

Warranties for commercial products are essentially the same as 

consumer products with one general exception. Consumer product 

warranties tend to be very short term – 30 days to one year. 

Commercial product warranties tend to be offered for longer 

periods – 90 days to 5 years. 
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Some manufacturers will provide full replacement, while others 

will only provide parts and require payment for labor charges. 

Most commercial product warranty periods start on date of 

manufacture, others on date of shipment, and others on the date 

of installation. There are no government or industry standards 

for warranties. The terms of the warranty are set by the 

manufacturer. Commercial law and court decisions help to mold 

the wording of warranty terms. 

EXTENDED WARRANTIES

Many manufacturers offer factory service and repair programs. 

For a small one-time fee (paid in advance) products can be 

returned to the factory (or authorized repair center) for “outof-warranty” service. Instead of providing the standard warranty, 

the manufacturer offers an extension (typically one to three 

years) beyond the basic time period. Coverage is the same as the 

basic warranty. Damages due to abuse, or lightning strikes, or 

power surges, floods, fire, etc., are not covered. Factory service 

can provide overall savings for a maintenance program when used 

for “commodity” type products. Commodity products are low cost 

and mass produced. These would include modems used for traffic 

signal controllers, or fiber optic modems used in FMS, or 

handheld 2-way radios used by roadway maintenance personnel. 

The products can be easily replaced with spares by a technician 

with minimal experience and returned to the factory for repair. 

Extended warranty programs help reduce the maintenance cost 

associated with component degradation and failure. Under the 

warranty, the factory will replace components that no longer 

meet specification, and upgrade the product to the latest 

version. Extended warranties do not provide for on-site service 

and trouble shooting of external system problems affecting the 

warranted device. 

The following is a typical hardware warranty from a manufacturer 

of modems/fiber optic modems used in traffic signal and freeway 

management systems: 
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XXX COMMUNICATIONS, LLC 

XXX Communications LLC 

Traffic Electronics Manufacturer Specializing in Communications 

LIMITED WARRANTY 

XXX Communications LLC (XXX) warrants to the Buyer that all XXX goods (equipment and component parts) when sold 

are free from defects in materials and workmanship under normal use and service for a period of one year from the date of 

shipment, as evidenced by XXX 's or its agent's packing list or transportation receipt. XXX 's obligation under this 

warranty shall be limited to the repair or replacement of goods, at XXX 's option, which XXX 's examination shall disclose 

to its satisfaction to be defective. In no event shall XXX 's liability for any breach of warranty exceed the net selling price 

of the defective goods. No person, including any dealer, agent or representative of XXX, is authorized to assume for XXX 

any other liability on its behalf. 

XXX has no obligation or responsibility for goods which have been repaired or altered by other than XXX 's employees. 

This warranty is the only warranty made by seller and is expressly in lieu of all other warranties express or implied, 

and warranties of merchantability and fitness for any particular purpose are specifically excluded. 

WARRANTY CLAIM PROCEDURES 

Defective goods must be returned, transportation charges prepaid, to XXX for correction. XXX will pay return 

transportation charges for warranty repair. Upon redelivery of goods corrected under this warranty, the repaired or replaced 

portions shall be subject to this warranty for a period of 90 days or until expiration of the original warranty, whichever is 

later. All claims of failed or defective goods must be in writing and received by XXX within the specified warranty period. 

XXX will provide Buyer a return authorization number as authority to return the goods and for use in monitoring repair 

status. 

Repair or replacement of defective goods will be at XXX’s discretion and for the Buyer's account when the cause of failure is 

determined by XXX 's examination to be misuse, mishandling or abnormal conditions of operation. In such event a firm price 

quotation for correction of the goods may be submitted to the buyer. No repair or replacement work will be initiated prior to 

receipt of the buyers written authorization to proceed and approval of price, except as may be necessary to complete XXX’s 

examination of the goods. If returned goods are determined not to be defective or if the Buyer elects not to authorize 

correction at its expense of goods not covered by this warranty, XXX may charge a reasonable amount for such evaluation. 

Any amounts due XXX under these conditions will be subject to the same payment terms as the original sale. The Buyer will 

not recover from XXX by offset, deduction or otherwise, the price of any goods returned to XXX under this warranty.
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Note that there are statements which limit the liability of the 

manufacturer, and the fact that the warranty starts on the date 

of shipment. There is no agreement under the standard warranty 

with respect to acceptance of a system or other testing. 

RELATIONSHIP OF WARRANTIES TO SYSTEM SPECIFICATIONS

There is nothing in the terminology of a warranty that makes the 

manufacturer responsible for the functioning of their products in 

a system. Manufacturers of hardware generally do not take 

responsibility for system construction and system integration. 

Because they do not have total control over the situations in 

which their products are used, manufacturers will only take 

responsibility for the quality of their manufacturing process and 

the components used. 

A number of specifications for freeway management and traffic 

signal systems will require that a system be installed, optimized 

and pass acceptance testing before a warranty period starts. This 

is contrary to the statements in manufacturer warranties. Many 

products are delivered three to six months before installation. 

Some manufacturers will take this into account and extend the 

warranty start date, if requested in advance. However, the terms 

of the warranty do not change. 

Most systems are installed by a general contractor (GC) or 

systems integrator. The GC is ultimately responsible for meeting 

the D.O.T. specifications. If the end objective is to hold the 

general contractor responsible for the system until it passes 

final acceptance testing, then state this in the specifications. 

Don’t confuse manufacturer warranty terms with contractual 

purchasing terms. Often, the general contractor asks a 

manufacturer if their product meets specification, but fails to 

ask if the manufacturer will agree to the purchase terms. The 

end result is that the general contractor does not account for 

the testing and acceptance period in their bid pricing. Ultimately, 

a low bid price translates into system optimization delays while 

the GC and the equipment vendors work to resolve contractual 

issues. 

SERVICE PLANS

A “do-it-yourself” systems maintenance and service policy doesn’t 

always make sense when you’re trying to manage time, people and 

budget. Maintenance service plans help to off-load some of the 
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cost of keeping a communication system running. Advantages of a 

service plan are: 

• Provide a fixed cost to help control budgets 

• Assurance that service personnel are available 

• Routine system and hardware checks to help maximize “uptime” 

• Can provide for technology and software updates on a 

regular basis 

• Considered as an operational cost rather than a capital 

expenditure 

• Provide for emergency repairs and system restoration 

without additional costs. 

• Eliminate the need to support “specialty” technicians on 

staff focused on a small portion of your overall operation. 

Service plans (or maintenance agreements) are a fixed fee 

contract with a hardware vendor, system integrator, or 

maintenance services company for the routine maintenance and 

repair of hardware and systems. Contracts are typically based on 

the following elements: 

• Number of devices 

• Number of different vendors products 

• Types of devices 

• Individual “Mean-Time-Between-Failure” (MTBF) factors 

• Area of system deployment (state, region, local) 

• Age of respective devices and system 

• Services to be provided 

• Other factors (based on a review by the services provider) 

The largest factor in determining the fees for a service contract 

is the total number and types of devices. Service companies have 

statistics that indicate how often a product, or type of product, 

will need routine maintenance and general repairs. They use this 

as a baseline to determine pricing. Generally, the greater the 

number of devices, the lower the unit cost. One device may 

require two service incidents per year plus two routine 

maintenance calls per year, but 10 devices may still only require 
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two service incidents per year, plus routine maintenance. A 

service incident can be defined as the requirement for an actual 

repair due to failure. Therefore, a service company may charge 

$500 per year to maintain a single device, and $1,000 to service 

10 devices. The cost of the service incidents is spread over 10 

units. 

Variety of devices (modems, video CODECS, CCTV cameras, etc.) 

and manufacturers will affect the total fees because of a need to 

maintain spare parts and devices, and technicians with different 

skill sets. A large system spread over an entire state will require 

more resources than the same system deployed in a small area. 

Maintenance contracts can be limited to a few services, such as 

emergency repairs only. Or, they may include a whole suite of 

services including a requirement to replace devices that have 

been in the field for more than 3 years. The more services 

required, the greater the cost of the contract. 

There are some things that most service plans do not cover. They 

won’t cover repairs required because of acts of vandalism, faulty 

electrical service, power surges, damage due to “acts-of-god”, 

outages of telecommunication lines, or faulty installation. 

However, you can make stipulations in a contract and pay extra to 

provide coverage because of those problems. 

Before starting a service contract, make certain that your 

system is fully functional and that all problems created by faulty 

installation have been corrected. Don’t expect the service 

contractor to make up for the short-comings of a poor 

installation, or faulty design. 

To learn if a maintenance/service contract is a good option for 

your operation, complete a full equipment inventory, and ask 

qualified vendors to submit an estimate for their services using 

an RFI process. Don’t be concerned about vendor qualifications at 

this point. The objective is to determine potential costs and the 

number of vendors interested in providing services. If you 

determine that a service/maintenance contract will help save 

money, or improve your overall operation, then use a formal bid 

process. Apply the technician qualifications listed at the 

beginning of this chapter. Also request a list of current clients 

and complete a user satisfaction survey (contact existing clients) 

before selecting a vendor. Don’t forget to refer to the FHWA 
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Handbook “Guidelines for Transportation Management Systems 

Maintenance Concepts and Plans” for more information. 

Conclusions 

All communication systems require some form of maintenance. 

Current design and manufacturing techniques have eliminated a 

lot of the requirement to constantly check that equipment is 

running to specification. Most current communication hardware 

and systems, once properly installed and optimized, will run 

trouble-free for life. However, that does not eliminate the need 

for checking the system at least once every three to six months. 

The technicians can check for loose connections or moisture and 

dust, or other problems which may affect system performance. 

The technician can also verify equipment inventory. A good 

maintenance program will help to assure relatively trouble free 

system performance, and ultimately lower overall cost of 

operations. 
Chapter 7 

7. CHAPTER SEVEN – SYSTEM EXAMPLES

Introduction 

Departments of Transportation have been learning how to develop 

telecommunications systems to support traffic and freeway 

management for many years. There has been a concerted attempt 

to create a standardized architecture that would support 

requirements for most deployments. However, one constant that 

has evolved is that no two systems can be configured in the same 

way. Many elements (i.e.; modems, video codecs, transmission 

media, etc.) of a communications system are consistent in their 

functionality (system to system), but, it is the unique 

arrangement of those elements that differentiates between 

systems. Each user has their own set of requirements which a 

unique (in overall design) telecommunications system is required 

to support. 

This chapter will look at two very different approaches to using 

telecommunications technologies supporting freeway operations 

and traffic signal management: 

• The Utah Department of Transportation Salt Lake Valley 

Regional Freeway Management and Traffic Signal System 

• The City of Irving Texas Traffic Management System (As 

this handbook is being written, the system is in the process 

of being installed). 

Both systems, unique in their approach to providing a 

telecommunications system, have several factors in common: 

• Both are upgrades from a legacy system 

• Both are the result of requirements to expand overall 

traffic management services 

• Both have a requirement to merge with, and transition from, 

legacy systems 

• Both will use latest generation telecommunications 

equipment supporting broadband video. 

• Both will allow traffic data to be transported to multiple 

users 

• Both will upgrade to take advantage of recently developed 

IEEE 802 series standards. 
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• Commonly used telecommunication devices (modems, routers, 

video CODECs, etc.) have the same functionality in both 

systems. 

The primary differences are that one system was created to 

support a regional traffic control plan, the other created to 

cover a small urban/suburban city area. Each system is unique 

because each was designed to meet a specific set of end-user 

requirements. The UDOT system was originally designed to 

support multiple functions incorporating both traffic signal 

control for local streets, and freeway operations. The City of 

Irving system was originally designed to support traffic signal 

management for local streets. 

Utah DOT System 

BACKGROUND

In the early 1990’s, the Utah Department of Transportation 

(UDOT) began plans to develop CommuterLink, an Advanced 

Traffic Management System. This system, started as a regional 

coordination of signals across jurisdictional boundaries within the 

Salt Lake Valley, has grown to include over 600 traffic signals, 

1400 detector stations, 250 closed circuit television cameras 

(CCTV), 70 VMS and a wide range of ancillary transportation 

management systems such as 511, a website, HAR, RWIS, etc. To 

support this system, UDOT has installed its own dedicated fiber 

optic communication network. 

The communication network encompasses most of the valley, and 

reaches outwards to include the Cities of Ogden to the North, 

Spanish Fork to the South, and all other major cities in between 

such as Provo and Orem. With over 100 miles of fiber optic cable 

(as of the publication date of this handbook) installed, the 

system is expected to double by 2006. This network is dedicated 

exclusively to transportation and security related services and 

links the UDOT Traffic Operations Center (TOC), the Salt Lake 

City and County Traffic Control Centers (TCC’s), the Utah Transit 

Authority (UTA) dispatch center, and various emergency 

management centers. 

In response to the new expansion efforts, capacity limitations 

and some end of life hardware announcements - such as the video 

matrix switch - UDOT requested that an alternatives analysis, 

and future needs assessment, be performed to identify new and 
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Manufacture Discontinue -

the manufacturer of a 

product decides to stop 

manufacturing a product (or 

product line), and provide 

minimal warranty and parts 

support. 

proven state-of-the-art video technologies and other 

communication technologies that could be used in an upgraded and 

expanded CommuterLink. The result of this analysis was a 

recommendation for full-scale replacement of the existing 

Javelin video matrix switch, and the conversion from the existing 

ATM and SONET network to an Ethernet over IP solution. 

In the original concept, placement of multiple video matrix 

switches was envisioned within Regional centers to serve the local 

areas, with a fixed and limited number of ports being shared 

between centers (i.e., limiting the transfer between the TOC and 

Regional Hubs to any 8 video signals at any one time). 

Implementation of this concept was delayed until after the 

Olympics because the need was not there, and because new 

CommuterLink software was also required to control these 

multiple switches. 

With the expansion of the number of CCTV cameras and the 

provisioning of video links to additional agencies, the analysis was 

expanded to include consideration of the communication 

requirements necessary to interface with these centers. The use 

of a video matrix switch with remote nodes is tightly intertwined 

with a communication 

infrastructure, and one cannot be 

analyzed without the other. The 

resulting analysis took into 

account all current and envisioned 

future CommuterLink requirements 

of the State, County, and 

municipal agencies within the 

state of Utah, while preserving to 

the greatest extent possible, legacy systems. Also considered are 

recurring and upgrade costs that are associated with a “do 

nothing” approach. This option is in reality a misnomer, because 

significant resources are still required to maintain and / o r 

replace obsolescent equipment (i.e., Hub Ethernet switches, fiber 

modems, etc.). 

Note: The above background information was excerpted from an 

assessment study completed by a consultant for the Utah 

Department of Transportation. The study makes an important 

observation about communications technologies and planning – as 

technology advances, plans must change.
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“IP Multicast” – A process 

that permits distribution of 

a CCTV camera image to many 

users. The image is sent to a 

multicast switch that allows 

users to view using a Web 

Browser application on their 

deskto p com p uter.

The original plan was to deploy several matrix type video switches 

in various locations throughout the regional system. 

Unfortunately, matrix video switches require significant 

telecommunications infrastructure to support their ability to 

route video between several locations. Simply put, they are 

“bandwidth hogs”. During the period of the initial deployment of 

the CommuterLink system communication technology, standards, 

and processes evolved to provide the ability to route video with 

significantly less bandwidth and telecommunications 

infrastructure support. The overriding factors were the 

continued development of the IEEE 802.3 series of standards, 

and MPEG video compression standards. Video can now be routed 

from its source to a desktop computer using “Video-over-IP”. The 

UDOT system takes advantage of these new capabilities. During 

this same period, the matrix video switcher product line was sold 

to a new manufacturer. The new company decided to “manufacture 

discontinue” the product line. 

UDOT asked the consultant to 

look at alternatives to replacing 

the video matrix switch. The 

resulting investigation concluded 

that replacement of the matrix 

switch with video over IP would 

provide a significant operational 

advantage, and provide significant 

cost savings via the use of lower 

cost communications infrastructure hardware. The actual recommendation was to migrate to 

a digital IP communication network with IP Multicast for 

switching and distribution of the video. However, the existing 

ATM/SONET telecommunications infrastructure would have to be 

replaced, or modified. There would be an initial capital outlay to 

effect this change, but the savings on future equipment 

purchases (and maintenance) would pay back the initial outlay. 

Most important, UDOT would gain the ability to route video 

without having to install and maintain expensive video matrix 

switchers. 

THE SYSTEM - EXISTING

The current system was evaluated for its ability to support video 

over IP with the objective of re-using as much of the current 
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telecommunication system as possible. Because the existing 

system was based on using a video matrix switch there was a 

single point-of-failure. A matrix switch is nothing more than a 

large input-output device. In this case, the switch had a capacity 

of 300 inputs and 200 outputs. The switch would allow any one of 

the inputs to be output on one, two, three, or more outputs. The 

mechanics of the switch are such that every one of the inputs 

and every one of the outputs must be directly connected to an 

analog video source, or monitor. This was a reasonably efficient 

design for television production studios of the 1980s and 1990s, 

and certainly, in the place of any other reasonable alternative, 

very useable for the CommuterLink system. Lower capacity (and 

lower cost) switches are used in the security industry. 

Video Matrix switches were designed to take an analog video 

source and route it to a recording unit, or a video monitor within 

a television production studio, or within a large office building, 

or between several buildings in a campus environment. To use it in 

a transportation environment, the video from CCTV cameras must 

be transported from the field to the Traffic Control Center. This 

requires using a significant amount of fiber optic strands (or 

coaxial cables) to support a large number of CCTV cameras for 

direct camera to switch connections. Another option is to convert 

the video to a compressed digital signal, multiplex it with other 

video signals and transport to a TOC where the signal is demultiplexed, un-compressed, and then connected to the switch. 

Either of these scenarios creates a situation that is hardware 

intensive, and costly to deploy and maintain. 

Deployment of the CommuterLink systems occurred over a period 

of years and utilized three generations of communication 

distribution networks. The distribution networks progressed from 

a requirement to use one strand of fiber per CCTV camera, plus 

two strands of fiber for a multi-drop PTZ communication link, 

plus two strands of fiber for a multi-drop traffic 

controller/traffic device data link, to a single strand of fiber 

for all three systems. UDOT uses two primary fiber optic cable 

networks: 

• Backbone – designed to provide service from communication 

hubs to the TOC 

• Distribution – designed to provide service from field 

cabinets to the communication hubs. 
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The change in the design of the distribution network systems 

provided a significant savings in the amount of fiber strands and 

the amount of communication equipment required in the field 

cabinets. However, there was no change in the amount of fiber 

required between the hubs and the TOC. 

Between the hubs and the TOC, UDOT used three separate 

communication networks: 

• ATM to provide connectivity between various computer 

systems 

• SONET to provide communication for low speed data 

channels that served camera PTZ, changeable message signs, 

traffic signal controllers, and other devices 

• Video to provide transport of full motion video from 

cameras. 

The UDOT Network diagram provides a graphical representation 

of the three communication networks used for the overall system. 

The first generation system used separate fiber strands for each 

network in both the distribution and the backbone cables. 

Subsequent generations used fewer fibers in the distribution 

ATM ATM

Switch

SONet

Mux

ATM

Switch

SONet

Mux SONet

Ethernet

LAN Switch

ATM LAN Emulation

Card

LAN Switch

ATM / SONET

Ethernet

ATM / SONET

ATM LAN Emulation

Card

Video

Tx / Mux

Video

Rx / Mux Proprietary

T1

Mux

T1

Mux

Low-Speed Data

(PTZ, TSC, VMS, Etc.)

Low-Speed Data

(PTZ, TSC, VMS, Etc.)

Fiber (Typical)

Video

Monitor

Figure 7-1: Diagram UDOT Current System
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cable, but continued to use separate fibers in the backbone 

cable. 

THE SYSTEM - NEW

UDOT originally considered deploying additional analog video 

matrix switches to route video to other centers and user 

agencies. The existing fiber optic cable infrastructure would 

have to be expanded to support the additional switches. With the 

knowledge that the video matrix switch product was taken out of 

production and no longer supported by the manufacturer, UDOT 

looked at alternative video distribution strategies. This led to a 

complete review of existing systems and their communication 

requirements. 

The decision was made to complete a phased replacement of the 

telecommunication system and the analog video matrix switch. 

This process would be facilitated by the fact the existing fiber 

optic able infrastructure would not have to be replaced. A 

recommendation was made to convert the video signal to a digital 

IP format in the field cabinet. 

The comparison shows that significant savings are gained by 

converting to an IP architecture. Table 7-1 provides a list of 

estimated costs and a proposed upgrade schedule: 

Table 7-1: Deployment Cost Estimates 

Architecture Comparison - Urban Surface Street Configuration

( 16 Cabinets + Hub )

0

50,000

100,000

150,000

200,000

250,000

1D+0V 2D+0V 3D+0V 4D+0V 4D+1V

( Data Channel + Video Channels ) / Cabinet

Cost ( $ )

Existing

IP

Figure 7-2: Graph - Comparison of Savings Realized by UDOT Converting to an IP Architecture
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Deployment Cost 

Estimate 

Proposed 

Schedule 

TOC Ethernet LAN Switch Upgrades $250,000 FY04 

Video Decoder Equipment at the TOC 

and all Existing Partner Agency 

Locations 

$750,000 FY04 – 06 

Hub Ethernet LAN Switch Upgrades $650,000 FY04 – 06 

Cabinet Ethernet LAN Switch Upgrades $520,000 FY04 – 06 

Cabinet Serial Port Adapters $120,000 FY04 – 06 

Video Encoder Equipment for 200 Field 

Cabinets $800,000 FY04 – 06 

Total $3,090,000 

UDOT can continue to use the existing systems and provide 

upgrades over time to minimize overall budget impact. As shown in 

the above table, there are no expenses to modify the existing 

fiber optic cable infrastructure. Affiliated user agencies can be 

added at minimal cost because the video, and other data, can be 

Drop 1 Drop 2 Drop 3 Drop 4 Hub

9.6 Link 9.6 Link 9.6 Link 9.6 Link

Using traditional TDM protocols all devices on a common 

circuit must use the same data transmission rate

Drop 1 Drop 2 Drop 3 Drop 4 Hub

100 Mb 

Link

100 Mb 

Link

1000 Mb 

Link

1000 Mb 

Link

Using Ethernet many devices can share a common circuit 

Figure 7-3: Diagram - Comparaison Multi-Drop VS. Ethernet
Telecommunications Handbook for Transportation Professionals 

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routed using standard Ethernet architecture and lower cost offthe-shelf hardware. 

A major advantage of using the Ethernet architecture is that it 

can support multiple devices requiring different data 

transmission speeds. Multi-drop communication circuits – such as 

those used with traffic signal controllers – require that all 

devices communicate at the same data rate. The compressed video 

signal from a CCTV camera cannot be added to a multi-drop 

circuit used for traffic signal controllers unless the video signal 

is transmitted at the same data rate. Most traffic signal 

controllers use a data rate of 9.6 Kbps and most compressed 

video signals are transmitted using a data rate of between 384 

Kbps and 1 Mbps. Using Ethernet and IP protocols, each device 

can transmit at its own data rate. Therefore, many different 

devices can share a common data communication circuit. The end 

result is a simplification of the overall communication system, 

i.e., fewer strands of fiber, and less hardware. 

The full report: CommuterLink Communication System Analysis – 

Alternative Architecture Options - is available on the USDOT 

Joint Program Office web site. 

City of Irving Texas 

BACKGROUND

Irving, Texas, a community of about 200,000 residents, is part of 

the Dallas-Fort Worth Metro Area, and home to the Dallas 

Cowboys Football Stadium. The Traffic and Transportation 

department is responsible for the operation and maintenance of 

the traffic signal system- a system with 175 signalized 

intersections. Most operate on a “time-of-day” signal plan, and a 

few are closed-loop. The current system uses several versions of 

the NEMA traffic signal controller, and there is no centralized 

control. The department relies on telephone callers to report 

problems and dispatches technicians to investigate and effect 

repairs. The City of Irving is seeking to update its current 

traffic signal system to provide for centralized control and 

problem location. The traffic department is proposing to replace 

the variety of signal controllers with the 2070 type. 

The update calls for the total replacement (over time) of the 

NEMA type controllers, addition of CCTV cameras, traveler 

information signs, and centralized control of all traffic signals. 
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Central control would provide immediate notification of signal 

problems and allow for dynamic re-timing of signals to account 

for special events or significant traffic incidents. The use of 

CCTV cameras would provide real-time viewing of congestion 

problems and support temporary re-timing plans. 

PROPOSED UPDATE

An overall development plan with the objectives of standardizing 

on one controller type, one software system, one cabinet type, 

and centralized signal control was created. The department 

recognized the need to provide a telecommunications 

infrastructure to support the plan, and the construction of a 

private fiber optic communications network was considered. 

TEA21 funding was requested, and granted. However, the level of 

funding was substantially less than needed. The ultimate 

objective of adding all signals to the communication network 

could not be realized if a fiber network was used. The estimated 

cost of the fiber optic network was $10 million. 

The City looked for alternate communication technologies to 

support their plan. Their first consideration was the use of 

leased telecommunication services from local carriers. This plan 

was rejected because: 

• The overall cost exceeded funding levels 

• Available bandwidth was insufficient to handle the individual 

(3 MB) video feeds required for the system 

• The city did not want to incur a monthly recurring expense 

The City investigated wireless systems and discovered that they 

could provide total coverage at a substantially reduced cost over 

the fiber optic and leased telecommunication networks. 

Requirements for the system included: 

• Broadband capability to support video 

• Point-to-multipoint to support centralized control 

• Ability to add locations with minimal system disruption 

(scaleable) 

• Ability to add locations with easy to configure 

communications hardware 

• Communication system reliability 
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• Overall initial system costs kept within budgeted levels 

In addition to the centralized control of traffic signals, the 

Irving Traffic Department wanted to provide: 

• CCTV cameras with pan-tilt-zoom 

• Changeable message signs 

• Dynamic lane assignment 

• Video incident detection 

• Additional advanced traffic management features 

• Real-time traveler information 

The city has made a significant investment in a wireless 

infrastructure to support operational agencies and services. They 

currently use 5.8 GHz microwave (Wi-Fi 802.11a), 24/23 GHz 

microwave, and 18 GHz microwave. A group of experienced, 

licensed radio technicians are on staff to maintain and operate 

the radio networks. 

Considering several different wireless network topologies, the 

city sought a design that would provide the necessary bandwidth, 

secure transmission and high availability (99.999%). The typical 

point-to-point-to-point (multi-drop) design used for most traffic 

signal wireless communication systems did not prove to be 

adequate for a system that would ultimately be required to 

support more than 70 CCTV cameras, and almost 200 signalized 

intersections. 

The city’s Communication & Electronics Department investigated a 

wireless system designed to provide broadband internet access. 

They found a product that is compliant with the IEEE 802.16 and 

802.16a standard. The 802.16a standard provides for a 

significant reduction in the potential for interference from other 

radio systems on the same or adjacent channels. The IEEE 802.16 

was developed as the “Air Interface for Fixed Broadband 

Wireless Systems.” This standard describes wide area wireless 

networks (WAN) and is designed to provide coverage in terms of 

miles. Compare this with the IEEE 802.11 wireless standard 

series developed for local area wireless network (LAN) coverage, 

with coverage distances measured in terms of feet. 
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5.8 GHZ ATTRIBUTES

• Operates in 5.8 GHz UNII/ISM frequency 

spectrum 

• Scaleable throughput 

from 20 Mbps to 60 

Mbps 

• Base station can provide 

up to 360 degree 

coverage in 60 degree 

segments 

• Simplified installation 

using a self-enclosed 

radio/antenna module 

with Ethernet 10/100 

baseT connections. 

• Compliance with IEEE 

standards: 802.1d; 

802.1q; 802.16; 802.16a. 

• Additional field units 

can be installed without 

disrupting current 

operations. 

1

3

1

4

4

2

4 Wireless Channels used to 

create 360 degree coverage

Figure 7-4: Diagram - Wireless Channel Alignment 

for 360 Degree Coverage
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THEORY OF OPERATION

The FCC has designated four operational communication channels 

within the 5725 to 5825 MHz frequency range. Each channel 

occupies 25% of the available spectrum. Each of the four 

channels can be used to cover a 60 degree arc. Re-using two of 

the four channels permits a six channel array for coverage of a 

360 degree circle. Following are examples of how the four 

wireless channels can be re-used to provide total coverage 

without over-lap. 

Each of the individual coverage hexagons has an array of six base 

stations at the center and referred to as a “Hub Site”. The base 

stations are networked to provide for a 360 degree coverage 

4

5

3 1

2

4

6 5

1 3

2

6

5

3

2

1

6

4

1

6

2 4

5

3

5

3 1

6

2 4

4 Wireless Channels reused to create a wide area 

coverage with no overlapping

Figure 7-5: Diagram - Channel Re-use Plan for Wide Area Coverage
Telecommunications Handbook for Transportation Professionals 

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area. Field units, also called “Subscriber Units”, have a highly 

directional antenna pointed toward the sector base station 

providing the best line-of-sight coverage. It is also possible to 

create communication path redundancy for a subscriber site. 

THE IRVING PROPOSAL

The initial plan calls for 

the development in two 

phases of six (6) coverage 

zones each. The first phase 

will use a single base site 

with six coverage zones. 

The second phase will use 

two base station sites with 

three coverage zones each. 

Future system upgrades will 

permit additional zones to 

be added as required. 

Some of the coverage zones 

may overlap, but the 

subscriber units are set to 

a specific radio channel to 

prevent interference from 

other base stations. Also, 

the subscriber unit 

antennas are highly 

directional and aimed at a single base station. 

8

9

6

2

5

1

3

4

11

12

10

Possible coverage scenario using 

4 radio channels to cover 12 

communication zones.

7

Figure 7-6: Diagram - Proposed Channel Re-use Plan
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199

Notice that a single cable runs from the antenna/radio system to 

the cabinet. Inside the cabinet is a communication module that 

provides power and Ethernet to the radio unit at the top of the 

pole. The VIP signal, and PTZ signal, from the camera are 

connected via the communication module to the CAT 5 pairs in the 

P ow e r & C a t 5 w ir e 

in sam e ca ble

T o S e ctor B a se S ta tio n

Figure 7-7: Drawing - Typical CCTV Site
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200

cable. The CCTV camera has a built-in 12 CODEC-VIP module that 

converts the video to IP. 

Following (Figure 7-8) is a site schematic diagram: 

Individual site antennas are oriented toward a specific base 

station unit. The highly directional system prevents overlap and 

allows for optimization of communications traffic through any 

single system. Irving TTD has assigned each signal device a 

communication zone within the coverage grid. They have also 

proposed locations for CCTV cameras and other equipment. The 

following map shows the overlay of the coverage zones and where 

each device and signal controller is located: 

 

12 See chapter 5 section on video over IP. 

Radio – Antenna

System

Power – 

Communication

Module

CCTV

Camera

PTZ

Cabinet Power 

Supply

Power

Power

CCTV Camera

PTZ Module

VIP

&

PTZ

DC Power

&

Ethernet

Figure 7-8: Typical CCTV Site Schematic
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The overall objective of the Irving Traffic & Transportation 

department is to update the current system, standardize on the 

types of devices being deployed, and provide for greater 

efficiencies in the overall management of their system. The use 

of a technology initially developed to provide broadband internet 

service is a reasonable choice given the total cost of 

Figure 7-9: Map of Proposed Irving Texas System
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202

implementation and operation. Fixed broadband wireless 

communications systems are also being applied for security, water 

and wastewater management, and agricultural operations systems. 

TIE-IN TO MAIN COMMUNICATION NETWORK

The City has a microwave communication backbone that connects 

all major systems. The backbone system is a point-to-point 

microwave communication link. Five sites are set up in a loop 

configuration to allow for a self-healing ring and redundant paths 

to all sites. The paths are rated at 100 Mbps to carry maximum 

bandwidth in either direction of the loop and operate in the 18 to 

23GHz licensed microwave range. 100 Mbps is currently the 

maximum available, but several manufacturers are in the process 

of testing with 240 Mbps systems. The schematic shows how the 

Traffic system ties into the microwave communications backbone. 

The broadband base stations are connected to a microwave radio 

backbone for transmission to the Traffic Operations Center. 

TOC

Base Station 

Unit

CAT 5 Cable

Line-of-Sight

RF Communication

Link

Site

System

Router

18 GHz MW

Backbone Cable

Router

CAT 5 Cable

Video 

Server

Traffic

Signal

Server

CMS

Server

CAT 5

Figure 7-10: Schematic - Microwave Backbone Configuration
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Conclusion 

This chapter has provided two very different solutions for a 

similar problem – updating an existing system with the 

incorporation of legacy devices and newer technology. Both user 

agencies evaluated their needs and options. Utah has an existing 

fiber optic communications network that it wanted to update. 

Irving, Texas has an existing traffic signal system that needed 

modernization. The same general requirement resulted in two very 

different approaches to the use of communication systems. The 

examples used point to the fact that there are many different 

telecommunication system designs that can be used to solve 

similar problems. Each design (solution) is unique to the needs of 

the end users. The lesson learned is to consider all possibilities 

and select the one that meets your needs.

D

C

E B

A

B i- D ire ctio n al 

C om m u nic a tio n F low

1 8- 2 4 G H z Lice nsed 

M icrow a ve S y stem

Figure 7-11: Diagram - Microwave Backbone
Chapter 8 

8. CHAPTER EIGHT – CONSTRUCTION

Introduction 

Chapter Two presented the term media to describe the physical 

layer of a communication system that is used to convey 

information between two or more points. This chapter presents 

guidelines that should be used in the handling of the media during 

construction. The items described 

in this chapter are typically the 

responsibility of a general 

contractor, however, it is important 

for project managers and 

consultants to have a good 

knowledge of the construction 

process. General design and 

construction practices are the same 

as those associated with almost any 

civil works project. Conduit and 

direct-bury cable projects need to 

be designed using cable and conduit 

manufacturer recommendations for bending radii, and cover depth 

specifications. Towers and poles supporting radio antennas need 

to be designed using manufacturer recommended mounting and 

support guidelines. 

Many of the presented guidelines have been developed by 

manufacturers wanting to make certain that customers are 

satisfied with their products. Other 

guidelines have been developed based 

on observation of common mistakes 

made by construction contractors. 

The most important recommendation 

that can be made is to carefully 

monitor the construction process. 

Don’t let contractors take 

“shortcuts”. Make the manufacturer 

construction and media handling 

guidelines part of the project 

specifications. There may be good 

reason to not follow the 

recommendations (or the specification), and the contractors 

should be required to explain the need to deviate. Most requests 

Figure 8-1: Fiber Cable Route 

Construction – Photograph Courtesy 

Adesta, LLC

Figure 8-2: Fiber Cable Route 

Construction – Photograph Courtesy 

Adesta, LLC
Telecommunications Handbook for Transportation Professionals 

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for this type of action will be in the form of a “path” realignment. Treat the request as you would for any other highway 

construction project. 

The physical design of the media path should conform to national 

and local construction design codes. Most municipalities issue 

construction permits. Many have specific codes relating to the 

locations of conduit or radio towers. 

For very large projects, hire an independent construction 

management firm to observe the testing and construction 

process. Train in-house personnel to observe smaller projects. 

Require construction contractors to follow manufacturer 

recommendations for installation of their products. 

Much of this chapter is devoted to the care and installation of 

fiber optic cable. Copper (twisted pair, coaxial, and antenna 

cable) transmission media cable require similar care and testing 

during installation. 

Handling and Installation of Fiber Optic (and Copper) Communications 

Cable 

Most ITS, Traffic, FMS systems use fiber optic, or copper cable 

as the primary communications transport medium. Use of the 

recommended procedures during installation can save a 

substantial amount of money. Most media problems occur because 

of a lack of care during installation. This section provides 

guidelines for the installation of “outside plant” communication 

cable. Each cable manufacturer will provide specific information 

related to the product they provide about care and handling 

during installation. 

Following is a list of recommendations for the handling and 

installation of fiber optic communications cable. These same 

general procedures can also be followed when installing coaxial or 

twisted pair cable. The general procedures and requirements 

apply for all fiber optic communications cable whether installed 

aerially on communications utility poles, or in underground 

conduit, or structure attached conduit, or inner-duct placed in 

conduit, or direct burial. 

• Receiving and inspecting the cable 

• Unloading, moving and storing the cable 

• Testing cable on reels 
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• Documentation and record maintenance 

• Cable Installation 

RECEIVING AND INSPECTING FIBER OPTIC CABLE

Let your cable manufacturer or distributor customer service 

representative know of any special packaging or delivery 

requirements (no shipping dock available, call before delivery, 

etc.). Put this information in the specifications so that 

contractors will be aware of these requirements. Make certain 

that personnel with test equipment are available. It is important 

to test damaged (or suspect) cable reels before accepting 

delivery - request 24 hours notice. 

When the shipment arrives, make sure the cable types and 

quantities match the bill of lading. Inspect every reel and pallet 

of material for damage as it is unloaded. Suspect cable should be 

set aside for a more detailed inspection before the shipping 

documents are signed. The delivery persons may be on a tight 

schedule, but they aren’t paying for the cable! 

Notify the general contractor and the manufacturer/distributor 

that there are damaged cable reels before signing for the cable. 

Follow-up the telephone call with a written notice via e-mail or 

fax. 

• Receipt of the cable does not imply acceptance! 

• You may be pressured (by the distributor) to accept the 

cable by being told that you will have to wait 18 months for 

new cable. 

• Remind the person applying the pressure that they won’t get 

paid until the order is complete. 

• Accept a 30 day delay in return for having a fully functional 

system. The delay will cost less than replacing damaged 

cable. 

Some additional points to consider: 

• Reels of optical fiber cables are shipped on their rolling 

edges not stacked flat on their sides. Make sure you note 

the orientation and condition of the reel in your inspection. 

• If any cable damage is visible or suspected and if it is 

decided to accept the shipment, note the damage and the 

reel number on ALL copies of the bill of lading. 
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• If the damage is too extensive to accept the shipment, 

advise the carrier's driver that the shipment is being 

refused because of the damage. Immediately notify the 

cable manufacturer/distributor, Customer Service 

Department so that arrangements can be made for a 

replacement shipment. 

• Cable performance test results taken at point of 

manufacture and reel loading are provided with each reel. 

Compare them to your own tests using the methods outlined 

in the cable testing section. 

UNLOADING, MOVING AND STORING CABLE

When unloading the cable reels from the delivery truck, 

exercising care is important. The reels may look like two wheels 

on an axle, but they should never be rolled off the back-end of 

the truck. The reels are heavy and may contain from 5,000 to 

15,000 meters of cable. Following are guidelines for unloading, 

moving and storing of communication cable reels: 

• Optical fiber cable reels are typically very heavy and, 

therefore, they must be loaded and unloaded using a crane, 

special lift truck or forklift. 

• Forklifts must pick the reel up with the flat side of the reel 

facing the forklift operator. 

• Extend the forks under the entire reel. 

• Keep all reels upright on their rolling edges and never lay 

them flat or stack them. Optical fiber cable reels are 

always stored on the rolling edge 

• All reels are marked with an arrow indicating the direction 

in which the reel must be rolled. Roll only in the indicated 

direction. 

• DO NOT drop reels off the back of the truck onto a 

stack of tires, onto the ground or any other surface. The 

impact may injure personnel and will damage the cable. 

• The reel is labeled with handling directions. Consult these 

directions if you have any doubt about handling the reel. 

• To prevent reel deterioration during long term storage, 

store optical fiber cable in a manner that protects the reel 

from the weather. 
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TESTING THE CABLES

• Manufacturers test the cable for continuity at the factory 

once it has been loaded onto the reel. This is your assurance 

that there are no breaks in any of the fiber (or copper) 

strands that make up the cable. The results are published 

and added to tags on the cable reel and to the paperwork 

that accompanies each cable reel. Do not accept any cable 

reels that lack the testing documentation. There are five 

phases associated with testing of fiber optic cable starting 

at the point of manufacture: 

1. Factory cable reel testing and documentation, 

2. Visual inspection at the delivery site for shipping 

damage, and possible reel test, 

3. Pre-installation testing, which occurs when the cable is 

delivered to the job site, and before it is installed, 

4. Installation testing, which occurs after the cable is 

pulled through the conduit (or mounted on poles) and at 

every splice point, 

5. Final acceptance testing, which occurs just prior to 

activation. 

Why is testing so important, and why so many tests? Each test 

phase occurs at a responsibility hand-off. 

• Factory to shipping company 

• Shipping company to general contractor (or DOT) 

• General Contractor to installation (path construction) 

company 

• Installation Company to splicing contractor 

• Splicing Contractor to end-user 

Each entity will claim that the cable was in good condition when it 

made delivery of the product or service. Testing at each stage 

assures that liability for damage can be placed with the 

appropriate company. A significant portion of the cost of 

constructing the fiber optic cable system is in the final 

installation (cable pull, splicing and quality testing) of the cable. 

Imagine having to replace 15,000 feet of cable because of damage 
Telecommunications Handbook for Transportation Professionals 

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209

sustained during the pulling. Knowing that the installation 

contractor is responsible will save a lot of time and finger 

pointing. 

Following is a list of testing guidelines: 

• Testing reels of optical fiber cables at delivery is not 

required (most manufacturers suggest that this be done to 

ensure that damage did not occur during shipping), however, 

testing prior to, and after construction is essential to 

identify any cable performance degradation caused during 

installation. Testing prior to installation provides a baseline 

of performance. 

• Pre-installation Testing - This typically consists of an OTDR 

(Optical Time Domain Reflectometer) test performed at 

1550 nm. All optical fiber cables must be bi-directionally 

OTDR-tested prior to shipment and the test report attached 

to the reel. Bi-directional testing is important to verify 

results and to make certain that no potential problems were 

missed. Remember, the data can flow in two directions on 

the fiber strand. Test to make certain that it will. 

• A pre-installation test will verify the characteristics of the 

cable and check for any shipping damage. The tests must be 

jointly conducted by the system operator and the 

construction contractor in order to preclude future 

difficulties should a 

cable be damaged 

during construction. 

• Installation Testing - 

Cable should be 

tested once it has 

been placed in the 

conduit, or on the 

poles, and prior to 

splicing to make sure 

that there has been 

no installation 

damage. Installation 

testing is usually done 

with an OTDR. 

• Splice testing is done after each splice to ensure that a 

clean, low-loss connection was made. OTDR, local injection 

Figure 8-3: Fusion Splicing Fiber Strands -

Photograph Courtesy Adesta, LLC
Telecommunications Handbook for Transportation Professionals 

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210

detection and profile alignment can be used alone or in 

combination for splice testing. 

• Post Installation - Final Acceptance Testing - The usual post 

installation testing method is to perform end-to-end OTDR 

testing from both directions. The results should be 

compared to the pre-installation test. It is highly 

recommended that an ongoing testing program be established 

after the system is powered up. 

• It is important that technicians testing the fiber use the 

same brand and model of test equipment and the same 

testing profile. Use of different test equipment and profiles 

will result in confusion and inconsistent test results. 

• Make certain that someone on your staff (or the 

communication engineering consultant) is able to understand 

the test results to verify that all specifications have been 

met. 

DOCUMENTATION AND RECORD MAINTENANCE

“The best defense is a good offense”, is a phrase that should be 

applied to the construction of a communication cable system. 

Optical fiber installation involves multiple fibers in a cable that 

may be very long and have many splices and connections. If cable 

is damaged during installation and not detected by on-going field 

testing, the replacement costs can be extremely high. It is 

recommended that the following records be maintained and kept 

current on a daily basis: 

• schematic drawings – to include “as-built” information for 

street maps records 

• splice loss data 

• end-to-end optical loss measurements 

• end-to-end OTDR signature traces 

• end-to-end power meter tests 

The documentation is needed to provide historical references for 

maintenance and, emergency restoration. By maintaining this data, 

the system operator is assured of a prompt repair response by 

the quick identification of the location of any problem that may 

occur within a cable. Data collection starts with the delivery of 
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the fiber cable, continues through construction and for the life 

of the system as new devices are added. 

Following is a list of data that should be collected for the 

permanent record: 

• Calculated data obtained from cable reel data sheets and 

splicing logs. 

• Measured data, such as OTDR data, is obtained from end-toend cable testing. 

• Total amount of cable pulled between splice points – 

including slack coil loops 

• Placement and use of pull boxes and cable splice boxes 

• Accurate street maps showing the location of fiber cable 

and all accessory items 

• Accurate location information of any repairs 

• Maps that show where other utilities cross the fiber 

cable, or are in close (parallel) proximity to the cable 

• A record of all communication devices connected to the 

fiber cable 

• Where conduit (or the cable trench) is shared – list the 

other users 

• Any other information that might be needed to support 

changes or emergency repairs. 

General Cable, Installation and Design Guidelines 

The following guidelines are presented to assist in the general 

design, construction and installation of fiber optic cable systems. 

Many of these guidelines can also be used for other types of 

communication cable. 

CABLE PULL-BOX/SPLICE-BOX PLACEMENT

• Every street (up to 50 feet wide) crossing – one (1) box 

located within 10 linear feet of the crossing, unless a 

traffic device (signal, DMS, video detector, etc.) is located 

near (within 50 linear feet) of the crossing. 

• Every freeway, railroad, or bridge crossing – two (2) boxes 

located (one each) at the terminal points of the crossing. 
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• All mid-span splices must be placed in a splice box and 

secured in an appropriate cable tray. 

• All splice boxes used for aerial cable installations should be 

mounted on a convenient utility pole. If no space exists on 

the pole, then a suitable in-ground splice/pull box must be 

installed near the utility pole. All cable leaving the aerial 

installation must be installed in conduit. 

• All splice points must contain sufficient slack (50 foot 

minimum) to allow for future addition of communication 

devices, cable and splice repairs, or additional runs of 

“drop” cable. This would be especially true if the cable is 

located within a freeway right-of-way. 

• All splice boxes must be properly grounded according to 

NEC. EIA/TIA and 

Bellcor (Telcordia) 

standards. 

• Aerial mounted splice 

boxes should only be 

used for temporary 

repairs – in fact, many 

carriers use them for 

permanent repairs. 

• Mid-span cable meets 

(points where ends of 

cable reels meet) must 

be fusion-spliced and 

enclosed in a splice 

box. Never use a 

mechanical splice to 

connect cable reel 

ends. 

CABLE INSTALLATION AND PULLING GUIDELINES

Pulling Tension: 

• Each manufacturer has specific instructions and 

specifications for the amount of tension that may be used 

when pulling a fiber optic cable. The contractor is required 

to follow the cable manufacturer’s specifications and 

recommended installation procedures. 

Figure 8-4: Aerial Fiber Optic Cable Splice 

Box - Photograph Courtesy Adesta, LLC
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• Kellems or crimp-on grips are used to pull the optical fiber 

cable. Use the correct-sized grip for the cable being pulled. 

• If Aramid ® yarn is part of the cable structure; tie it to the 

grip to further distribute the pulling force. NEVER EXCEED 

the maximum pulling tension.

• Excessive pulling force will cause the cable to permanently 

elongate. Elongation may cause the optical fiber to fail by 

fracturing. 

• Good construction techniques and proper tension monitoring 

equipment are essential. 

• When installing aerial cable place enough cable blocks along 

the route to keep cable sag to a minimum. Excessive sagging 

will increase pulling tension. 

• When pulling, do not let the cable ride over the reel flange 

as it may scuff or tear the jacket. 

• Tail loading is the tension in the cable caused by the mass 

of the cable on the reel and reel brakes. Tail loading can be 

minimized by using little to no braking during the pay-off of 

the cable from the reel – at times, no braking is preferred. 

• Dynamometers must be used to measure the dynamic tension 

in the cable. 

• Break-away swivels should be used in conjunction with 

dynamometers to ensure that the maximum pulling tension is 

not exceeded. 

Cable Bending Radius Guidelines: 

• Cables are often routed around corners during cable 

placement. NEVER EXCEED the minimum bending radius. 

“Over” bent cable may deform and damage the fiber inside. 

• Bending radius for optical fiber cable is given as loaded and 

unloaded. 

• Loaded means that the cable is under pulling tension and is 

being bent simultaneously. 

• Unloaded means that the cable is under no tension or up to a 

residual tension of around 25% of its maximum pulling 

tension. The unloaded bending radius is also the radius 

allowed for storage purposes. 
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• Do not exceed minimum bend radii or the maximum pulling 

tension. 

• Follow all pulling tension and minimum bending radii 

instructions and specifications issued by the cable 

manufacturer. 

• In general, plan the cable path to eliminate as many curves 

and bends as possible. Curves and bends add to the 

attenuation of the fiber optic signal. 

Pulling Strategy Guidelines: 

• Fiber optic cables can be ordered in lengths on a single 

cable reel and can be installed in one continuous run. 

However, even a typical installation of 3 - 5 miles/5 - 8.0 km 

offers installation challenges because of the accumulation in 

pulling tension along such a long route. This tension can be 

eased by using intermediate assist devices like a series of 

mechanical winches or capstan drives connected to a master 

controller. However, if these devices are unavailable, a 

midpoint cable pull must be used for installing long lengths 

of optical fiber cable. 

• The cable is installed from a midpoint to the endpoints. 

• Make certain that all conduits are clear of obstructions. Use 

a water based lubricant to reduce outer sheath corrosion. 

• Existing conduit may need repairs – inspect carefully. 

• When installing aerial cable, make certain that the path is 

clear of tree limbs. 

General Cable Construction Guidelines 

Cable is generally installed using one of three methods: aerial, 

direct burial, or in 

conduit. This section 

provides some general 

guidelines for using these 

construction methods. The 

methods are listed in 

order of cost to construct. Aerial is generally considered lowest 

cost with conduit placement being the highest cost. 

FHWA has produced the “Design Guide for Fiber 

Optic Installation on Freeway Right-of-Way”, 

publication # FHWA-OP-02-069. Consult this 

document for additional information and guidance.
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AERIAL CONSTRUCTION

Aerial cable is typically strung from pole-to-pole, or from 

building-to-pole. Two types of cable are available: self-supporting 

or lashed. The self-supporting cable is designed with either a 

heavy duty central strength member, or in a figure eight 

configuration that has an external strength member that can be 

clamped. Lashed cable is similar to cable that can be direct 

buried and requires a “messenger support wire” to which the 

cable is affixed. 

When using aerial cable, the engineer must provide sufficient 

supporting utility poles in the route to minimize the effect of 

cable sag. This is caused by external forces such as wind, ice and 

extreme temperature changes added to the weight of the cable. 

Manufacturers provide specifications to assist with cable route 

design and planning. 

Here are some general guidelines: 

• Use of tight buffered cable is not recommended for aerial 

installation 

• Use a cable with a UV protected sheath to minimize effects 

from sunlight 

• Use a metallic armored cable to minimize damage from 

squirrels and birds. 

• Always follow the manufacturer recommendations for selfsupporting cable installations. Consult the manufacturer for 

additional information when varying from recommendations. 

• Allow for storage of sufficient slack loops to account for 

problems associated with cable breaks and pole damage from 

severe weather and vehicular accidents. 

Table 8-1 is excerpted from a Corning Cable product brochure for 

self supporting fiber optic cable. Please consult the cable 

manufacturer’s documentation for recommendations about 

installation under severe weather loading conditions such as high 

wind or severe ice and snow accumulation areas. 
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Table 8-1: Example of Manufacturer Recommended Span Lengths for Areial Cable Segments 

Maximum Span Lengths 

Maximum Span Lengths for NESC Loading Conditions 

Fiber Count Heavy Medium Light 

 m ft m ft m ft 

2 – 36 504 1655 733 2405 844 2770 

37 – 72 427 1400 622 2040 721 2365 

73 – 96 496 1540 671 2200 751 2465 

97 – 144 500 1640 553 1815 553 1815 

145 – 216 335 1100 450 1475 494 1620 

Notice that as the number of fiber strands contained in the cable 

increase, the distance between utility poles decreases. The same 

is true for loading factors. 

Construction of aerial cable involving the use of existing utility 

poles, requires access permits from the owner of the pole. In 

most cases, the owner is the local electrical power utility, but 

some poles are owned by telephone companies. Utility poles are 

marked with identification tags. 
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The electrical power lines are always placed at the top of the 

pole. Telephone 

carriers are placed 

at the next lower 

level with about 10 

feet of vertical 

separation from the 

electrical lines. 

Other users are 

located above the 

telephone lines, but 

with at least 10 feet 

of vertical 

separation from the 

electrical utility. 

The lowest set of 

lines must be placed 

at least 15 feet 

above grade. If 

there is not enough 

room to accommodate 

all valid users, it is 

necessary to raise 

the height of the 

pole. The last user is 

responsible for 

paying the cost of 

installing the 

extension (or taller 

pole) and moving all users to their appropriate position. Using 

existing utility poles can be very expensive. 

Figure 8-5: Typical Telephone Pole
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DIRECT BURIAL CONSTRUCTION

Cable can be buried directly in soil using one of two general 

construction methods: open trench construction, or cable plow. In 

both instances, a cable rated for direct burial should be used. 

These cables are designed with a metallic armor sheath to 

prevent damage from rodents that may try to chew through the 

cable. The direct burial method is especially useful in rural and 

suburban locations. The non-paved portion of a rural road or 

highway right-of-way is a good candidate for this construction 

method. The route must be carefully planned taking care to avoid 

other buried utilities (water, electrical, telephone, gas, etc.) and 

meeting environmental requirements. 

Using the open trench construction method, a backhoe is used to 

dig a 36 inch deep trench. The trench is backfilled with an 

appropriate material to prevent cable bends due to settlement. 

The trench is then filled to a level of 24 inches. A yellow warning 

tape is then laid in the trench before completing the fill process 

to terrain level. The 36 inch depth is an average. The cable 

should always be buried below the frost line. The actual depth of 

the cable may vary based on road crossings, or drainage ditch 

(drainage lines) crossings. The object is to keep the cable out of 

harm’s way. 

A second direct bury construction method uses a plow to open the 

earth, lay the cable and then cover. This is an economical and 

efficient construction method. However, no warning tape is 

installed. 

Use of these methods does not eliminate the need to consider 

placement of slack cable and access handholes. There will always 

be a need to add communication devices and access nodes to a 

system. 

Direct buried cable is always identified at the road level using 

orange marker poles. The poles have information indicating that 

communication cable is buried below together with contact 

information in case of damage to the cable. Markers should be 

place about every 1000 feet, plus on either side of a road 

crossing, drive way crossing and bridge crossing. 

A variant of the direct bury cable construction method is direct 

bury of flexible conduit. If plans call for installation of 
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additional fiber cables (in the same route) within a few years, 

the burial of flexible tube conduit with the initial cable provides 

significant savings over re-opening a trench. “Level 3” (a 

communication carrier) used this construction method to provide 

additional resources for the future. When “Level 3” needs to 

install additional fiber cable in their route, the flexible tube 

conduit can be used to minimize construction costs. This method 

also reduces traffic congestion due to construction. 

CONDUIT CONSTRUCTION

Placing cable in conduit is the most expensive solution for 

constructing a fiber optic cable route. Starting from scratch 

requires a significant amount of planning, especially in urban 

areas where most conduit is used. All utilities in (or near) the 

proposed construction path must be located and marked. The path 

may have to be realigned to avoid some of the utilities, or a 

proposal developed to temporarily interrupt service and then 

repair the damaged utility lines. Environmental issues must be 

addressed. Where construction is proposed for existing streets 

or roads, repair and restoration costs must be considered. 

Maintenance and protection of vehicular and pedestrian traffic 

must be implemented. 

The conduit structure must be designed to meet bending radius 

requirements of the communication cable. The inside conduit 

diameter should be at least 25% larger than the outside diameter 

of the cable. This helps to prevent cable drag when pulling 

through the conduit. 

Cable installed in conduit should be rated for immersion in water. 

All in-ground conduit eventually contains some water. Cables 

designed for this purpose are constructed with a sealant that 

prevents water from penetrating the fiber (or copper) 

transmission media. 

If the conduit is buried at a depth of greater than three feet, it 

may be necessary to dig a trench that is wide enough to allow 

space for construction personnel. Trenching at a depth of more 

than six feet, will require “shoring” walls (see local construction 

codes for specific requirements) to prevent collapse and injury to 

construction personnel. 

Most conduit used for telecommunications cable projects is high 

density polyethylene (HDPE). The ASTM has developed a 
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220

recommended standard, ASTM F2160, "Standard Specification for 

Solid Wall High Density Polyethylene (HDPE) Conduit Based on 

Controlled Outside Diameter (OD)". This standard was developed 

to assure that conduit from different manufacturers could be 

used with assurance that the inside and outside diameters of 

conduit pipe and the thickness of the conduit wall would match. 

Some DOT’s may require the use of steel conduit for bridge 

crossings or other types of construction. Using appropriate 

couplings, steel and HDPE can be mixed. HDPE is lighter in weight 

and easier to handle than steel, however, under certain loading 

circumstances it may not be as rigid. 

Wireless Systems Construction 

Wireless media are used to support communication links between 

devices and the TCC. This is often viewed as a low cost 

alternative to the installation of 

communication cable. Many 

departments are using spread 

spectrum radio in the 900 MHz 

and 2.4 GHz range. 

This section will focus on 

mounting of radio antennas and 

transmission line for “line-ofsight” (also called microwave) 

radio systems. These are the 

systems commonly used for 

traffic control and freeway 

management. 

Spread Spectrum Radio, DSRC, 

and the emerging 802.16 

Wi-Max, or WLAN systems 

all require line-of-sight 

design. The design and 

construction of towers and 

poles is completed within 

standard civil engineering 

practices and local codes. This also holds true for building 

mounted antenna supporting structures. 

“Line-of-sight” is a term used in radio system 

design to describe a condition in which radio 

device antennas can actually see each other. High 

frequency radios, such as those used in Spread 

Spectrum Radio require line-of-sight between 

antennas.

Figure 8-6: Installation of Wireless System -

Photograph Courtesy GDI Systems, LLC
Telecommunications Handbook for Transportation Professionals 

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PLANNING FOR WIRELESS SYSTEMS

System planning is critical to the successful installation, 

operation and proper performance of any communication system, 

wireless systems are no exception, and this is especially true for 

line-of-sight (microwave) wireless. Unless your proposed 

microwave link will be operating over a very long path, you should 

be able to confirm whether a visible line-of-sight path exists 

between the two proposed antenna sites. This is only a first-step 

process, and is often accomplished by using a combination of 

strobe lights, mirrors (which reflect the sun), binoculars and 

spotting scopes. Being able to see one site from the other will 

not guarantee that the visible path is appropriate for a 

microwave signal, but at least you who know that the possibility 

of such a path exists. 

In many instances there may be obstacles to overcome such as 

buildings, trees, small hills and elevated roads, and it may not be 

possible to confirm that line-of-sight exists without additional 

aid. Keep in mind that even a "perfectly clear” visual path may not 

actually be so. As an example, small branches of deciduous trees, 

barren in the winter, may not be visible until spring or summer 

when growth appears. Even the skeleton of a new building may not 

be visible until the sides go up! Establishing line-of-sight for 

traffic signal systems should be easy to accomplish because of 

the short distances involved (a few blocks). 

When establishing line-of-sight, it is extremely important to plan 

for the future. In urban areas, new building construction may 

result in total path obstruction. In areas where construction is 

not anticipated, the rapid growth of trees or foliage may severely 

affect the path over time. While a number of software products 

are available for assisting with path work, combining a 

topographical mapping of the path with a subsequent path walk or 

drive is often an excellent way to start the line-of-sight 

confirmation process. 

Assuming an appropriate line-of-sight path from radio site to 

radio site can be established, both the feasibility and viability of 

a point-to-point microwave radio link will be dependent upon the 

gains, losses and receiver sensitivity corresponding with the 

system. Gains are associated with the transmitter power output 

of the radio, and the gains of both the transmitting and receiving 

antennas. Losses are associated with the cabling between the 
Telecommunications Handbook for Transportation Professionals 

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radios and their respective antennas, and with the path between 

the antennas. Other losses can also occur if the path is partially 

obstructed, or if path reflections cancel a portion of the normal 

receive signal. Manufacturers will state respective RF power 

output and gain for each of their products. 

Radio transmitters are described in terms of power output 

expressed in watts. The power output may also be expressed in 

terms of decibels of gain (dB). Radio receivers are rated in terms 

of sensitivity (ability to receive a minimal signal). The rating is 

listed in terms of milliwatts (mW), or decibels of gain (dB). 

Antenna cable is rated in terms of signal loss per foot and 

expressed as dB of loss per foot. The antenna is rated in terms 

of gain (dB). There are a number of software programs that will 

calculate path loss by frequency and use the specifications of the 

system hardware to help determine the overall system feasibility. 

One of the first items to consider for any microwave path is the 

actual distance from antenna to antenna. The further a microwave 

signal must travel, the greater the signal loss. This form of 

attenuation is termed free space loss (FSL). Assuming an 

unobstructed path, only two variables need to be considered in 

FSL calculations: 

• The frequency of the microwave signal – numerically higher 

frequencies require more power to cover a given distance. 

• The actual path distance – the greater the distance the 

greater the signal loss. 

A signal transmitted at a frequency of 6 GHz will have more 

available power than a signal transmitted at 11 GHz. For example, 

a microwave system at 6 GHz can expect to cover about 25 miles 

between communication points. The same system using a frequency 

of 11 GHz will only cover about 10 miles. 

When RF energy is transmitted from a parabolic antenna, the 

energy spreads outward, much like the beam from a flashlight. 

This microwave beam can be influenced by the terrain between 

the antennas, as well as by objects in or along the path. When the 

centerline of a beam from one antenna to another antenna just 

grazes an obstacle along the path, some level of signal loss will 

occur due to diffraction. The amount of signal loss can vary 

dramatically, influenced by the physical characteristics and the 

distance of the object from the antenna. 
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223

A microwave beam can also be reflected by water or relatively 

smooth terrain, very much in the same way a light beam can be 

reflected from a mirror. Again, since the wavelength of a 

microwave beam is much longer than that of a visible light beam, 

the criteria for defining "smooth terrain" is quite different 

between the two. While a light beam may not reflect well off of 

an asphalt road, a dirt field, a billboard, or the side of a 

building, to a microwave beam these can all be highly reflective 

surfaces. Even gently rolling country can prove to be a good 

reflector. 

A microwave beam arriving at an antenna could effectively be 

canceled by its own "mid-path" reflection, causing tremendous 

signal loss. Long microwave paths can also be affected by 

atmospheric refraction, the result of variations in the dielectric 

constant of the atmosphere. 

For relatively short 2.4GHz microwave paths, only reflection 

points and obstructions are usually of real concern. The effects 

of atmosphere and earth curvature will not usually come into play, 

so the engineering of these paths is quite straightforward. For 

long or unusual paths, however, all aspects of path engineering 

must be considered. 

Interference Issues - Spread spectrum microwave radio systems 

are among the most interference tolerant communication 

networks in use today. Spread spectrum signals are very difficult 

to detect and, by their nature, are highly resistant to jamming 

and interference. As more and more signals are transmitted, the 

"noise level" in the band increases accordingly. Once the noise 

reaches an identified level, communication in the band is 

effectively negated. 

In the U.S., the 2.4GHz band is license free, making it very 

difficult to know whether or not another spread spectrum radio 

is operating in a manner which could possibly interfere with one's 

own link. While these links are usually able to spread narrow band 

interference, other spread spectrum signals in the 2.4 GHz band 

could possibly interfere if they are of the proper frequency and 

amplitude. It is extremely difficult to predict the effect of an 

interfering signal unless specific information is known about the 

interferer. In general, other spread spectrum signals in the 2.4 

GHz band tend to raise the band's noise floor. For this reason, 

even when working with paths which are very short and not 
Telecommunications Handbook for Transportation Professionals 

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224

subject to any sort of fading condition, a fade margin of 15 dB or 

greater should always be maintained for the path. 

A WORD ABOUT ANTENNAS

All RF systems have an antenna (or several in an array). The 

transponder used in a vehicle for toll collection has an antenna. 

The fact that it can’t be seen doesn’t mean that it isn’t present. 

The antenna is built in-to the package. 

A cost comparison of all the elements 

that make up a radio system would show 

the antenna as the lowest cost piece. 

However, most of the problems that a 

radio system may have can be traced to 

either improper installation, or 

improper selection, of the antenna. 

Follow the recommendations listed 

below for proper installation. 

All antennas have similar 

characteristics. They are designed with 

vertical and horizontal polarity. The 

manipulation of these characteristics 

creates a specific antenna coverage 

pattern. Some antennas are designed to 

provide a circular pattern referred to as omni-directional. 

Others have an elliptical pattern referred to as uni-directional. 

Antenna manufacturers will routinely provide the horizontal plane 

pattern as part of their product literature. An engineer can 

request a copy of the vertical pattern if necessary. The antenna 

pattern display is for an Antenna Specialists, Inc., 2.4 GHz 

Spread Spectrum radio system. The antenna projects two highly 

directional lobes. When setting up a radio system, it is critical 

that the installers match the pattern lobes to the system design. 

If the direction of the lobes is off by just a few degrees, that 

may cause the system to have a marginal performance. 

GUIDELINES FOR HANDLING & INSTALLATION OF WIRELESS ANTENNA AND 

TRANSMISSION CABLE

RF Transmission cable should be treated with the same care as 

fiber optic communication cable. This is important. To prevent 

interference with other radio systems on the tower the 

transmission cable is constructed with an internal shield of 

Figure 8-7: Example of Antenna 

Coverage Pattern - Antenna 

Specialists Products
Telecommunications Handbook for Transportation Professionals 

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225

copper or copper foil. If this shield is broken, your system could 

cause interference with other systems at the site. Also, once the 

shield is cracked, your system is subject to interference. Some 

radio transmission cable uses a hollow copper tube to act as a 

“wave guide”. If the hollow tube becomes damaged your system 

might not function properly. The following guidelines apply: 

• All cable should be inspected and tested when received. 

• All test results should be compared with factory preshipping tests. 

• Inspect the cable nomenclature to make certain that you 

received the correct product. 

• Notify the supplier (or manufacturer) of all discrepancies as 

quickly as possible. 

• Follow the manufacturer recommendations for installation 

• Cover all exposed cable ends to make certain that moisture 

does not penetrate the cable assembly. 

Mounting cable on a pole or tower structure requires the use of 

qualified personnel, test equipment, and care to prevent damage 

to the transmission line: 

• Use a hoist line that supports the total weight of the cable 

–refer to manufacturer specifications 

• Use pulleys at both the top and bottom of the pole (or 

tower) to guide the hoist line. 

• Support the cable reel on an axle so that the cable can be 

freely pulled from the reel. Have a crew member control the 

rotation of the reel. 

• Short lengths of cable coiled and tied. Uncoil the cable on 

the ground away from the pole before hoisting. 

• After raising the cable to the top of the pole, anchor it to 

the support structure from the top down. 

• Never anchor the cable to an electrical (or lighting) conduit. 

• The top and bottom of the cable attached to the pole should 

be electrically grounded to the pole with a grounding kit. 

• The antenna input connection cannot be used as the cable 

ground at the top of the pole. 
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226

• Test all connectors to make certain that they do not “leak” 

RF power. 

Conclusion 

The information provided in this chapter should be reviewed by 

project managers responsible for the design and implementation 

of communication networks outside plant. Construction of 

communication infrastructure is expensive - don’t add to the cost 

by permitting contractors to take short-cuts. Require that 

manufacturer installation guidelines be followed. 

There are times when guidelines must be modified. Make certain 

that you understand potential problems and require that 

contractors provide a written explanation for the record. 

RESOURCES: 

The Rural Utilities Service (RUS) is a division of the United 

States Department of Agriculture. RUS provides assistance to 

Rural Telephone Companies via the publication of construction and 

equipment standards. These publications are based on existing 

telecommunications industry practices and are available to the 

general public via the internet. There is a list of accepted 

products for purposes of obtaining RUS loans and grants. This 

does not infer that other products won’t meet the requirements 

of a specific project. 

http://www.usda.gov/rus/telecom/publications/pdf_files/1755.pdf

http://www.usda.gov/rus/telecom/publications/bulletins.htm
Chapter 9 

The term “World-Wide-Web” is a 

verbal description of the image 

presented by the interconnecting 

communication links between the 

network nodes – it appears to 

emulate a spider web. 

9. CHAPTER NINE – THE INTERNET

Introduction 

The internet is a major communication tool used by commercial 

enterprise, and government agencies to support trade, operations, 

and interaction with customers and suppliers. Many individuals 

use the internet every day, at work and at home. Throughout the 

world, the internet is used as a primary source of communication 

and information services. In fact, the International 

Telecommunications Union (ITU) estimates that, as of 2002, more 

than 650 million individuals, worldwide, use the internet. A Harris 

Poll Survey, in January 2004, revealed that 146 million adults in 

the United States use the Internet, and 37% have access to 

broadband connections. In this chapter, you will learn about the 

Internet's structure, how it works, and its history. The chapter 

will also look at how transportation agencies use the internet to 

provide information and facilitate interaction with other 

government agencies. Consistent with the other chapters in this 

Handbook, the information presented is basic and designed to 

provide an elementary understanding of the internet and 

communication requirements. 

WHAT IS THE INTERNET? 

The Internet is an international network of computers connected 

by wires such as telephone lines. Schools, businesses, government 

offices, and many homes use the Internet to communicate with 

one another. You probably have access to the Internet via a 

computer at work, and may have access from your home computer. 

Many have access via their cell phone, and soon, you may have 

access via an embeded device in your automobile. 

Gaining access is simple. A 

computer, modem, telephone line, 

an account with an Internet 

Service Provider (ISP), and web 

browser software, is all that’s 

necessary. Most individuals and 

businesses pay for internet 

access, but there are also a 

number of providers that will permit access without fees. 
Telecommunications Handbook for Transportation Professionals 

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228

The most popular component of the Internet is electronic mail (email). The use of e-mail has changed the way in which individuals, 

corporations and government agencies communicate. E-mail allows 

for the almost instant delivery of information, and has caused a 

reduction in the use of voice communication via the telephone. In 

general, the use of e-mail is becoming a universal tool fo r 

communication. 

Organizations and individuals are able to create web sites to post 

information about their products, services, and themselves. 

Departments of transportation post information about roadway 

maintenance, traffic congestion, and other traveler information 

on their websites. 

HISTORY OF THE INTERNET

The Internet evolved 

from a network 

developed originally to 

support scientific 

research to the “World 

Wide Web” (WWW) over 

a period of 40 years. In 

the early 1960’s, the 

United States 

Department of Defense 

(DOD) created the 

Advanced Research 

Projects Agency (ARPA). 

One of its first projects 

was to create a system 

to link research centers 

and Universities for 

purposes of sharing 

information. 

13Today, it is a worldwide 

operation consisting of 

millions of computers and 

computer networks. A 

public, voluntary, and 

cooperative effort 

 

13 Drawing found on internet – source CERN 

Figure 9-1: Actual Sketch of the Original Internet 
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between the connected institutions and not owned or operated by 

any single organization. The underlying infrastructure is, 

however, owned and operated by a number of telecommunication 

companies. 

The Internet and Transmission Control Protocols were initially 

developed in 1973 by American computer scientist Vinton Cerf as 

part of a project sponsored by the United States Department of 

Defense Advanced Research Projects Agency (DARPA) and 

directed by American engineer Robert Kahn. 

Internet technology was a primitive precursor of the Information 

Superhighway, with the goal of computer communications to 

provide schools, libraries, businesses, and homes universal access 

to quality information that will educate, inform, and entertain. 

The original demonstration project was small and consisted of 

four nodes. Each node provided a combination of processing and 

network connectivity capability. The current system has a 

combination of generalized nodes and specialized nodes providing 

different types of support for the world-wide-web. 

The Internet and the World-Wide-Web 

The average individual did not become aware of the internet until 

the mid-1990s. It was basically the province of scientists and 

university researchers and a few computer “geeks” able to 

understand how computer networks and software functioned to 

Figure 9-2: Map - Location of Major MCI Internet Nodes in United States
Telecommunications Handbook for Transportation Professionals 

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allow this type of communication. Not until the introduction of 

graphical user interfaces (GUI) and the innovations of companies 

(CompuServe, America-On-Line and others long forgotten) wanting 

to popularize and commercialize the process did the internet 

evolve into the “world-wide-web” (WWW). America-on-Line (AOL) 

introduced a user friendly graphical interface, in 1994, which 

made it easy for a person with limited computer skills to access 

(or browse) and use the internet. Other companies soon followed 

the example with their own proprietary web interfaces. These 

interfaces are commonly referred to as “Web Browsers”. 

Originally, a user had to enter a specific destination code (more 

later). The new GUI interface systems provided the less 

experienced internet user with a way to simply “browse” web 

pages as if they were reading a magazine. 

The World Wide Web, is a network that links computers together 

via a world wide communication network. The communication 

network is composed of a hierarchy of nodes, linked via an 

infrastructure of fiber optic, copper, and wireless communication 

facilities. This is sometimes referred to as the “Infostructure”. 

The nodes are owned and operated by companies that are in 

business to provide a service to other companies that provide 

internet access to businesses and individuals. A subsidiary of 

MCI operates major internet switching nodes in the United 

States. 

This map (figure 9-3) shows the location of the primary internet 

switching points in the United States. These nodes are owned and 

operated by a subsidiary of MCI.

These nodes are interconnected to efficiently manage internet 

traffic and prevent “bottle-necks”. They are connected via a 

series of survivable fiber optic (chapter 2) communication rings. 

Nodes in the United States are connected to other nodes in 

Europe and Asia to support a world wide web of internet systems. 

Internet nodes can be very large and be spread over several 

buildings, or very small occupying only enough space to house 

several small computers. The MCI MAE-East facility is located on 

Long Island, but is supported by a number of alternate nodes 

spread throughout the New York City metro area. Major internet 

service providers, such as AOL, AT&T WorldNet, MSN, and Yahoo 

have major access points located in close proximity (same 

building, or within a few blocks) of the MCI facilities. This allows 
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these major ISPs to provide a large number of users efficient 

access to the internet. Major ISPs have multiple high bandwidth 

links (OC-192 or 10 GB) to the MCI nodes. This is also true for 

the major telecommunication carriers such as Sprint, Verizon, 

SBC QWEST, AT&T, etc. These companies are considered as Tier 

One carriers. All other providers access the internet via one of 

the Tier One carriers. 

Departments of transportation using the internet will contract 

with a service provider (Internet Service Provider) for access. 

The ISP will arrange for all necessary communication connections, 

access servers, webmaster support, and help desk to trouble 

shoot problems. Later in this chapter internet connection and 

setup options will be discussed. All ISPs provide similar services: 

• Communication connectivity to Carriers. 

• Routers to direct internet traffic 

• Switches to create virtual communication paths 

• Computers to support internet traffic. 

• An electrically protected environment for computing and 

communication equipment. 

• Shared floor space for companies to place equipment for 

internet access. 

• Modem banks for dial-up access 
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The following diagram (figure 9-3) shows a typical set of 

connections for ISP and large corporate users to access the 

internet. Notice that the large corporate user has installed a 

redundant communication link to the internet. Internet Service 

Providers may also install redundant links, or they may have a 

distributed network that provides redundancy without the need 

for duplicate communication links. The drawing shows SONET 

hubs and SONET broadband communication links. Once standards 

are fully implemented, this architecture will most likely change to 

Gigabit Ethernet hubs (or switches) with 10 GigE/GigE 

communication links. 

The use of redundant links serves two purposes. First, the need 

to maintain a connection for services. Second, redundant links can 

also be used to support temporary requirements for increased 

capacity. Traveler information systems (ATIS) may become 

overloaded during a major incident. The primary communication 

link may not be able to provide adequate throughput, and the 

redundant link is used to temporarily share the load. Most 

broadband communication links provide service for both voice and 

data and TMCs have both center-to-center and center-to-public 

SONET

Hub

SONET

Hub

OC-48

OC-3

Router

DS-3

DS-3

Mux

Office LAN

Office LAN

Typical Internet Connections

Router

Bay

Router

Bay

ISP

System

Router

Bay

Sm all

ISP

System

OC-3

Fortune

100

Company

MCI

Internet System

Customers can use

either PSTN for

access, or leased

DS-1.

PSTN Access Only

Figure 9-3: Diagram General Internet Architecture
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requirements. Later sections in this chapter provide more 

information about how Transportation Management Centers can 

use the internet or internet like services to fulfill “mission 

critical” requirements. 

How Does the Internet Work? 

Two primary elements make the internet work. First, the internet 

is built as an overlay to the world wide telecommunications 

infrastructure. Portions of the network were specially built to 

meet the needs of the internet. However, most of the 

communication network is based on the use of the common 

infrastructure. Second, there is a common set of communication 

protocols and an agreed set of standards for the software 

language used by web browsers. This commonality permits a 

person in Japan to view web pages created in France. 

The Internet – or the World-Wide-Web - is formed by connecting 

local networks through special computers in each network known 

as gateways. Interconnections are made through various 

communication paths, including telephone lines, optical fibers, and 

radio links. The connections between the main gateways are 

permanent; however, the connections for individual users (at 

home, or the office) are setup as needed. Additional networks can 

be added by linking to new gateways. Information to be delivered 

to a remote machine is tagged with the computerized address of 

that particular machine. The following diagram (figure 9-4) is a 

schematic of how an individual in a small corporate office might 

obtain traffic congestion information via the internet. Notice 

that only the ISP is directly connected to the internet system. 

All other users are routed to the internet via the PSTN or leased 

lines from an intermediate communication carrier. 
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The DOT must enter into agreements with both the ISP and a 

carrier to be able to provide traveler information services via 

the internet. An alternative solution is available. The ISP 

provides all of the services and systems as part of a package. 

However, the DOT can provide its own services. This would 

require developing a network of internet servers and routers. The 

DOT would have to duplicate the systems and services that it 

obtains from an ISP. The decision to do this is based on economic 

and organizational requirements. 

In the example above, the connections are all permanent by virtue 

of the high speed leased lines. However, if users at home wanted 

to access the DOT Traveler Information web pages, their 

connection would be temporary. The network would be created on 

an “ad hoc” basis. As soon as the home user logged –off, the 

connections would go away. 

SONET

Hub

Office LAN

Typical Connection to a DOT

Traveler Information Service

via the Internet

Router

Bay

Router

Bay

ISP

Internet Access

Gateway

Small

Corporate

System

Router

Workstation

Communication

Server

DS-1

Leased

Router

Bay

Router

Bay

ISP

Internet Access

Gateway

Internet

Data Communication

Network

Office LAN

DOT

Traveler

Information

System

Router

Traveler

Information

Server

Communication

Server OC-48

OC-48

DS-3

Leased

SONET

Hub

Figure 9-4: Diagram - Traveler Information Provided via the Internet
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ADDRESSING – FORMATS

Various addressing formats are used by the different services 

provided by internets. Addressing is similar to a telephone 

number- it lets the system know which web site you want to visit. 

One format is known as dotted decimal, for example: 

123.45.67.89. Another format describes the name of the 

destination computer and other routing information, such as 

"machine.dept.univ.edu." The suffix at the end of the internet 

address designates the type of organization that owns the 

particular computer network, for example, educational 

institutions (.edu), military locations (.mil), government offices 

(.gov), and non-profit organizations (.org). Networks outside the 

United States use suffixes that indicate the country, for 

example (.ca) for Canada. A (.us) suffix is now available for the 

United States. 

Once addressed, the information leaves its home network through 

a gateway. It is routed from gateway to gateway until it reaches 

the local network containing the destination machine. Internets 

have no central control, that is, no single computer directs the 

flow of information. This routing is referred to as the Internet 

Protocol (IP). This protocol specifies how gateway machines route 

information from the sending computer to the recipient computer. 

Another protocol, Transmission Control Protocol (TCP), checks 

whether the information has arrived at the destination computer 

and, if not, causes the information to be resent. The overall 

protocol is referred to as TCP/IP – Transmission Control 

Protocol/Internet Protocol. 

To support a diverse set of users across the Internet, it is 

important to use a technology that is independent of a computing 

platform so that any network device can access the web service. 

Such a technology should be compact using little bandwidth and 

very portable so it can be used on many devices. There are 

several very powerful languages and protocols that are used 

between disparate systems located on the Internet, such as: 

• Extensible Markup Language (XML) 

• Simple Object Access Protocol (SOAP) 

• Java 
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Extensible Markup Language 

XML was created during the mid to late 90s as a way to take raw 

data such as text, graphics, or binary transmissions from nearly 

any source and apply an organizational structure that is both 

contextual and visual. XML can be used to deliver structured 

content including text, vector graphics, and electronic 

transactions across a network like the Internet. 

Simple Object Access Protocol 

SOAP follows the typical client/server model and is designed to 

use standard technologies like XML to transmit small amounts of 

information across a network using a standardized language and 

format. SOAP does not use any specific transport protocol and 

does not use any programming model. It is a language that can be 

used to send commands and information as well as a standardized 

method of organizing and encoding information. Because SOAP is 

independent of transport protocol and programming model, it is 

well suited for communication between systems that would not 

otherwise be able to communicate. Therefore, a SOAP-aware 

application is able to create, send, receive, and interpret the 

commands between disparate systems and act upon them as 

intended. 

Java 

A programming language that is designed to be platformindependent and portable. In other words, Java is not based on a 

specific computing platform; it is based on its own workspace, 

which can exist in any computing environment. Java applications 

can operate exactly the same on any computer regardless of the 

operating system or hardware configuration used. Java creates a 

self-contained computing environment that can run within other 

operating systems and interact with an operating system to 

perform tasks. Java consists of three major components: 

• Java programming language 

• Java application libraries 

• Java virtual machine 
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Each of these technologies is used in some capacity to deliver 

web services. However, the World Wide Web Consortium (W3C) is 

beginning to standardize which protocol should be used when 

delivering web services. In a working draft created in May 2003 

called Web Services Architecture, the W3C outlines the core 

technologies behind a web service and gives some guidelines on 

how the service should be developed, designed, and deployed. The 

W3C seems to have agreed upon XML as the basis for a 

standardized web service, but only time will tell which language 

will be chosen. More than likely there will still be a variety of 

languages used to create web services, even after a standard has 

been established. 

For more information see: Web Services Architecture - 

( http://www.w3.org/TR/ws-arch/ ) - W3C Working Draft May 14, 

2003. 

Computer interaction has dramatically changed our world, 

bridging the barriers of time and distance, allowing people to 

share information and work together. Evolution of the 

Information Superhighway is continuing at an accelerating rate. 

The available content has grown at a rapid pace, and will continue 

growing rapidly, making it easier to find any information on the 

Internet. All Government Agencies, Universities, and virtually all 

commercial enterprises use the internet as a primary means of 

providing information to the public. New applications provide 

secure business transactions and new opportunities for commerce. 

New technologies continue to increase the speed of information 

transfer. Internet users are now able to download feature length 

movies and Broadway Shows. 

TYPES OF INTERNET NETWORKS

There are several different configurations of internets. Most 

common is the Internet used by millions every day. The system is 

open to anyone with a modem, telephone line, and a web browser. 

Companies, government agencies, schools and other organizations 

have discovered that the simple common internet protocols can be 

used to create a very powerful internal communication network. 

Setting up an internal internet provides organizations with the 

ability to communicate using the same software and systems used 

for external communications. 
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Intra-Net 

These networks are called “Intra-Net”. They are only accessible 

by individuals directly connected via a local area network. Most 

users are familiar with the PSTN version that allows access via a 

standard telephone line connection using a modem. Access can 

also be gained via cable TV system links, broadband DSL links, 

and direct connections via DS-1 or DS-3 links. Intra-Nets are 

private networks contained within an enterprise. It may consist 

of many interlinked local area networks and also use leased lines 

in the Wide Area Network. Typically, an intranet includes 

connections through one or more gateway computers to the 

outside Internet. The main purpose of an intranet is to share 

company information and computing resources among employees. 

An intranet can also be used to facilitate working in groups and 

for teleconferences. An intranet uses TCP/IP, HTTP, and other 

Internet protocols and in general looks like a private version of 

the Internet. With tunneling, companies can send private 

messages through the public network, using the public network 

with special encryption/decryption and other security safeguards 

to connect one part of their intranet to another. Typically, larger 

enterprises allow users within their intranet to access the public 

Internet through firewall servers that have the ability to screen 

messages in both directions so that company security is 

maintained. 

Extra-Net 

An extranet is created when part of an intranet is made 

accessible to customers, partners, suppliers, or others outside 

the organization. A DOT could create an extranet to share 

information with incident responders. Local police departments 

could be provided with images from CCTV cameras to support 

coordinated management of a specific incident. 

An Extra-Net is a private network that uses the Internet 

protocol and the public telecommunication system to securely 

share part of a business's information or operations with 

suppliers, vendors, partners, customers, or other businesses. An 

extranet can be viewed as part of a company's intranet that is 

extended to users outside the company. It has also been 

described as a "state of mind" in which the Internet is perceived 
Telecommunications Handbook for Transportation Professionals 

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as a way to do business with other companies as well as to sell 

products to customers. 

An extranet requires security and privacy. They require firewall 

server management, the issuance and use of digital certificates 

or similar means of user authentication, encryption of messages, 

and the use of virtual private networks (VPN) that tunnel through 

the public network. Companies can use an extranet to: 

• Exchange large volumes of data using Electronic Data 

Interchange (EDI) 

• Share product catalogs exclusively with wholesalers or those 

"in the trade" 

• Collaborate with other companies on joint development 

efforts 

• Jointly develop and use training programs with other 

companies 

• Provide or access services provided by one company to a 

group of other companies, such as an online banking 

application managed by one company on behalf of affiliated 

banks 

• Share news of common interest exclusively with partner 

companies 

Role of the Internet for Traffic, ITS, Freeway Management & Traveler 

Information 

If the Internet was viewed from the perspective of the National 

Architecture, it would be shown as a communication element. The 

architecture model might be modified showing the Internet as an 

underlying element of wide area wireless and wire line 

communications systems. 
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Departments of transportation have looked to the internet as a 

way to communicate with the traveling public. The Web is 

primarily used to provide information about current travel 

conditions, including: 

• Locations of congestion 

• Video views of highway sections 

• Video views of intersections 

• Highway segment travel times 

• Construction locations and possible travel times 

• Special events 

The internet

Vehicles

Travelers

Remote

Traveler

Support

Personal

Information

Access

Centers

Traffic

Management

Fleet and

Freight

Management

Transit

Management

Emissions

Management

Information

Service

Provider

Emergency

Management

Toll

Administration

Commercial

Vehicle

Administration

Archived Data

Management

Maintenance &

Construction

Management

Maintenance &

Construction

Vehicle

Transit Vehicle

Commercial

Vehicle

Emergency

Vehicle

Vehicle

Roadside

Commercial

Vehicle Check

Parking

Management

Toll Collection

Roadway

Wide Area Wireless (Mobile) Communications Wireleine (Fixed Point to Fixed Point) Communications Vehicle to Vehicle Communications Dedicated Short Range Communications

Figure 9-5: National ITS Architecture Sausage Diagram with Internet added
Telecommunications Handbook for Transportation Professionals 

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• Weather conditions affecting travel 

• Link to other transportation agencies 

• Link to Department of Motor Vehicle services 

Examples of current internet sites 

• Virginia Department of Transportation: 

http://virginiadot.org/default_myvdot.asp

• Kansas Department of Transportation: 

http://www.ksdot.org/public/kdot/

• California Department of Transportation: 

http://www.dot.ca.gov/

The above are a few examples of DOT web sites. More can be 

found at the following resource web site: 

http://www.betterroads.com/linkspages/linksdot.htm . Better Roads is a 

publication of James Informational Media, Inc. 

Many DOT sites provide a significant amount of traveler 

information in a traditional WWW access mode. Some sites 

provide access to driver license and automobile registration via 

secure links. Others even provide access for trucking firms to 

file for travel permits. This is all accomplished through the use 

of secure web pages that allow users to complete a financial 

transaction on-line. Many of these sites require the user to 

complete an application for secure access to the financial 

transaction web pages. However, the telecommunication portion of 

the system has no impact on the overall transaction. It is in fact, 

transparent, and simply provides the connection between service 

provider and customer. 

USE OF THE INTERNET FOR CENTER-TO-CENTER COMMUNICATIONS

The internet can be used as a telecommunication tool to allow 

transportation agencies to provide for a more efficient 

operation. In addition to providing access for the public to obtain 

services and receive information, it can be used to help support 

secure, efficient “Center-to-Center” communication links. Using a 

combination of internets, intranets, and extra-nets, agency-toagency links are easy to accomplish. 
Telecommunications Handbook for Transportation Professionals 

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To better understand the role of the internet and its various 

telecommunications applications, let’s look at the basic elements 

needed (table 9-1), and a schematic. The elements (from a 

telecommunication perspective) are as follows: 

Table 9-1: Internet Communication Elements 

Basic Elements 

Elements Explanation 

Web Based Applications The actual set of web pages and 

capabilities of the specific DOT system 

Application Servers 

One or more, computers used to run and 

store the applications, web pages, user 

information, required databases, etc. 

Communication Servers 

One or more computers used to manage 

access between the WWW and the 

application severs 

Routers 

Used to route information to and from the 

WWW, and between the application and 

communication servers 

LAN 

Local Area Network (the physical network) 

connecting routers application and 

communication servers 

Communication Network 

Access Hardware 

The actual equipment that connects the 

DOT Web system to the WWW 

Communication Facility 

This is the actual copper, fiber, or RF 

path used to get from the DOT computer 

site to the WWW 

The above table and schematic (figure 9-6) show how a typical 

DOT system may connect to the internet. However, there are 

several variations. 
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A virtual permanent connection -

“VPC” – is communication path that 

is permanently in place, but is not a 

fixed communication link such as a 

T-1. The communication path is 

always available and private, but 

does not always take the same 

route between two points; 

therefore, it is “virtual”. 

Some DOTs may have contracted their system to a company that 

provides all of the necessary application servers and 

communication pathways. In that case, the DOT would have 

remote access to the system to provide updates and additions. 

The contract with the private company would include all necessary 

services, including periodic maintenance and equipment updates. 

Overall design of an internet system is normally handled by a 

specialist using support from the Information Technology 

Department (IT), the ISP, and the carrier providing the leased 

communication facility. 

The Internet is a powerful tool and 

can be used as part of an 

operational program for 

distributing information between 

DOT facilities and allied traffic 

management agencies (Center-toCenter). An operational scenario 

that has traffic incident data 

shared by a state DOT district 

TMC, local streets TMC, local police, and disaster management 

agency can take advantage of the internet infrastructure. The 

Application Application 

Server

Application Application 

Server

Application Application 

Server

Application Application 

Server

Office LAN

Router

Communication 

Server

Communication 

Server

Router

ISP Gateway

DS-3 

Communication 

Hardware

DS-3

Communication

Circuit

DS-3

Communication

Circuit

DS-3 

Communication 

Hardware

Figure 9-6: Internet Elements Schematic
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internet can be used to provide a robust and economical 

communication network. The primary advantage being that 

connectivity is via an existing telecommunication system that is 

maintained and updated on a regular basis. Cost of the base 

system can be proportionately shared, with communications 

access links paid individually by each user agency. Effectively, 

the combined agencies create a wide-area intra-net. The network 

is closed to web surfers and the public via the use of fixed 

communication access circuits called “virtual permanent 

connections” (VPC). 

Special secure web pages are created providing authorized users 

access to the system using a standard web browser. All 

information is provided in the same general format to all users. A 

central database is created to allow for retention of information 

that can be used at a later date for statistical research. The 

Local Streets TMC

DOT TMC

Video

Streaming

Video 

Server

Traffic 

Volume 

Detectors

Application 

Server

VMS Application 

Server

Office LAN

Router Communication 

Server

ISP Gateway

DS-3 

Communication 

Hardware

DS-3

Communication

Circuit

Traffic 

Signals

Application 

Server

Office 

LAN

Router

Communication 

Server

DS-1 

Communication 

Hardware

DS-1

Communication

Circuit

Police 

Dept

Police 

Dispatcher

General 

Server

Office 

LAN

Router

56K DSU/

CSU

56K

Circuit

Figure 9-7: Schematic - Multiple Agency Center-to-Center Links via the Internet
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“Firewall” - is a term used 

to describe a software 

application designed to 

prevent unauthorized 

access to the initial entry 

point of a system. 

data contained on the web pages can have additional security 

layers with some users able to only view the information, and 

others being able to download the data. Figure 9-8 is a schematic 

of a system that can be used by several agencies to share 

information. 

Notice also, in figure 9-7, that each entity has a different 

communication link. The size and cost of the Intra-net link is 

determined by user requirements and is paid for by the using 

agency. In this schematic, the DOT and Local Streets are each 

providing applications to the shared system. The serving agency 

controls the release of information. 

Each agency can set varying levels of 

access and determine which 

information will be provided. The ISP 

charges a fee for operating and 

maintaining the internet gateway and 

the overall web site. Users share this 

cost and the cost of any mutual 

applications. Notice that there is no direct PSTN access to the 

system. 

Individual agencies can provide dial-up access via their own 

system for selected employees. A firewall is used to prevent User Interface Application

Database

Device B

(This could be 

another Central 

Control System or a 

field controller)

Communications 

Link

 (NTCIP Standards 

apply here)

User Interface

Application

Database

Communications Link

 (NTCIP Standards 

apply here)

Internet

Figure 9-8:ITS Center-to-Center Communication Diagram
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unauthorized access to the system. Only specific users are 

permitted access for limited applications. 

The NTCIP committee is in the process of developing Center-toCenter communications protocols. These protocols can be used in 

the above scenario. Figure 9-8 provides a relationship diagram of 

the NTCIP protocols. 

Conclusions 

The internet is a powerful tool used to disseminate information 

to many individuals. Since 1995, the internet has become a 

“ubiquitous” form of communications. Individuals, corporations 

and government entities use the internet extensively for sharing 

information, running operations, and transacting business. Some 

of the largest users are financial institutions. Following is a list 

of examples of how transportation agencies are using the 

internet: 

• Amtrak sells tickets and provides schedules 

• The Bay Area Rapid Transit Systems (BART) uses the 

internet to provide schedules, station locations, ticket 

sales, and other information. 

• Colorado DOT provides access to “oversize – overweight” 

permit applications. 

• Mississippi allows current residents with a valid driver’s 

license to pay for a renewal online. 

• The City of Houston, Texas provides access for payment of 

minor violation and parking ticket fines online. 

Most states and many municipalities provide extensive 

information about transportation services and general and 

specific traveler information via the internet. Commuters can log 

onto web sites throughout the country to get the latest traffic 

and mass transit condition information before leaving work for 

the trip home. Traffic and transit updates can be delivered via 

wireless services while a traveler is enroute. 

The internet and the WWW have become the defacto standard 

for communications services. Transportation agencies have 

embraced the use of the Internet and the World Wide Web as 

part of their overall operational program.
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10. CHAPTER TEN – THE FUTURE

Introduction 

Predicting the future is always a little dangerous, especially for 

technology intensive systems and services such as 

telecommunications. This handbook was written over a two year 

period that saw major developments in the way that 

telecommunication services are provided, and in their supporting 

technologies. The intent of this chapter is to provide a look at 

some of the telecommunications technologies that may have an 

impact on the development of Transportation Management 

Centers, Traffic Signal Systems, and Freeway Management 

Systems. The following information is provided based on 

technology developments at the time of publication of this 

document. 

CIRCUIT SWITCHED VS. PACKET SWITCHED

Prior to 2004, most industry analysts were indicating that the 

major telecommunication carriers would continue to invest most 

of their money in the maintenance and upgrade of existing circuit 

switched voice based networks- the general consensus being that 

the significant investment in those types of networks would 

continue through 2050. In January 2004, several major 

telecommunication carrier companies announced that they were 

shifting the investment of those dollars to implementation of 

packet switched internet telephony networks. They indicated that 

the shift would be aggressive, looking to make services based on 

those systems available network wide by 2010. 

The overall effect of these changes will make the transmission of 

digital data via these networks less expensive and require less 

hardware. Departments of Transportation will derive significant 

benefits from the changes. Traffic signal systems that 

traditionally used dedicated leased telephone lines will be able to 

use packet switched circuits. Instead of paying for a leased line 

on a 24/7 basis (even when the line is not in use) they will pay for 

the amount of data actually transmitted (the number of packets 

used). Hardware for these systems will be less complex, and lower 

in cost. DOTs will see a reduction in the overall complexity and 

cost of hardware required in the TMC together with a reduction 

of the cost to operate and maintain this equipment. 
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Between 1998 and 2004, the IEEE 802 committees developed a 

number of standards for the efficient transmission of data using 

both wireline (including fiber) and wireless. These new standards 

help to provide for the “seamless” transmission of data from one 

medium to another. All of these new standards will be easier to 

implement via the new packet switched networks. The new 

standards allow for relatively simple transition from wireline to 

wireless, and back, with minimal degradation of data quality and 

bandwidth. 

A major problem created by the transition from circuit switched 

to packet switched is the requirement to identify the origin and 

destination of the communication. Currently, telephone numbers 

are used. The caller simply enters the telephone number of the 

called and the system recognizes the hierarchal (a thirteen digit 

code) order to route the call. Each circuit can be identified via 

the: 

• Country Code (3 digits) 

• Area Code (3 digits) 

• Exchange Code (3 digits) 

• Circuit Code (4 digits) 

The pair of wires connected to each telephone instrument can 

ultimately be identified (and called) by a telephone number. 

The Cellular Telephone system simply replicated the circuit 

switch method by providing each wireless handset with a 

traditional telephone number. The system works for voice 

connectivity, but is problematic for broadband data networking. 

The emerging requirement for wireless handsets to be mobile 

computers (rather than mobile telephones) has created a need for 

a new switching and connection protocol. 

“Session Initiated Protocol” (SIP) is an emerging communication 

protocol that improves the ability of packet switched networks to 

identify origin and destination points within a network. SIP uses 

the universal resource locator (URL) protocol to provide 

connections. These are the same identifiers used to browse web 

pages. A URL is a type of address that describes the location of 

information on the World Wide Web, e.g., www.fhwa.dot.gov . With 

SIP, even phone numbers are converted to URLs. Reaching an 

individual can be as simple as entering his or her e-mail address. 

The similarity of SIP to HTTP not only makes it ideally suited for 
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the IP environment, but it's easy for HTTP experts to program it 

without learning a new language 

Trends for Transportation 

A number of new telecommunication technologies will begin to be 

used on a broad scale by Departments of Transportation and 

Tolled Facilities operations. Some of these are: 

• High speed Ethernet 

• Resilient Packet Ring (RPR) 

• Broadband Wireless 

• Radio Frequency Identification(RFID) 

HIGH SPEED ETHERNET

Ethernet is generally considered as a high speed 

telecommunication topology, but for purposes of this discussion 

one (1) gigabit (GigE) and ten (10) gigabit (10GigE) are considered 

as high speed. There are (as this handbook is being written) 

discussions of higher speeds (beyond 10 Gig) for Ethernet. 

Many devices used in Traffic Signal and Freeway Management 

systems are being manufactured with Ethernet communication 

ports. This will allow for direct connection of the devices without 

the need to use protocol converters (serial to Ethernet). 

GigE 

GigE will provide significant capabilities for transporting video 

and other data from field devices to the TMC. Most desktop 

computers and work stations started shipping with GigE capability 

embedded into the “motherboard” by the fourth quarter of 2003. 

Eventually, GigE will become the standard for LAN for desk-top 

to desk-top communication within the center. Two processes, 

voice and video over IP, will be greatly facilitated by the use of 

GigE. 

Chapters 2, 5, and 7 presented the concept of VIP (video over 

IP). CCTV cameras are designed with built-in video CODECS and 

Ethernet transmission ports. The use of these devices will 

simplify the deployment of visual observation systems for traffic 
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and transportation management. The following is a comparison of 

traditional CCTV systems and VIP systems: 

Table 10-1: Comparison Traditional CCTV vs. VIP Systems Requirements 

Traditional VIP 

CCTV Camera CCTV Camera with internal CODEC & 

VIP 

PTZ Unit PTZ Unit with built-in connection via 

the VIP module 

Video Encoder Router 

Fiber (or copper) Transmission 

System 

Fiber Transmission System 

Video Decoder 

Video Switch 

Analog Monitors 

PTZ Controller 

PTZ Communication System 

Software in operator Work Station 

Rack system to hold all of the 

hardware in the TMC 

Electricity to power the equipment 

in the TMC 

Added HVAC capability in the TMC 

No additional equipment, electricity 

or HVAC required in TMC 

Fewer pieces of hardware reduces the overall complexity of the 

system, and reduces the total cost of deployment and 

maintenance. This is one example of how new telecommunications 

standards and systems will help provide economies and 

efficiencies in the development of Freeway and Traffic 

Management systems. 

Voice-over-IP (VoIP) will provide an ability to reach individuals 

regardless of the type of communication system being used. 

Dispatchers at a desktop work station will be able to reach field 
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personnel by selecting an individual’s personal identification 

number in an application such as Microsoft Outlook. The 

dispatcher won’t have to worry about pushing buttons on a 

communication console, or which communication network to use. A 

software application will take care of the process. 

10GigE 

A primary objective of the 802.3ae working group was to develop 

a 10 Gbps communication protocol with a transmission link 

distance of up to 40km over single mode fiber 14. The 10 Gbps 

802.3 solution was developed to extend Ethernet capabilities 

providing higher bandwidth for multimedia, distributed 

processing, imaging, medical, CAD/CAM, by improving the 

performance of: 

• LAN Backbone and Server and Gateway Connectivity 

• Switch aggregation 

• the MAN, WAN, Regional Area Network (RAN), and Storage 

Area Network (SAN) 15

10GigE is (as of the publication of this handbook) only starting to 

be deployed. Its initial use is as a backbone transport system. 

There is no (current) plan to use this type of system for desktopto-desktop communication. 

Department of transportation could take advantage to 10GigE for 

Center-to-Center communications, and connecting major field 

communication hubs to a TMC. 

RESILIENT PACKET RING (RPR) 

Fiber optic networks are widely deployed throughout the world. 

They are normally deployed in a ring architecture. These rings 

are currently using protocols that are neither optimized nor 

scalable to the demands of packet networks. An RPR networks 

standard (IEEE 802.17) is being developed to provide for the 

optimization of bandwidth allocation and throughput, resiliency to 

faults. This will also result in reduced equipment and operational 

costs. 

 

14 http://grouper.ieee.org/groups/802/3/ae/objectives.pdf - IEEE 802.3ae committee, July 2001. 

15 http://grouper.ieee.org/groups/802/3/ae/criteria.pdf - IEEE 802.3 High Speed Study Group, 

Criteria 
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The current SONET standard was developed to provide for the 

efficient operation of fiber optic ring networks. However, its 

primary goal was to support circuit switched networks. Moving 

data in and out of a SONET network is very cumbersome, and 

requires significant investment in multiplexing equipment. 

Additionally, SONET is bandwidth inefficient. That’s because it 

is a traditional TDM protocol that provides fixed bandwidth for 

data circuits – even those that are unused. The biggest advantage 

of SONET is its ability to restore circuits within a ring 

architecture. Communication circuits are provided an alternate 

path within 50ms of an outage due to physical damage. 

RPR is being developed to support Packet Switched networks and 

utilize the 802.3 series of communication protocols. Bandwidth is 

provided when needed. RPR also provides for circuit restoration 

as efficiently as SONET. 

Engineering personnel responsible for the design and development 

of Traffic and Freeway management systems should learn more 

about RPR. There is a strong likelihood that RPR will play a 

significant role in communication networks of the future. You can 

learn more by visiting the following web sites: 

• The IEEE 802.17 Working Group - 

http://grouper.ieee.org/groups/802/17/ 

• The RPR Alliance - http://www.rpralliance.org/

BROADBAND WIRELESS

IEEE published the 802.16 standard in April, 2002. The standard 

was developed to provide for broadband internet access and to 

meet the demand for low cost (by comparison to trenching) 

deployment of services. The standard is designed to support 

spectrum in the 10 to 66 GHz range. A modified standard, 

802.16a has also been approved to support both licensed and unlicensed spectrum in the 2 to 11 GHz range. 

The new standards are actually referred to as the “air interface” 

for broadband services. They are designed to complement the 

802.3 wireline standards and provide for efficient media 

transitions in a mixed system. There is a need to be able to 

extend the reach of broadband internet access beyond the 

wireline infrastructure. DSL for example has a limited distance 

(typically 18,000 feet from a central office). Wireless systems 

are seen as the answer. An IP based wireline system can be 
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extended using a wireless broadband link without changing the 

communication protocol. The transition from one media to the 

next is seamless. 

Wireless communication links have been used by many 

Departments of Transportation to connect remote devices to a 

main system on a limited basis. The City of Irving Texas decided 

to upgrade its entire traffic signal communications 

infrastructure to an 802.16a standards based system. The City 

was originally looking at a fiber communications network that was 

estimated at more than $10 million. The broadband wireless 

system is being implemented (as this handbook is being written) 

for less than $750,000. 

Dedicated Short Range Communications Systems (DSRC) are part 

of the broadband wireless services. However, current system 

development is based on the 802.11a standard. There is a 

difference between the two standards. 802.11 was developed as a 

wireless local area network (LAN) and 802.16 was developed to 

support “fixed” broadband access. Both complement and work 

together within the overall series of 802 standards. 

DOTs will continue to look at wireless as part of an overall 

telecommunication strategy. Broadband wireless will play a key 

role in the development of future systems. 

More information can be found at the following web sites: 

• IEEE 802.16 Committee - 

http://grouper.ieee.org/groups/802/16/

• Worldwide Interoperability for Microwave Access - 

http://www.wimaxforum.org 

• Wireless Communication Association - http://wcai.com/

RADIO FREQUENCY IDENTIFICATION (RFID) 

RFID systems first appeared in the 1980s for tracking and access 

applications. RFID has been used to track containers moving from 

ships to dock storage to land transportation. Manufacturing has 

used RFID to track major parts (such as automobile axles) 

through a warehouse and onto an assembly line. RFID devices are 

used to open gates to a parking lot. The “tags” used by Toll 

Collection Authorities are a type of RFID. 
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Technology advancements over the past 20 years have seen the 

development of RFID into a universally accepted means of asset 

tracking and data collection. RFID Tags have been reduced in size 

from their original inception. Manufacturers are beginning to 

embed the tags in many items, and major retailers are starting to 

require the tags to help prevent theft. In the not too distant 

future, tags may replace bar-coding as the universal form of 

product identification. Theoretically, a shopping cart full of 

groceries could be scanned without having to remove the items 

from the cart. A shopper could pack items into bags in the cart. 

The cart would have an active reader that would display a running 

total. When finished, the shopper could charge the purchase to 

an account and leave the store without having to wait in a 

checkout lane. 

A major advantage of RFID devices is that they can be embedded 

within the structure of an item. The tag activates on receipt of a 

radio signal from a reader device. A drivers license could have an 

embedded tag for instant identification. 

RFID Tags could be placed in sections of roadway. Maintenance 

crews could be directed to locations that need repair or 

restoration. Their vehicle would have a tag reader that reports 

the completion of the repair. A police officer at the scene of an 

accident could scan in an identification tag in a damaged section 

of guardrail. The information would be directly reported to a 

DOT District maintenance office to schedule repairs. 

A number of organizations are working to develop standards for 

RFID. More information is available at the following locations: 

• RFID Standards – 

http://www.aimglobal.org/standards/rfidstds/RFIDStandard.htm

• RFID Journal - http://www.rfidjournal.com/

Conclusions 

Between 1876 and 1986 the most that could be said about 

telecommunication technology and process was that it is 

consistent. In the laboratory, change was dramatic, in the field, 

change was very slow. Since 1986, new technology and process has 

been introduced almost as rapidly as it was developed. 
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Carriers are being forced by the new technologies to change the 

way they do business. The traditional telephone companies are 

now forced to compete with cable companies and wireless 

companies. Time-Warner Cable company is effectively competeing 

with Verizon for traditional telephone services with the 

introduction of VoIP. Many individuals are now using wireless 

carriers for their primary voice telephone services. 

All of these changes will have a profound impact on how 

departments of transportation deploy and use technology for 

management of traffic signal and freeway management systems. 

The use of Gigabit Ethernet and broadband wireless technologies 

will provide significant implementation savings over current 

systems technologies. These same technologies will make it easier 

to provide for interoperability between transportation agencies, 

as well as public safety and other municipal and state agencies. 
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11. APPENDIX

IEEE 802 Standards & Working Groups 

Table 11-1: IEEE 802 Standards List 

IEEE 802 Standards & Working Groups 

Standard Status 

802.1 Internetworking Active 

802.1d Spanning Tree Protocol Active 

802.1s Multiple Spanning Trees Active 

802.1q VLAN Frame Tagging Active 

802.2 Logical Link Control Inactive 

802.3 Ethernet (CSMA/CD) Active 

802.3u Fast Ethernet Active 

802.3z Gigabit Ethernet Active 

802.3ae 10 Gigabit Ethernet Active 

802.4 Token Bus Inactive 

802.5 Token Ring Inactive 

802.6 Distributed Queue Dual Bus (MAN) Disbanded 

802.7 Broadband Technology Disbanded 

802.8 Fiber Optic Technology Disbanded 

802.9 Voice/Data Integration (IsoEnet) Inactive 

802.10 LAN Security Inactive 

802.11 Wireless Networking Active 

802.11a 54 Meg Wireless Network Active 

802.11b 11 Meg wireless Network Active 

802.11g 54/11 Meg wireless Network Active 

802.12 Demand Priority Access LAN (100BaseVG-AnyLan) Inactive 

802.14 Cable Modem Disbanded 

802.15 Wireless Personal Area Network Active 

802.16 Wireless Metropolitan Area Networks Active 

802.17 Resilient Packet Ring Active 

802.18 LAN/MAN Standards Committee Active 
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802.19 Coexistence TAG Active 

802.20 Mobile Broadband Wireless Access Active 

802.21 Interoperability WG Active 

Comparison Analog Voice & VoIP 

• Technology — analog to digital. VoIP erases the line between 

voice and data. VoIP converts analog information (the human 

voice) into data packets, the same digital containers used to 

shuttle email messages and download web pages. 

• Network — PSTN to IP. A traditional phone call stakes out a 

single path over the public switched telephone network 

(PSTN). VoIP uses Internet Protocol, the language of the 

Internet. It separates a conversation into packets, which 

flow over data networks — the Internet, company intranets, 

or proprietary IP networks managed by Carriers (such as: 

Verizon, SBC, Sprint, MCI, etc) or alternate service 

providers (such as: AOL, COMCAST, etc.). 

• Network connection — phone line to broadband. In a 

traditional voice system, desktop phones connect to the 

outside world via a telephone line, and data systems connect 

through a data/broadband network. With VoIP, phones plug 

into a broadband connection (through a modem or similar 

device) or the in-house company LAN. This convergence helps 

to drive down costs by combining the voice and data 

networks. 

• Phone numbers — place to device. In the pre-VoIP world, a 

phone number belongs to a location. With VoIP, the number 

goes with the device. 
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Calculating Fiber Optic Loss Budget 

CRITERIA & CALCULATION FACTORS

Design of a fiber optic system is a balancing act. As with any 

system, you need to set criteria for performance and then 

determine how to meet those criteria. It’s important to 

remember that we are talking about a system that is the sum of 

its parts. 

Calculation of a system’s capability to perform is based upon a 

long list of elements. Following is a list of basic items used to 

determine general transmission system performance: 

• Fiber Loss Factor - Fiber loss generally has the greatest 

impact on overall system performance. The fiber strand 

manufacturer provides a loss factor in terms of dB per 

kilometer. A total fiber loss calculation is made based on 

the distance x the loss factor. Distance in this case the 

total length of the fiber cable, not just the map distance. 

• Type of fiber - Most single mode fibers have a loss factor 

of between 0.25 (@ 1550nm) and 0.35 (@ 1310nm) dB/km. 

Multimode fibers have a loss factor of about 2.5 (@ 850nm) 

and 0.8 (@ 1300nm) dB/km. The type of fiber used is very 

important. Multimode fibers are used with L.E.D. 

transmitters which generally don’t have enough power to 

travel more than 1km. Single mode fibers are used with 

LASER transmitters that come in various power outputs for 

“long reach” or “short reach” criteria. 

• Transmitter – There are two basic type of transmitters used 

in a fiber optic systems. LASER which come in three 

varieties: high, medium, and low (long reach, medium reach 

and short reach). Overall system design will determine which 

type is used. L.E.D. transmitters are used with multimode 

fibers, however, there is a “high power” L.E.D. which can be 

used with Single mode fiber. Transmitters are rated in 

terms of light output at the connector, such as -5dB. A 

transmitter is typically referred to as an “emitter”. 

• Receiver Sensitivity – The ability of a fiber optic receiver 

to see a light source. A receiving device needs a certain 

minimum amount of received light to function within 
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specification. Receivers are rated in terms of required 

minimum level of received light such as -28dB. A receiver is 

also referred to as a “detector”. 

• Number and type of splices – There are two types of splices. 

Mechanical, which use a set of connectors on the ends of the 

fibers, and fusion, which is a physical direct mating of the 

fiber ends. Mechanical splice loss is generally calculated in a 

range of 0.7 to 1.5 dB per connector. Fusion splices are 

calculated at between 0.1 and 0.5 dB per splice. Because of 

their limited loss factor, fusion splices are preferred. 

• Margin – This is an important factor. A system can’t be 

designed based on simply reaching a receiver with the 

minimum amount of required light. The light power budget 

margin accounts for aging of the fiber, aging of the 

transmitter and receiver components, addition of devices 

along the cable path, incidental twisting and bending of the 

fiber cable, additional splices to repair cable breaks, etc. 

Most system designers will add a loss budget margin of 3 to 

10 dB 

CALCULATING A “LOSS BUDGET” 

Let’s take a look at typical scenario where a fiber optic 

transmission system would be used. 

Two operation centers are located about 8 miles apart based on 

map distance. Assume that the primary communication devices at 

each center is a wide area network capable router with fiber 

optic communication link modules, and that the centers are 

connected by a fiber optic cable. The actual measured distance 

based on walking the route , is a total measured length (including 

slack coils) of 9 miles. There are no additional devices installed 

along the cable path. Future planning provides for the inclusion of 

a freeway management system communication link within 5 years. 

Note: All distance measurements must be converted to 

kilometers. Fiber cable is normally shipped with a maximum reel 

length of 15,000 feet (or 4.5km). 9 miles is about 46,000 feet or 

14.5km. Assume that this system will have at least 4 mid-span 

fusion splices. 

Table 11-2: Fiber Loss Budget Calculation 
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Fiber Loss 14.5 km x .35dB -5.075 

Fusion splice Loss 4 x .2dB -.8 

Terminating 

Connectors 

2 x 1.0dB -2.0 

Margin -5.0 

Total Fiber Loss -12.875 

The manufacturer of the router offers three 

transmitter/receiver options for single mode fiber: 

Reach Transmit Power Receiver 

Sensitivity 

Short -3dBm -18dBm 

Intermediate 0dBm -18dBm 

Long +3dBm -28dBm 

To determine the correct power option add the transmit power to 

the fiber loss calculation. 

Reach Transmit Power Fiber Loss Loss Budget 

Short -3 -12.875 -15.875 

Intermediate 0 -12.875 -12.875 

Long +3 -12.875 -9.875 

Compare this to the receiver sensitivity specification 

Reach Receiver 

Sensitivity 

Loss Budget Difference 

Short -18 -15.875 +3.0 

Intermediate -18 -12.875 +6.0 

Long -28 -9.875 +19.0 
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Because a loss margin of 5.0dB was included in the fiber loss 

calculation, the short reach option will provide sufficient 

capability for this system. In fact, the total margin is 8.0db 

because the difference between the loss budget and receiver 

sensitivity is 3.0db. 
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Rural Telecommunications Requirements Testimony 

STEVE ALBERT – SENATE HEARING

United States Senate 

Committee on Environment and Public Works 

Subcommittee on Transportation, Infrastructure and Nuclear Safety 

Hearing on Intelligent Transportation Systems Program 

September 10, 2001, 3:30 p.m. 

Oral Testimony of Stephen Albert, Director 

Western Transportation Institute, Montana State University 

and 

President, Rocky Mountain Chapter 

of Intelligent Transportation Society of America 
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Good afternoon Chairman Reid, Ranking Member Inhofe, and members of the Committee. I 

would like to begin by thanking you for this opportunity to share our views and perspective on 

Intelligent Transportation Systems and specifically Advanced Rural Transportation Systems or 

rural ITS. 

My name is Stephen Albert, I am the director of the Western Transportation Institute at Montana 

State University. WTI’s mission is to “make rural travel and transportation safer, more 

convenient and more accessible.” Founded in 1994 by the California Department of 

Transportation, Montana Department of Transportation and MSU, WTI is the nation’s leading 

research Center focusing on rural transportation issues. With over 30 ongoing research, 

demonstration and evaluation projects in 30 states and 10 National Parks, WTI was recognized in 

1998 by ITS America for our “outstanding achievement in rural ITS.” In addition to serving as 

WTI’s director I also serve as the Rocky Mountain ITS America Chapter president. 

I am here representing not only western states, but the entire rural community and we thank each 

of you for raising awareness of rural America transportation needs and ITS applications. My 

testimony was developed from speaking with stakeholder groups on the east coast, southern 

United States, mid-west and Alaska. 

My testimony will address the following three areas: 

• magnitude and severity of rural transportation challenges facing this nation; 

• specific examples and benefits of successful ITS deployment; 

• future focus areas where additional emphasis and resources should be placed. 

1. What are the Rural Challenges? 

For the last ten years the rural constituents have heard our transportation leaders highlight 

congestion as our nation’s leading challenge. Programs such as Operation Time Saver, Model 

Deployment Initiative and other urban initiatives have been the showcase of USDOT. However, 

these showcase programs have little, if any, direct application to approximately eighty-percent 

(80%) of our nation’s surface roads, or roughly four million miles of roadway. Unlike urban 

areas that have congestion as the primary single issue, rural needs are more diverse, complex and 

only tangentially congestion-related. So what are the rural challenges? 

1.1 Safety and Non-Interstate Roadways 

In rural areas safety is of paramount importance. According to Federal Highway Administration 

(FHWA) statistics, sixty-percent (60%) of the crash fatalities occur on rural highways, while 

only 39% of the vehicle miles traveled occur on these roads – a disproportionate relationship. 

These combined facts make rural crash rates 2.5 times greater than urban areas. Furthermore, 

single vehicle crashes on 2-lane rural roads accounted for 54% of all rural crashes in 1998. 

1.2 Digital Divide – no wireless communication coverage 

Vast rural areas of the United States are without wireless communications, which impacts safety 

and increases infrastructure deployment costs. Preliminary research conducted by WTI in five 
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western states indicates that the notification time to learn of a crash is two to three times longer 

where no wireless communication exists, and near jurisdictional borders. 

 

1.3 Weather Impacts Every Day Life 

Weather can be deadly in many regions of the United States. According to FHWA, there are 

approximately 7,000 fatalities and 450,000 persons injured each year due to weather related 

events. 

1.4 Tourism and Economic Viability 

Tourism is a critical concern to the economic viability of many rural communities. Travel and 

tourism in the United States is the nation’s largest export industry and second largest employer, 

accounting for over $515 billion in expenditures, resulting in 7.6 million jobs and accounting for 

1.3 billion domestic trips. An efficient transportation system is essential to rural communities 

who depend on tourism revenues for their survival. Providing real-time information to tourists, 

via ITS, is the key to encouraging greater tourist activity in rural areas and enhancing their 

economies. 

1.5 Federal Lands, National Parks and Native Americans 

In order to provide a framework on the impact of the National Parks, consider the following 

statistics: 

Scale – 374 parks in 49 states, 18 million acres; 

Employees – 19,200; 

Economic activity - $14 billion, supporting 309,000 jobs; and 

Visitation – 266 million visitors, demand increasing 500 percent over the next 40 years. 

The second area is our sovereign Native American lands where safety, economic viability and 

transportation are the key issues. Research has shown that Native Americans die in motor 

vehicle crashes at rates six times that of the rest of the Nation and 3/4 of Native American traffic 

fatalities involve alcohol. Also, only 29% of tribes have any form of transit system. 

1.6 Animal Conflicts 

Each year there are approximately 726,000 animal-vehicle crashes. These crashes rarely result 

in fatalities but at approximately $2000 per incident in property damage the annual cost 

nationally amounts to over $1 billion. 

1.7 Public Mobility 

According to the Federal Transit Administration, approximately 38 percent of the rural 

population has no access to public transportation and another 28 percent has little access. Low 

population density in rural service areas makes it difficult at best to deliver public transit 

services. 

1.8 Commercial Vehicles, Goods Movement and Long-distance Trips 

The movement of goods is critical to the economy of the United States and the rural Interstate 

System is an essential component in the process. Rural interstates are, in essence, the arteries 

over which flow the goods to be distributed to citizens throughout the country. On many rural 

highways, 30 percent of traffic is commercial vehicles, and their numbers continue to grow. 
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1.9 Diversity and Understanding 

Rural areas are challenged in that there are few issues and application similarities among 

different locations and regions (i.e. Cape Cod, Mass, Brandon, VT and Eureka, CA). 

I believe very strongly that now is the time for USDOT to step up to the plate and provide a level 

playing field and provide adequate resources to respond to rural transportation needs by 

providing sufficient funding and guidance that urban areas have enjoyed over the last several 

years. 

2. Advanced Rural Transportation Systems Success Stories 

Now, having made that last statement, I do want to recognize a number of success stories that 

have taken place in rural areas. 

 

2.1 Crash Prevention and Security 

Colorado DOT has implemented a dynamic downhill speed warning system on I-70 west of 

Denver, outside the Eisenhower Tunnel. The system measures truck speeds, weight, and number 

of axles and advises the driver of the appropriate speed. The truck speed warning system was 

installed on a narrow curve that has a design speed of 45 mph. The average truck speed around 

this curve has dropped from 66 mph to 48 mph since the installation of the warning system. The 

system has eliminated approximately 20 truck runaways and 15 truck related crashes per year. 

California DOT has implemented a similar speed system for passenger cars and trucks near 

Redding California along I-5 in Sacramento Canyon. 

2.2 Emergency Services 

Virginia DOT sponsored the Northern Shenandoah Valley Public Safety Initiative to enhance the 

collection and communication of critical accident victim patient data between the on-scene 

emergency medical personnel and the receiving hospital through the use of hand-held portable 

digital assistance devices. Use of the off-the-shelf PDA’s has improved patient outcome, 

improved on-scene, en-route and emergency room patient services, improved data collection, all 

in addition to incident management coordination. 

2.3 Tourism and Traveler Information 

As you know our National Parks are experiencing increasing visitation and traffic congestion. 

The Yellowstone National Park Smart Pass will provide frequent users and local residents with 

an electronic pass and a designated lane at entrance gates to bypass congestion. Similar systems 

are being implemented in Rocky Mountain and Zion National Parks. 

2.4 Traffic Management 

The Arizona DOT and Oregon DOT utilize the internet whereby organizations can enter road 

closure, lane restrictions, unsafe road conditions, and parking information into the system and all 

agencies can view the status of those conditions. The ODOT TripCheck system includes images 

from closed circuit cameras at mountain passes and other locations. During the peak usage the 

number of users have exceeded 350,000 per month. 

2.5 Surface Transportation and Weather 

Accurate road and weather information can mean the difference between life and death. 
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The Greater Yellowstone Weather and Traveler Information System will integrate a mountain 

pass pavement temperature prediction model, and a road and weather condition information 

system that delivers trip-specific weather forecast and road reports via cellular telephone by 

dialing #SAFE. The #SAFE system will provide road and weather information 40 to 60 miles 

(or 1 to 1 1⁄2 hours travel time) ahead of the direction of travel. The #SAFE system has been used 

by over 300,000 motorists, with a monthly average of 16,000 per month and the median use of 

the system is 25 times per year mostly in the winter. 

2.6 Operations and Maintenance 

In California and Arizona, the state DOTs have instrumented snowplows and the mountain pass 

roadways with technologies to allow for vehicle tracking in the roadway for lane guidance and 

collision avoidance systems to warn motorists of close proximity. 

3. What are the Future Needs? 

While there have been success stories as highlighted by my previous testimony, there are some 

very real gaps and opportunities that must be addressed. As I mentioned earlier, USDOT has 

predominately concentrated on urban ITS and discounted the need to address rural challenges in 

any realistic programmatic level. To quote one DOT Chief Engineer, “the highest use is not 

necessarily the highest need.” The time to address rural needs has arrived and we need federal 

leadership and commitment. The following recommendations are proposed from rural ITS 

constituents around the country. 

3.1 Conduct Outreach and Professional Capability Building Seminars 

Given that federal dollars to develop Early Deployment Plans were only available to urban areas 

with populations over 50,000 and guidelines exist that regionally significant projects need to 

develop regional architecture, there should be a commitment to provide outreach and training in 

rural areas more than at just a statewide level. Also, it is important that these outreach and 

professional capability building activities occur in rural communities where stakeholders live 

rather than large urban centers. 

3.2 Integrate Funding and Increase Awareness 

To integrate funding and increase awareness of opportunities, it is recommended that a blueribbon committee be formed to create a one-stop shopping process or even a clearinghouse, 

develop an awareness program for rural funding opportunities, review the project initiation 

approval process, and determine if a block-grant approach may be more feasible for ITS 

deployment that would horizontally cut-across federal agencies. 

3.3 Improve Communications Coverage to Provide a Basic Level of Detection, Increased Safety 

and Reduced Deployment Cost 

If we are to manage our rural roadways in a safe and prudent manner then some level of basic 

infrastructure to detect problems and a communication system to transmit that data must be 

created and funded. Rural America has large pockets of “dead zones” (no cellular wireless 

service). A new or improved model needs to be developed to increase communications 

coverage. This new model may be similar to the Rural Utility Service but at a minimum it may 

require a federal subsidization for private carriers that cannot achieve the return on investment 

that the high volume urban subscriber models deliver. 
Telecommunications Handbook for Transportation Professionals 

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267

3.4 Develop Regional Projects and Partnerships 

Travelers do not see the jurisdictional state boundaries, nor do they care, and yet most ITS 

projects are developed with only a single state in mind. Regional scale projects focused on the 

travel sheds that motorists use need to address a national system and to encourage public-private 

partnerships to develop the economies of scale needed to minimize risk. 

3.5 Implement Regional Servers for Data and Information Exchange between Stakeholder 

Groups 

To accelerate the ability to exchange data and information to provide for communication, 

cooperation and coordination, funds should be allocated to implement regional “internet” based 

servers throughout the 50 states. 

3.6 Increase Research Funding and Provide for More Adaptive Standards 

To date there has been only a marginal amount of research as to the quantified benefits of rural 

ITS. Funding for research, specifically targeted for rural ITS, should be set aside to allow for a 

more robust evaluation of current and planned deployment. 

3.7 Create a Rural Model Deployment Initiative 

If the USDOT truly wants to take a leadership role, then an opportunity I recommend is to create 

a Rural Model Deployment Initiative similar to the Metropolitan Model Deployment Initiative, 

but concentrated on a more regional/rural scale. 

3.8 Build on Successful Tourism Partnerships to Create Jobs 

Tourism is the economic engine of rural America! To allow ITS to be more effective the focus 

and attention toward tourism partners that may ultimately be the implementers of ITS must be 

increased to spur economic activity and create jobs. 

In closing, while there are isolated success stories that can be highlighted, there are still many 

challenges yet to be addressed. In keeping to the rural spirit, the Subcommittee and USDOT 

have an opportunity to be “pioneers” in making a renewed rural ITS commitment. As we like to 

say in the West – Our forefathers were pioneers, not settlers! 
About the Author 

268

ABOUT THE AUTHOR

Sheldon Leader 

Mr. Leader has over 30 years of experience in the design and 

implementation of communications systems, including: Public 

Safety Wireless Systems, E 9-1-1 Operation Centers; computer 

aided dispatch, fiber optic SONET and DWDM communications 

networks; wireless communications systems; automatic GPS for 

vehicle location systems; voice and data communications systems. 

Mr. Leader has been active in the development of new 

communications networks that serve municipal, state and federal 

government agencies, and private enterprise. 

Since 1991, Mr. Leader has been active in the design and 

development of Intelligent Transportation Systems and Freeway 

Management Systems. Mr. Leader has served as Chair of the 

Telecommunications Committee of ITS America, and Secretary of 

the TRB Committee on Communications.
Glossary 

GLOSSARY

1000Base-LX Gigabit Ethernet transmitted over fiber 

using long wave laser transmitters 

1000Base-SX Gigabit Ethernet transmitted over fiber 

using short wave laser transmitters 

1000Base-T Gigabit Ethernet over twisted pair. 

100Base-FX 

100 Mbps Fast Ethernet system based on 

4B/5B signal encoding transmitted over 

fiber optic cable. 

100Base-T 

Term used for the entire 100 Mbps Fast 

Ethernet system, including both twistedpair and fiber optic media types. 

10Base2 

10 Mbps Ethernet system based on 

Manchester signal encoding transmitted 

over thin coaxial cable. Also called Thin 

Wire and Cheapernet 

10Base5 

10 Mbps Ethernet system based on 

Manchester signal encoding transmitted 

over thick coaxial cable. Also called Thick 

Net 

10Base-F 

10 Mbps Ethernet system based on 

Manchester signal encoding transmitted 

over fiber optic cable. 

10Base-T 

10 Mbps Ethernet system based on 

Manchester signal encoding transmitted 

over Category 3 or better twisted-pair cable

802.1 

IEEE Working Group for High Level 

Interfaces, Network Management, Internetworking, and other issues common 

across LAN technologies 

802.3 

IEEE Working Group for Carrier Sense 

Multiple Access/Carrier Detect Local Area 

Networks. 

802.11 IEEE standards for low power, short range 

wireless LAN. Also referred to as Wi-Fi. 

802.15 

802.16 

802.17 

802.20 

Address 

A unique identification of a device attached 

to a network. The address can used to 

identify either a specific location such as a 

port on a switch, or a specific device. 
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ADSL 

Asymmetric Digital Subscriber Line. Most 

common form of DSL where the data rate 

being transmitted to the subscriber is high 

than the data rate transmitted from the 

subscriber. 

Aerial Cable. A cable suspended in the air on poles or 

other overhead structures 

Alternating Current (AC) 

Electric current that continually reverses 

its direction. It is expressed in cycles per 

second (hertz or Hz). 

Analog 

A signal that varies continuously such as a 

sound wave. Analog signal have 

frequency and bandwidth measured in 

hertz. 

ANSI American National Standards Institute 

APPA American Public Power Association. 

ASTM American Society of Testing and 

Materials. 

ATM 

Asynchronous Transfer Mode. A digital 

transmission switching format with cells 

(packets) of a fixed length to help 

facilitate voice and video transmission. 

Attenuation 

Power loss in an electrical or 

telecommunications system. In cables, 

expressed in dB per unit length, usually 

dB per 1000 feet, or per kilometer. This 

term is also used to express loss in fiber 

optic cable. 

AWG 

Abbreviation for American Wire Gauge. 

Based on a circular mil system. 1 mil 

equals .001 inch. Used to determine the 

size of conductors. 

Backbone 

A transmission network that carries high 

speed telecommunications between 

locations. This is normally the main 

portion of a telecommunication network, 

with branches going to individual 

buildings. In a local area network, this is 

usually the link between routers, switches, 

and bridges. 

Balun 

An adapter for connecting an unbalanced 

coaxial transmission line to a balanced 

two-wire system. 
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Band Marking 

A continuous circumferential band applied 

to a conductor at regular intervals for 

identification. 

Bandwidth 

The information carrying capacity of the 

system. In analog systems, this is also the 

highest frequency that can be carried. 

Baud 

The number of signal level transitions per 

second in digital data. The term is often 

confused with bits per second. 

Telecommunications specialists prefer to 

use "bits-per-second" to provide an 

accurate description. 

BER 

Bit Error Rate. The number of bit errors 

that occur within the space of one second. 

This measurement is one of the prime 

considerations in determining signal 

quality. The higher the data transmission 

rate the greater the standard. A DS-1 

signal is considered acceptable with a 

BER of 10-6, but an OC-3 signal requires 

a BER of no more than 10-12. 

Bps Bytes per second. Term used by software 

engineers to describe bandwidth. 

bps 

Bits per second. Term used by 

telecommunication engineers to describe 

bandwidth. 

Bridge 

A device that allows multiple 

communication circuits to use a common 

circuit. Only one circuit can be connected 

to the common at any given moment 

Broadband 

Generally used to describe data 

transmission requirements of greater than 

128 Kbps. 

Broadcast Transmission Sending the same signal to many 

locations. 

Building Wire 

Insulated single conductors, 600 volts, 

used for supplying power for lighting, 

operating machinery, controls, etc. 

Usually installed through conduits/trays 

inside buildings. 

Bundle A group of wires (or fiber strands) 

contained within a single wrapper. 
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Bus 

An electrical transmission path for 

carrying information, usually serving a 

shared connection for multiple devices. 

Byte Eight bits of data. 

Cable 

A group of individually insulated 

conductors in twisted or parallel 

configuration, with an overall outer jacket.

Carrier Hotel 

A large building where communication 

carriers place equipment to provide 

connections between their respective 

systems . 

Carrier Sense 

Carrier Sense is the process used by 

devices on Ethernet to determine whether 

the cable is currently being used by a 

transmitting station. If electrical signals 

are detected on the cable, then carrier has 

been detected and a station is currently 

transmitting on the cable 

Category 5 

Commonly referred to as "Cat 5". A type 

of twisted pair copper cable that meets 

standards for transmitting high speed 

signals. 

CATV An acronym for Community Antenna 

Television. 

CCITT 

International Consultative Commission on 

Telephone and Telegraph, an arm of the 

ITU (International Telecommunications 

Union) a standards setting body. 

CCTV Closed Circuit Television. 

Central Office 

Commonly referred to as a "CO". A 

telephone company facility for switching 

signals among local telephone circuits. 

Also called a "Switching Office". 

Certificate of Compliance (C of C) 

A certificate showing that the product 

being shipped meets customer's 

specifications. 

Certified Test Report (CTR) 

A report providing actual test data on a 

cable. Tests are normally run by a Quality 

Control Department, which shows that the 

product being shipped conforms to test 

specifications. 

Coaxial Cable A cable consisting of two conductors with 

a common axis, separated by a dielectric. 
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Collision 

A collision is a condition where two 

devices detect that the network is idle and 

end up trying to send packets at exactly 

the same time (within 1 round-trip delay). 

Since only one device can transmit at a 

time, both devices must back off and 

attempt to retransmit again. 

Color Code 

A system for circuit identifications 

through use of solid color insulations 

and/or contrasting tracers. 

Composite Cable 

A cable containing more than one gauge 

size or a variety of circuit types, e.g., 

pairs, triples, quads, coaxials, etc. 

Conduit A tube through which insulated wires and 

cables are run. 

Connector 

A device mounted on the end of copper, or 

fiber optic cables to facilitate link of the 

cables. 

Control Cable A multiconductor cable made for 

operation of control or signal circuits. 

Cord A small, flexible insulated cable. 

Core 

In cables, a component or assembly of 

components over which additional 

components (shield, sheath, etc.) are 

applied. 

CPE (Construction Term) Jacketing compound based on chlorinated 

polyethylene. 

CPE (Network Term) 

Customer Premise Equipment - a term 

used by telephone companies to identify 

equipment owned by a customer 

Crosstalk 

Signal interference between nearby 

conductors caused by pickup of stray 

energy. It is also called induced 

interference. 

Crosstalk The unwanted transfer of a signal from 

one circuit to another. 

CSMA/CD 

Carrier Sense Multiple Access/Collision 

Detect. The formal name for the medium 

access control (MAC) protocol used in 

Ethernet. 

CWDM Coarse Wave Division Multiplexing 
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Cycles Per Second 

CPS. The frequency of a wave, or the 

number of oscillations it makes persecond. 

One cycle per second equals one hertz. 

Dark Fiber 

Optical fiber installed without a 

transmitter or receiver. These fibers are 

the un-used fibers in a cable. Some fibers 

are held in reserve for future requirements. 

Others are often leased to different carriers 

(or large customers) for use in their 

individual systems. 

Data Link A data communications connection 

between two points. 

Data Link Layer 

Layer 2 of the OSI reference model. This 

layer takes data from the network layer 

and passes it on to the physical layer. The 

data link layer is responsible for 

transmitting and receiving Ethernet 

frames, 48-bit addressing, etc. It includes 

both the media access control (MAC) 

protocol and logical link control (LLC) 

layers. 

dBm Decibels below 1 mW (milliwatt) 

dBu Decibels below 1 uW (microwatt) 

DCE 

Data Communications Equipment. Any 

equipment that connects to Data Terminal 

Equipment (DTE) to allow data 

transmission between DTEs. A modem is 

a type of DCE. 

Decibel (dB) 

A unit to express differences of power 

level. Used to express power gain in 

amplifiers or power loss in passive circuits 

or cables. Also, a logarithmic comparison 

of two power levels, defined as ten times 

the base ten logarithm of the ratio of the 

two power levels. 

Dielectric Nonconductive material 

Dielectric Strength 

The voltage which an insulation can 

withstand before breakdown occurs. 

Usually expressed as a voltage gradient 

(such as volts per mil). 

Digital 

An encoded signal. Normally encoded in 

discrete levels to represent a binary signal 

of ones and zeros. 
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Digital Subscriber Line 

DSL. A service that transmits digital 

signals (to homes and small offices) via 

the existing copper wire used for voice 

transmissions. 

Direct Burial Cable A cable installed directly in the earth. 

Direct Current (DC) An electric current which flows in only 

one direction. 

Drain Wire 

In a cable, the uninsulated wire in intimate 

contact with a shield to provide for easier 

termination of such a shield to a ground 

point. 

DSSS 

Direct Sequence Spread Spectrum – One 

of two types of spread spectrum radio 

transmission 

DTE 

Data Terminal Equipment. Any piece of 

equipment at which the communication 

path begins or ends. A PC is DTE. 

Duct 

An underground or overhead tube through 

which electrical conductors are pulled. 

Gives mechanical protection. EIA. 

Electronic Industries Association. 

Duplex 

A bi-directional transmission of the 

transmit and receive elements of a 

communication signal occurring 

simultaneously. 

DWDM Dense Wave Division Multiplexing 

EIA/TIA 568 

This is the color-code connection standard 

for an RJ-45 (8 conductor) connector. 

There are two wiring standards: 568A and 

568B. The only difference between the 

two is that two pairs of colors are 

swapped. The 568B is an older standard 

defined by AT&T. All new installations 

are supposed to use 568A. What really is 

important is that everything be consistent 

in all your wiring. Otherwise, you'll get 

yourself confused. Note that the difference 

is only in what color is used for what pin, 

not what signal is on what pin, so in a 

patch cable with both ends pre-wired, it 

doesn't matter. 

Electricity 

The energy produced by the flow of ''free'' 

or valance electrons moving from one 

atom to another in a conductor. 
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E&M Signaling 

Ear (receive) and Mouth (transmit), a 

signal outside of the voice frequency 

range that can be used to activate a fuction 

in a telephone switch. 

EMI 

Electromagnetic Interference. The noise 

generated when stray electromagnetic 

fields induce currents in electrical 

conductors. 

Encoding 

A means of combining clock and data 

information into a self synchronizing 

stream of signals. 

Ethernet A local area network standard. 

F.D.D.I. Fiber Distributed Data Interface. 

Facilities 

Term used by telecommunication 

engineers to indicate communications 

systems 

FHSS 

Frequency-Hopping Spread Spectrum – 

One of two types of spread spectrum radio 

transmission 

Fiber Optics 

A light wave or optical communications 

system in which electrical information is 

converted to light energy, transmitted to 

another location through optical fibers, 

and is there converted back into electrical 

information. 

Figure 8 Cable 

An aerial cable configuration in which the 

conductors and the steel strand which 

supports the cable are integrally jacketed. 

A cross section of the finished cable 

approximates the figure 8. 

Filled Cable 

A cable construction in which the cable 

core is filled with a gel material that will 

prevent moisture from entering or passing 

through the cable. 

Frame 

A packet of transmitted information. The 

frame contains all of the necessary 

information to indicate the origin and 

destination, control information and the 

actual data. 

Frequency Division Multiplexing 

FDM. Combining analog circuits by 

assigning each a different carrier 

frequency and merging them into a single 

communication signal. 

FTTC Fiber-to-the-Curb 
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FTTH Fiber-to-the-Home 

Full Duplex 

Transmitters and receivers simultaneously 

send and receiver signals in both 

directions on the same pair of wires. 

FXO Foreign Exchange Office 

FXS Foreign Exchange Station 

Gauge A term used to denote the physical size of 

a wire. 

Gbps Giga bits per second, or Gbit/s. One 

billion bits persecond. 

GHz Giga Hertz. One billion hertz, or cycles 

per second. 

Ground 

A conducting connection between an 

electrical circuit and the earth or other 

large conducting body to serve as an earth 

thus making a complete electrical circuit. 

Half Duplex Transmitters and receivers send or receive 

on the same pair of wires. 

HDTV High definition (or high resolution) 

television 

Hertz Frequency in cycles per second 

Hierarchy 

A set of transmission speeds arranged to 

multiplex a successively higher number 

of circuits. 

Homerun 

A cable run that goes directly from a jack 

in a wall plate to a centralized position 

(patch panel). There are no stops or 

interruptions between the 2. 

Hub 

Hubs act as the center of a "star" topology. 

They have between 4 and 20+ ports. 

Internally, hubs are "dumb" devices that 

just resend information they receive. All 

devices attached utilize a part of the rated 

speed, be it 10 or 100Mbit/sec. Hubs 

know nothing about a packet's destination. 

Therefore, hubs are generally the cheapest 

connecting device in a star topography, 

although for a busier network, switches 

are more robust. 

Hybrid Cable 

A cable design to meet many 

requirements. Most commonly, hybrid 

cables will contain a mixture of twistedpair and coaxial, or coaxial and fiber. 
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IAEI International Association of Electrical 

Inspectors. 

IBEW International Brotherhood of Electrical 

Workers. 

ICEA Insulated Cable Engineers Association 

(Formerly IPCEA). 

IEC Independent Electrical Contractors 

association. 

IEEE Institute of Electrical and Electronics 

Engineers. 

IMSA 

International Municipal Signal 

Association. Publishes specifications for 

cables and wires used in municipal, 

county, and state Traffic Signal, 

Communication and Fire Alarm systems. 

Inside Plant Telecommunications facilities placed 

inside a building. 

Insulation 

A material having high resistance to the 

flow of electric current. Often called a 

dielectric. 

Internet 

The worldwide collection of networks 

based on the use of TCP/IP network 

protocols. 

Intranet A collection of networks supporting a 

single site or corporate entity. 

IP Internet protocol. Standard format for 

transmitting data via the internet. 

ISA Instrument Society of America. 

ISDN 

Integrated Services Digital Network. A 

digital transmission standard using 144 

kbps containing two 64 kbps voice 

channels and one 16 kbps data channel. 

ISO International Standards Organization. 

ITE Institute of Transportation Engineers 

IUEW International Union of Electrical Workers.

Jacket 

An outer covering, usually nonmetallic, 

mainly used for protection against the 

environment. 
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Jitter 

Also called phase jitter, timing distortion, 

or inter-symbol interference. The slight 

movement of a transmission signal in time 

or phase that can introduce errors and loss 

of synchronization. The amount of jitter 

will increase with longer cables, cables 

with higher attenuation, and signals at 

higher data rates. 

LAN 

Local Area Network. Integration of 

computer and communication systems that 

wire computers, peripheral equipment and 

telephones together so they can all ''talk'' 

to each other. 

LASER Light Amplification by Stimulated 

Emission of Radiation. 

LED Light Emitting Diode. A semiconductor 

that emits light. 

Light guide An optical fiber bundle. 

Longitudinal Shield 

A tape shield, flat or corrugated, applied 

lengthwise with the axis of the core being 

shielded. 

Loose Tube 

A protective tube loosely surrounding 

fiber strands. The tube may be filled with 

gel to protect against moisture infiltration. 

Loss Attenuation of an optical or electrical 

signal, normally measure in decibels 

Loss Budget 

An accounting of overall attenuation in a 

system. The budget is the amount of 

acceptable loss. 

MAC Media Access Control. A portion of the 

Ethernet frame. that 

MAN 

Metropolitan Area Network. Backbone 

system deployed in metropolitan areas to 

connect Telephone Companies, Carriers, 

Carrier Hotels, and large office buildings. 

Margin 

Allowance for attenuation (or loss) in 

addition to that explicitly accounted for in 

a system design. 

Mbps Megabits per second. Also expressed as 

Mbit/s. 
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Messenger Cable 

The linear supporting member, usually a 

high strength steel wire, used as the 

supporting element of a suspended aerial 

cable. The messenger may be an integral 

part of the cable, or exterior to it. 

Microbending 

Tiny bends in fiber that allow light to leak 

out and increase loss. microbending 

occurs during installation and is usually 

unavoidable. Loss budget margins should 

account for microbending. 

Mil 

A unit used in measuring the diameter of a 

wire or thickness of insulation over a 

conductor. One one-thousandth of an inch. 

(.001") 

Modal Dispersion 

Dispersion arising from differences in the 

times that different modes take to travel 

through multimode fiber. 

Mode 

An electromagnetic field distribution that 

satisfies theoretical requirements for 

propagation in a waveguide. Light has 

modes in a fiber. 

MODEM Modulator-Demodulator 

Modem 

A device used to convert signals from one 

form to another. It can be used to convert 

the output of a computer to a voice 

channel equivalent, or an electrical signal 

to an optical signal. 

Multimode Transmits multiple modes of light. 

Multiplexer A device that combines many 

communication circuits into one circuit 

MUX Abbreviation for Multiplexer 

NAED National Association of Electrical 

Distributors. 

Nanometer A unit of measurement, 10-9 meters. Light 

wave frequencies are stated in nanometers.

NAPE National Association of Power Engineers. 

NEC 

National Electric Code. A standard 

published by the National Fire Protection 

Association (NFPA) and incorporated in 

OSHA (Occupational Safety and Health 

Act) regulations. 

NECA National Electrical Contractors 

Association. 
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NEMA National Electrical Manufacturers 

Association. 

Network A system of cables or wireless pathways 

that link communication nodes. 

NFPA National Fire Protection Association. 

NIC 

Network Interface Card. This is the 

interface between a computer (or other 

device) and the Ethernet network. 

Node A communication point usually comprised 

of communication devices. 

NRECA National Rural Electric Cooperative 

Association. 

NRZ 

Non-Return-to-Zero. An electrical 

communication signal which uses a "low" 

signal for zero and a "high" signal for one. 

The electrical signal value never reaches 

zero. 

NTSC 

National Television System Committee. 

Analog video broadcast standard used in 

North America. 

O.D. Outside diameter. 

OC-x Optical Carrier rate specified for SONET; 

OC-3, OC-12, OC-48, etc. 

OFDM 

Orthogonal Frequency Division 

Multiplexing – a frequency division 

modulation technique for transmitting 

large amounts of digital data over a radio 

wave. OFDM works by splitting the radio 

signal into multiple smaller sub-signals 

that are then transmitted simultaneously at 

different frequencies to the receiver. 

Ohm 

Unit of resistance such that a constant 

current of one ampere produces a force of 

one volt. 

OSI Open Standards Integration 

OTDR 

Optical Time-Domain Reflectometer. An 

instrument that measures transmission 

characteristics by sending a short pulse of 

light down a fiber and measures the 

reflected light pattern. 

Outside Plant Telecommunication facilities that are 

placed outside of a building. 
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P.O.P Point of Presences - A location of 

telecommunication carrier equipment 

P.O.T.S. "Plain Old Telephone Service" - a 

reference to basic voice telephone service 

Packet 

A technique used to break large quantities 

of data into small groups, or packets, to 

facilitate transmission with very few 

errors. 

Packet Switch 

A switch that moves data packets from 

multiple transmissions and provide for 

efficient sharing of communication 

facilities. 

Patch Cable (Cord) 

A twisted-pair, or fiber optic jumper cable 

used to make a connection between a 

network interface, or network port, and a 

media segment, or to directly connect 

stations and hub ports together. 

PCS 

Personal Communications Service. A 

group of frequencies in the 1.8 to 2.0 GHz 

range reserved for cellular telephone 

communications. 

PE Polyethylene. 

PHY 

Physical Layer Device. The name used for 

a transceiver in Fast Ethernet and Gigabit 

Ethernet systems. 

Physical Address 

The 48-bit MAC address assigned to a 

station interface, identifying that station on 

the network. 

Plenum 

The air return path of a central air 

handling system, either ductwork or open 

space over a dropped ceiling. 

Plenum Cable 

Cable approved by Underwriters 

Laboratories for installation in plenums 

without the need for conduit because the 

insulation and jacket compounds used 

have low flame-spread and low smoke 

characteristics. 

Point-to-Point Transmission 

Carrying a communication signal between 

two locations without branching to other 

locations. 

Polyethylene A thermoplastic material having the 

chemical identity of polymerized ethylene.
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Polyvinyl Chloride (PVC) 

A thermoplastic material composed of 

polymers of vinyl chloride which may be 

rigid or flexible depending on specific 

formulation. 

Port A connection point on a hub, router, bridge, 

switch, etc. 

Protocol 

A set of agreed upon rules and message 

formats for exchanging information among 

devices on a network. 

Pulling Eye 

A device fastened to a cable to which a 

hook may be attached in order to pull the 

cable through a duct. 

PVC (Construction Term) Polyvinyl chloride. 

PVC (Network Term) Permanent Virtual Circuit 

REA 

Rural Electrification Administration of the 

U.S. Dept. of Agriculture. Publishes 

telephone cable and wire specifications 

and a list of approved manufacturers of 

cable, wire and related installation 

supplies. 

Receiver 

A device that detects a communication 

signal and converts it into sound, data, or 

video. 

Regenerator 

A receiver-transmitter device that detects 

a weak signal, converts it to its original 

state, and then transmits is as a strong 

signal. Most problems in the received 

signal are corrected. 

Repeater 

A receiver-transmitter device that detects 

a weak signal and boosts its power for 

continued transmission. This device is also 

called an amplifier. Any problems in the 

received signal are simply retransmitted. 

Resistance 

In DC circuits, the opposition a material 

offers to current, measured in ohms. In 

AC circuits, resistance is the real 

component of impedance, and may be 

higher than the value measured at DC. 

RF Radio Frequency. A general term used to 

indicate a radio system. 

RG/U 

Abbreviation for Radio Grade, Universal. 

RG is the military designation for coaxial 

cable and U stands for ''general utility''. 
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Ribbon Cable 

A cable in which many conductors 

(copper or fiber) are embedded in a plastic 

material in parallel, forming a flat, ribbon 

like structure. 

RJ-11 

RJ-11 is standard modular phone 

connector. There are 3 different types: 2, 4, 

and 6 conductor connectors. They're all the 

same, except that contacts or wires are 

missing. Ordinary phone connectors are 4-

conductor (2 pairs = 2 phone lines). 

Sometimes you get a phone wire that only 

has 2 conductors in it; this will screw you 

up if you're trying to run more than 1 phone 

line. There's also a little-bitty version of 

this connector that only has 2 conductors 

on it. It will fit in the same socket. 

RJ-45 

RJ-45 is the 8-conductor version of an RJ11. It looks like a regular modular phone 

connector, only it's wider. You need to use 

RJ-45 for Ethernet, because the connection 

standard puts the Ethernet on some of the 

outer connectors not in RJ-11. RJ-11 plugs 

will fit into an RJ-45 socket, but because 

the plastic plug is smaller, some of the 

contacts will get bend back a little 

Router 

A device that has enough intelligence to 

be connect one, or many, devices to other 

devices. Typically used in Local Area 

Networks to connect desktop computers to 

printers or file servers. 

SDH 

Synchronous Digital Hierarchy. The 

international version of the SONET digital 

hierarchy. 

Segment 

A segment is a piece of network wire 

bounded by bridges, routers, repeaters or 

terminators. 

Sheath The outer covering of a communication 

cable. 

Shield 

A metallic layer placed around a 

conductor or group of conductors to 

prevent electrostatic interference between 

the enclosed wires and external fields. 
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Signal-to-Noise Ratio 

The ratio of signal to noise measured in 

decibels. An indication of signal quality in 

analog communication systems. 

Simplex 

Simple uni-directional transmission. 

Transmitter on one end and a receiver on 

the other. 

Single Mode Normally referring to commonly used 

type of fiber optic cable. 

SNMP 

Simple Network Management Protocol. A 

protocol specified by the Internet 

Engineering Task Force (IETF) for 

exchanging network management 

information between network devices and 

network management stations. 

SONET Synchronous Optical Network. 

STP Shielded Twisted Pair 

Subscriber Loop 

The part of the telephone network that 

runs from the central office to individual 

subscribers. 

Switch A device that direct electricity, or light, 

along different physical paths. 

Switch 

Switches act as the center of a "star" 

topology, much like hubs. They have 

between 4 and 20+ ports. Internally, 

switches are different that hubs due to their 

intelligent design. Switches "remember" 

what device is attached to what port, and 

will relay packets only to the proper 

destination port. Because of this, all devices 

attached are able to utilize their maximum 

rated speed, be it 10 or 100Mbit/sec/port. 

This cleaver design makes switches more 

expensive, but in a busy network, switches 

can keep the traffic flowing. 

T - Carrier 

Normally refers to a T-1 transmission 

system, but can be any of standard North 

American Digital Hierarchy transmission 

rates. 

TDM Time Division Multiplexing 

Telemetering Cable 

Cable used for transmission of 

information from instruments to the 

peripheral recording equipment. 
Telecommunications Handbook for Transportation Professionals 

Glossary 

286

Temperature Rating 

The maximum temperature at which an 

insulating material may be used in 

continuous operation without loss of its 

basic properties. 

Tensile Strength The pull stress required to break a given 

specimen. 

TIA/EIA 

Telecommunications Industry 

Association/Electronics Industry 

Association. An organization that sets 

telecommunications standards for 

buildings, cables, and connectors. Also sets 

practices and standards for construction of 

telecommunication systems. 

Tight Buffered 

A type of fiber optic communication cable 

where the fiber strands are tightly wrapped 

by the covering sheath. 

Tinned Copper Tin coating added to copper to aid in 

soldering and inhibit corrosion. 

Tray 

A unit or assembly of units or sections, 

and associated fittings, made of metal or 

other noncombustible materials forming a 

rigid structural system used to support 

cables. Includes ladders, troughs, 

channels, solid bottom trays, and similar 

structures. 

Trunk 

Trunk Line. A communication link 

running between telephone company 

central offices. Also a communication link 

that connects a customer location to a 

telephone company central office, but is 

not directly connected to a switch. 

Twisted Pair Pair of copper wires wrapped around each 

other. 

UL 

Abbreviation for Underwriters 

Laboratories, a nonprofit independent 

organization, which operates a testing and 

listing service for electrical and electronic 

materials and equipment. 

UTP Unshielded Twisted Pair. 

Watt 

A unit of electrical power. One watt is 

equivalent to the power represented by 

one ampere of current under a pressure of 

one volt in a DC circuit. 
Telecommunications Handbook for Transportation Professionals 

Glossary 

287

Waveguide A structure that guides electromagnetic 

waves along its length. 

Wavelength 

The distance an electromagnetic wave 

travels in the time it takes to oscillate 

through a complete cycle. 

WDM 

Wavelength-Division Multiplexing. 

Multiplexing of signal by transmitting 

them at different light frequencies through 

the same fiber. 

WEP Wired Equivalent Privacy – a security 

protocol for wireless local area networks 

Wicking The flow of a liquid in a wire or cable due 

to capillary action. 

Wi-Fi Wireless Fidelity 

Wi-Max Broadband Wireless 

 

WPA 

Wi-Fi protected access - a Wi-Fi standard 

that was designed to improve upon the 

security features of WEP. 
Federal Highway Administration

U.S. Department of Transportation

400 7th Street, S.W. (HOP)

Washington, DC 20590

Toll-Free “Help Line” 866-367-7487

Publication No.: FHWA-OP-04-034

Telecommunications Handbook

for Transportation Professionals: 

The Basics of Telecommunications

www.ops.fhwa.dot.gov