NTIA-REPORT-80-36

Command Post/Signal Center

Bus Distribution System

Concept Design

R. F. Linfield

M. Nesenbergs

P. M. McManamon

Prepared for

U. S. Army Communications-Electronics

Engineering Installation Agency, CCC-SEO

Fort Huachuca, Arizona 85613

U.S. DEPARTMENT OF COMMERCE

Philip M. Klutznick, Secretary

Henry Geller. Assistant Secretary

for Communications and Information

APRil 1980
The views, opinions and/or findings contained in this report

are those of the authors and should not be construed as an

official Department of the Army policy or decision, unless

designated by other official documentation.

ii
Preface

The study, whose results are presented in this report, was

supported by the U. S. Army Communications-Electronics Engineering

Installation Agency, Fort Huachuca, Arizona on Project Order Number

CCC-PQ-15-78. Administration of the progr,am was performed by the

agency by Mr. Howard R. Smith of the Systems Engineering Office

(SEQ) ; Mr. R. E. Brackett and ,Mr. J • Smith of the SEO served as

technical monitors of the program.

Technical and management supervision at the National Telecommunications and Information Administration, Institute for Telecommunication Sciences in Boulder, Colorado was provided by Dr. P. M.

McManamon, Associate Director for Advanced Communication Networks.

The authors wish to thank LTC Frensted of the 3rd Corps, Fort

Hood, Texas, and Captain Bryd of the 11th Signal Battalion, Fort

Huachuca, Arizona. It is from them and members of their teams of

specialists that we obtained valuable insight into what a real

tactical situation is like and what the Army Field Commander1s

operational communications needs really are.

iii

TABLE OF CONTENTS

Page

LIST OF FIGURES viii

LIST OF TABLES xii

ABSTRACT 1

1. OBJECTIVE AND SCOPE 1

1.1. Background Information 1

1. 2. Problem Statement 4

1. 3. Technical Approach 5

1.4. Report Organization 6

1. 5. Summary of Conclusions and Recommendations 9

2. THE TACTICAL COMMUNICATIONS ENVIRONMENT 11

2.1. Physical Aspects 11

2.2. Communicator's Standpoint 11

3. CP/SC USER'S OPERATIONAL REQUIREMENTS 18

4. CP/SC SERVICE REQUIREMENTS 23

5. CP/SC TERMINALS AND TRAFFIC 25

5.1. Types of Terminals 25

5.2. Distributions and Densities 25

5.3. Traffic Generated 37

5.4. Traffic Statistics· 37

5.5. Terminal and Traffic Projection Summary 43

6. FUNCTIONS AND OPERATIONS FOR CP/SC NODE 50

6.1. Interface Functions 50

6.2. Multiplexers and Concentrators 52

6.3. Switching Functions 54

7. CP/SC SYSTEM STRUCTURE AND IMPLEMENTATION 60

7.l. Switching Systems 60

7.2. Concentrators and Multiplexers 60

7.3. Transmission Links 66

v
TABLE OF CONTENTS (cont.)

Page

7.4. Deployment 69

8. OVERALL CPISC NETWORK DESIGN 76

8.1. General Network Objectives 76

8.2. Hierarchies 82

8.3. Network Design and Topology 90

8.4. Survivability Aspects 103

8.5. Structured Configuration Networks 115

8.6. Remaining Network Issues 126

9. CPISC DISTRIBUTION SYSTEM CONCEPTS 130

9.1. Existing Configurations 132

9.2. Initial Improvement Phase 134

9.3. Transitional Improvement Phase 134

9.4. Final Improvement Phase 137

9.5. Summary of Phased Improvement to Distribution System Concept 137

10. SYNTHESIS OF CPISC BUS ALTERNATIVES 140

10.1. Major Functions Performed by a Transparent Bus 142

10.2. Functional Tradeoffs 144

10.3. Bus Synthesis Tradeoff Summary 162

11. SELECTION OF PREFERRED ALTERNATIVES 167

11. 1. CPISC Distribution System - Existing Structure 168

11. 2. CPISC Alternative I Bus Distribution System 170

11.3. CPISC Alternative II Bus Distribution System 174

11. 4. CPISC Alternative III Canonical Bus Distribution System 174

11. 5. CPISC Alternative IV Canonical Bus Distribution System 179

11. 6. CPISC Alternative VBus Distribution System 179

11. 7. Summary Assessment of Candidate Alternatives 179

11. 8. Selection of Preferred Alternative 186

12. FUNCTIONAL DESIGN REQUIREMENTS 191

12.1. Objectives 194

12.2. Functional Design of Preferred Alternative 195

vi
TABLE OF CONTENTS (cont.)

13. REFERENCES

14. BIBLIOGRAPHY

14.1. Military Environment

14.2. Tactical Systems

14.3. Bus Architectures

14.4. Network Design and Survivability

vii

Page

202

203

203

203

205

207
LIST OF FIGURES

Page

Figure 1. Photograph of cables and connectors currently used for CP/SC

distribution system. 3

Figure 2. Report organization. 7

Figure 3. Typical theater. 12

Figure 4. Corps area network organization. 14

Figure 5. Interconnection of functional units for a typical area

signal center. 16

Figure 6. External traffic links to command post used for operation

Braveshield exercise. 17

Figure 7. Traffic categories estimated for corps main during operation Braveshield exercise. 19

Figure 8. Information flow to command post. 20

Figure 9. General service classification scheme. 24

Figure 10. Traffic rates generated by various types of terminals. 39

Figure 11. CP/SC size relationships in terms of number of telephone

calls per hour. 46

Figure 12. CP/SC size relationships in terms of maximum telephone

traffic load. 47

Figure 13. CP/SC size relationships for teletype terminals and

message/hour. 48

Figure 14. CP/SC sizing based on maximum teletype traffic. 49

Figure 15. Basic functions and operating modes for digital and analog

services. 51

Figure 16. Frequency division multiplexer. 53

Figure 17. Synchronous time division multiplexer. 55

Figure 18. Switch technology classifications. 56

Figure 19. Control technologies used in circuit switching systems. 57

Figure 20. Signaling technologies for remote switch control. 58

Figure 21. Tactical command post configuration. 70

viii
LIST OF FIGURES (cont.)

Page

Figure 22. Main command post configuration. 71

Figure 23. Tactical operations center, main CP. 72

Figure 24. Fort Huachuca deployment exercise equipment layout. 73

Figure 25. CP/SC facilities and interconnections during Braveshield

exercise. 75

Figure 26. Typical life cycle of the command post network. 77

Figure 27. Conceptual definition of the command post network. 83

Figure 28. A four-level hierarchy network. 85

Figure 29. Typical CP/SC link distance distributions. 87

Figure 30. The star network. 92

Figure 31. Space-division-mu1tip1exing (SUM) or common trenches for

the star network. 93

Figure 32. A four-level hierarchy with centralized switching. 95

Figure 33. Fully interconnected, distributed switch hierarchy level. 96

Figure 34. Link and capacity assignment. 99

Figure 35. The structured configuration networks for two to five

switches. 101

Figure 36. The general structured configuration. 102

Figure 37. The number of links required by several common topologies. 104

Figure 38. The (D,P) contour as a function of link and node outages. 107

Figure 39. Asample network and its equivalent topology. 109

Figure 40. Loop network with uniform links and nodes. 111

Figure 41. Worst case probability of blocking for the uniform loop

network with a single link outage. 112

Figure 42. The most severe cuts and bottlenecks in simple networks. 114

Figure 43. A simplified four-node structured configuration. 117

Figure 44. Current CP/SC configuration. 133

ix
LIST OF FIGURES (cant.).

Page

Figure 45. Initial improvement phase. 135

Figure 46. Transitional improvement phase. 136

Figure 47. Final improvement phase. 138

Figure 48. Transparent link structure for demonstrating technical

feasibility of bus-type network. 141

Figure 49. Basic communications functions. 143

Figure 50. Steps in pulse coding an analog signal. 147

Figure 51. Common digital signal formats for transmission. 148

Figure 52. Common modulated carrier signals. 150

Figure 53. Noncoded pulse waveform representations. 153

Figure 54. Multiplexing analog terminals on analog and digital buses. 155

Figure 55. Multiplexing digital terminals on an analog bus. 156

Figure 56. Multiplexing digital terminals on an analog bus with separated

access. 157

Figure 57. Multiplexing terminal with different source rates. 158

Figure 58 ..Losses of current telecommunication media. 160

Figure 59. Trend line for relative cost per circuit mile (Abraham,

1960) . 161

Figure 60. Transparent bus structures for time continuous analog

signals. 163

Figure 61. Transparent bus structures for time discrete analog

signals. 164

Figure 62. Transparent bus structures for digitized analog signals. 165

Figure 63. Transparent bus structures for digital signals. 166

Figure 64. Existing CP/SC link structure. 169

Figure 65. Existing CPISC cable run structure. 171

Figure 66. Alternative I for CP/SC link structure. 172

Figure 67. CP/SC Alternative la bus distribution system. 173

x
LIST OF FIGURES (cont.)

Page

Figure 68. Alternative II for CP/SC link structure.

Figure 69. CP/SC Alternative lIb bus distribution system.

Figure 70. Alternative III for CP/SC link structure.

175

176

177

Figure 71. CP/SC Alternative III canonical bus distribution system. 178

Figure 72. Alternative IV for CP/SC link structure. 180

Figure 73. CP/SC Alternative IV canonical bus distribution system. 181

Figure 74. Alternative Vfor CP/SC link structure.

Figure 75. CP/SC Alternative V bus distribution system.

182

183

Figure 76. Estimates of bus channel capacity for various bus

distribution systems. 189

Figure 77. Application of Alternative III to subsequent bus distribution system improvement phases. 192

Figure 78. Local and remoted components of a switching hub. 193

xi
LIST OF TABLES

Page

Table 1. Impact of CP/SC Distribution System on Measures of

Effectiveness 22

Table 2. Command Post Equipment Summary 26

Table 3. Equipment List of Large Headquarters Command Post 33

Table 4. ATACS Equipment and Channels for Unit Sizes 36

Table 5. Characteristics of Traffic Generated by Various Types of

Terminals 38

Table 6.

Table 7.

Tab1 e 8.

Table 9.

Table 10.

Table 1l.

Table 12.

Table 13.

Table 14.

Table 15.

Typical Speeds of Computer Peripherals and Memory

Busy Hour Voice Traffic ~oad

Busy Hour TTY Traffic Load

Busy Hour Data Traffic

Busy Hour Facsimile Traffic

TTY Message Traffic Levels

Call Processing Functions Performed by Circuit Switch

Elements

AN/TTC-38 Switching System Characteristics

AN/TTC-39 Switching System Characteristics

Army Tactical PCM Specification (from ATACS, 1974)

40

41

41

42

42

44

59

61

63

67

Table 16. Characteristics of Field Wire and Field Cable 68

Table 17. Qualitative Cross-Correlation Between Conventional Network

Objectives 79

Table 18. Hierarchy Level Impact on General Network Objectives 89

Table 19. Necessary and Sufficient Link Capacities for Various Size

Networks 118

Table 20. Link Summary for Differently Sized Switch Networks and

T=300, E=3 121

Table 21. Typical Average Command Post Distances 123

Table 22. Total Link Distances 124

xii
LIST OF TABLES (cant.)

Page

Table 23. The Single Wire-Pair (WP) and Tl Bus Totals 125

Table 24. Phased Evolution of CPISC Distribution System Concepts 139

Table 25. A Comparison of Carrier Modulation Systems 152

Table 26. Evaluation of Preferred Alternatives 184

Table 27. Ranking of Five Bus Distribution System Alternatives 188

Table 28. Channel Capacity of CPISC Alternative Bus Distribution

Systems . 190

Table 29. Service Performance Specification 200

xiii

COMMAND POST/SIGNAL CENTER

BUS DISTRIBUTION SYSTEM CONCEPT DESIGN

Robert F. Linfield, Martin Nesenbergs and Peter M. McManamon*

The communications network structures currently used to

interconnect terminal clusters and switching nodes within an

Army tactical command post and area signal center are reviewed.

With this background, five alternative structures are defined

in terms of their functional requirements. These candidate

alternatives are evaluated and a preferred structure is selected

based on a number of critical issues including deployment time,

flexibility, performance, and survivability. The preferred

alternative is a transparent bus-type distribution system incorporating analog-to-digital conversion for analog sources, time

division multiplexing, and digital transmission facilities. A

three-phase improvement plan is also outlined. The three phases

are 1) imbedding the transparent link into the existing network

structure, 2) merging these links with digital switches, and

3) changing the topology by adding switches to enh~nce survivability.

1. OBJECTIVE AND SCOPE

This report presents bus distribution network concept alternatives to the

present network structure for the U. S. Army Command Post/Signal Center field

installations. The overall objective has been to conceive different network

alternatives which lend themselves to small installation and removal times while

retaining or enhancing the survivability features of the existing networks. This

program was conducted by the Institute for Telecommunication Sciences (ITS) for

the U. S. Army Communications-Electronics Engineering Installation Agency (CEEIA)

in Fort Huachuca, Arizona, on Project Order Number CCC-PO-15-78.

The following introductory paragraphs provide background information, a brief

statement of study objectives, the ITS approach towards these objectives, an

outline of this report, and a summary of the conclusions and recommendations.

1.1. Background Information

The tactical nature of transportable Army Command Posts and Signal Centers

(CP/SC) poses many real operational problems to the Army Field Commanders. This

appears particularly true for the internal CP/SC communications distribution

systems. Such a system must often be installed, modified, or transported rapidly.

*The authors are with the U. S. Department of Commerce, National Telecommunications

and Information Administration, Institute for Telecommunication Sciences, Boulder,

Colorado 80303.
The system must be survivable, movable, and flexible. Its telecommunications

performance must meet all operational requirements faced by the transportable

CP/SC scenarios. In addition, new distribution system concepts must be adaptive

to changing technologies.

In the study reported here, we are concerned with the operational and technical system requirements for a system capable of replacing the individual wire/cable

lines currently used to interconnect the various shelters, tents, vehicles, etc.,

within a command post at Army, Army group echelon, and an area signal center

typical of corps or higher echelon.

A typical CP/SC consists of several functional elements dispersed over an

area 3 km to 5 km in diameter. Basic functional elements include command headquarters, operations center, communications center, signaling center, radio park,

helipad, and life support areas. The command post utilizes communications facilities extensively both for internal and external transfer of information. The

information may be analog (e.g., voice) or digital (e.g., teletype) in nature.

Field wire and cable systems are used by tactical signal units to:

o Provide telephone service within the posts and major headquarters.

o Provide trunk circuits between unit switchboards at various levels of

command (e.g., division, brigade, and below).

o Extend telephone circuits from multichannel terminal equipment to subscribers and switchboards within and between units in assembly areas.

o Provide the primary means of communication when radio silence is necessary and for interconnecting preselected defensive sites.

Figure 1 illustrates the current connectors and cables used to inte~connect

functional elements in the field. The photograph shows a connection panel on one

of the mobile shelters used in a signaling center. This particular shelter contains patch panels for distributing information between telephone subscribers,

switching centers, data terminals, radio receive and transmit sites, and the like.

The shelter may also contain technical control equipment. It serves as a large

IIjunction boxll

, centrally located and star-connected to all of the functional

elements in the area.

Most of the cables shown in Figure 1 contain 26 wire pairs. Reels containing

250 feet of this cable are deployed manually by two-man teams. These reels can be

seen below the shelter. Each cable is terminated with a special quick connect and

release connector. These are joined to the shelter via connectors called hocks.

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panels like the one on the right in the photograph.

The time required to install a CP/SC varies considerably depending on the

sizes the terrain and the cabling procedure (e.g. s buried vs overhead vs on the

ground). Currentlys a complete setups excluding planning and transport times could

require two or three days with 20 percent to 30 percent of this time required for

interconnections. A principal objective of this program is to reduce this deployment time to 1 day or less. Thus s the interconnect time should be on the order of

6 to 8 hours. Howevers reduction of the deployment and interconnect times should

not be achieved at the expense of other essential performance characteristics.

This appliess in particulars to survivability. Network survivability must be

maintained at least at present CP/SC levels.

To achieve this objectives a functional design and specification of a bustype distribution system is needed. The principal study effort reported here

seeks to determine what the CP/SC internal communications network should do.

Therefore the emphasis is on operational requirements and design functions s and to

a much lesser degree on physical structures and implementations.

1.2. Problem Statement

The ultimate objective of this program is to develop and implement a bus-type

distribution system which could be used to replace the existing wire pair and

cable distribution systems in transportable Army command posts and signal centers.

The goal is to provide a means whereby the CP/SC deployment time can be substantially decreased and s at the same times maintain performance at current levels.

Another primary purpose of the study program reported here is to develop

new network topologies which are applicable to the functional design and specification for a bus-type distribution system. To do thats one must consider various

candidate network and bus alternatives. A subsequent program phase would involve

an engineering test model development based on the functional design and specification.

The critical issues addressed in the current study include the following.

Installation Speed Improvement. The time and manpower saved by the use of

bus techniques to install the internal CP/SC distribution compared to currently

used wire pairs and cables.

Flexibility. The flexibility of bus techniques in making the transition from

analog to digital and mixes of services, i.e., voice and data.

4
Service and Performance. The practical limitations of bus capacity in terms

of bandwidth~ number of subscribers~ physical length, signal design, and media

used. Performance aspects involve the quality of service, i.e., access time,

grade of service and delivery delay. For voice signals the intelligibility and

recognizability of the speakers may be most essential.

Survivabil~. This is an essential command post network objective. Survivabil i ty is closely rel ated to vul nerabil ity, nondestructi bi 1ity, robustness, and

re1i abil i ty .

The above issues are recognized as basic measures of effectiveness (MOE's)

and are considered in some detail in Section 8 of this report. Note that the

installation speed improvement and survivability tend to be conflicting requirements if not properly recognized in the functional design.

Additional MOE's are introduced in Section 11 for selecting and evaluating

alternative bus-type link structures. These MOE's are security, modularity,

range, capacity, development risk, cost, and power distribution.

1.3. Technical Approach

An in-depth look at new and evolving technologies is needed to ascertain

whether and how new system concepts, such as a bus distribution system could

beneficially replace existing facilities.

The project was divided into three basic tasks. Task I, Determination of

Requirements, was concerned with identifying, collecting and interpreting the

actual operational requirements of the transportable CP/SC. In performing this

task, a considerable amount of information on tactical communications requirements

and the field commander's needs was collected. This was accomplished by a literature search, discussions with cognizant persons, and visits to tactical field

exercises. The latter included one practice CP/SC deployment exercise conducted

by the 11th Signal Battalion at Fort Huachuca, Arizona, and another full-scale

tactical maneuver called BRAVESHIELD at Fort Hood, Texas. The results of this

task are summarized in various sections of this report.

Task II, Definition and Evaluation of Preferred Alternatives, dealt with

communications distribution system solutions to the CP/SC requirements developed

in Task I. There are a number of bus-type systems which have been tried on a

small-scale basis. Examples include ETHERNET, SPIDER and MITRIX. These and other

bus architectures were reviewed under this task to determine the service they

5
provide (e.g., data, voice, or both), the transmission technique (analog or digital)

employed, the transmission media used (wire, coaxial cable, radio, fiber optical),

the bus access concept (polled, multiple access, or dedicated), the method of

multiplexing or concentrating (time division or frequency division), and other

pertinent characteristics.

With this background information and given the operational requirements from

Task I, overall network topologies were examined using state-of-the-art transmission media to determine alternative bus configurations which might meet the unique

requirements of a CP/SC.

Included in this evaluation of design alternatives for network topology was

an evaluation of system capacity (e.g., bandwidth, data rate, integrated voice/data,

traffic intensity, and priorities) and control protocols. Measures of effectiveness were defined for the distribution system so that preferred alternatives could

be selected.

Task III, Summary Assessment, determined one or two preferred system alternatives after evaluating and summarizing the results of Tasks I and II.

Preliminary analysis of these alternatives emphasized comparisions with

existing systems, projections of critical tactical operational advantages and

disadvantages in the field, and bus concept versatility for the anticipated future

transition from all analog, to part-analog and-digital, to an all-digital network.

1.4. Report Organization

This report is organized into two major parts as indicated in Figure 2. The

first part includes Sections 1 through 7 and is concerned with CP/SC operational

requirements and the existing facilities used to meet these requirements. The

second part includes Sections 8 through 13. Here the emphasis is on new technologies with potential applications for improving the existing facilities.

Section 2 describes the environment in which tactical communications systems

must operate from the user's viewpoint. It is here that the CP/SC bus distribution

application area is defined by giving an overview of the currently envisioned

tactical army structure and its communications needs. This tactical environment

must be considered in any tactical system implementation. It is necessary background material for the five subsequent sections as indicated by Figure 2.

The user's needs are described in Section 3. Here the user is the tactical

field commander, his staff and support elements. The kinds of services which

might be provided to meet this user's operational requirements are classified in

6
2. The Tactical Environment

-.....J

3. USER 4. SERVICES 5. INTERFACE 6. FUNCTIONS 7. SYSTEM

8. Overall CP/SC Network Design

9. DISTRIBUTION

SYSTEM

CONCEPTS

10. SYNTHESIZE

ALTERNATIVES

II. SELECT

PREFERRED

ALTERN.

12. FUNCTION

DESIGN & SPEC

13. REFERENCES &

APPENDICES

Figure 2. Report organization.
Section 4. Providing any service class involves an interface between the user and

the system. For telecommunications systems the interface usually involves some

form of media conversion (e.g., acoustic to electrical). Interface terminals

which have potential application in a CP/SC are discussed in Section 5. The types

of terminals along with their densities and distribution are considered along with

the traffic generation in the tactical environment. In order to transfer this

traffic certain functions must be performed. These functions define what a

system must do, but not how it is accomplished. Functional aspects are considered

in Section 6. Finally, Section 7 addresses the basic system elements used in

current CP/SC networks. In this section the existing concepts used in switching,

signaling, concentrating, multiplexing, and transmission are introduced. Some

aspects of network deployment and system implementation also are covered.

In summary, Sections 2 through 7 introduce the basic concepts needed to

understand the second part of the report, i.e., Sections 8 through 12.

In this second part, the emphasis is on more specific aspects of internal

CP/SC networks, their basic concepts and distribution system subelements. Section

8 covers the overall aspects of CP/SC network design. This is of major importance

to the sections that follow. It is in Section 8 that the general network objectivJs are defined. It also presents fundamental measures of merit - namely installation speed, survivability, service quality, performance, and upgradability.

The concept of hierarchal structuring is introduced. In the relatively small

command post network application this hierarchal level approach breaks up the

design problem into manageable size. This is followed by a subsection on network

design and topology where it is shown how the capacity assigned to various levels

impacts on the survivabil ity. Thi s 1eads to structured network configurati ons

which appear to be suitable for CP/SC applications. Methods for quantifying the

survivability of these structure configurations are then presented.

In Section 9 some important concepts for distribution system design are

reviewed. A three-phased improvement plan is described for evaluations of the

bus-type system. Only by considering the impact of later stages can an optimum

system be developed for phase one.

Using the assumed evolutionary process some functional tradeoffs are described

in Section 10. Preferred alternatives are described in Section 11 so that a

functional design and specification can be outlined in Section 12. Conclusions

and recommendations are summarized below. A selected bibliography for major

topics is listed in Section 13.

8
1.5. Summary of Conclusions and Recommendations

Our review of tactical communications systems currently used in Army command

posts and area signal centers resulted in the following general conclusions.

1. There may be no such thing as a typical CP/SC. Each installation varies

in size, equipment used, configuration, cabling technique and deployment, time depending on the tactical situation, the terrain, and the commander's

needs.

2. Telephone and teletypewriter terminals are presently the major source

of traffic. This analog and digital traffic mix is primarily carried

on 4-wire circuits using multiple wire pair cables.

3. At corps level, and echelons above corps, the number of terminals on a

post ranges from a few hundred to one thousand or more. These are

geographically dispersed in small clusters over an area whose largest dimension is 5 km.

4. Terminal clusters are star-connected to switching and distribution

centers using twisted wire pairs and 26-pair cables. Interconnecting

cables is a major logistics problem. A 300 meter spool of 26-pair

cable weighs over 100 kilograms and several kilometers of such cable

are required.

5. The time required to move a CPISC is highly dependent on the time

required to dismantle, transport, and reinstall the cabling system.

This deployment time could be reduced by replacing the multiplicity of wire pairs with a transparent bus-type distribution system.

6. Network topologies, different from the star-network currently used, could

improve survivability and deployment time if properly configured. This

is feasible as switches, terminals, and transmission facilities are in

a transition to all-digital networks using large scale integrated circuitry.

Based on these conclusions and the result of our near- and far-term forecasts

concerning future tactical terminals and switching equipments, we recommend a threephase improvement program to be conducted at approximately 5-year intervals.

The three phases involve: 1) imbedding transparent bus-type links into the

existing network structure, 2) merging these links with digital switches, and

3) changing the network topology by adding switch nodes to produce an all-digital

structured configuration.

The initial improvement phase requires a development program whose major

activities are concept development, validation, system development, system implementation and system operation. The later sections of this report are concerned

with the concept development activity. Five alternative link configurations are

defined in terms of the major functions to be performed. The major functional

classifications are signal conversion, media matching and transfer mode. The

9
five candidate alternatives selected for further evaluation are listed below for

analog sources. The inverse functions are not listed but are implied.

Alterna t i ve Signal Multiplexing Media Transfer

Conversion Matching Mode

I Discrete Time Pulse Analog

Time Division Amplitude Over DualSampling Modulation Wire Pair

II Narrowband Frequency Frequency Analog

Frequency Division Modulation Over Single

Modulation Coaxial

Cabl e

III Pulse Code Time Bipolar Or Digital

Or Division Unipolar Over

Continuously Binary Coaxial Or

Variable Waveform Fiber Optical

Slope Delta Cabl e

IV Pulse Code Frequency Frequency Quasi-Analog

Or Division Modulation Over

Continuously Coaxial

Slope Delta Cable

V Linear or Time Unipolar Digita1

Adaptive Division Pulse Pulses

Prediction Modulation Over

Coding Fiber Optical

Cabl e

These five alternatives are evaluated using ten selection criteria, namely,

deployment time and manpower, flexibility to the transitional environment, channel

capacity, range, security, performance, development risk, cost, power distribution,

and modularity. Based on our subjective grading, Alternative III has been selected

as the preferred system.

In order to complete the concept development and validation the following

research and development activities are recommended.

1. Development of "Proof of Principal II hardware for capacity, cost, risk

and field adaptability evaluation.

2. Finalize concept design quantitatively based on the initial evaluation.

3. Produce limited quantity of bus distribution systems for field test

validation.

10
------ - -- 

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2. THE TACTICAL COMMUNICATIONS ENVIRONMENT

In this section the environment in which tactical communications systems must

operate is characterized. The first subsection summarizes the physical aspects of

the environment. The second subsection describes the Army theater of operations,

the communications concept for the corps area, the corps signal brigade, and the

functional elements involved in a CP/SC from the communicator's standpoint. The

subsection also defines the CP/SC external and internal communications traffic

requirements in general terms and thereby provides background for subsequent

sections.

2.1. Physical Aspects

Tactical communication systems introduce unique requirements for mobility,

transportability and size, weight, and power restrictions. Tactical communications

systems are more demanding than commercial and public systems regarding operational capability under adverse physical conditions. This physical environment involves

transport via land, sea and air facilities. Restrictive environmental standards,

therefore, must involve the following:

o bounce, shock, and vibration exposure;

o desert, rain, and arctic climates; and

o dust, sand, moisture, salt, and altitude changes.

In addition, provisions must be made for reasonable human comfort control for

operating personnel.

Tactical system standards quantify these physical environment requirements.

These can be found in the appropriate series of military standards documents.

These standards must be kept in mind when reviewing commercial systems for applicability to the CP/SC area.

2.2. Communicator's Standpoint

Today the Army's theater of operations is typically divided by the theater

commander into two zones - a combat zone and a communications zone (COMMZ).

Figure 3 represents such a theater of operations. The COMMZ is a large geographic

area containing the various combat support and service units for the theater army.

Typical sizes range from 0.6 Mkm2 to 1 Mkm 2. Theater forces may vary from three _

to five corps deployed on the line. A U. S. Army Corps consists of one infantry

division, two mechanized divisions and two armored divisions. The corps also

11
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o

I,{)

1f---~-..L.._.L---L---+-_-,---_DIL.-

V1

_

S

I-L0N_S-.L._t--........L.----'-_...a...-...........--t

I

CORPS

IT

CORPS

ill

CORPS

-J--------~---------&------___I

THEATER

COMMUNICATIO NS

ZONE

COMMZ

""

T

Figure 3. Typical theater.

12
includes a separate signal brigade and an armored cavalry regiment. The signal

brigade is of principal concern here.

Corps boundaries encompass an area about 140 km x 250 km. The number of

nondivisiona1 troops in this area may approximate 120,000.

The corps signal brigade provides the communications for the diverse units in

this large area. This corps signal brigade may have 5,000 personnel, 1,300 vehicles, 500 shelter contained assemblages, and over 2,600 km (1,600 miles) of wire

and cable. It provides communications to corps of up to six divisions. The

signal brigade contains the following organization elements:

1. Headquarters and Headquarters Company,

2. Command Operation Battalion,

3. Cable and Wire Battalion,

4. Radio Battalion, and

5. Four Area Signal Battalions.

At full strength each Corps Area Signal Battalion contains four area signal

companies. Each company is capable of establishing an area signal center. The

signal center includes multichannel systems and terminal facilities, extension

links, messenger service, communications system control elements, and equipment

maintenance facilities. The missions, capabilities and other major characteristics

of the signal brigade's organizational units are covered in detail in the Army

Field Manual FM 11-92, dated November 1978.

An example of the network organization of transmission links and switching

nodes in the corps area is shown in Figure 4. Each node may correspond to a CP/SC

for various organizational units from corps to division to brigade level. Transmission facilities to the COMMZ usually involve large distances and require

troposcatter links. In the corps area 1ine-of-sight (LOS) microwave links provide

connectivity over shorter ranges. At the division and brigade level VHF radio

links are normally used. The different means available to electronically transmit

messages are multichannel radio, cable, radio teletypewriter (RATT), AM and FM

single channel radio, and radio wire (RWI) facilities.

Future corps multichannel communications systems may employ tactical satellite

terminals (TACSAT) and automatic switchboards. The TACSAT terminals will be used

to establish communications until LOS links are installed.

The backbone grid network of the corps communications system conceptually

illustrated in Figure 4 is primarily multichannel radio augmented by cable as

13
Division

Support

Command

To

Adjacent.......:---+--------l

Corps

Division Main

Corps

Support

Command

Commz

Corps

Area

Nodes

Figure 4. Corps area network organization.

14
required. Multiplexing equipment combines multiple circuits into one carrier

signal for transmission over a single radio or cable link. The multichannel

circuit can be a voice (telephone), data, facsimile, or teletypewriter circuit.

In this report the communications traffic requirements within and to each

node are the main interest. External communications systems are only of interest

because of their impact on the internal traffic and the local distribution systems.

This is because traffic generated by a node and traffic terminating at a node must

be carried by the internal network. The nodes also serve as relay points and for

routing purposes. This traffic mayor may not be carried on internal links. The

corps main node in Figure 4 includes a main command post, operations center and

signal center with associated terminal equipment. Another node is the rear CP,

usually collocated with the corps support command (COSCOM). Still another node

serves as a tactical command post (TAC-CP). It provides a forward command point

and may serve as an alternate command post if required. Other area nodes provide

links to division main command posts and division support commands (OISCOM).

Alternate communications circuits are provided via OISCOM nodes and the brigade

trains to the brigade commanders. Figure 5 illustrates the functional elements

of one corps main node. The functional elements are interconnected using a starconnected network as indicated. The main patch panel serves as a distribution

center and usually includes the technical control facility. The telephone switch

center (manual or automatic) provides telephone service throughout the area. This

includes life support areas, military police, helipad, and the like.

All functional elements are located in mobile shelters, tents or even buildings. They are dispersed over a 5-km area and covered for concealment from the

air. Usually the radio transmitters and receivers are located some distance away

on a hilltop or roof of a building. This so-called "radio park" provides the main

links for long-distance circuits to and from the command post. Multichannel

cables carry multiplexed PCM signals to and from the radio park. These and other

land lines are installed according to the field commander's requirements. They

are sometimes carried on poles or strung in trees, sometimes completely or partially buried, and sometimes just laid on the ground. The current tactical situation

is usually the controlling deployment factor.

External links to a node, both radio and land lines, determine most of the

traffic. An example of the external links used at one node visited is shown in

Figure 6. This site was installed at Fort Hood, Texas, during the tactical exercise

denoted BRAVESHIELO 19. The entire command post, including the radio park, covered

15
--'

0'\

Local Telephone

Lines

Figure 5. Interconnection of functional units for a typical area signal center.
Los-Microwave

(Exercise HqtrsJ

Logistic

Support

(Coscom)

Land Lines

To DCO Ft. Hood

JOINT

OPPOSITION FORCES

COMMAND POST

SIGNAL CENTER

INTERNAL NETWORK

Typically 3X5 km Area

Troposcatter

Link

165 km toAFS

~~

DCS

(Autovon)

VHF Links

(Opair)

Figure 6. External traffic links to command post used

for operation Braveshield exercise.

17
an area estimated to be 3 km by 5 km as shown by the inset in the figure. This

post was the main corps headquarters for the Joint Opposition Forces (JOPPFORS)

during the exercise. LOS microwave links, troposcatter links and VHF links terminated in the radio park on a nearby hill. Other land-line links provided connectivity to Fort Hood, to the corps support area, and to the Defense Communications

Systems Automatic Voice Network (AUTOVON).

A rough estimate of traffic categories at this post was obtained from the

operating personnel. This is shown in Figure 7. Note that for this post the

largest percentage of traffic was relayed traffic. Only 10 percent was local

traffic. This includes the circuit switched telephone traffic and private line

field telephone services.

Information on the mobility of the corps and division level command posts was

also obtained during the visit to Fort Hood. A corps command post may be required

to move 50 to 100 km every 5 to 10 days. The moves fora division command post

are highly dependent on the tactical situation, i.e., 1 day for high intensity

situations 3 days for medium intensity situations and 10 days for low intensity

situations. Relocation distances are of course much shorter for division CP's

than corps CP's and typically are less than 25 km.

This review of the tactical communications environment provides background

for sections that follow. First the field commander's communications needs are

examined so that the various classes of communications service can be defined.

Then specific terminal equipment used now, and planned for the future, are characterized so the command post traffic handling capabilities can be determined.

3. CPjSC USER'S OPERATIONAL REQUIREMENTS

A major difference between commercial communications networks and the military networks is the user population they serve. Helping to achieve the Army's

mission is an ultimate goal for designers of military networks. Cost is therefore

not always the primary concern as it is for commercial systems designers. Commanders must have communications that are responsive to their needs. Here we review

those needs, summarize important measures of effectiveness for military networks,

and address certain problems that exist in the CPjSC communications environment.

Figure 8 depicts the information flow to and from a command post. These

inputs and outputs are required by the tactical field commander so he can perform

his command, control, and intelligence functions.

18
TRAFFIC FROM CP

OUTSI DE INSIDE

u..J 40% 20%

C)

- RELAY ED OR IG. (J)

I-- a... ::::> c:...:> C>

C>

I--

c:...:>

-

u....

u....

<C

c::::

I--

u..J

C)

(J) 30% 10% :z:

- TERM INATING INTERNAL

Figure 7. Traffic categories estimated for corps main

during operation Braveshie1d exercise.

19
Higher Level

Feedback

Plans

a

Instructions

New Commands

New Operational

Data

Dynamic

,.--- Information

COMMAND

POST

- EVALUATE SITUATION

- MAKE DECISIONS

- ISSUE COMMANDS

- FOLLOW EXECUTION

Lower Level

Feedback

Static

Information

Issue Commands

Figure 8. Information flow to command post.

20
which may evolve from this program should

They also should not introduce new ones.

There are a number of tools for providing the information flow depicted in

Figure 8. These include FM voice radios; hardwired, switched, and private telephones; hard copy messages (includes radio, teletype, facsimile, and courierdelivered written messages); and telemetry data from various sensors. From the

tactical user's standpoint there are a number of factors to consider in the design

and implementation of these systems. Pertinent factors include:

1. Inclusion of operational features which enhance the commander's

effectiveness,

2. The commander's demand for timely response to tactical events, and

3. The background and training of CPISC operating and maintenance personnel.

The effectiveness of any system after implementation depends on how well it

meets the user's needs. Measures of effectiveness (MOE) for military communications

systems have been developed by the Army's Training and Doctrine Command (TRADOC)

using panels of combat officers with command experience. The resulting MOE's are

listed in Table 1. Most are self-explanatory. The MOE "upgradability" has been

added to the original list to account for subsystem designs which encompass periods

of transition from "old" to "new" systems.

Each MOE can be assigned a relative weight and used to evaluate the effectiveness of a tactical system. In this table a subjective evaluation has been made to

determine the irnpact of each MOE on major design aspects of a cPlse distribution

system. The major design aspects are the distribution network's topology, method

of control, signaling techniques, and the transmission media. Note that some

aspect of the distribution network has high impact on at least two or more of the

MOE's listed in the table.

Network topology, for example, has a high impact on survivability, service

quality, upgradability and mobility. We include installation speed under mobility.

The impact of these MOE's on overall network design is considered in Section 8.

Another major concern in Section 8 is quantifying the network survivability.

Other MOE's are considered in appropriate sections of the report.

In the past, and even today, many tactical systems in operation have serious

deficiencies when evaluated against certain MOE's shown in Table 1. Existing

systems are often too vulnerable, too big, too hard to move, require too much

power, and are too easily detected both visually and by electronic and thermal

signatures.

Bus-type distribution systems

reduce most of these deficiencies.

21
Table 1. Impact of CPISC Distribution System on Measures

of Effectiveness

Measures Network Network Comm. Transmission

of Effectiveness Topology Control Technique Media

Survivability High ~1edi um Low ~1ed i urn

Operability Low High Medium Low

Security ~1edi um Medium Low High

Re1i abil ity Medium ~ledi um High Medium

F1 exi bi 1ity Medium High Low Medium

Transportability t~ed i urn Low Low High

EM Signature Medium Low Medium High

Ma i nta i nabil ity Medium High Low t,1ed i um

Service Quality High High High Medium

(Performance)

Availability Medium High Medium Medium

Upgradabil ity High High t~edi um ~ledi um

Mobil ity

(Installation Speed) High Low Low ~1ed i um

22
In subsequent sections we examine existing CP/SC communications systems in

more detail in order to establish a baseline architecture for such systems. This

baseline architecture provides the basis for comparing alternate system configurations. Since our interest is limited to the distribution network portion only,

the number of MOEls used for comparison purposes is limited to those which have

the greatest impact.

4. CP/SC SERVICE REQUIREMENTS

In order to indicate the CP/SC service requirements, it is useful to examine

a general service classification scheme and then to determine which service classes

are used in a CP/SC environment. Figure 9 illustrates one such scheme for classifying telecommunication services. This scheme uses five major bases for division:

1. The nature of the information communicated between end users (analog or

di gital).

2. The type of user information source (voice, sensor or image for analog

services; operator, device medium or application program for digital

services).

3. The number of users participating in an individual transaction (two or

more) .

4. The operating requirement with respect to communications security

(secure or nonsecure).

5. The nature of user application (strategic, tactical or administrative).

There are, of course, other bases of division which could be considered such as

the simultaneity of user information flow (simplex, half duplex or full duplex),

the quantity of information transferred, the terminal compatibility, the switching

technique (circuit, message or packet), the control signaling scheme (common

channel or perchannel), and many others. The method used depends on the viewpoint.

In Figure 9 emphasis is user oriented - not technology oriented.

In nearly all service classification schemes the specific application (i.e.,

administrative, tactical or strategic) determines the quality of service or performance. For the CP/SC the tactical user application is the prime concern.

Referring to Figure 9 the primary tactical services currently provided fall

under two classes: 1) analog, voice, 2-point, nonsecure systems primarily are

used for telephone service; 2) digital, operator, 2-point, nonsecure systems

primarily are used for teletype service. There are a few secure systems,

however, in each class. In the future it is expected that nearly all services

will be secure, that multipoint connections will be used, and that all types of

information sources shown on the figure will be needed.

23
TE LECOMMUN ICATION

SERVICES

VOICE

2-POINT

ANALOG

SENSOR IMAGERY

MULTIPOINT

OPERATOR

2-POINT

DIGITAL

MULTIPOINT

SECURE NON-SECURE SECURE NON-SECURE

STRATEGIC

TACTICAL

ADMINISTRATIVE

STRATEGIC

TACTICAL

ADMINISTRATIVE

SPECIFIC

APPLICATIONS

Figure 9. General service classification scheme.

24
Specific terminals ·and associated equipment currently being used for CP/SC

installation are listed in the following section. Some transitional equipment and

future TRI-TAC systems also are listed. These provide the bases for projection of

CP/SC traffic requirements.

5. CP/SC TERMINALS AND TRAFFIC

The user desiring telecommunications services must interface with the system

at some point. This interface provides the means for media conversions and subsequent transmission of information. In this section we describe the interfaces

or terminals used at a CP/SC installation. This leads directly to estimates of

the internal traffic intensity and traffic types carried by this node.

5.1. Types of Terminals

There are numerous types of communications equipments used by the tactical

forces and numerous ways in which this equipment is deployed. Individual command preferences at all levels - division, corps and echelons above corps - and

requirements result in numerous types of command post installations.

Table 2 lists various equipment available in the current army tactical

(ATAC's) equipment inventory. The table also contains a transitional equipment

column listing new equipment which is expected to be used in the 1980's. During

this period many of the tactical systems will be undergoing change. This is

principally because of a transition from all-analog to"all-digital switching and

transmission systems. By the 1990's a new class of digital equipment developed

under the TRI-TAC program is expected to be in use. This terminal and sWitching

equipment is listed in the third column.

The summary listings in Table 2 include voice terminals, message terminals,

switches, multiplexing terminals, technical control systems, and operations centers.

The type designator is given in the type column using the AN nomenclature. TheAN

nomenclature consists of the name followed by the type indicator letters. A brief

description of equipment characteristics follows the AN designator.

5.2. Distributions and Densities

USACEEIA has prepared Tables of Organization and Equipment (TOE's) for transition planning strategy. These tables determine equipment inventories at typical

installations. The TOE and equipment characteristics (bandwidth, number of channels, etc.) provides an upper bound to the capacity requirements for the local

25
Table 2. Co"~and Post Equipment Summary

---" _.

-

,

IT ATACS (CURRENT) TRANSITIONAL (1980-90) TRI-TAC

---_....

,

T.YPE

AN/ DESCRIPTION MODEL DESCRIPTION MODEL DESCRIPTION . I

TA-l

I

I\LS

I TA-(

) DSVT, DIGITAL SUBSCRIBER

I VOICE TERMINAL

TA-236 2W, Rotary Dial, DC

,

I CVSD, 16/32 KB/S I 4W

TA-312 2W, Ringdown, DC

TA-341 4W, 3x4 Push Button,

MTDF

TA-.720

I TA-838 4W, 4x4 Push Button,

(Field), MTDF

I TA-938 4W, 4x4 Push Button,

(Office), MTDF

INAL GSQ-80 MESSAGE CENTER ,TGC-40 TTY CENTRAL, 2FD

paper tapes& rec& printer

TSC-58 TELEGRAPH TERMINAL

5 or7 level code,

replaces MSC-29, l£!L replaced MGC~17, 2FD

BRIG-DISCOM-DIV

MGC-19 TTY OPERATIONS CENTRAL

CORPS, ITGC-41 TTY CENTRAL, 4FD ,

I

jpaper tapes& rec.

I MGC-22 TTY TERMINAL TAC LEVEL I ICORPS & DIV. MAIN. SC's

CORPS HDQ,:

I

iTGC-42

ITTY RELAY CENTRAL, 6FD

I

MGC-23 TTY RELAY CENTRAL TAC 16/TH-22 TELEGRAPH

I tape, .§£:J2. 112/KW-7 KEY GENERA'J'OR I i j 6/TRANSMIT TTY, UGC-72

MGC-32 TTY OPERATIONS CENTRAL

j 116/UGC-73 REPERF

I

i

I THEATER f 2/UGC-74/75 TTY I

.\ CORPS AREAS- NODES SC'5

II

I:

I

I

I

1

I

i

I

I

I

:

I

\

I

I

I

I

i

I

;

I

i

,

!

I

i

i

!

NAME

MESSAGE TERM

EQUI

VOICE TERMI

~~-_. __._--

N

0\
Table 2. (Continued)

I EQUIPMENT ATACS (CURRENT) TRANSITIONAL (1980-90) TRI-TAC

NAME

TYPE

ANI DESCRIPTION MODEL DESCRIPTION MODEL DESCRIPTION

I

HSPR Hi Speed Pulse Restore

19.2 MB/S

LSPR Low Speed Pulse

Restorer on CX-11230

Max 2304 KB/S

LSCDM Low Speed Cable

Driver on CX-11230

2048 KB/S

LGM, Loop Grp MUX

WF-16 input

7,8,15 or 17 input of

16/32 KB/S +1 overhead eh

256-576 KB/S out

I '

iGM , Group Modem

Diphase 15/72-~L§

rates

Dipulse 4/288-2304 KB/S

rates

Bipolar 1/1536.2 KB/S

• rate

MGM, Master Grp MUX

.115 Switched rates

72 KB/S - 4.9 MB/S

I

TGM, Trunk Grp· MUX

12 Switched rates

72 - 2304 KB/S

4 Groups in

Super out 128-4608 KB/S

MD-I026

TD-12l8

TD-12J-9

TD-1235

TD-1236

TD-1237

Pulse Form Restorer ITD-I023

Unattended repeater in 96

ch PCM in CX-.1l230 Cable

!TD-982

I

TELEPHONE TERMINAL

2 of TD-352, TD-204,

CV-1548 & TSEC/KG-27

1

2 Groups of 12 or 1/24 ch

TELEPHONE TERMIN.l\L

(Secure)

i2,TD-754 CABLE COMB.

!2,TD-660 MUX

·2,CV-1548 CONVERTER

12,TSEC/KG-27 KEY GEN.

I DUAL 12 ch PCM I

capacity~ Corps & Area SC's

I

TELEPHONE TERMINAL

2,TD-204 CABLE MUX

2,TD-352 MUX

1 2 ,GV-1548 CONVERTER

1

2,TSEC -/KG-27 KEY GEN.

I

Groups: 2/12 or 1/24 ch

TELEPHONE TERMINAL

:8,TD-352 MUX

.8,TD-204 CABLE COMBINER

i8,CV-1548 CONVERTER, 12 ch

8,TSEC/KG-27 KEY GEN.

8 Groups of 12 or 4/24 ch

TCC-72

TCC-69

TGC-61

Medium

C-6709

TCC-60

;High capacity- Area scts

TCC-73 ITELEPHONE TERMINAL

4,TD-204/TD-754 CABLE C.

8,TD-660 MUX

8,CV-1548 CONVERTER

8,TSEC/KG-27 KEY GEN.

i2,TD-976 ASYNC-DIGITAL I .( (V) 1 only) COMBINER

,2-48 or 1-96 ch PCM

I

JCONVERTER: Radio/Wire Integ

'''Phone patch"

MULTIPLEXER/

TELEPHONE

TERMINALS

MULTIPLEXER/

TELEPHCNE

TERMINALS

N

.....
Table 2. (Continued)

!

TRI·TAC

DESCRIPTION IMODEL I DESCRIPTION

- AUTO., 300/600 CXT jTTC-39 IAUTO., 300/600 CKT 4W

AUTO.,~, 2W TTC-42 AUTO., 75/150 CXT 4W

AUTO., 30/60/90 CKT \TYC-39 IAUTO., 25/50 MSG line,

SHELTER SB-3614 w CNCE &,TTC-39

SB-38fi5 IAUTO. , 30/60/90 CKT

ULS

SB-36l4

TTC-4l

lMAN., 98 CXT-20TK, 2-SB139 : - AUTO., 344/620 VF/WB

50 KB/S PER TDM sLoT

AUTO.,

MAN., ~, SB248

MTC-9

MTC-3

MTC-7

TTC-28

TTC-25

TTC-29

TTC-23

"0"''''''''' I AT"'" 'CURRENT) I .....".,""AL (19'0-90)---- -rN

00

TTC-35 MAN., 50/100 CXT, SB3082

TTC-38 AUTO., 300/600 VF/WB

SB-22 MAN., 12 CXT

SB-86 MAN., 60 CKT

TTC-30 AUTO., 378 lines c~ossba~ mech.

Low Capacity- Division

TD-I025

ADC, Asyne Digital Cdmbiner

rePlac,e TD-353 & TD-203( I

TD-206 TD-1234

(BiPolar)

8 of 576 KB/S into 4.9 MB/S

MULTIPLEXER/

TELEPHONE

TERMINALS TCC-65 TELEPHONE TERMINAL

4,TD-660A MUX (DIPULSE)

4,TD-204/TD 754 CABLE

4,CV-1548 CONVERTER, 12 ch

4, TSEC/KG-27 KEY GEN.

QUAD. 12 ch PCM

TD-1065

TD-976

HSSDB, Hi Speed Serial

Data Buffer

16/32 ~/S to 576 KB(S

TD-1233/

TTC

RLGM 4 channels Digital

16/32 KB/S or 144 KB/S

RLGM/CD 2 ch Cable Driver

2-72 KB/S or 144 KB/S

RMC Remote MUX/Combiner

I-digital group or 8ch.

72, '128, 144, 256 or 288

KB(S of 16/32 KB/S CVSD
Table 2. (Continued)

N

\0

EQUIPMENT ATACS (CURRENT) TRANSITIONAL (1980-90) !

; l'RI-TAC I

TYPE

NAME AN/ DESCRIPTION MODEL DESCRIPTION : MODEL DESCRIPTION -

RADIO (LOS) GRC-144 4.4-5 GHZ, 30 mile GRC-I03 220-404.5 MHZ GRC-144 4.4-5.0 GHZ

48/96 PCM Ft1 394.5-705 MHZ 14.5-15.35 GHZ

3/TRC-138, TCC-73/TCC-62 695-1000 MHZ 3/TRC-138, MD-I026/

1350.5-1849.5 MHZ MD-I024

GRC-103 220-404.5 MHZ TRC-151, TD-I069, 1152 KB/B to 4.9 MB

394.5-705 MHZ TD-1065 96 ch PCM

695-1000 MHZ SINGLE/DUAL 12/24 ch TAC j6/72/144 @ 32 KB/S

1350.5-1849.5 MHZ TRC-152 SAC 32/64/128

6/12/24 ch PCM @

IRPTR 288,576,1152 KB/S

2/TRC-145 TD-660,

CV1548, KG27 DUAL 12 ch I

3/TRC-113, TD-204/754 !

i

12 ch i

I

GRC-50 601. 5-999. 5 MHZ

1350.5-1849.5 MHZ

4/12/24 FDM or 12/24 PCM @

576, 1152 KB/S

3/TRC-II0, TD-202/204 I 12/24 ch I

2/TRC-117, TD-352, TD-202/

I 204, CV-1548, KG-27

DUAL 12 or single 24 ch I

2/TRC-151, TD-660, TD-202, I TD-754, CV-1548, KG-27

RPTR 12/24 ch !

3/TRC-152, TD-660, TD-202, i

TD-754, TTC-65 or TTC-72

I

i I

I I RADIO (TROPO) GRC-143 4.4-5 GHZ, 100 mile, 1 KW-FM iGRC-143 1/TRC-112, TD-352,

I 12 ch PCM @ 250 KHZ BW ! I TD-660

24 ch PCM @ 500 KHZ BW 12/24.ch or 18/36 ch

1/TRC-112, CV-425, TD-352/ TRC-170 2 KW to 10 KW

TD-660, 24 ch QPSK

2/TRC-121, CV-42·S, :48 ch ,65 KW 1.85 KW 6.6 KW @

100/150/200 miles I

I

; 60-32 KB/S or 120-16 KB/S

2.084 MB/S @ 4. 10-5 BER

I I ! I I
Table 2. (Continued)

w

o

--- I

: EQUIPMENT ATACS (CURRENT) I

, TRANSITIONAL (1980-90) TRI-TAC

TYPE

NAME AN/ IDESCRIPTION MODEL DESCRIPTION MODEL DESCRIPTION

!

TECH. CONTROL/ TSQ-84 ITECH. CONTROL FACILITY TYC-5A DATA COMM. TERMINAL TSQ-lll CNCE, CQl.lb-1 NODE CONTROL

PATCH PJI··JEL rc !replaces SB-675 MSC Interface & Control Mode I (V) ELEMENT

I 14W, 432 CKTS AUTODIN

I 2/CV-1548 Converter, ·24 ch , 12/CV-2636 Converter,24 ch TSQ.,84 (A) TECH. CONTROL FAC. UPDATE I

i !12/TH-22 TELEGRAPH TERM. Mini computer-displayI ' . keyboard i

jTSQ-85 ,VIDEO TECH. CONTROL FAC. I .

I iforms up to 96, 6/12

I !channel PCM video groups I 'to TRC-138 or TCC-73 (V) 1

\ : 96 ch

i \=PANEL

I

\TSC-76 I

,DIVISION !

I I I

iMSQ-73 !TECH. CONTROL FACILITY

; ;240 VF & 120 TTY CKTS

,--- I

I 'SB-675 1

'COMM. PATCH PANELS

~2W, 468 CKTS I

! i

1

1

COMMUNICATION MSC~25 iTACTICAL SC OPERATIONS

I OPERATIONS & ENGINEERING

CENTER ,

i

:MSC-3lA AREA SC OPERATIONS & !

ENGINEERING i ! ! ,

.MSC-32A 'OPERATIONS CENTRAL

\1/SB-22, 2/TT-98, 3/TH-22

:4/TA-312, (used with MSC-31A) I

j I :

I I ; I

I

! i

I I I

I ! !

I I I j

I !

I

I I ,

I
Table 2. (Continued)

COMMUNICATION

SATELLITE

TERMINALS

w

--'

I

1-

!

NAME

EQUIPMENT

I

I

TYPE

ANI

PSC-l

ATACS (CURRENT)

,I?ESCRIPTION MODEL

I

TRANSITIONAL (1980-90)

r

f

DESCRU

''''''''-

I

MODEL

PSC-l

MSC-65

TSCVT

MSC-64

TRI-:TAC

,DESCRIPTION

UHF MANPACK

WSorSMC~ I

VINSON voice or burst mode

i

i UHF Mobile TAT SATCOM TE~.

Ivarious modems & DAMA

!

i"TACTICAL VEHICLE (INTACS)

'Single channel voice or

. record

Brigate up to Theater

,"command Post Vehicle"

:UHF Mobile SATCOM TERMINAl{

100 W with omrii or direc- I

. tional antenna .

75 B/S and/or FM voice

half duplex
distribution area under ideal conditions. The results obtained from the TOE for a

large headquarters signal operating company at the echelons above corps (EAC)

level are shown in Table 3.

Referring to Table 3, the telephone switching centers, switchboards, telephone and teletypewriter terminals, and telephone and teletypewriters sets, etc.,

through which the traffic flows or originates help to define an upper bound on the

traffic that can be handled in the CP/SC. The number of channels that each unit

is designed to carry and the bit rate associated with each channel can be used to

calculate the maximum traffic possible. The two columns on the right side of the

table indicate this maximum traffic for all the assigned units of that type. Note

there are two TTC-38 telephone switching centers, two TSQ-84 technical control

centers, four TRC-138 Is, five TCC-62 telephone terminals, and two TCC-69 cable

telephone terminals through which the telephone traffic flows. There are 1150

telephone sets that originate or receive the traffic. The same division of the

message handlers and message originators can be made for the telegraph and teletypewriter equipment. The four GSQ-80 message centers, the TGC-30 teletypewriter

central and MGC-23 teletypewriter relay central would be handlers and the GGC-3,

PGC-l and KW-7 teletypewriters would be originators of record traffic.

Table 4 summarizes telephone (voice) and teletypewriter (message) terminals

which might-be found in various size units. The voice switch commonly used by

each unit also is indicated. The number in parentheses following the switch type

indicates switch capacity by number of lines it can handle.

The TTY terminals may operate full-duplex (FOX) or half-duplex (HOX). Two

half-duplex circuits are equivalent to 1 FOX. Note that the corps headquarters

MGC-22 has 4 FOX or 8 HOX circuits available. The SC contains a total of 6 FOX.

This also may be divided to handle some HOX circuits.

The distribution and density of the equipments at a CP/SC is highly variable.

In general, however, units tend to be clustered in several groups in the command

post area. The telephone terminals probably are the most widely dispersed although

here, too, the pattern shows clusters with lower density. Teletypewriter terminals usually are collocated in shelters, tents, or buildings in a small area called

the communications center. Switches, patch panels, and technical control centers

are separated some distance away but also are clustered together. Radio terminals

may be still farther away at some high point known as the radio park.

32
w

w

Table 3. Equipment List of Large Headquarters Command Post

NO. OF CHANNELS/ .BANrWIIJIH/ TOl'AL

NOOENCIATURE DESCRIPI'IOO UNITS UNIT OIANNEL .<;; BANIWrImI

'rrC-38(V) 2 Auto., 'lelephone Central

Office Sw. (4 W.) 2 600 tenninals 4 kHz 1200 4.8 MHz

300 Hz-l08 kHz

TSFC/KIr7 Cipher Machine 2

TS<r84 Comrunication Tech.

COntrol Center (4 W.) 2 432 4W. 4 kHz 864 3.456 MHz

circuits

48 Fm TrY 74.2 BPS 96 7.12 KBPS

1 Intercom 4 kHz

CV-2/TX IBta Signal Converter 2

TSFC/KW-7 Electronic secure

Teletypewriter 83

TXC-l Facsimile set 2

GS<r80 Message Center 4

MCS-32 ~rations central

(IDeal Tel. & TrY) 1 4 'lelephones 4 kHz 4 16 kHz

4 TI'Y' 74.2 BPS 4 296.8 BPS

1 Intercom 4 kHz 1 4 kHz

MRR-8 Radio Receiving set 3/2
w

.j:::a

Table 3. (Continued)

NO. OF CHANNELS/ BANI:WIIJI'H/ TOTAL

NG1ENCLATURE DESCRIPrION UNITS UNITS CHANNEL CHANNELS IWIDiIIJrn

VRC-46 Radio set 6

TRC-138 Iepeater ~dio set

(3 GRC-144) 4 288 ch PCM 48 BPS 1152 PQJI 55.3 KBPS

3 (IDeal) Voice 4 kHz 12 48 kHz

1 Intercom 4kHz 4 16 kHz

TSFC/BIr1 Tape Reader 2 2 74.2 BPS 4 296.8 BPS

TH-22/TG 'lelegraph 'lerminal 16

SB-22/PT 'lelephone Manual

Switchboard 1 12 Voice 4 kHz 12 48 kHz

TA-312/PT 'lelephone set 10 1 4 kHz 10 40 kHz

{DC Pulse)

TA-341/Tr 'lelephone set" 1140 1 4 kHz "1140 4.56 MHz

(D'IMF)

CV-1919/G 'lelephone Signal

COnverter

(2 to 4 wire, mMF) 1 3 4 kHz 3 12 kHz

TCC-62 'lelephone Terminal 5 96 PCM 48 BPS 480 23.04 KBPS

TCC-69 'lelephone Terminal

{TOO MUX cable or Radio 2 24 PCM 48 BPS 48 PCM 1.3 KBPS

1 (IDeal) Voice 4 "kHz 2 8 kHz

1 Intercom 4 kHz 2 8 kHz
w

C'1

Table 3. (Continued)

NO. OF CHANNELS/ BANrMID'lH/ TOrAL

NOMENCIA'IURE DESCRIPTIOO UNITS UNITS CHANNEL CHANNELS J3ANIWID'lH

M:;C-22 'Ieletype Terminal

Central 4 4 74.2 BPS 16 1.19 KBPS

TGC-30 'Ieletypewriter Central 1

Office

MGC-23 'Ieletypewriter Relay

Central (tape) 3

GGC-3 'Ieletypewriter Set

(tape-reperforator) 16 1 74.2 BPS 16 1.19 KBPS

PGC-l 'Ieletypewriter Set

(page printer) 16 1 74.2 BPS 16 1.19 KBPS
Table 4. ATACS Equipment and Channels for Unit Sizes

Size Voice Message

Unit Terminal/Wire Switch (Lines) Termi na1 (CKTS)

Squad TA-1/WD-1 ----- -----

Platoon TA-1/WD-1 SB-993 ( ) -----

Company TZ-312/WD-1 SB-22 (12) -----

Battalion TA-312/WD-1 SB-3082 (50) RTTY VSC-2 or

& WF-16 GRC-142

Brigade TA-312/WD-1 TCC-35V1 (50) GRC-122 (lFDX)

& WF 16 or TTC-29 (60) RTTY or

or MTC-7 GRC-142 (lFDX)

Division TA-341/CX-4566 TCC-35V2 (100) RTTY , GRC-122 (lFDX)

TA-312/WD-1 or MTC-3 & I

I

or TTC-23 (100) MGC-17 (2FOX) or I TGC-30 (1 FOX) I

Corp TA-341/GX-4566 TTC-38Vl (300) MGC-22 (4FOX) I

I

HDQ/CP or TCC-25V2 (600) & I

or MTC-9 (600) MGC-23 RELAY 1

I

SC TA-341/CX-4566 TTC-38V2 (600) RTT, GRC-122 (1 FOX) I

or TTC-25V1 (300) & I

I or MTC-1 MGC-19 (5FDX)

FDX - Full Duplex

HDX - Half Duplex

36
5.3. Traffic Generated

The characteristics of traffic generated by various types of terminals are

summarized in Table 5. Traffic rate data are plotted in Figure 10 to show the

rate ranges one might expect from various types of terminals. Typical speeds of

computer peripherals and various computer memory devices are summarized in Table

6. Although computer terminals do not currently appear in the TOE listing, they

undoubtedly will in the future. Card readers and data processing equipment already are being adapted for tactical use from commercial sources. Such equipment

is particularly useful by the corps support command (COSCOM) located in rear

areas. It is used as a data bank for ordering equipment spare parts, or replacement units.

5.4. Traffic Statistics

Traffic data from the Communications Systems Requirements study known as

COMSR were furnished by the USACEEIA/SEO for evaluating the traffic load on a

large command post. These traffic data correspond to a large headquarters using

the equipment listed in Table 3. Evaluation results are summarized in Tables 7

through 10 for voice, TTY, message, and facsimile traffic, respectively. An

adjustment factor of 0.111 was used to convert the daily average traffic load to

busy hour traffic in each case.

The traffic load in Table 7 (voice) and Table 8 (message) is shown in Erlangs

(call-hour/hour). For the voice circuits the average holding time per call was

found to be 3.33 minutes and about 0.1 Erlangs for the CPo These values are

similar to those found for many civilian telephone calling habits.

The average message traffic load of 0.035 Erlangs is based on sending 1 page

of text at 100 words per minute. It assumes there are 10 words per line and 10

lines per page.

This also can be derived from the traffic volume data given in Table 5. For

alpha coded text the volume is 3 x 104 bits per page. The number of words per

page is derived as follows:

3 x 104 (bits/page) x 1/5 (char./bit) x 1/6 (words/char.) = 100 (words/page).

The average traffic load in Erlangs per circuit is obtained from:

BHCA/circuit x (No. of pages) x 100 (words/page) x 1/100 (No./word) x

1/60 (hours/min) = Erlangs (call-hour/hour/circuit)

where BHCA is busy hour call attempts.

37

VllllTrlT1l

IN BITS PER· SECOND

104

VIIIIIZZZI

VIIIIIIII[lllT~

vlllllllllllllI

lZZ1

IZZZZJ

rllllJ

11111III

VIIIIIIIJ

[lll)

VIIIII

1IIIIIIIIIl

DIGITIZED VOICE 102

LINEAR PCM

LOGARITHMIC PCM

DIFFERENTIAL PCM

CVSD

APC

SBC

LPC

CHANNEL VOCODER

FORMAT VOCODER

DATA TERMINALS 0J

1..0 TTY

CARD I/O

MAG I/O

GRAPHIC CRT

OPTICAL SCAN

FACSIMILE

with FEC

without FEC

IMAGERY

SSTV

Figure 10. Traffic rates generated uy various types of terminals.
.;:.

o

Table 6. Typical Speeds of Computer Peripherals and Memory

Character

Type Words/Minute Characters/Second Bits/Second Period

Microsecond

Memory

CCD 7.5 M 625 K 5 M 1.6

CORE 6M 500 K 4 M 2

DISC (Rigid) 6 M 500 K 4 M 2

DISC (Floppy) 3 M 250 K 2 M 4

. DRUM 24 M 2 M 16 M 0.5

Magnetic bubble 4.5 M 375 K 3 M 2.67

~1agnetic tape 300 K 25 K 200 K 40

Semiconductor 15 M 1.25 M 10M 0.8

Peripherals

Li ne pri nter 15 K 1250 10K 800

Card reader 15 K 1250 10K 800

Card punch 6 K 500 1500 2000

Paper tape reader 6 K 500 1500 2000

(hi speed)

Paper tape punch 1200 100 800 10 K

(hi speed)

Paper tape punch 100 8 64 125 K

(10 speed)

CRT termi na1 57 K 4750 38 K 210

Teletypewriter 120 10 120 100 K
Table 7. Busy Hour Voice Traffic Load

Level of Originated Received

P.riority %of Total Load, Er1angs %of Total Load, Er1angs

Traffic Traffic

Routine 80.0 0.076 76.3 0.0627

Priority 14.8 0.014 16.4 0.0134

Immediate 2.8 0.0027 4.7 0.0039

F1 ash 1.6 0.0015 2.6 0.0022

Flash Override 0.0 0.0 0.0 0.0

OrigjRec. Avg. 100 0.094 100 0.082

Overall Avg. 0.088

Table 8. Busy Hour TTY Traffic Load

Level of Originated Received

Priority %of Total Load, Er1angs %of Total Load, Er1angs

Traffic Traffic

Routine 57.7 0.020 77.9 0.038

Priority 39. 1 0.015 20.7 0.009

Immediate 38.8 0.002 1.59 0.001

F1 ash 0.0 0.0 0.0 0.0

Flash Override 0.0 0.0 0.0 0.0

OrigjRev. Avg. 100 0.037 100 0.048

Overall Avg. 0.042

41
Table 9. Busy Hour Data Traffic

Level of Originated Received

Priority Number of Characters Messages Number of Characters Messages

Routine 3.02 x 105 91

Priority 1 x 103 21

Immediate 8 x 102 2 None Originated

Flash 0 0

Flash Override 0 0

Table 10. Busy Hour Facsimile Traffic

Level of Originated Received

Priority Number of Pages Messages Number of Pages Messages

Routine 65 17 2 8

Priority 3 4 0 0

Immediate 0 0 0 0

F1 ash 0 0 0 0

Flash Override 0 0 0 0

42
Table 9 indicates the number of characters and messages transmitted from the

large headquarters during a busy hour using optical character readers. Usually

these are data requested from the headquarters for the support command data processing equipment. No processing equipment is located at the headquarters so no

data are received.

Table 10 shows the number of pages and the number of messages of facsimile

transmitted and received over a one day period.

Table 11, summarizes TTY traffic data obtained during the visit to the

BRAVESHIELD exercise at Fort Hood, Texas. The table indicates the TTY message

statistics for the Joint Opposition Army Headquarters gathered over the six previous days of the exercise. Note that the number of messages transmitted and

received continually increased as the exercise progressed. There were nearly 2.5

times more incoming messages than outgoing messages. This is partly because in

the tactical environment outgoing transmissions can be harmful if detected and

pinpointed by opposition forces.

It appears that, for this exercise, priority P is used most often, closely

followed by O. The average message duration, shown as holding time in the table,

varies somewhat between priorities and days of operation. A typical holding time

is about 1 minute corresponding to 100 word messages. This is less than half the

message holding time used to obtain TTY traffic loads in Table 8.

No traffic statistics were available for the voice circuits used at the

BRAVESHIELD exercise. However, because of staff relocations and telephone changes,

there was a need for operator-assisted calls at the corps headquarters. All other

calls were routed automatically by an electronic switching system. On the second

day of the Fort Hood maneuvers, there were approximately 150 operator-assisted

calls over a twelve hour period at the JOPPFOR command post. The total number of

automatically switched telephones at this post was 116. These operator-assisted

calls probably were less than 1 percent of the total number of switched calls.

At the division headquarters two manual switchboards were used. These handled

200 to 300 calls per busy hour for 100 line terminations. The 300 calls per busy

hour correspond to 0.175 Erlangs per line, assuming 3.5 minutes average holding

time per call.

5.5. Terminal and Traffic Projection Summary

In the previous subsections we have developed a basis for projecting the number of terminals and the traffic load they generate as a function of the CP/SC

43
Table 11. TTY Message Traffic Levels

Priority Day Day Day Day Day Day Priority

1 2 3 4 5 6 Totals

Received

Z (Flash) 0 0 0 1 0 0 1

0 (Immediate) 4 22 28 41 75 122 292

P (Priority) 7 29 66 61 56 95 314

R (Routine) 1 8 15 14 12 16 66

Total 12 59 109 117 143 233 673

Cum-Total 12 71 180 297 440 673 673

Transmitted

Z (Flash) 0 1 0 0 3 0 4

0 (Immediate) 0 4 2 7 40 39 92

P (Pri ority) 0 8 14 25 34 40 121

R (Routine) 0 4 3 5 10 14 36

Total 0 17 19 37 87 93 253

Cum-Total 0 17 36 73 160 253' 253

Average Holding Time (s)

Z (Flash) 0 20 0 0 21.6 0

o (Immediate) 0 53 13.5 13.3 73.8 30.1 NA

P (Pri ority) 0 62 42.6 24.7 74.8 42.5

R (Routine) 0 67 69.5 29.7 78.6 35.4 .

44
size. This sizing relationship is summarized in Figures 11 through 14 for telephone and teletype terminals and the traffic load they generate.

Figure 11 relates the total call attempts per hour to the total number of

telephones. This assumes an average holding time per call of 3 minutes and an

average traffic load per telephone of 0.1 Erlangs. Two curves are drawn. One

curve assumes all calls originate to, or are received from, stations external to

the CP/SC. The other, lower, curve assumes all calls are local calls, i.e., they

originate and are received on the CP/SC. In a real tactical environment the true

curve must be somewhere between the two.

Also on Figure 11 we have estimated the CP/SC size in terms of the number of

telephone terminals existent on the post. These sizes are divided into five

categories: very small «100 telephones), small (100 to 200 telephones), medium

(200 to 500 telephones), large (500 to 1000 telephones), and very large (>1000

telephones). Generally small and very-small size posts may be found at echelons

below corps level. Medium and large posts are found at corps level and very large

posts are found at echelons above corps level. The number of call attempts per

hour expected for each category also is indicated on the figure.

Figure 12 shows the size relationship as a function of the estimated maximum

telephone traffic load. The maximum load is given in Erlangs, E, and is obtained

from:

E = A x T

where A is the maximum number of call attempts per hour assuming all calls are

external, and T is the average holding time per call in hours. The CP/SC size

relationships also are indicated on this figure.

A similar sizing relationship is given for teletype terminals in Figures 13

and 14. In Figure 13 holding time per message is assumed to be 1.5 minutes and

the average traffic load per terminal is 0.04 Erlangs. All messages originate

from, or are received from, external stations.

It is apparent from Figures 12 and 14 that the maximum traffi~ load for a

given size CP/SC is primarily caused by telephone usage. Teletype terminals

generate only about 5 percent of the total traffic.

These projections are useful for determining the maximum load carrying capacity of local bus-type distribution systems. Such systems are described later in

this report.

45
2K 5K 10K

Very Large

500 IK

Small Medium Large

20 50 100 200

Ave. Holding Time = 3 Minutes 5K

........~--- EBC ----...I+- Corps-+ll-oll....;....---EAC ----....

10Kr-----.-------......---..----.-------......---..,..;.--------....----

2K

IK

::J

0

:I 500

Q)

a.

en

0 200

u

100

50

Total Number of Telephones

Figure 11. CP/SC size relationships in terms of number of telephone

calls per hour.

46
;:]

0

I IK

Q)

Q.

(/) 500

0

u

0

- 200

100 -

50

20

100

.

01 0.2 0.5 1.0 2.0 5.0 10

Average Holding Time, hours

Figure 12. CP/SC size relationships in terms of maximum telephone

traffic load.

47
Holding Time = 0.025 Hours (1.5 Min)

(I-V2 Pgs@ 100 w/m)

0

Q)

CJl

E E 0 Cf) ::J Q) -J

>- 0 -0 CJl >- E Q) 0

Cf) -J

I I 5 10 20 50 100 200 500 IK

Num ber of TTY Terminals

500

5

200

l...

100

..... '01(;-----EBC -------:.I~--

IKr----r----r---.......-----T---~-..._;_.,.__~--~-___.

Q)

a.

50

CJ'l

o

(/)

(/)

Q)

20

'0

Q)

10

z

Figure 13. CP/SC size relationships for teletype terminals and

message/hour.

43
Message Lengt h in Pages

Q6 6

::J

:E 100

10•

001 0.01 0.1

60

Message Length in Hours

. Figure 14. CP/SC sizing based on maximum teletype traffic.

49
6. FUNCTIONS AND OPERATIONS FOR CPIse NODE

In the previous sections we have summarized the tactical environmental, the

tactical commander's communications needs, services available to meet these needs,

and the interface terminal equipment he may use. In this section we examine the

functions and operations that a communication system must provide at a CPISC node.

Emphasis is on the internal distribution systems consisting of terminals, transmission, and switching systems.

In order to provide a particular service a system must have certain functional capabilities or attributes. A complete set of attributes specifies the terminal, transmission, and switching system.

Figure 15 summarizes these basic functions. At the same time this figure

indicates basic modes of operations which are performed to provide information

transfer. The operating mode depends on the class of service (analog or digital)

~hich is used and the type of faci'lities available to provide that service. Thus

an analog terminal using digital transmission and switching facilities requires a

codec for analog to digital conversion and vice versa. Note that in this figure

no looping is permissible, i.e., the terminal-to-switch path must follow the same

path back to the terminal since it depicts a single terminal 's connection to the

nearest switch.

In addition to the basic functions of the terminal, the transmission link, and

the switch, there are other functions which must be performed or which may be

added to increase efficiency or reduce cost. For example, control signals are

needed in addition to the information signals so the terminal can access the

network. This includes addressing, alerting, and supervisory signals. Multipliers

or concentrators may be inserted to permit sharing the transmission resources.

In the following subsections we review the basic and auxiliary functions in

more detail.

6.1. Interface Functions

The primary function of the interface terminal is media conversion. The

telephone, for example, converts the acoustic speech signal into an electrical

analog signal. The teletypewriter converts mechanical pressure on the keyboard to

a binary key stream. An additional function involves matching the converted

signals to the transmission media. The TTY binary key stream, for example, modulates a carrier for transmission via wire or cable. A digital source may be

converted to light pulses for transmission on a fiber optical cable. Analog

50
ANALOG

SWITCH

ANALOG

TERMINAL

DIGITAL

SWITCH

a) Analog Service

ANALOG

SWITCH

MODEM

DIGITAL

TERMINALS

DIGITAL

SWITCH

Figure 15.

b) Digital Service

Basic functions and operating modes for digital and analog

services.

51
sources can be converted to digital sources or vice versa using coders and decoders

(codecs) for both transmission and switching. Digital sources may be converted to

analog sources and vice versa using modulators and demodulators (modems).

The terminals on a switched network also provide the control signals for

destination addressing service requests and alerting desired users. Special overhead signals may be used to check circuit status, monitor faults, and provide

overall network management. For transmission of both the control signals and

users information check bits may be added for error detection and correction.

6.2. Multiplexers and Concentrators

Multiplexers and concentrators provide functions for increasing the volume of

data transmitted. This is accomplished by sharing the same transmission path with

a number of sources. This sharing of paths may occur on a time or frequency

basis. Efficient sharing methods reduce the cost per. information bit transmitted

since fewer transmission facilities are required. Fewer transmission facilities

in a CPISC application can also reduce deployment time. Thus multiplexing or

concentrating CPISC communications onto a minimum number of bus type paths is

desirable.

The distinction between multiplexing and concentrating is primarily their

impact on grade of service. Paths through concentrators may be blocked or delayed.

Paths through multiplexers cannot be blocked. This is because multiplexers permit

traffic from several terminals to share the transmission facility by fixing the

allocation of circuits. Concentrators, on the other hand, allocate circuits

dynamically and the transmission facilities are shared randomly as needed.

The bandwidth required at the common output of a multiplexer is the same as

the sum of the bandwidth of the input channels. The bandwidth of the common output

of a concentrator is less than the sum of the bandwidths of the input channels.

As noted previously, multiplexers and concentrators may be of different types.

Frequency Division Multiplexers (FDM's) modulate high frequency carriers from

several sources and these modulated carriers are transmitted in parallel over some

transmission medium. Such an FDM multiplexer is shown by the block diagram in

Figure 16. FDM's are readily cascadable. Synchronous Time Division Multiplexers

(STDM) operate by interspersing information signals in a synchronous time relationship. Specific time slots in the output channel are dedicated to each input

channel. STDM's are more expensive to cascade because a complete STDM unit is

required at intermediate points. Ameans of clocking the time slots is essential.

52
(.J1

w

SUBCARRIER

GENERATOR

I

1 "

L...- Analog 2 Bus

3 ..

Terminals Low Pass

Filters

Modulators

Demodulators

Band Pass

Filters

Figure 16. Frequency division multiplexer.
Asynchronous time division multiplexers (ATOM's) are actually concentrators.

Time slots are assigned on a dynamic lias available" basis. An ATOM block diagram

is shown -in Figure 17. Delays may occur and if adequate buffering is not provided

then some sources may be blocked. The ATOMs are more complex and therefore more

costly but utilize the transmission facilities more efficiently.

6.3. Switching Functions

Switching provides the means for time sharing transmission facilities among

a number of users. There are two basic types of switches, circuit switches and

store-and-forward switches. Circuit switches generally provide a continuous bidirectional path with essentially no delay during information transfer. An initial

delay for setup time is required. Store-and-forward switches are unidirectional

and substantial delays may be encountered. Figure 18 illustrates one method of

classifying switch types. The store-and-forward switch may be either a packet

or message type.

The type of switching function desired depends on the user and the traffic

generated. Usually circuit switches are more efficient for continuous traffic

(speech), message switches for interruptable traffic (TTY), and packet switches for

interactive traffic (computer terminals).

Switches may also be categorized by the technology used to control the switch.

Those used for circuit switches are illustrated in Figure 19. Finally, switches

are distinguished by the method used to control the switch remotely. This is

shown in Figure 20.

In a tactical CP/SC the circuit switch is commonly used. Current technology

is analog, space division with metallic crosspoints. Both manual and automatic

switches are used. A hybrid circuit switch and store-and-forward switch is being

developed for future use on the TRI-TAC program. These switches are designated

TTC-39 and TYC-39, respectively. The TTC-39 circuit switch uses merged (analog

and di9ital) technology in the switching matrix. Detailed characteristics of an

ATACS and the TRI-TAC switch are 'given in Section 7.

Since the circuit switch is commonly used its call processing functions are

of interest. These functions are summarized in Table 12 for each major element

of the switch. The per-line functions are required on a continuous basis. Percall functions are required only during the information transfer time while persetup functions are required only during the access and disengagement time.

54
U1

U1

TERMINAL

1

I TERMINAL I •

2

TERMINAL

3

BUFFER

Time

I .. Multiplexed

Bus

Figure 17. Synchronous time division multiplexer.
SWITCH TECHNOLOGIES

CIRCUIT SWITCH STORE-AND-FORWARD SWITCH

MESSAGE

TERMINAL

EMULATOR

VIRTUAL

SERVICE

PACKET

DATAGRAM

SERVICE

HYBRID - - - - _. ---------

DIGITAL

SPACE TIME

DIVISION DIVISION

-- ......-

COMBINATIONS -------

MERGED

TIME

DIVISION

=---- -- ---- ----- -------- -------- ANALOG

SPACE

DIVISION

(J1

0">

FREQUENCY

DIVISION

METALLIC SEMICONDUCTOR

CROSS POINT CROSS POINT

Figure 18. Switch technology classifications.
c.n

-.....J

MANUAL

(1880)

DIRECT

ELECTRO-MECHANICAL

(1920)

INDIRECT CONMON

CONTROL TECHNOLOGY

ELECTRONIC

(1950)

FULLY PARTIALLY WIRED

.WIRED (ACTION

(DISTRIBUTED) TRANSLATOR)

STORED PROGRAM

(1970)

SINGLE MULTI

PROCESSOR PROCESSOR

~ACOMMON DISTRIBUTED

STORE STORE

Figure 19. Control technologies used in circuit switching systems.
SIGNALING TECHNOLOGY

ANALOG TRANSMISSION

-------QUASI-ANALOG

TRANSMISSION

DIGITAL TRANSMISSION

PER CHANNEl COMMON CHANNEL BORROWED BITS ALLOCATED BITS

(Jl

co DC PULSE AC PULSE ASSOCIATED NONASSOCIATED ASSOCIATED NONASSOCIATED

SINGLE

FREQUENCY

IN BAND OUT-Of-BAND

MULTIFREQUENCY

QUASIASSOCIATED

FULLY

DISASSOCIATED

---_.

Figure 20. Signaling technologies for remote switch control.
(Jl

\0

Table 12. Call Processing Functions Perfonned by Circuit Switch Elements

VI

........ Signaling Control Unit Switching Matrix Interface VI QJ C :::l C 0 0 ": -r-

--J

.......

+J

::5 Attending Input Scanning Battery Feed C I U 'r- (Service Request Overload C +J

0..

QJ

L1..

:::l C Detection) Protection 0

.........

u Hybrid

VI

...- C Supervising Interconnection Codec ...- 0

to 'r- (Ca11 Compl eti on Supervision U +J I U Detection) (Answer and C QJ ::::J clear) 0.. L1..

Addressing Registration Establish Connection Ringer Access VI

C (Sending and Translation Release Connection Test Access

0

'r- Receiving Output Oistri-

+J

U Alerting buting C

:::l (Dial Tone, Path Selecting L1.. Ringing, Busy, Routing 0-

:::l etc.) Busy Text

+J

QJ Establish V')

I Connection

QJ Release 0.. Connection
7. CP/SC SYSTEM STRUCTURE ANO IMPLEMENTATION

Previously, in Section 5, Table 2 listed the Army Tactical Communication

Systems (ATAC's) current equipment inventory, new transitional equipment to be

fielded in the 1980's and a new class of digital equipment being developed under

the TRI-TAC program. In this section specific characteristics of some of this

equipment are defined in more detail. Emphasis is on those units which could

have specific application in a CP/SC bus-type architecture or units which interface with this architecture.

7.1. Switching Systems

Manual Telephone Switches under ATACS include the AN/MTC-l, 3, 9 andAN/TTC23, 29, and 35. Automatic switches include the AN/TTC-25, 28 and 38. The TRI-TAC

equipment includes the AN/TTC-39 and AN/TTC-42 circuit switch, AN/TYC-39 message

switch and SB-3965 unit level switch.

Tables 13 and 14 characterized the AN/TTC-38 and AN/]TC-39 switches, repectively, in terms of the major switch elements.

In addition to these manual and automatic switches the Army occasionally uses

commercial switches. At two of the field exercises which were observed an automatic switch manufactured by Western Electric Corporation, the WECO 400, was

deployed. This switch ~amples the voice signals 8000 times/second and switching

is accomplished by time slot interchange of the pulse amplitude modulated (PAM)

samples. The racks containing the switch elements are shock mounted in a semitrailer for transportability. Maximum capacity of the WECO 400 is 368 lines and

32 trunks.

7.2. Concentrators and Multiplexers

The Army Tactical Communication Systems (ATACS) in the field today are in the

process of being upgraded to allow integration with TRI-TAC equipment. The following equipment is of interest here because it could have application in a bus-type

CP/SC architecture.

Time Division Digital Multiplexer (TODM), TO-1069/G

This TOOM is designed to multiplex several low rate bit streams into a

16 or 32 kb/s channel.

High Speed Serial Oata Buffer, TO-1065/G

This buffer is designed to interface TRI-TAC 16 and 36 kb/s digital subscribers into a ATAC·s 48 kb/s PCM system. Twelve digital subscribers can

replace twelve PCM subscribers.

60
Table 13. AN/TTC-38 Switching System Characteristics

General

Model

Introduced

Application

Interface

Min. Terminations

Max. Terminations

Load/Line (Erlangs)

Adapter

Multiplexer/Concen£rator:

Signaling

Lines

Trunks

Swi tch/Matrix

Technology

Crosspoints

Carried Load (Erlangs)

Control

Technology

Architecture

Max. Capacity (SHCA)

Note

AN/TTC-38

1975

Tandem/End office (Tactical)

320

640

2- or 4-wire

SF/DC supervision, DC pulse or DTMF addressing

SF/DC supervision, DC pulse or DTMF addressing

Analog space division, 4 ~tage

Semiconductor (see note 1)

180

SPC

Central

2700 (600 lines)

1. Crosspoints are normally PNPN diodes which switch 12 channel group level FDM, 4-wire, wideband (80 kHz channel) information.

61
Processor(s)

Number and type

Number of Registers

Word Length (Bits)

Table 13. (cont.)

Custom (See note 2)

24

Instruction Length (Bits): 24+1 parity

Data Bus (Bits)

Address Bus (Bits)

Clock Rate (MHz)

Cycle Time (]..Is)

Access Time (]..Is)

Storage

o Semipermanent

o Permanent

o Off-line

Instruction Set

12.5 MHz

5.6 '

5.6

Ferrite Core

65 K (48 Kimplemented)

Paper tape

Call Processing Inst. 47 K

Maint. &Adm. Inst.

Peripherals

Note

Remote page printer

2. A second processor/memory unit provides backup. Transfer interrupt period is approximately 100 ms.

62
Table 14. AN/TTC-39 Switching System Characteristics

General

Model

Introduced

Application

Interface

Min. Terminations

Max. Terminations

Load/Line (Er1angs)

Digitizer

Multiplexer/Concentrator:

Signaling

Lines

Trunks

Switch/Matrix

Technology

Crosspoints

Carried Load (Er1angs)

Control

Technology

Architecture

Max. Capacity (BHCA)

AN/TTC-39

198?

Tandem/End office

150

750

CVSD @16 or 32 kb/s

DC pulse or DTMF addressing plus others

SF/DC supervision, MF addressing plus others

Digital and analog

Time divided and space divided

180 (600 lines)

SPC

Centralized

3300 (600 lines)

63
Processor(s)

Number and Type

Number of Registers

Table 14. (cont.)

Custom L3050

Word Length (Bits) 32

Instruction Length (Bits): 32

Data Bus (Bits)

Address Bus (Bits)

Clock Rate (MHz)

Cycle Time (~s)

Access Time (~s)

Storage (words) 524 K(max.), 262 K (min.)

o Semipermanent

o Permanent

o Off-line

Instruction Set

Magnetic tape

Call Processing Inst. 195 K

Maint. &Adm. Inst. 30 K

Peripherals

64
Asynchronous Digital Combiner, TD-976/G

Combines up to eight 576 kb/s group bit streams into a 4.9152 Mb/s bit

stream foY' radio or cable transmission.

TRI-TAC equipments being developed for fielding in the 1980 to 1990 era also could

have CP/SC applications in a bus-type architecture. Of particular interest is the

series of digital multiplex and combining equipment known as the Digital Group

Multiplex (DPM) equipment. The following are included in this group.

Remote Loop-Group Multiplexer (RLGM), TD-1233

The RLGM multiplexes four 32 kb/s or 16 kb/s channels and the control

signals into a 144 kb/s or 72 kb/s channel group.

Remote ~1ultiplexer Combiner (RMC), TD-1234

The RMC can accept one digital group input plus up to eight single digital channels. The group input can range from 72 kb/s to 288 kb/s depending

on the source. Two RMC's can be operated in tandem.

Master Group Multiplexer (MGM), TD-1237

The MGM will handle up to 12 digital groups with switchable bit rates

from 72 kb/s to 4.9152 Mb/s. Output rates are 9.36 Mb/sor 18.72 Mb/s.

The Defense Communication System (DCS) may have sites in the COMMZ area at

principal nodes to provide access to the DCS strategic backbone. Digital systems,

either installed or planned, include AN/FRC-162, 165 and 169 radios which use 3-

level partial response transmission systems. The Dig~tal European Backbone (DEB)

will use a new Digital Radio and ~'lultiplex Acquisition System (DRAfvlA). The first

level multiplexer of DRAMA,the AN/FCC-9a), performs analog-to-digital conversion

and time division multiplexing for 3, 6, 12 and 24 voice channels. The digitization

process for 24 channels is essentially the same as for T-carrier used in North

America, i.e., 24-channel, 8-bit PCM at 1.544 Mb/s. The 3-,6-, and 12-channel

modes are used for the Defense Satellite Communications System and the 24-channel

mode for the DCS. The output ports of several first-level DRAMA multiplexers can

be combined in a second-level multiplexer (TD-1193) as follows:

Number of Number of Date Rate

1.544 Mb/sPorts Voice Channels (Mb/s)

2 48 3.168

4 96 6.336

6 144 9.504

8 192 12.672

Digital data can be interleaved by replacing voice channel cards in the

first-level multiplexer. Data rates specified are 0 to 20 kb/s and 50 kb/s

asynchronous and 56 kb/s, 64 kb/s, and 128 kb/s synchronous.

65
The basic process used for voice digitization within the ATACS, TRI-TAC and

DCS are compared below.

ATACS DGM DCS

Digitization Process PCM CVSD PCM

Code Bits Per Channel 6 N/A 8

Number of Channels 12 18 24

Channel Rate 48 kb/s 16 or 32 kb/s 64 kb/s

Group Rate 576 kb/s 576 kb/s 1.544 Mb/s

Signaling Format Unbalanced/NRZ Balanced/NRZ Balanced/NRZ

Table 15 lists the ATAC's PCM specifications for digital voice systems currently

in the field.

7.3. Transmission Links ,

The transmission links provide the access path between end users. Tactical

command posts use various types of transmission media to provide this access path.

The internal CP/SC distribution system is primarily hardwire. Examples of

Army tactical wire and cable are listed and characterized in Table 16.

Types WD-l, WD-14, and WD-36 are a single twisted-pair for a single channel

(circuit) that can be easily reeled out and may be abandoned when moving on. They

are used to connect field telephones which are installed to take over communications

from mobile radios and thereby minimize EM signatures. They are used mainly by

the battalions, companies, and platoons near the forward battle area. VHF/FM

radio is used in conjunction with the twisted pairs to form an integrated radio

and wire system using phone patches.

Four-wire circuits include the WD-16 and spiral four, WD-8. These field wire

cables may be used for an overload backup system in the division level nodes and

corps level nodes. The main interconnection wire in a main CP/SC in the CX-4566,

a 26-wire pair cable. Several 75 m sections of CX-4566 may be paralleled for

carrying the heavy loads of traffic between the message center switch patch panel.

Several lengths in tandem may be used to extend connections to remote sites.

Coaxial cables are used where PCM signals and/or multiplexers are required to

carry 12-, 24-, and 48-channel traffic to the Radio Park, toward the rear echelons,

to the helipad and forward artillary post.

The CX-11230 twin coaxial cable is designed for use with new digital equipment and eventually is expected to replace the .older CX-4245 cables. With a pulse

6G
· Table 15. Army Tactical PCM Specification (from ATACS, 1974)

Characteristics common to all systems:

General

Type of Multiplexing

Type of Coding

Channel Sampling Rate

Digits per Sample Primary Power, Medium and High Traffic

Primary Power, Low Traffic

Audio

Input Level for Full Modulation

Output Level for Full Modulation

Input and Output Impedance

Bandwidth

Signal-to-Noise Ratio FIA

Signal-to-Noise Pulse Crosstalk Ratio FIA

Total Distortion

Delay Distortion

Systems

Low

Traffic ~1edi urnTraffic

Time Division

Pulse Code

8000 per Second

6

109-121 volts 47-63 Hz

109-121 volts 47-420 Hz

-4 dBm

-4 dBm or +1 dBm

600 ohms floating

300 to 3500 Hz

55 dB min.

53 dB min.

3.2% max.

200 JJS max.

High

Traffic

Number of Channels 6 or 12 12 24 48

Volume, cu m (radio

terminal) .07 0.16 0.27 0.28

Weight, kilograms (radio

terminal) 50 100 170 190

Power Consumption,

watts (radio terminal) 80 187 344 278

Bit Rate, kb/s (radio 288 or

system) 576 576 1152 2304

3-dB Bandwidth (radio

system) 240 240 240 935

Pulse Type (ratio system) binary binary biternary binary

Bit Bate, kb/s (cable

system) 2304 2304 2304 2304

Pulse Type (cable system) dipulse dipulse dipulse dipulse

*Two cable systems required for 96 channels.

67

96

0.51

712

526

4608

935

biternary

2340*

dipulse
Table 16. Characteristics of Field Hire and Field Cable

COMMON

TERM

BASIC

CABLE

OR

WIRE ASSEMBLIES LENGTH

ATTN

PER

km

TENSILE

STRENGTH

WEIGHT IN kg LOADING

ADDITIONAL

INFORMATION

0'

WD-1/TT 0.4 km Extruded nylon outer cover (WD-1/TT)

(std A) 0.8 km 1.5 Wet 20 Braided nylon outer cover (WD-14/TT)

Field Wire WO-14/TT 1.6 km 1.0 Dry kg/km 90 None Stranded conductors, 4 copper

(Std B) 4 km 3 steel

Cable, Tel MX-6894/TT 0.4 kin 3.7 Wet 3 Solid Aluminum Conductor #23 AWG

(Assault Wie) WD-36/TT MX-6895/TT 1.8 km 2.2 Dry kg/km 12 None FSN MX-6894 3895-089-7278

(Std A) MX-6895 3895-089-7279

'Cable, Tel 1.6 km 1.6 Wet 20

( Four-Wire, wF-16/U 1.2 Dry kg/km 90 None 7 conductors are copper-cadmium

Field Wire) (LP) alloy, stranded

1320-6 (use

WF-8/G 0.4 km o:>il CU-260

Spiral Four (Std A) CX-1606/G 30 m 0.8 unloaded .130 315 4 CH CXR· o:>nductors are all copper,

CX-1512/U 4 m 0.45 loaded kg/J-..In only) stranded, #19 AWG

Inter-Area

o:>axial CX-4245/G 0.4 km 24 @ 2.304 160 200 None Two coaxial conductors (twisted)

Cable (Std B) MHz kg/kl1l

Inter-Area Two coaxial conductors, improved

o:>axial CX-11230/G 0.4 km 24 @ 2.304 100 340 None connector, improved shielding

Cable (Std A) 30 m MHz kg/km

CX-4566/G 75 m

Twenty-Six WM-130/G or 250 315 None Stranded conductors, 6 copper,

Pair Cable (Std A) 7.5 m 1.5 kg/km 1 steel - #24 AWG

CX-4760/G 5 m
restorer (Type TD-982) at 0.8 kilometer intervals the CX-11230 can provide a 96

digital voice channel capacity at 4.9252 Mb/s. With the high-speed pulse restorer

(TO-1219) located at 0.4 kilometer intervals this capacity can be increased to

18.72 Mb/s.

The spiral four cable is a portable four-conductor field communication cable

used for voice and carrier frequencies up to approximately 12.5 kHz. Approximately

half kilometer lengths of this cable are terminated with a molded connector containing a 6 mh loading coil for decreasing transmission losses.

The U. S. Air Force uses a 100 pair cable (not shown in Table 16), Type 407

L, for multichannel use. This cable is spooled in 300 meter lengths with connectors assembled.

Two types of fiber optical cables (not shown in the table) are under consideration for tactical use. A 2-fiber version is intended ultimately to replace the

WF-16 field wire for digital voice subscribers. A 6-fiber cable ultimately would

replace several 26-pair cables.

7.4. Deployment

Representative deployments of the mobile shelters housing communication

equipment for various tactical CP/SC situations are given in the Army training

circular TC 101-5. Three configurations are illustrated in Figure 21 for a

tactical command post, Figure 22 for a main command post, and Figure Z3 for the

operations center within the main command post.

The actual deployment in the field may vary considerably from that depicted

in the figures, because of terrain, tactical situations, and individual commander1s

preferences.

Two separate visits to tactical field exercises were made during the course of

this program. One visit was made to observe a practice CP/SC deployment exercise

conducted by the 11th Signal Battalion at Ft. Huachuca, AZ. The other, to observe

the CP/SC operations in a tactical field maneuver conducted at Ft. Hood, Texas.

The purpose of both visits was to obtain background information on current procedures on current deployment configurations and operational procedures and on

potential constraints to deployment time in a realistic tactical environment.

The equipment layout for the deployment exercise at Ft. Huachuca is depicted

in Figure 24. A commercial 400 line switch was employed for local telephone

switching and for interfacing with a nearby dial central office on the base. The

various equipments in addition to this switch included the technical control center,

two LOS microwave radio links and a variety of terminal equipments. A total of

69
"Covered and concealed from the air."

{fl RADIO . I

CONTROL -"

MULTICHANNEL

SWITCHBOARD

RADIO

RELAY

Figur~ 21. Tactical command post configuration.

70
MSG

CEN

~CORPS MUlTICHANN rrrr-;, RATT EL ~R':;T

UJJJJMAINT '-"(y

RWI.~

~ATT

SIG PlT

~CP GENR

r X- X- X- :

X

~-X_.X1 m

!~<op ! I · i I )(

I

i "\R.8 I )( )( ~'8 )( I \.. )(-'1.-'1.-)

M~~S-X_X-'HHt'-X-:OF/IJ tJ ~WI !lJ DISTR

HHC

COMMCEN ..

"eovered and concealed from the air."

DIVISION

MULTICHANNEL

SYSTEM

Figure 22. tlain command post conf"19uration

71
x

GENR

USAF RADIO

[][I)

INTEL RATT

TACP, R&S

"Covered and concealed from the air."

ADMIN

G1, G4

x---x---x---x ---x ---x\

x

/'I--X""" R~~TR ~GENR /'GENR '\ ITo

x

r~ATSEssol~ I 'CBRE I RATT X ...-'---'-----.,

x

I. CENTER

'--X-X-XI

X

I

X

I

X

I

X

I

X

X, ENTRANCE J

"'-X---X--X-D-X --- X -- X --X /

~x

x

I

x

I

x

I

x

I

x

I

x

I

Figure 23. Tactical operations center, main CPo

72
LOS

RADIO

TRC-138

JOC

STAFF

TECH. CONT.

TSO-98

o

I!)

(\J

I

(\J

_ a.

r()w

(\J

c\J

MESSAGE

CENTER

Gsa-80

MSC-32

TSC-58'S

D·STE

SEVCOM

LOS

RADIO

TRC-138

WECO

400

SWITCH

fHDQl

Figure 24. Fort Huachuca deployment exercise equipment layout.

73
20 trailer mounted shelters containing these elements and associated power units

were deployed over an area about 300 meters in diameter. The terminal equipment

included radio teletypewriters (RATT) and conventional teletypewriters (TTY), digital

subscriber terminal equipment (DSTE), torn-tape senders and receivers, secure

voice, and secure data terminals. Mobile shelters for all of these terminals were

collocated in a physically secured area compound, i.e., the message center. This

message center contained 15 vans a1ined back to back. The major equipment elements

were star connected to the technical control center outside the compound using

groups of 26 wire pair cables (CX 4546) as indicated in Figure 24. These cables

were laid on the ground and deployed manually from reels containing either 7.6 m

or 76 mof cable. Connections were made to each shelter on panels containing

standard 26-wire connectors (hocks). See Figure 1. A total of 26 reels of cable

was used at this particular site.

The installation of a CP/SC including the internal cabling is accomplished by

command post personnel who check out and operate the systems. Remote cables from

the signaling center to the radio park, the dial central office and other longer

hauls are uS'ually installed by a special cable platoon. A typical cable platoon

consists of approximately 40 men who are specially equipped for this purpose.

The time required to install a CP/SC varies considerably depending on size,

terrain, and cabling procedure (e.g., buried vs. overhead vs. on the ground).

Typically a complete installation excluding planning and transport time could

require two or three days with 20% to 30% of this time required for the interconnections.

The tactical deployment and operations of a Communications-Electronic (C-E)

!network used for exercise Braveshie1d 19 were observed at Ft. Hood. The primary

site of interest was the Joint Opposition Forces (JOPPFOR) headquarters and

associated communications facilities. This headquarters included a joint operations

center (JOC) opposition Army headquarters (OPP-AR), communications center, signaling

center,life support area (LSA), radio site, military police (MP) sites and a

he1ipad. These were interconnected as shown in Figure 25. This installation was

unique in that C-E equipment was collocated for both corps and division level

operations. Normally these facilities would be separated by 50 km to 100 km or

more.

The geographic area which included all the facilities shown in Figure 25 was

about 3 km by 5 km.

74
(/0)

Figure 25. CP/SC facilities and interconnections during

Braveshield exercise.

75
Cabling to each JOPPFORS site is summarized below. The numbers in parentheses

refer to the links shown on Figure 25.

(1)

(2)

(3)

(4)

(5)(6)

(7)(8)(9)

(i 0)

Two 0.4 km runs of PCM cable

Four 400 meter runs of 407 L cable

One 500 meter, lOO-pair cable

One 26-pair cable

In-house wire and 26-pair cable for intra-signal and center

connections

Spiral four cable

Two runs of 26-pair cable

At this location most of these cables for the longer runs were buried underground

by special cable teams prior to the start of the exercise. The 20 rna and 60 rna

teletype circuits sometimes caused crosstalk problems when collocated in trenches

over distances of several hundred feet.

Each separate area had its own power generating plant so that 60-cycle power

cables were not buried in the same trenches as the communication cables.

Approximately 200 telephones were scattered throughout the area. Of these,

approximately half were switched automatically using the WECO 400 switch. The

rest were switched from manual switchboards.

8. OVERALL CP/SC NETWORK DESIGN

8.1. General Network Objectives

The CP/SC communications plant consists of three parts: the user terminals,

the network links, and the network nodes. The majority of user terminals are

field telephone sets. Teletypes and other data equipment comprise a lesser part.

The present network links are single or multiple twisted wire pairs. Rather

typically, one finds 26 such pairs in one multi-wire cable. The network nodes can

be small automatic switches, such as PABX's, manual switchboards, multiplexers

(MUX), concentrators, radio transmitters or receivers, and so forth.

The basic objective of the command post network is to provide required communications services during the service time part of the CP/SC life cycle. Part (A)

of Figure 26 illustrates the four parts of that life cycle. The cycle commences

at a given site with the arrival of the equipment. This is the initial transport

phase. It is followed by deployment and installation of the network. Once installed and working, the network provides its intended service to the military

76
(A)

z: CPISC (.!:) 0 ...".

........ ,,-

........ I--

<I:W NETHORK -lw

-l:E: IN-SERVICE t;;:E: -l ........ .......- .........

<I: I-- <I:I--

I-- TIr~E :E:

C/) C/) ........ z: q

TRANSPORT ........ TRANSPORT

(B)

WORKING

CIRCUITS

TI~lE

Figure 26. Typical life cycle of the command post network.

77
command post. At the conclusion of the CP mission, the service time gives way to

dismantling and securing all movable gear into transport vehicles. Finally, of

course, the removal turns into another transport phase. A new cycle of the CP

network can now begin at a different staging area.

This section is concerned with three of the phases: the installation time,

the in-service time, and the dismantling or removal time. As shown in Figure 26,

part (B), the full capacity of the working circuits is only available during the

established in-service time. Various fragments of the network may be functional

and working during the installation and dismantling times.

In providing the needed communications services to its tactical users, the

network must meet many functional objectives. They include transportability for

rapid arrival and departure. They call for fast and trouble-free installation of

the system. They also encompass initial troubleshooting, turn-on, modification,

normal maintenance, as well as emergency operational measures. The emergency

measures can seldom be fully anticipated, as they occur in response to destructive

field events of varied magnitude.

This section reviews the general CP/SC objectives. It also presents functional

measures of merit. The latter are design yardsticks to check how specified requirements and objectives are met. To do that, the three network parts, terminals,

links and nodes are viewed as a joint mechanism throughout the three~part life

cycle of the network. This approach is emphasized in Table 17.

Table 17 presents 16 conventional network objectives. In alphabetical order

they are: availability, connectivity, ... , transportability, upgradability.

There tends to be considerable overlap, or mutual impact, or cross-correlation

between these parametric descriptors. This cross-correlation is indicated in

Table 17 by the numbers, scaled 1 to 10, at the intersection of two parametric

objectives. For instance, service availability has a relatively low cross-correlation

to system performance (score 2), but a high correlation to grade of service, i.e.,

probability of blocking (score 9). The numbers in Table 17 are to be interpreted

as approximate and very vague indicators only. The given numbers reflect the

authors' subjective judgement only. They are apt to vary among individual designers,

because of non-uniform interpretations of the parameter definitions, time varying

importance of certain objectives, as well as the mission-oriented nature of certain

command posts and their military significance.

In what follows, installation speed, survivability, service quality, performance and upgradability are recognized as most basic. Service and performance are

combined into one, because of their relatively similar cross-correlation properties.

78
Table 17. Qualitative Cross-Correlation Between Conventional Network Objectives

-0

Q)

>, Q) Q)

>, >, Cl.. U .,.... V') .,.... >, r- >, .,.... .,.... > .,.... r- r- s:: Q) >, .,.... .0 .,.... >, Q) >, .,.... 0 Q) >, r- r- ::s u >, .0 .,.... V') ::s .,.... .,.... .jJ .,.... a ..,.... s:: .,.... .jJ .,.... > .0 .0 >, r- r- .,.... s:: 4- r- .,.... 0 Q) .,.... E .,.... .,.... r- 0 .,.... s:: .jJ

-0 Cl.. > U .,.... .0 .0 r- .0 0) U V'l .,.... .,.... 0 r- Q) .,.... .,.... Q)

s:: > > ::s .,.... 4- ::s s:: .jJ "0 X V') s::

0) U r- Q) "0 .,.... V'l Q) s::

Cl.. ::s Q) Q) Q) Q) Cl.. 0 s:: r- ::E 0 :::::> l- V') V') V') ex: 0.. 0 ::E ::E ...... c.!l LJ... UJ u

Ava il abi 1ity 6 7 7 2 4 9 5

Connectivity 4 8 3 3 5 6 2 1

EM Signature 6 6 6 4

,

Flexibility 7 I 1 1 2 3 4 2

Grade of I Service , 5 6 4 2 3 i

Installation !

Speed f

\ 7 4 5 8

-+--i

Maintain- ,

i

bil ity 1 i 2 5 9 3 5 7 ! i

Modularity 6 1 5 1 1 3 I

Operabil ity I 6 5 4 I

Performance 8 6

Re1i ab i 1ity I 3 7

Security i 2 f

Service i

Qual ity I 1 "

Surviv- I

I

i

abil ity ,

I 3 i

Transport- I I

ability I I

79
The summary definitions and descriptions of these main network design objectives

are given next.

8.1.1. Installation speed

It is often imperative that at new command post sites the communications

plant be installed and working in a short time. This includes the deployment or

dispersement of terminals to their assigned locations; the placement of nodes in

shelters (e.g., vans or tents); and their interconnection with the required capacity lines or links. The total installation is, of course, not complete until the

system works. To this end, initial diagnostics and installation repairs are often

needed.

Field reports indicate that at present most time and man-machine effort is

consumed in link (e.g., multi-pair cable) installation, such as burial of the

cable a one~third meter or so below the ground. Together with other time-consuming

installation jobs, it tends to take more than one day to set up a modest command

post.

A key objective therefore is to reduce the network, and particuarly the

cable, installation time. This cabling requirement is alleged to be more critical

than installation times for all other CP elements. It is deemed more urgent than

the removal or dismantling times required later by the various equipments. There

also appears to be far more merit in reducing installation time than, for instance,

in minimizing in-service repair or maintenance efforts.

8.1.2. Survivability

Survivability is essential to the command post and its network objective. It

is stressed throughout the network design section.

The definition of survivability is closely related to invulnerability, nondestructibility, robustness, and even reliability in the larger sense.

Network reliability refers to the probability, or percent of time, that a

network will work satisfactorily under normal conditions, or to the user's confidence in the network is satisfactorily working. Survivability and invulnerability, on the other hand, address network performance under adverse, damaging,

and specially debilitating circumstances. If said circumstances are caused by

nature, such as floods, storms, extreme temperatures, or even by human oversights -

not to mention man-made accidents - one may talk of system vulnerability or

invulnerability. When the conditions are substantially caused by actions by

enemies or potential hostile forces, one tends to use the term survivability.

80
The above definitions, unfortunately, are neither precise nor widely accepted.

Survivability will be used in the present context to depict the network ability to

work or the probability of its working satisfactorily in the tactical command

post environment. One should stress that the phrase IIworking satisfactorilyll

can be subject to many interpretations. Such interpretations, see Table 17, are

related to service availability, grade of service, operability, performance,

service quality, etc. They are discussed next.

8.1.3. Service and performance

A circuit switching network provides communications circuits or paths between

terminals so that communication can occur. At the military command post level, at

least to the authors' knowledge, it is an unresolved tactical requirement whether

all terminals should be able to reach all other idle terminals. And whether this

should be so at all times and under all tactical scenarios. Without going into

further detail, we stipulate here that as a network service requirement lIall

essential CP connectivityll shall be provided.

Another issue concerns the quality aspects of the service. Here one encounters

the probability of network blocking (i.e., the grade of service) and the associated

statistics of delay, such as mean delay and variance thereof. Once the connection

is established, the signal quality is affected by the transmission path. Signa1-to~

noise ratios, phase and amplitude distortions, crosstalk, and other effects,

become apparent. For data messages, there may be too many errors or deletions to

suit the recipient. For voice signals, the intelligibility, the clarity, or the

recognizability of the speakers may be essential.

It is realistic to require that, in addition to providing terminal interconnection, the CP network be engineered to provide signal quality performance measures that satisfy the military standards for data and voice communications.

8.1.4. F1exibi1ity/Upgradabi1ity

Telecommunications and related technologies have developed rapidly over the

last ten to twenty years. More advanced developments may be predicted for the

future. The design must be flexible in order to adapt to changing technology. No

matter how expedient or firmly established a CP network design may appear now,

there is a strong possibility that it may be upgraded within the next five to ten

years. This upgrading compatibility represents a significant, albeit a somewhat

long term, network design objective.

81
The network design must combine present utility with realistic future upgradability. There should be a minimum of technical constraints, so that at some

unforeseen future date the CP/SC communications network can be modified, either

partly or fully, to take advantage of advanced engineering developments.

8.1.5. Other measures of effectiveness

Elsewhere in this report, various measures of system effectiveness (MOE1s)

are introduced. Some of them, such as availability, EM signature, flexibility,

maintainability, operability, removability, security, and transportability were

partly listed in Table 17. They are not explicitly analyzed in this network

design section. However, this does not imply that they have no impact or significance in command post network design. Additional studies may be needed to establish and document the CP/SC roles of these and other network objectives.

8.2. Hierarchies

This section introduces hierarchal structuring to command post network design.

Hierarchal structures have been employed with considerable success in the engineering of numerous large telecommunication networks. In the relatively small command

post network application, the hierarchal approach may be justified for several

reasons.

8.2.1. Reasons for hierarchal levels

To start, a properly chosen hierarchy breaks up the design problem into

smaller, more manageable elements. It identifies difficult subsystems and isolates

trouble spots from the rest of the system.

Second, the hierarchal model promotes engineering in response to modified

design objectives. This happens, for instance, when different numbers are tried

for the previously emphasized objectives of installation speed, survivability,

service, performance, and so forth.

Third, the good hierarchal levels tend to help themselves. That is, they

suggest improvements in the level makeup. Usually this occurs through separation

into independent subsystem functions. Identification of their unique parameters

and their optimal numerical values are important to hierarchal level design.

Consider the general problem illustrated in Figure 27. Given user terminal

statistics and external gateways, a network is to be specified. Typically, the

82
Network

to be Specified

through Node

and Link Functions

that Meet the

Network Design Objectives

• • •

Use r

Figure 27. Conceptual definition of the command post network.

83
specification is functional in nature. Later specification is more quantiIt defines the functions in terms of parameters and their numerical

initial

tative.

values.

The hierarchal approach taken here assigns both nodes and links to different

system parts, called hierarchal levels, or sometimes hierarchies. Each part has

some unique identifying features. Usually, the number of hierarchy levels does

not exceed six or so.

8.2.2. Hierarchal example

One elementary and quite practical approach to hierarchy assignment is shown

in Figure 28. The figure illustrates four hierarchy levels with relatively

straightforward functions.

The first and lowest level consists of user terminals, such as telephone

handsets, and their station loops. A station loop is usually a twisted-wire pair.

In the exceptional cases of four-wire operation, as might occur for data or secure

voice, more than one pair may be deployed. The network functions performed at

this hierarchal level number 1 are the familiar local telephone loop functions.

The second hierarchy level in Figure 28 contains loop or line concentrators

and multiplexers (MUX'es), as well as the concentrated tie lines (or buses or

trunks), that tie the MUX units to the higher level switches. Note: To distinguish

between the two, a MUX may be visualized as an unintelligent, pre-wired, multiterminal patch-board. A concentrator, on the other hand, may possess various

degrees of intelligence. It may select any of several channel routes for a requesting terminal. Neither concentrators, nor MUX'es, perform any circuit switching.

At the third hierarchy level, the switching, processing and control functions

take place. At this level, Figure 28 shows three switches, plus a pair of operator consoles. There are also various trunks and tie-lines included in level

three. The switches could be small PBX's, or PABX's, or manual switch boards.

The switches are heavily interconnected to provide redundant backup paths in case

of bus or even switch outages.

The fourth and highest level in Figure 28 is shown to consist of a satellite

earth station, plus a radio center, and the associated tie trunks to the switch

level. In the notation of Figure 27, the satellite and terrestrial radio facilities serve as exterior gateways for the relatively localized command post network.

84
co

01

@

/

®

Hierorchy Levels /

CD

SATELLITE

STATION

User Terminals

Figure 28. A four-level hierarchy network.

RADIO

CENTER
The general objectives of Section 8.1 must be addressed from the vantage

point of a given hierarchy. Thus, installation speed, survivability, performance,

and potential for updating are projections (viz., like coordinate axes) of the

corresponding functions performed at the hierarchy levels of Figure 28.

Clearly, installation time is reduced when the sum total of cable spans and

distances is reduced. In the four levels of Figure 28 this has different implications. At levell, the matter is perhaps the simplest. Each user terminal has

nominally one path to the network. As long as that remains so, and no nodes are

added, deleted, or reconfigured, the line distances of level 1 can be minimized

only by connecting the user stations via a star configuration to their nearest

concentrator, multiplexer, or to a switch.

At the second hierarchy level, there are more options. First, one must

select the appropriate number and types of concentrators or MUX units. Second,

one must assign them to suitable locations, so as to reduce the overall cable and

line distances. This topological problem extends outside level 2 proper. It

depends on the geographic scattering of user terminals, as well as on the nodal

constraints.

At the third level, most communications traffic is further concentrated,

switched, and otherwise controlled. The switching centers may often, but not

always, be in relatively central locations, not too distant from each other.

Therefore, the total cable distance is not dramatically increased by redundant

interconnection of the switches. At .the same time, the enhanced connectivity

between switches aids the broad survivability objectives of the network.

The fourth level has the radio gateways. This so called radio park is

ordinarily quite remote from the hub of the command post. The actual placement is

dictated by the terrain, the EM emission, hazards and command decisions. At this

level the networking options are somewhat limited. A single link to each of the

radio transmitter/receiver vans may lessen the cable length. However, to increase

the CP tactical survivability, some backup circuits may be worthwhile. Figure 28

shows two paths to both the satellite station and to the radio center, respectively,

at the hierarchy level 4.

8.2.3. Levels and distance objective

A quantitative summary of typical link distances for the main network elements

is given in Figure 29. It is seen that all communication units of a command post

are distributed within roughly 3 km=2 mi of the central switches of the post. By

86
Level 4:

Level 2:

o

Concentrators1MUXIS

to Switches

2 3

Terminals to

Switches (without Concentrators)

-----"""-

"""-.........

"-

I

Levell:

o

Terminals to

Concentrators

-- - 2 3

Distances (km)

Figure 29. Typical CP/SC link distance distributions.

87
definition, closest to the center may be the switches themselves. They, plus the

nearby controls, comprise hierarchy level 3. The distribution of distances to the

radio park (level 4) appears to have the largest mean, namely 2 to 3 km.

If there were no concentrators or multiplexers, that is, if level 2 were

removed, the distances to individual terminals could be widely dispersed. This is

shown with the broken curve in Figure 29, level 1. Without concentration, the

user terminals could be located anywhere from 0 to 3 km from the switches. The

introduction of level 2 concentrators serves to reduce the station loop lengths to

the order of 1 km or less. To achieve that, however, the concentrator to switch

distances must be taken into account. Figure 29, level 2, shows these concentration/MUX distances to average around 1 km.

8.2.4. Levels and other objectives

Different network design objectives are differently affected by hierarchy

level modifications. One has already seen how the level 2 introduction reduces

station loops at a cost of concentrators and their higher capacity cables. The

net effect could be a reduction in overall installation time. There is, however,

a problem of contrary objectives. To enhance survivability or connectivity of

entire user groups, redundant concentrator cables may be desirable. Survivability

measures that add extra cable spans counteract the objective of minimizing the

installation effort.

Survivability enforcing cable redundancy seems more effective at the higher

hierarchy levels, such as levels 3 and 4 in Figure 28. Other objectives, such as

those discussed in Section 8.1, also appear to be somewhat level selective or sensitive. This sensitivity of objectives at the suggested hierarchy levels is summarized

qualitatively in Table 18. Three descriptors, low, medium and high, are used to

reflect the bearing that a certain hierarchy level has on the assumed objectives.

Thus, for example, level 2 is alleged to have a higher impact on installation

speed.

As a preliminary design tool, Table 18 can be used as follows. At the first

pass, all highs should be addressed. That is, level 2 should be designed to minimize installation speed. Level 3 should be tailored for improved survivability,

performance and upgradability. And for the final high, level 4 should stress

survivability.

The second pass may concern medium impacts, and so forth. Conflicts between

different objectives and level pairs are resolved through cost-benefit! tradeoffs.

88
OJ

1.0

Table 18. Hierarchy Level Impact on General Network Objectives

GENERAL NETWORK OBJECTIVES

INSTALLATION SPEED SURVIVABILITY PERFORMANCE UPGRADABILITY

4 MEDIUM HIGH MEDIUM r~EDIUM

3 MEDIUM HIGH HIGH HIGH

HIERARCHY 2 HIGH MEDIUM LOW MEDIUM LEVEL

1 LOW LOW MEDIUM MEDIUM
8.3. Network Design and Topology

The overall design of a network has four parts:

(1) Identifications of nodes and terminals.

(2) Assignments of links or connections.

(3) Capacity assignment.

(4) Flow control specification: switching, routing, management, and so

forth.

The first two parts are inherently topological. The last two parts are strongly

dependent on topologies used.

For the command posts, the number of nodes and terminals are relatively

small: there may be 1 to 6 switching nodes and from 100 to 500 user terminals.

Their locations are often determined by terrain conditions, field commander

decisions, and other nontechnical factors. The first topological part (1) is

thus removed from the technical design arena.

In this section we review the remaining parts (2) and (3) of the network

design. Secause of program constraints, part (4) is not included in this study.

Part (2) discusses the connectivity issues. It presents most of the topological

material contained in this study.

8.3.1. Linking of nodes

In the real operational world, with its uncertainties and day-to-day changes,

precise optimal algorithms may not be superior to common sense and quickly imp1eented rules of thumb. In what follows, we review the connectivity problem based

on the premise of overall utility. Emphasis is placed on the key objectives

introduced earlier in Section 8.1.

The CP/SC networks may contain several node types (e.g., multiplexers, concentrators, automatic switches, manual switchboards, etc.) and at least two kinds

of user terminals (i.e., ordinary field telephones and teletypes). When one talks

of nodes and terminals in the general context, one presumes that the entities

mentioned could be any of the above.

Consider the four-level network hierarchy discussed earlier in Section 8.2.

Network design must, among others, specify the topological connectivity between

levels and within each level. For example, at the level 1 of user terminals, the

station loops are nominally strung without backup - in a star configuration - to

the nearest network node. This star topology appears as a leading alternative for

level 1 connectivity.

90
At higher hierarchy levels, such as at level 3 of the switches, there may be

far more connectivity and the appropriate network may contain several loops. Note

that in Figure 28, the three-switch net at level 3is fully interconnected by the

single loop shown. The inclusion of the two consoles makes this a five-node

network. That version has more loops, but is not fully interconnected.

Consider the situation of Figure 27, where the set of user terminals and

exterior gateways is specified. To have something concrete to talk about, let

there be 300 terminals, 3 gateways, and assume that only one switching node is

available. Then the first network topology alternative is the familiar star, see

Figure 30.

The star configuration has three hierarchy levels. Levell has ·the 300

terminals and their respective station loops. These are the previously mentioned

twisted-wire pairs. Level 2 consists of the central switch hub. It contains all o

network controls either automatic or manual. Level 3 has the three exterior

gateways. Depending on the amount of distant vs. local traffic, the links to the

gateways must be appropriately sized multichannel cables.

The three-level star network of Figure 30 must be assessed in terms of the

general network objectives of Section 8.1. One finds, of course, that the installation time objective boils down on just how fast the 300 plus 3 lines can be deployed.

The total line distances (see Figure 29) are estimated to be:

Single twisted pair, not buried

Multipair cable, buried

450 km.

8 km.

Thus, a grand total of roughly 460 km lines must be laid.

The burial or trenching distance is reducible when groups of terminals are

clustered (as in a HQ' S complex or a message distribution tent). One merely

gathers as many lines as possible into a common trench (see Figure 31).

A simple extension of this spatial combining (sometimes called space division

multiplexing OY' SDM) assembles clustered users onto multipair cables. In typical

division or even corps-level installations, the 26-pair cable is quite adequate.

Often the cable may be only partly, such as half, wired. In rare instances at

corps level, the 100-pair cable is really needed.

The SDM cables extend from the switch outward. They terminate in individual

junction boxes, wherefrom station loops are fanned out in their own directions.

Return briefly to the trench distances for Figure 31. Realistically, let 50%

or 150 of the 300 terminals share common 26-pair cables. Then (see Figure 29 for

typical distances) the line distances are on the order of:

91
SWITCH

1

2

3

299

Figure 30. The star network.

92
1

SWITCH

1

Common

Trenches

3 4

Figure 31. Space-division-mu1tip1exing (SDM) or common

trenches for the star network.

93
Single twisted pair, not buried

Multipair cable, buried,

300 km.

20 km.

Now, a grand total of 320 km lines must be laid. The approach illustrated in

Figure 31 thus compares favorably with the pure star of Figure 30.

The three-level hierarchy of star, as shown in both Figures 30 and 31, has

apparent survivability shortcomings. After all, the failure of a single node, the

centralized switch, brings the entire network to a halt. Individual line cuts

affect only a single terminal, if they occur on the user terminal side. On the

other hand, if they occur on the gateway side, they tend to cause serious exterior

connectivity problems.

The other network objectives of service, performance, future updates, and so

forth, seem to offer no particular difficulties to the star configuration.

The three-level hierarchy can be extended in several ways to higher level

hierarchies. A simple extension is shown in Figure 32. The new hierarchy consists

of the previously mentioned four levels. An additional level of concentrators and

multiplexers is added on the user terminal side of the switch. And, the exterior

gateways are mutually interconnected to enhance their survivability against link

outages. By the way, the links between gateways, the links between gateways and

the switch, and the links between the concentrators/multiplexers and the switch

are assumed in Figure 32 to be higher circuit capacity multichannel buses. These

could be the previously mentioned space division multiplexed (SOM) , frequency

division multiplexed (FOM), time division multiplexed (TOM), or any other transmission mode or medium with sufficient capacity. The buses, be they cables or

optical fibers, should be buried for field survivability.

Basically, the single switch in Figure 32 still occupies the same vulnerable.

spot as in Figures 30 and 31. The outage of the switch node has catastrophic

consequences on the entire network.

To improve the network survivability, additional switching nodes should be

provided. It is intuitively clear, that, depending on the number of switch nodes

and their connectivity, the individual node and link outage consequences can be

variously suppressed. This enhances survivability. However, it also requires

more installation time for both the added cable spans and for the setting up of

the switches. This is particularly true, whenever all the switches are fully

interconnected among themselves.

Figure 33 shows the fully interconnected versions of the switch hierarchy

level only. This would correspond to level 3 in Figure 28. The four parts of

94
3

SWITCH

1

. ". .

Multi -Channel

Buses

299

300

Figure 32. A four-level hierarchy with centralized switching.
1

1

1

3

4

2

5

2

2

3

2 Switches

3 Switches

4 Switches

5 Switches

Figure 33. Fully interconnected, distributed switch

hierarchy level.

96
Figure 33 show the fully connected topologies for 2, 3, 4 and 5 switches. The

network elements on other hierarchy levels, such as user terminals, external

gateways, or multiplexers, are purposely not shown in Figure 33.

There is no question, that the high switch network survivability inherent in

the large number of fully interconnected nodes is bought at the expense of expanded

cable plants. Roughly, for such configurations, the total cable distance grows in

proportion to the square of the number of switches. The installation time grows

proportionally. This contradicts the first design objective, namely that of

minimal installation time. Some configurational compromise appears needed.

Various compromise networks are introduced in the next sections.

8.3.2. Capacity assignment

Both links and nodal elements can generally be engineered to carry varied

amounts of telecommunications traffic. In circuit switched applications for

command post networks, this boil s down to spec ifyi ng the number of call s (or busy

terminals) that can be served at the sundry levels of the network. The specification usually is only valid for a time period of interest, such as the worst case

or busy hour of the day. It is also based on the realization of a desired grade

of service for the community of users.

Insufficient switch and/or line capacity results in calls not getting through

when the other (called) party is idle (on hook). The probability of such call

blocking is normally referred to as the grade of service. A typical design objective in the commercial telephone world is a busy hour 1% grade of service. Then,

on the average, one out of a hundred calls is likely to be blocked. If blocked, a

service request could be dropped (lost) or allowed to wait (queued).

In the CP environment, the priority classes (i.e., P, R, 0, Z) may preempt

each other according to specified rules. This reduces the probability of blocking

for the higher classes to essentially zero. And, since the number of high-classification terminals is small, it increases the blocking of the lower classes only

by a very slight amount.

The following ideal grade-of-service situation will be assumed here. In its

fully implemented operational state, with no link or node outages, it is assumed

that the network is fully nonblocking. That means that any pair of idle terminals

can promptly communicate with each other. Grade of service impairments then occur

only when some nodes or links, or both, are disabled.

To protect against such grade df service degradations, i.e., to reduce the

network vulnerability to subsystem outages, one may supplement and reinforce the

97
network in various ways. For a fixed node arrangement, one can add more links

(viz., increase the connectivity) or one can add link capacities, or both.

A two-step capacity assignment is illustrated in Figure 34. Both parts (A)

and (B) display the same concentrator and switch hierarchy levels of a potential

installation. Three switches and two concentrators are shown. Each of them is a

hub (i.e., collection point) for a number of user lines. That number of terminals

is indicated adjacent to the nodes of Figure 34. Thus, switch 1 serves 48 stations, switch 2 has 36, and switch 3 is the homing point for 24 station loops.

The two concentrators are assumed to have 12 and 6 terminals, respectively.

Part (A) may be viewed as the first step of network design at this hierarchy

level. Part (A) proposes a star configuration which centers at the largest node

(i.e., at switch 1). The capacities of links are assigned to concur with the

number of stations at the lesser of the two end nodes. For instance, between

switch 1 and switch 3, which have 48 and 24 terminals, respectively, one installs

24 channels. Then, given enough switching capacity, all idle users at switch 3

can be served. This assignment ensures total absence of blocking in part (A).

Trouble occurs when either switch 1 or any of the links in part (A) of Figure

34 is disabled. In the first case nearly all nodes are disconnected from each

other. In the second case, one node is separated from the network.

To enhance the survivability of this network, one proceeds to the second step

of the design. This is shown in part (B) of Figure 34. Here one adds new links

to increase survivability for all nodes. The procedure is simple. One constructs

a secondary star around the second largest node. That is, one adds new links from

switch 2 to all those other nodes, that previously had no direct path to switch 2.

This secondary network is drawn with broken lines in part (B) of Figure 34.

The new individual link capacities may again be picked to be the lowest

number of terminals at the two end points.

If anyone of the nodes is deleted from (B) the rest of the network remains

intact. By that one means that the remaining network is still connected and

nonblocking. When a single link is severed, the network does remain connected.

However, it mayor may not exhibit some blocking. For instance, if the largest

link between switches 1 and 2 is cut, some nonzero probability of blocking might

occur. On the other hand, if either of the 6 circuit links from concentrator 2 is

cut, the blocking probability is still zero throughout the network.

The second step of part (B) has made the first step network of part (A) more

survivable. But, it does represent added cables, trenches, and more sophistication

at the switches and concentrators. The extra distance (see Figure 29) is on the

98
SWITCH

3 24 (A)

24

48

SWITCH

1

36 SWITCH

2 36

12 6

SWITCH 24 (B) 3

...... ...... 24

"......

SWITCH 36 SWITCH 48 1 2 36

--

12 6

Figure 34. Link and capacity assignment.

99
order of 3 km t which is perhaps 75% of the total distance in step 1, part (A)t of

Figure 34. The additional installation time is expected to be commensurate.

The star configuration of part (A) represents a minimum capacity nonblocking

topology. Part (B) enlarges the'capacity by nearly 54% over the minimum.

The procedure can be variously generalized. Third, fourth,and so on t substars may be added. Or, the individual link capacities can be increased to the

point where connectivity implies nonblocking. UsuallYt one-half of the total

number of terminals is a safe upper bound for the link capacity throughout the

network. From Figure 34, adding the terminals yields,

4~+36+~4+12+6 = 63

This suggests that part (B) with all 1inks increased to 63 channels must be nonblocking in the presence of a single link outage. This is a relative increase

of some 465% over part (A)! It is safe t but far more than is necessary.

There do exist capacity efficient network design algorithms. UnfortunatelYt

they are rather complex. For the command post network design, simpler methods

appear desirable. In addition to the multistep star approach of Figure 34 t the

structured configuration of the next,section should not be overlooked.

8.3.3. The structured conftguration

The previous sections oQlinktopologies and capacities should be viewed as

simple working introductions to a complex design problem. No complete solutions

have been offered here. In fact t no problem has been defined with the necessary

generality in mind. The general topic is quite theoretical and only tractable

with numerical algorithms. It calls for completeness and depth beyond the scope

of this short study.

The examples given here demonstr~te what can be done with simple tools. The

list of topologies can be expanded i,nto tree networks t loops, grids (meshes), and

numerous hybrids thereof. We shall skip that, as most of such networks and their

rudimentary properties must be familiar to the readers.

Instead, it appears more !J1eani,ngful .to consider a sequence of structured

network configurations, that seem suitable for the concentrator and switch levels

of the command post networks. The simple concept is introduced graphically in

Figure 35 for 2, 3, 4, and 5 switching nodes. For an arbitrary number of N

nodes, the structured configuration network is defined in Figure 36.

100
SWITCH

1

SWITCH

2 2 Switches

SWITCH

3

SWITCH SWITCH

1 2 3 Switches

SWITCH

4

SWITCH

3

SWITCH

5

SWITCH

4

SWITCH

3

4 Switches

5 Switches

Figure 35. The structured configuration networks for two

to five switches.

101
SWITCH

1

SWITCH

N

•

•

•

SWITCH

3

SWITCH

2

Figure 36. The general structured configuration.

102
To start, order the nodes in accordance with the number of terminals they

serve. If Tn is the number of tetminals for the n-th node, then the ordering is

Tl .:. T2 .:. T3 .:. ... .:. TN'

Thus, in this sense, Tl is the largest node. T2 is the next largest node, and so

on. Finally, TN is the smallest.

For N=2 or 3, connect the nodes fully to each other. These are the two upper

networks in Figure 35. If N.:.4, construct a pyramid structure as follows. Interconnect nodes n=l and n=2. Connect nodes n=3, 4, ... , Nonly to nodes 1 and 2.

What results is a multi-loop structure with 2N-3 links for N~ nodes. For larger

N, this number is nearly double that for minimum spanning tree (such as the star

network). But, it is noticeably less than for fully connected networks with the

same number of nodes.

Figure 37 compares the number of links necessary to implement the more

common network types.

The notation for the structured configuration was introduced above in Figure

36. The nodes or switches are identified by n=l, 2, ... , N. Their individual

number of terminals at a node n are Tn' n=l, 2, ... , N. The link capacities

between nodes nand mare Cnm , n~m=l, 2, ... , N. The key question that must be

answered is how the structured configuration link capacities Cnm should be assigned

to meet survivability objectives. Effective capacity assignment must be a function

of the user terminal set, telecommunications traffic requirements, and other general

command post design objectives mentioned earlier.

Note in conclusion of this section, that the second step, part (B), of Figure

34 for N=5 nodes is a special case of this structured topology. It was arrived

at from a different point of view, where a secondary star was added on top of a

primary star.

8.4. Survivability Aspects

Universal definition of survivability is difficult. The reasons are understandably many. Perhaps the most prevalent reason has to do with the individual

systems users and the subjective urgencies that they encounter. System nonperformance in such instances may contribute to losses outside the system itself.

The urgency in a tactical environment is certain to vary as a function of time,

place, mission, random events, and a series of strenuous circumstances. The

survivability of some communications paths may always be essential. Or the opposite may be true, unless some actions happen to reverse the roles. It appears

103
12 13 14 15

Structured

Configuration

8 .9 10 II

Number of Nodes (N)

,/

,/

/

/

/

/

/

/

Fully /

Interconnected

/

/

/

/

/

/

I

I

/ .,,----- .""", ,.,...

/ .".-",.,

Ordinary Loop .".- -::: .".""".

I ",.,:::-'"

I //

//

///

/Tree (Star)

I ,;"///

1./,;"

I ////

I / /

/ / /

I // /

~/ /

/

I

/

2

3

50

20

Q)

.0

E

:3

Z 10

(J)

.::J:.

.5

....J

't5

Figure 37. The number of links required by several common topologies.

104
nearly impossible to find uniformly accepted documented definitions to suit everybody. The definitions, to be attempted next, are intended soley for the tactical

command post scenarios.

8.4.1. Two dimensions of survivability

In this section survivability is defined as a two-component entity, (D,P).

The first component, D, describes the disconnection or disjointedness resistance

of the network. It concerns the connectivity' characteristics of a given topology.

Consider any given set of link and node outages. Suppose further that this

outage scenario separates the originally connected network into j>l disjointed

pieces or subnetworks. If the total number of terminals is T, let T(l), T(2),

... , T(j) be the number of terminals in subnetworks 1,2, ... , j, respectively.

Then the T(i)terminals in the i-th piece can only talk to each other. Consider

next the entity

D[{i,I(j)}] = min T(1)'+ T(2) + ... + T(i) T

T(i+l) + T(i+2) + ... ~T(j)

T

It depends on i, as well ~s on the integer assignment I(j) to the collection of

subnetworks. To include all cases, let O~i'::j. Then there are j+l choices for i,

and j~ choices for X(j) .. Entity D[{i,I(j)}] hasfjossibly (j+1)~ different value's

in the interval [0, t]. 'We define "disjointedness,,'D as the largest of these

(j+l): values:

D = max D[{i, I(j)}].

When the network is connected one has j=l and D=O., Otherwise, for j~2 one obtains

a single valued number in the range t D t. ,

When no links or nodes are disabled, one may use subscript zero and the

identity DO=O, to mean that no part of the user terminal population is ,disconnected

from the main of the network. States Dl~O, or D2>0, ... , may denote that outages

of the first kind (subscript 1), such as for a single severed link, mayor may not

alter the network connectivity. Outages of a second kind (subscript 2), such as

for disabled nodes or link groups, if larger than zero, mean that some subnetwork

must now be disconnected from the main network.

Larger D values signify that more terminals are rendered unreachable from the

central core of the network. For the same outage index i, smaller Di values are

thus desirable. They stand for higher survivab5,Jity.

The second survivability component, P, refers to probability of blocking or,

as it is commonly known, the grade of service. Since blocking is apt to vary

,'} ,! ;:. 105 c.·" I •
considerably from one part of the network to another, some meaningful average, or

worst case "bott.leneck" formula appears needed. In what follows, the worst case

approach is used to generate a unique P number.

Blocking can occur both when a system is damaged or not. Ideally, one could

postulate that a sound command post network is nonblocking and thus, PO=O. Larger

P values imply more blocking somewhere in the network. They denote a worsening of

communications and less survivability in the-same command post environment.

The pair (O,P) quantifies survivability and makes partial configuration

comparisons possible on the basis of numbers.

Let (O,P) and (OI,P I) be two survivability vectors for two topologies, Sand

S·, of the same system. Then, given link and node outage state i, one says that S

is more survivable than SI, subject to i, if 0i<Oi' and Pi<Pi ' both hold. If these

inequalities hold for all i, then S is more survivable under all circumstances.

If there exist outage statesi and j,under which the inequalities are reversed

and differ, then the discrimination is not clear-cut. If 0.=0.' and P,.=P,,' hold, , ' "

the two survivabilities are the same, conditional on i.

In practice, some outage states are more likely than others. Thus, the

outage of a single link is more likely than that of two or more links. Single

nodes are apt to fail more frequently than two or more nodes. Quantitative comparison of systems, therefore, can be done initially by analyzing the single link

outage and the single node outage impacts.

The approach is illustrated in Figure 38. Figure 38 shows, the number of node

outages as the ordinate, and the number of link outages as the abscissa. All

squares depict the same network, with the same nodes, links, and capacities.

For an undamaged topology, with zero link and zero node outages, Figure 38

assumes a connected network (i.e., 0=0) and no blocking (i.e., P=O). As link

outages and node outages are increased in number, there eventually comes a point

beyond which either 0>0 or P>O materializes. At that instance, one has either a

disjointed, or disrupted network, or call blocking somewhere in a perhaps connected

network.

Which of the two, 0>0 or P>O, manifests first or disrupts the network more,

again depends on several factors. One factor is the presence (or absence of multiple backup links. The link capacities is another factor. If, for example, the

network is assembled of numerous circuits, but all with relatively low capacity,

then (0=0, P>O) may occur ahead of (0)0, P=O). On the other hand, huge capacity

on most links may suffice to guarantee that (0=0, P>O) never occurs.

106
p 10..-1 Ip ~}O-l

D=O I D= 0 I D~ 0 I D 10-1 , ••• I

0

I P =0 I P~ 10-3 I P 10-2 P = 0

0 1 2 3

NUMBER OF LINK OUTAGES

(I) LLJ "'2.' . '(.!)

. .::;)

o

lJ.J

o

o·

z

u..

o

0:::

lJ.J

l=O

::E

::;)

Z

--'

o

..'"

Figure 38. The (D,P) contour as a function of link and node outages.
Let T=Tl

+T2

+... +TNdenote the total number of terminals in the command post

service area. Let E be the number of exterior gateway or outside lines. Then, as

long as the lowest link capacity, C

min , satisfies

C. > 1/2[T+min(T,E)], mln -

network connectivity implies absence of blocking in that network. Then, of course,

D=O implies p=o and connectivity is tantamount to survivability.

At the other extreme one may consider small individual link capacities.

Suppose now that the highest link capacity, C

max ' is quite small, such as

C «T/2, max

but that there is an abundance of alternate routes and backup links. One feels

that under these conditions blocking (i.e., P>O) should precede network disconnect ion (i. e., D>O).

In the extreme case, such as on Christmas Day or Mother's Day, the public

switched network may be extremely blocked and yet connected, i.e., P>O and D=O.

Then, in the additional presence of any subnetwork outages, grade of service

appears to be the more realistic measure of network survivability.

8.4.2. Determination of D

Determination of D involves analysis of topology. Sometimes it is easy, at

other times, difficult. Consider a scenario where link cuts comprise the most

outages~ and examine a network such as shown in Figure 39, part a). What is the

least number of link cuts that separate this eight-node apparently connected

network into two or more disjoint subnetworks? What are the corresponding D>O

values that occur first? The answer to the first question is: two link cuts.

They should be administered to the links (3,7) and (4~8), causing D=0.5. The

validity of the claim is seen from the simple equivalent topology of part b),

Figure 39.

To this writer's knowledge, there is a scarcity of algorithms to solve such

problems. For larger networks, with many nodes and many links, simple enumeration

of all possible cases may consume too much time. New computer algorithms may be

needed.

The command post situation tends to alleviate these complexities for two

reasons. First, the CP networks are relatively small. That is, the number of

nodes and higher level links is typically under ten. Quick inspections then may

108
a) Sample Network

b) Equivalent Topology

Figure 39. A sample network and its equivalent topology.

109
reveal connectivity flaws and disconnectivity, i.e., 0>0, possibilities. And

second, the command post network layout is under the control ofCP/SC commanders.

Commanders can purposely adhere to simple and well-connected network architectures.

8.4.3. Determination of P

This section determines several examples of grade of service or probability

of blocking, as they might occur in command post network applications. The analysis applies to the switch and concentrator levels of the n'etwork hierarchy.

To make matters as simple and applicable as possible, the networks are

selected to possess simplifying symmetries or to be small in size. The latter

assumption corresponds, in an approximate way, to the size~cale envisioned for

all present and future CP/SC networks. Furthermore, all the switches are assumed

to be intrinsically nonblocking and fully available.

As the initial example, consider the symmetric loop or ring network. Let the

geometry and notation be as given in Figure 40. There are a total of N>3 identical switching nodes. Each serves the identical number of TIN terminals. The

links between the nodes are all of the same uniform capacity C=T/4 in both directions.

For the unimpaired network (without outages), this is the minimum capacity

necessary to guaranteenonblocking operation in all traffic cases.

When a single link is severed, this network is still connected and 0=0. When

two links are severed, the network is cut in two, with l/N~D~1/2.

A single link outage, however, can degrade the service. Figure 41 shows the

worst-case loss in the loop network that has suffered a single link cut. The

abscissa is T, the total number of terminals. The ordinate is the offered load,

a, per terminal in Erlangs. This load a is assumed to be identical for all T

terminals. A total of N nodes and N links is presumed to comprise the loop.

However, Ndoes not affect the worst-case loss. Thus, Ndoes not appear explicitly

in Figure 41.

The curves, denoted as P=5%, 1%, and 0.2%, represent the T and a loci where

the blocking probability has these values. The computation is based on the previously mentioned individual 1ink capacities of C=T/4 • . When no 1inks are out,

this represents the minimum nonblocking capacity assignment. Increase in C leads

to lower P values. In particular, if one sets C~T/2, then single-link outages

still imply P=O.

In Figure 41 a simultaneous increase in load/line and in number of terminals

is possible for fixed P. This is true, because the link capacity is proportional

110
T N-1

N

T

N ••• 1---------1 •••

T

4

T

N

T

4

T

W N

T

1 4 2

T T - - N N

T

4

Figure 40. Loop network with uniform links and nodes.

111
20 50 100 200 500 1000

-(/)

0'1

c 0.4

0

w'-"

0

0

c 0.3 E

Q)

0-

-0

0 0.2 0

...J

LINK

CAPACITY

0.1 C=T/4

Total Number of Terminals) T

Figure 41. Worst case probability of blocking for the uniform loop network

with a single link outage.

112
to T. If C were held constant t howevert then a different picture would emerge.

The product t aT t would then be roughly constant and equal to twice the load that

generates the P value of interest. For examp1e t if C=24 and P=l%t then t from

the Er1ang Bloss formu1a t aT=2(15.3) Er1angs. Hence t a=30.6/T. For T=300 t

this yields a=O.l t or approximately six minutes of talking activity per individual

telephone termina1 t per hour. In command post app1ications t one expects the

traffic intensity to be of this order of magnitude.

The characterization of the IIworst case" of blocking deserves several comments.

The effect of cutting one link in Figure 40 is indistinguishable from cutting

any other link. That follows from the uniform symmetry of the loop. The most

congested bottleneck must occur diametrically opposite the cut. Because then the

realizable maximum of one-half the terminals may want to communicate to the other

half across the bottleneck.

The situation becomes far more complex for more general topologies. The nonuniform loop may be the next illustrative examp1e t as shown in part (A) of "Figure

42. This is a network of four nodes and

T = 24 + 12 + 8 + 6 = 50

terminals. The number of channels per each link are indicated in Figure 42 to

be 15 t lOt 4 and 3t respectively. This network is nonb10cking when all links are

intact. Outage of a single link can produce some blocking.

The worst case occurs when the 15-channe1 link gets severed (see part (A) of

Figure 42). Then all three of the remaining links may become congested to the point

of blocking. The most severe bottleneck is the link with capacity C=3. Since the

call requests can number no more than min(18,32)=18, and there are only 3 channels

available t the blocking probability P is cleat'ly nonzero. If the 18 terminals on

one side of the bottleneck offer 0.1 Erlangs of load each, and if approximately

one-half of requests go to the other side of the bottleneck, then P=5%.

Mu1tiloop topologies may be configured to enhance connectivity and survivability. It is unfortunate that their analysis becomes rapidly so difficult.

Consider part (B) of Figure 42. Here, the node and terminal sets are the same

as in part (A). However, one link has been removed, two new links have been

added, and the total link capacity has been reduced from 32 channels in part (A)

to 28 channels in part (B).

It is claimed by inspection, that the most severe cut in (B) is that of the

12-channel 1ink t and the most severe bottleneck is comprised of two parallel 2-

channel links, as shown. The number of contending terminal set pairs is min(12,26)=

12. The number of server channels is 4. The approximate blocking probability

113
12

6

24

6

Most

Congested

.Bottleneck . CA)

12

Most

Congested

Bottleneck

Most

Severe

Cut

24

e

(8)

Figi.Jit'e 42. The most severe cuts a.nd bottlenecks in

simple networks.

114
(under the same ground rules as in part (A) of Figure 42) is now P;2.5%. Thus, in

part (B) despite reduction in total number of channels, survivability appears to

be increased in both the Dand P sense.

For more complicated multi loop networks, the determination of P becomes

quite involved. We shall not pursue that generality here. Rather, the following

section describes the survivability plus other aspects of the structured network

configuration.

8.5. Structured Configuration Networks

8.5.1. Disconnect survivability of the structured configuration networks

This section considers the structured configuration, as depicted earlier for

an arbitrary number of N nodes in Figure 36. Clearly, incapacitation of any

single node does not degrade the connectivity of that network. For a single node

outage, D=O.

For two node outages Dcan either be zero or larger than zero. If one or

both of the two deleted nodes are in the {3,4, ... ,N} set, then D=O still holds.

The network is connected with a multiloop or star configuration. Only when both

nodes 1 and 2 are out, is 0>0. In that case everything is disconnected. One

could define this catastrophy as D=l.

For single link outages, 0=0 remains. It takes at least two link outages to

separate any switch, or group of switches, from the rest of the network. For

example, two simultaneous outages of C1N and C2N (see Figure 36) would separate

node N from the network, causing D;l/N. On the other hand, N-2 simultaneous

outages of links C23 , C24 , ... , C2N fail to sever the network.

The outage of one node plus a simultaneous outage of one link can also disconnect the network. For instance, switch n (3~n~N) becomes isolated when either

node 1 and link C2n , or node 2 and link Cln is out.

One concludes that it takes two of any outage kind, nodes or links, to produce

D>O in Figure 36. It may be reasonable to assume that two outages are considerably more likely to take place than three or more outages. This suggests a probabilistic estimate, Pr{O>O}, of any disconnect event whatsoever. At a given time,

let:

P

n

P£

=

=

Probability of individual node outage,

Probability of individual link outage.

Assume that the outage events are independent of each other. Then for Pn«l and

P£«l,

115
is the disconnect probability of the structured configuration network.

8.5.2. Grade of service survivability

Many networks are designed to offer some nonzero blocking even when there

are no outages of any kind. Design decisions are made on the basis of traffic

statistics, user requirements and system economics.

Given no link or node outages, the structured configuration (Figure 36) can

be sized for various degrees of congestion. It depends on the number of server

channels {C12 , C13 , ... , C1N , C23 , ... , C2N }, as well as on the traffic generated

by the {Tl , T2, ... , TN} terminals, whether p=o or P>O applies. In what follows,

we review the P~O grade of service, survivability aspects of the structured configuration.

To simplify matters, assume the network configuration shown in Figure 43.

It has N=4 nodes. The number of terminals is structured to obey the inequality

For uniformity, modularity, and speed of installation, Figure 43 postulates

identical link capacity Cfor all five links. The present goal is to examine the

effect of various C choices on the worst case probability of blocking P.

According to Sections 8.3.2 and 8.4.1, C~(Tl+T2+T3+T4)/2 suffices to guarantee

nonblocking, i.e., P=O, as long as there is total connectivity, (as long as D=O

holds). It is also clear that such high C value is not always necessary. Smaller

values will often achieve the same objective. For instance, the link capacity

implies P=O for all traffic conditions of the structured network of Figure 43,

and subject to no outages of either nodes or links. The actual minimal necessary

capacity is even smaller. It is given by a rather cumbersome formula. That

formula, plus other related link capacity formulas, are summarized in Table 19.

Table 19 applies for P=O, or nonblocking, or perfect grade of service conditions of the structured configuration only. In the first column one finds N, the

number of nodes. The N=4 case is that of Figure 43. The general Ncase assumes

N>3. The links that join the nodes are all of the same capacity.

The second and third columns of Table 19 show the number of link and node

outages assumed for that particular row.

116
NODE

1

NODE

4

NODE

3

c

NODE

2

Figure 43. A simplified four-node structured configuration.

117
--'

--'

00

Table 19. Necessary and Sufficient Link Capacities for Various Size Networks

Outages Minimum Capacity Necessary Sufficient and Simple N

Link Node for P=O P=O Capacity

0 0 1/2min(Tl , T2

+T3)

3 0 1 T2 T2

+T3 •

1 0 min(Tl' T2+T3)

I 0 0 1/3maX[~T3' min(Tl , T2+T3+T4 ), min(Tl

+T4, T2+T3)J

! 41 0 1 1/2max[2T3, min(Tl , T2

+T3)J T2

+T3+T4 I I 2 i

i I 1 0 1/2max[2T3, min(Tl , T2+T3+T4), min(Tl

+T4, T2+T3)J i

,

i.

I 0 0 N~lm~x[N21T3' min(Tl+

t

Ti , T2+

tc

Ti )J I I

I N N N

N 0 1 N~2max [(N-2)T3, min(Tl+L Ti , T2+Lc Ti)J T2+T3+···+TN

i

I

N_l I

N_

l I

Nl N-2 1

i

N~2max[(N-2)T3' min(Tl+L Ti , T2+y'cTi )J (Conjectured) , 1 0

IN IN IN 1
The fourth column depicts the.minimum capacity necessary to ensure P=O, for

all conceivable traffic load conditions. In the extreme, all the terminals may

want to.call each other until there are no idle (on-hook) terminals left. This

capacity, see Figure 43, is assumed to be a fixed constant for all 2N-3 links.

In the text above, the minimal necessary capacity was denoted as CO'

The fifth and final column of Table 19 presents a simple workable upper

bound on the minimum CO' Being of the form

this upper bound offers a single formula for all N~3. That formula is sufficient

to give P=O under the number of link and node outages indicated.

Thus, it is alleged that (T2+T3+T4)/2 is sufficient to guarantee nonblocking

operation of the structured N=4 node network under all no outage or single outage

cases.

Several explanations may be appropriate for the general N formulas in Table

19. The formulas contain symbols IN and INc, where N=3, 4, 5, The IN represents an arbitrary integer subset drawn from the integer space S={3, 4, 5, ... , N}.

Typical examples of IN are ¢ (the empty set), {3}, {4}, ... , {3,4}, ... , {3,4,S},

.,., or even S (the entire space). Superscript c, as in INc, denotes the complement of IN'

The general N, minimum C, formulas are rather clumsy to use, even for relatively small N. Simpler functions of {Tl ,.T2, ... , TN} are desirable. The last

column, as noted earlier, represents such simplications. Unfortunately, the

claimed sufficient capacity for general N is unproved presently.

So far, the emphasis has been on p=o. Realistically, it remains to carry

through similar capacity assignment analysis for P>O values of interest. Recommended values are:

P = .2% - for enhanced operation,

= 1% for normal operation,

= 5% for degraded operation.

For all such practical P values, and assuming the structured network configurations for hierarchal levels of interest, a worst-case survivability analysis can

and should be performed.

119
8.5.3. Installation objective

This section reviews the installation objective of the structured configuration network. As discussed in Sections 8.1.1 and 8.2.3, the general objective is

to reduce the installation time of the CP/SC network. If the speed of available

machines and manpower remain relatively constant, then the installation time must

be roughly proportional to the network size. That size consists of link distance

in kilometers (1 km=0.62 mi), both buried in trenches and laid on surface, plus

all nodal installation. This section concerns the link distances only.

Assume the structured configuration switch network, hierarchy level 3 (Figure

28), with uniform link capacities. For N=4 switches, that network is as shown in

Figure 43. We also permit N=l, 2, 3, 4, 5, 6, by including the star configuration for N=l, and by otherwise following the model of Figures 35 and 36.

Beyond the switch hierarchy level, assume the four levels introduced in

Figure 28. Let there be T=300 terminals at level 1. Part of these terminals are

concentrated at level 2, by multiplexing unto Tl equivalent buses. For practical

layout reasons, assume that on the average, 20 out of 24 circuits are active. This

may be denoted as a 20/24 channel MUX.

Level 3 consists of the previously elaborated switches. There are N switches.

They collect all the MUX loops and direct user loops. Above the switches, at the

gateway level (see Figures 27, 28, 30, 31 and 32), assume E=3 exterior access

radio nodes.

Higher hierarchy levels above 4, by present assumption, are reserved for

higher military echelons and 000 backbone networks.

The number of links depends on the number of switch nodes N used. For the

structured switch configuration, plus the four-level hierarchy, the command post

link summary is outlined in Table 20.

As the number of switches increases, more terminals are clustered in their

proximity. Thus, the number of MUX'es decreases as N increases. More station

loops go directly to switches, and less to MUX, at level 1 accordingly. The

number of level-2 links (these are multiplexed loops) is assumed to be the same as

the MUX'es themselves. Thus, there is one bus per MUX and the MUX'es are configured in star fashion around the switches.

The number of switch level links is, as shown earlier for the structured

configuration, 2N-3 for all N=2, 3, .... Note that the total number of intracommand post buses consists of levels 2 and 3. Their total number is nearly

constant for all N. A slight minimum of 11 is noted for N=2, 3, 4.

120
--'

N

--'

Table 20. Link Summary for Differently Sized Switch Networks and T=300, E=3

,

t Number of Links

i . #

# Switch I 20/24 CH I At Terminal Levell ! I Nodes N t MUX I I To ~1UX At MUX Level 2 I At Swi tch Level 3 Gateway Level 4

I To Switch I I

!

I I I 1 !

I

l

. 12 240 60 12 0 5 ! , I

! i 2 I 10 200 100 10 1 6

i 3 I 8 160 140 , 8 I 3 7 I

i

I I

4 6 120 180 6 I 5 8

I 5 I 5 100 200 5 7 9.

I I 6 10 I 4 80 220 4 9

!
At level 4, which depicts the gateway or radio park links, the numbers in

Table 20 are more than the required connectivity minimum. The following rule is

used. The· three gateway nodes are fully interconnected among themselves. The

first, e.g., the largest, switch node is linked to two gateways. This yields the

5 links listed at level 4 for N=l. For every other switch node, a separate path

to some gateway node is added.

To assess the network distances of the various Nalternatives, the numbers of

Table 20 must be combined with typical CP/SC distances. Figure 29 is used here.

Thus, one claims the average distances listed in Table 21. Note that the average

distance between a terminal and a switch decreases as more switching nodes are

distributed in a given service area.

Table 22 lists the total link distances for each of the four hierarchy levels

and lists how many kilometers are to be buried in trenches, and how many are to be

laid on the surface. The network scenario here is still the same as in Table 20.

In particular, the total number of terminals is T=300, and there are E=3 exterior

gateways. These gateways are assumed to be interconnected by cables laid on the

surface. Their feeds from theCP switches, however, are assumed to be trenched.

The installation time objective is strongly related to the right-most columns

of Table 22. If digging trenches and burying cables does consume the bulk of the

installation time, then Table 22 has the following usefulness. First, the buried'

plant (viz., installation time) grows nearly linearly with the number of switches,

N. Second~ the buried plant (viz., installation tim~) increment is roughly 10%

for each single switch added. This simple rule, of course, is based in large part

on the scenario assumed.

The effect of the structured configuration network at level 3 is seen as

minor on the installation effort. It amounts to some 15% of the trench digging

task. As given in Table 22, most trench mileage is required by MUX loops (especially, when N is small) and by the redundant switch-to-radio park tie lines (when

N is larger).

Table 22 also shows that the links laid on the surface, such as wire pairs

(WP) or multiwire-pair (MWP) cables, depend but little on N. A maximum amount of

surface link distance seems to occur at N=3. It is due to the countereffects of

terminal-to-MUX and terminal-to-switch columns in Table 20, primarily. Since

surface deployment is apparently a much faster command-post process than cable

burial, the latter phenomenon may be an insignificant factor for the installation

time objective.

The total distances of various transmission media are also of interest. Table

23 assumes that only two media are used. They are the twisted single-wire pairs

122
Table 21. Typical Average Command Post Distances

Hierarchy Level From To Valid for N Average Distance (km)

MUX All 0.5

1 1.0

2 0.9

3 0.8

1 Terminal Switch 4 0.7

5 0.6

6 0.5

2 MUX Switch All 1.0

3 Switch Switch All 0.5

Switch Gateway All 2.5

4

Gateway Gateway All 0.7

123
--'

N

.p,

Table 22. Total Link Distances

Total Link Distances (km)

I

Level 1 Level 2 I Level 3 Level 4

I Tota1 Buri ed Total Surface N (Surface) (Buried) (Buried) (Buried) (Surface)

1 180 12 0 5 2 17 182

1

I 2 190 10 18 192 I 0.5 7.5 2 , ! t

I I 3 192 8 1.5 10 2 19.5 194

4 186 6 2.5 12.5 2 I

! 21 188

5 170 5 3.5 15 2 23.5 172

6 150 4 4.5 17.5 2 26 152
Table 23. The Single Wire-Pair (WP) and Tl Bus Totals

Installation Total

N T1 WP (km) Tl (km)

1 300 180 21

2 150 190 24

200 190 23

100 192 36

3 150 192 32

200 192 28

75 186 35

4 100 186 34

150 186 31

60 170 37

5 90 170 35

120 170 33

50 150 38

6 75 150 37

100 150 36

!

125
(WP) and the 24-channe1 T1 buses. Both are summarized in the table. One notes

that the WP numbers are the same as given for level lin Table 22. The total WP

distance does not depend on the terminal distribution {T1, T2, ... , Tn}' However,

the T1 bus mileage does depend on the Tn1s.

To estimate the total T1 requirement, one uses the last column of Table 19.

According to that column, C=(T-T1)/(N-2) provides a sufficient uniform capacity

assignment. For T=300 and N specified, one needs T1 to pin down uniquely the T1

bus totals. In Table 23, selected T1 values are indicated. Since T1 is restricted to the range, T/N~T1~T, there is only one case for N=l.

It is noted that for fixed N the T1 bus total distance decreases as T1 increases.

However, that effect does not appear to be as powerful as the previously mentioned

increase with N.

8.6. Remaining Network Issues

This section outlines the dominant outstanding command post network issues.

As shown in Section 1, see Fi~ure 2, the general tactical environment imposes

broad requirements on the whole command post system and services. We shall comment

briefly on these general CP issues. Thereafter, a considerably more thorough

discussion will be devoted to the communication network itself.

8.6.1. General and service issues

The general role of the present command post communication system is to

provide services in a tactical environment. Any changes in this role, contemplated

or imminent, contribute to the issues of future plans and designs. The future

issues thus deal with U.S. Army CP/SC deployment and utilization policies. They

concern present and future implementation. Service and system growth phases over

the next decade are \mportant to know.

From the organizational point of view, the CP roles in the higher echelons

affect the service plans. Service interfaces, that are either military, commercial,

or others, are key objectives and issues. User-oriented military service standards

would be extremely helpful in this area of service issues.

The goal of such a general and service-oriented attack would be to identify

first key service features or objectives. They could concern such aspects as

availability, reliability, grade of service, security, integrity, connectivity,

quality, etc. (see Section 8.1 for other measures of effectiveness). Next, to

formulate service requirements, one would have to assign clear definitions and

numerical ranges for these descriptors.

126
The quantification of service parameters is never easy. It depends in a

complex way on the entire service scenario. This includes all the service categories (analog, digital, priority, command levels), plus their tactical traffic

statistics. Such statistics often tend to have modest means, but huge variances.

This seems to be true for service request, or call arrival, or origination intensity distributions that exhibit busy-hour or high-demand peaks. One must also

include message-duration or call-holding-time distributions, as the latter determine the loads on the network, plus the ensuing congestion effects.

The traffic statistics are needed for grade of service determination under

realistic line or node outage conditions. This determination pertains to system

connectivity, reroutes (message or call detours), probability of blocking, delays,

and interrupts or preemptions. It is an issue that arises every time one is faced

with the decision of what capacity links or switches to add to (or delete from)

the CP network.

8.6.2. Technical network issues

Network issues are typically technical. They interface strongly with other

technical issues, such as those dealing with nodal (i.e., switch, console, concentrator) elements and user terminals. Functionally, the networks must provide two

flows: (1) control and signaling, and (2) information flow.

Technical compatibility is essential in network design. Existing and future

interfaces, such as at the TRI-TAC's new analog and digital TTC-39 switch are

basic compatibility requirements. Compatibility issues must be resolved, as they

arise in the implementation cycle of various subnetworks. In particular, this

concerns establishing and maintaining control, signaling, plus all the functions

needed to run communications with other interface systems.

When analog lines serve digital elements, or when digital lines serve analog

elements, the AD/DA conversion issues arise. Not only must data rates, formats,

and synchronization issues be settled, there are the immediate problems of fourwire (4W) versus two-wire (2W) operation, as well as all types of subtle protocol

issues. In the commercial world, as well as for the strategic military nets,

digital media are forecast for future generation transmission and switching. A

crucial present issue there is the transition period, when new digital elements

are required to be integrated with older existing analog elements.

In the tactical CP future, the integration of digital and analog subnetworks

may very well become an important future issue .. It mi ght ari se, for instance,

rather soon in the security arena. Encryption and decryption processes, and their

127
controls, are more effectively carried out with digital technology. The automatic

key distribution (AKDC) system is an example thereof.

Concentration and multiplexing (MUX), which is a recognized basic prerequisite

for higher capacity bus architectures, is also quite amenable with the aid of

digital carriers, such as time division multiplexing (TOM) and pulse code modulation (PCM).

The media issue for digital buses must also be thoroughly examined. While

either 2W or 4W operation is feasible, their tradeoffs are not at all identical.

Moreover, multi pair cables mayor may not be preferred over more forward looking

alternatives, such as coaxial cables, optical fibers, or other media.

A very general networking issue concerns the topological designs and hierarchal

function assignments to various levels of the network. Depending on how this is

done, other issues may emerge and require resolution. For instance, such general

system objectives as installation speed (Section 8.1.1), survivability (Section

8.1.2), service and performance (Section 8.1.3), upgradability (Section 8.1.4),

plus other measures of effectiveness, all tend to depend on the topological configuration of the network.

In the body of this report, and notably in Section 8.5, a certain multiloop

topology called structured configuration was introduced and examined. One would

like to say that it is the preferred configuration for CP networks, at least at

some hierarchal levels, but one is hesitant. After all, there remain numerous

other topologies that are unexplored. For example, the higher order loops should

be examined. Note: If a loop can be defined as a network where every node has

exactly two nearest neighbors, then a higher order loop is one where every node

has exactly n neighbors, where n>2.

The quantification of survivability was attempted in Section 8.4. Network

literature abounds with various definitions of survivability, vulnerability and

reliability. They differ from the (D,P) definition given in Section 8.4, in

several respects. These respects should be examined for the suitability for

command-post network survivability uses. Perhaps, a distinction should be made

between normal and stress conditions of operation.

It seems that every network analysis requires a numerical data base, or the

analysis loses its potency. The command post network is no exception. Many

numbers are needed. In what follows, examples are given where the quantitative

basis appears most desired.

To start, there is the issue of terminal, gateway, and nodal counts. This

section has assumed T=300 terminals and E=3 external gateways. The number of nodes

128
was left arbitrary in the 1-6 range. What;s needed is a range of numbers for all

kinds of terminals deployed, their traffic intensity numbers, and their required

performance numbers.

Percentages and total numbers are needed for P, R, 0, and Z priority phones,

as well as for digital and FAX machines. Their clustering around proposed CP

nodes needs numerical treatment. Extended to all terminals at all nodes, this

would provide more complete link distance data than suggested in Figure 29. This

would be particularly needed for the higher hierarchy levels, where cables are

prime candidates for burial in trenches. The added installation time for redundant cabling needs quantification, especially at levels 3 and 4 (see Figure 28).

The effective installation speeds by men and machines needs numbers for buried

cables, as well as for laying of surface wires. Realistic numbers must be known

to experienced field commanders. Moreover, it should be important to ascertain

how those numbers compare with installation and dismantling time objectives set

for various CP scenarios. Numbers are needed.

Realistic numbers are needed for present and future switches. They concern

line and trunk capacities, CPU limitations, switch network structures (including

full versus percent availability), console characteristics, queue management

and limitation numbers, and so forth. Distinction between manual and automatic

switches should be made on numerical grounds.

The distant and local call percentages are needed for realistic scenarios.

Service requirements should be specified numerically for both. The probability of

blocking should be specified in numbers, such as P=O, 0.5, 1, 5%, or other, and

under definite network outage conditions. The sizing of link and switch capacities

should be done for the selected P>O values. The fact that network blocking can

occur in switches, in links, or in some hybrid combination of both, should be

quantified and taken into account.

The importance of capacity assignment should be stressed for CP networks.

The role of minimum necessary versus arbitrary or any redundant capacity numbers

needs clarification. Further, the conjecture of sufficient capacity (T2+· .. +TN)/

(N-2) should be either proved or rejected for structured configuration networks

(see Tab1e 19).

Numbers ar,e needed for typical and worst-case disconnection or disjointedness

(0)0), as well ,as for worst-case grade of service (P>O). If pertinent, the

probabilities of node and link outages, P

n and P£, should be reflected in network

design. Methods should be developed for studying this for nonuniform capacity

structured networks and higher order loops.

129
In the case of small user classes, grade of service estimates based in Engset

(instead of Er1ang) formulas should be used.

Control, as a function of topological connectivity, has not been examined at

all. It should be done. In fact, the command post network topology should reflect the optimal numerical conclusions drawn from analyzing uses of CPU controls

for managing flow under various stress conditions. Flow, connectivity, and control

of paths between assumed hierarchy levels should be quantified. The latter would

necessarily involve link, connectivity, and capacity, algorithms that mayor may

not exist in a form needed by tactical networks.

Recognizing that different objectives or measures of effectivenss (MOE) may

contradict, a quantitative tradeoff machinery would be quite desirable.

For example, more survivability may call for more installation time. One is

good, the other is clearly bad. How does one go about choosing a compromise?

More generally, how does one select an optimum tradeoff in the configuration of

many variously intertwined objectives? The objectiv~s here are the previously

mentioned availability, connectivity, ... , transportability, upgradabi1ity (see

Table 17). This dilemma has, of course, arisen in the assessment of many systems.

It has never been solved with any generality in mind. Only simple rules of thumb

have been tailored for individual applications. The tradeoffs for command-post

networks may also have to be individually and roughly derived.

9. CP/SC DISTRIBUTION SYSTEM CONCEPTS

In the previous sections we have reviewed the service requirements and some

command-post communication system structures which are currently used in the

tactical environment. In Section 8 a structured network configuration for the

CP/SC local distribution system was described. It was noted that certain general

system objectives such as installation speed, survivability, service, performance,

upgradabi1ity, and oth~ measures of effectiveness depend on the topological

configuration used. A number of issues were raised concerning the number of

terminals, external gateways, and switching nodes required. Traffic statistics

are needed to determine the load carrying capacity for these elements in the

structured configuration. These and other problems must be resolved by additional

study in order to design and implement an optimum CP/SC distribution system.

Here we can only develop some general networking concepts and conjecture on

how the ultimate CP/SC structured network might evolve. This is necessary because

the ultimate configuration will, in large measure, determine what improvements can

be made, what functions should be performed, and how these functions might be

implemented.

130
Projecting the future is always a difficult exercise at best. However, we

already know that changing technologies and usage patterns continue to impact

military. communications systems. Thus it is essential to forecast these changes

so that initial improvements made to these systems are flexible and can be adapted

as changes occur.

Our near-term forecasts for bus-type transmission systems are based in part

on a review of such systems currently in use on specialized networks primarily for

the private sector. Bus distribution networks are found in a number of applications but mainly for digital computer access and intercomputer communications.

There are at least a dozen organizations planning to implement local networks this

year (1979) alone. Others are already in use, largely for data communication.

Some notable examples include: ETHERNET, a broadband broadcast system carrying

digital packets between locally distributed computers; MITRIX, a cable-TV network;

NBS net, a multi-user coaxial networ~; and SPIDER, a local packetized virtual

circuit switched computer network. The midterm forecasts are based on an evaluation of these and other state-of-the-art of technologies.

Commercial switch manufacturers are currently developing small units for use

in the Private Automatic Branch Exchange (PABX) market. The tendency for the

design of these PABX's is toward all-electronic digital switches with stored

program control using a combination of time division and space division switching

matrices. Military versions of these units capable of operating in a tactical

environment are sure to come. Their low cost, size and weight, and the specialized

features and functions offered make them very suitable for this application.

When connected by digital transmission facilities, digital switches provide a

number of advantages to the military user. For example, digital processing in the

terminals provides end-to-end security and does not involve the links or nodes. In

addition, data and voice services can be integrated on a single network.

In the long-term we forecast an increase in requirements for reliability and

survivability in CPISC networks. This can be achieved by adding redundancy, not

only to the transmission links, but to the switching nodes as well. This duplication is feasible because of the lower cost, size, and weights of all equipment involved. A properly implemented network configuration permits a graceful degradation of the grade of service when any node or link becomes inoperative.

In the following subsections these forecasts are considered in more detail.

A three-phase improvement plan for the CP/SC distribution system is outlined.

This plan leads to the structured network configuration in a logical cost-effective

manner. The three phases involve: 1) imbedding transparent bus-type links into

131
the existing network structure~ 2) merging these links with digital switches~ and

3) changing the network topology and adding switch nodes to produce an all-digital

structured configuration.

The improvements planned for each phase are summarized here only qualitatively.

Then~ in subsequent sections of the report~ we explore functional alternatives for

the first phase. This initial improvement phase requires implementing bus-type

links between the major existing CP/SC nodes.

Functional tradeoffs for the link design are described so that candidate

alternatives can be defined (Section 10) and evaluated (Section 11). Functional

design specifications for the preferred alternative are then developed (Section

12) .

9.1. Existing Configurations

There are basically three principle network topologies which emerge as candidates for local networks~ the ring~ the star~ and the ring/star.

Ring topologies transmit information by moving it along a ring from terminal

to terminal or at a higher hierarchical level from node to node. Rings offer

simple transmission~ are inexpensive but difficult to restore.

The star configuration uses simple point-to-point transmission from a central

switching point whic~ also serveS as a restoral point.

Star/ring networks are an attempt to utilize the best features of each topology. Nodes that fail on a ring can be bypassed from a central switching point.

The basic star configuration is currently used for command-post communications

as typified in Figure 44. This greatly simplified diagram depicts the major

centers on the post and the star-connected topology used. The main patch panel

provides a centralized control point for the traffic flow. This point also provides technical control facilities for major external links. Traffic distribution

is achieved by hardwiring the panel and by manual switching with patch cords. A

separate analog switch which may be manual or automatic serves local telephone

subscribers on the post and switches calls to distant subscribers via radio links

or land lines. Conventional analog signaling on a per-channel basis is used for

addressing and routing (e.g.~ de pulsing from a rotary dial) with the automatic

switch. Multiple-wire-pair cables and twisted-wire pairs are used to connect

terminals and adjacent centers. These are shown as lines in Figure 44. Some

multiplexed signals on coaxial cable are used to interconnect to the radio park1s

transmitters and receivers and to land-line repeaters. These are shown as solid

arrows on the figure.

132
--'

w

w

MAIN

PATCH

PANEL

• •

ANALOG

SWITCH

Locally

Distributed

Lines

Figure 44. Current CP/SC configuration.
Figure 44, the existing configuration, serves as a benchmark for subsequent

improvement to the distribution system.

9.2. Initial Improvement Phase

In the near-term (through 1985) the current inventory of ATACS equipments

(i.e., terminals, switches, and network structure) is not expected to change

drastically. Gradual changes will occur only as new TRI-TAC equipment is fielded.

Initially improvements can be made in the CP/SC connecting links. The primary

objective being to decrease deployment time by reducing the number of multiplepair cables that must be installed. Alternative bus-type structures for these links

are considered in Section 10. The preferred alternative must be selected on the

basis of subsequent improvement plans.

Figure 45, illustrates the initial improvements that can be made. The basic

topology in Figure 44 remains the same. Multiple wire-pair cables are replaced by

imbedding transparent buses into this existing structure. This can be accomplished

in a number of ways depending on the choice of multiplexing, interfacing and transmission media. It is essential that the chosen alternative be sufficiently flexible

so it can serve ATACS as well as TRI-TACS equipments and other new systems which

may evolve. Thus a fully transparent link whose output completely reproduces any

input is required. The technical feasibility of the selected technique can be

demonstrated using engineering models in the field and interconnecting to shelters

with existing connectors. The improvements achieved in deployment time would require

a more fully implemented system with special connectors installed on the shelters

and interface units installed inside.

9.3. Transitional Improvement Phase

By the 1990's ~e transition from ATAC's to TRI-TAC equipment should be

essentially complete. Some new systems using advanced concepts may begin to

appear. During these transitional periods (1985 to 1990) the CP/SC network topology is expected to remain star-connected. Digital switching systems capable of

handling both voice and data traffic will replace the analog telephone switch and

the main patch panel as shown in Figure 46. The network's traffic flow will

remain under a centralized control. Digital transmission links will merge with

the switch and the digitization of analog sources can in some cases be remoted to

new terminals. Under these conditions AID conversion is no longer required at the

link interface. Dispersed telephone lines will, in many locations be concentrated

in localized points for subsequent transmission to the switch. New features and

functions under software control will be provided from this central node. Examples

134
--'

w

(.J1

ANALOG

SWITCH

Locally

Distributed

Lines

Figure 45. Initial improvement phase.
--'

w

C"\

Locally

Distributed

Lines

Figure 46. Transitional improvement phase.
of new features offered include priority calling, automatic recall, redirection of

calls, multiaddress calling, call back, and conferencing. The control signals for

supervlslon, addressing and routing these calls will be digitally coded and transmitted using borrowed bits on a per-channel basis.

9.4. Final Improvement Phase

Beyond the 1990 l

s further improvements in equipment are expected to appear.

The network topology will change toward the star/ring configuration and the command

postls functional center will disappear. These changes are expected because of

an increased need for reliability and survivability. These can be achieved using

a structured network configuration as depicted in Figure 47. The centralized

switch of Figure 46 is replaced by two or three switches. Network control becomes

decentralized. Each switch can operate independently of the others in case of

link failures. More intelligence now resides in the terminals. End-to-end encryption is commonly used between terminals for both voice and data traffic. All of

the transmission links and nodal elements are digital. Gateways to remote sites

and other networks are the only interfaces where mode, code, speed, and protocol

conversion is required.

Control signaling is performed digitally using a common channel between

switching nodes and communications centers. Many new features and functions are

added to suppo~t new electronic office equipment.

Connectivity to widely dispersed terminals is reduced to some extent using

remote concentrators with limited switching capabilities. These units will be

capable of serving local subscribers on a stand-alone basis if connections to a

switch node fail. Equipment breakdowns, including a switch, do not disrupt communications. A graceful degradation in grade of service is effected when nodes or

links fail. Critical circuits are maintained using precedence and premption

calling with software control under failure conditions.

This decentralized structure enhances survivability but at the expense of

some deployment time. This expense is partially overcome by collocating major

centers and the switch nodes as indicated in Figure 47. In addition, the weight

and size of all equipment elements are reduced considerably using modular construction techniques and LSI circuitry. This improved mobility improves deployment

time.

9.5. Summary of Phased Improvement to Distribution System Concept

Table 24 summarizes the basic changes to be made in the CP/SC structure during

a projected three-phase improvement plan described in the previous paragraphs.

137 .
--'

Lv

CO

Locally

Distributed

Lines

Figure 47. Final improvement phase.
Table 24. Phased Evolution of CPISC Distribution System Concepts

Phase

Concepts

Terminals

Links

Nodes

Control

Signals

Overall

Network

Control

Current

(1979 )

Mostly analog

telephones &

low speed

teletypewriters.

Wire-pair

cables, twisted

pairs &spiral

four. A few

coax for

remoted

links.

Manual switching. Some

electromechanical.

Patch cord

distribution

for flow

control.

DC pulse from

rotary dial.

Some DTMF push- button dialers.

Analog transmission per channel.

Star connected

under centralized control.

Initial

Improvements

(1980 - 1985 )

Analog telephones, low

speed TTY, some

digital terminals and

facsimile.

Bus-type links

imbedded into

existing network. Some wire

pairs to dispersed stations.

SDM &TDM.

Automatic with

meta11 ic cross

points. Some SPC

switches with

AID conversion.

DTMF signals

di giti zed for

transmission on

per-channel

basis.

Star connected

under centralized control.

139

Transitional

Improvements

(1985 - 1990)

A few digital

telephones.

Mostly high

speed terminals including

computer access

terminals.

AID conversion

imbedded in

switch.

Di gita1 transmission on coax

or fiber using

TDM.

Fully automatic

digital switch

with SPC. Some

remote concentration for

terminal

clusters.

Digital codes

using borrowed

bits on digital

link on perchannel basis.

Star connected

under centralized control.

Final

Improvements

(Beyond 1990)

All di gita1

telephones.

Intelligent

data &message terminals. Electronicoffice

equipment.

All dig ita1.

AID conversion

in terminals.

TDM on coax or

fiber optical cables.

Digital switch

with SPC. Added

features &functions. Remote

concentrator

with 1imited

switching

capability.

Digital codes

using common

channel interswitch signal ing

(CCIS) .

Structured

network under

decentralized

control from

two or three

nodes.
The five year improvement phases shown in the table are somewhat arbitrary but

are related to the expected schedule for fielding TRI-TAC equipment. The basic

structure of the network, the connecting links, the switching nodes, the terminals

and the signaling technique are briefly summarized in this table for the initial,

(1980-1985) transitional, (1985-1990) and final, (1990-1) configurations.

These projections, although qualitative and admittedly somewhat arbitrary,

are needed in order to select a preferred alternative for the bus-type connecting

link. The choice to be made is primarily controlled by subsequent plans for improvements. A good example is the multiplexing technique used. A frequency

division multiplexed system using a frequency modulated carrier on coaxial cable

is one potential choice.

Such a system could prove cost-effective if the only consideration is to

replace the wire-pair cables currently used and therby decrease deployment time.

However, such a system would likely be changed if, as we project, the analog

switches are later replaced with digital switches.

The following sections are devoted to selecting the bus structure for the

first phase of improvement.

10. SYNTHESIS OF CP/SC BUS ALTERNATIVES

The first phase for improving the CP/SC structure requires replacing the

multiplicity of connecting cables and wires with a much smaller number of bus-type

links. This is accomplished using multiplexing techniques to carry the traffic

load. The so-called "mu ltiplexed bus" can then be imbedded into an existing

network structure. The most critical connections (i.e., those requiring the

longest time to deploy) would normally be replaced first.

This initial improvement phase requires three stages of concept development.

First, to evaluate a number of bus alternatives and to prepare a functional design

for the preferred alternative. This is the purpose of this and subsequent sections

of the report. Second, to construct an engineering model for test and evaluation

under field conditions. The purpose of this second stage is to determine technical feasibility and to validate the concept. The basic elements of such a model

are shown in Figure 48. Field tests would be conducted by connecting the bus

elements to suitable nodes using existing connectors. In the third stage of

development these connectors would be eliminated by installing the processing and

interface units inside the shelter using bus-type connectors. Deployment times

would be evaluated during actual field exercises.

In the following subsections we discuss several possible alternative configurations for performing the signal processing, multiplexing, and interfacing functions

140
Multiplexed

Buses to

Other Interface Units

r-- Analog Circuits

U')

::..::::

c...::>

c:> • = • SIGNAL INTERFACE I-

'----

OMM. PROCESSING UNIT IELTER r- & tMU LTI PLEXING LI NK DRIVER

U')

::..::::

c...::>

c:> • = • '---- Digital Circuits

C

SH

4::>

Figure 48. Transparent link structure for demonstrating technical feasibility

of bus-type network.
indicated in Figure 48. Then in Section 11 we evaluate a number of candidate

alternatives for a bus-type link.

10.1. Major Functions Performed by a Transparent Bus

A number of functions must be performed by any bus-type link. Specific

functions depend on the type of source (analog or digital) the signal design

(analog, quasi-analog, or digital) and the transmission medium (radio, optical,

or guided waves).

Major functions to be performed are indicated in Figure 49. Specific functions

are shown by the block diagram across the top of this figure. These are grouped

into the major classifications of information conversion, signal conversion, media

matching, and physical transfer. Each class is described in the paragraphs below,

assuming transfer from source to destination. The inverse of certain functions

must be performed by the link at the destination. This includes, for example,

demodulation, detection, decoding, digital-to-analog conversion, and finally media

conversion from electrical signals to human usable form.

Information Conversion

The conversion process transforms information in human usable form (e.g.,

printed words and numbers, visual display characters, acoustic speech, holes in

tape, etc.) to and from electrical form. For the multiplexed bus it is assumed

that these information conversion functions reside in the terminals and nodes and

are not performed by the link. Thus, the starting point for the transparent bus

structure is an electrical signal which may be analog or digital.

Signal Processing

These functions involve changing the initial electrical form to another form

suitable for transfer. The new form would ensure that the information is not

inadvertantly or surreptitiously changed. The functions include filtering, AID

conversion, and digital encoding in various combinations. The encoding functions

include binary to m-ary code conversion, encryption for security, and error

control to enhance reliability.

Media Matching

This ensures successful entry, transmission, and delivery by shaping the

signaling waveform and, if necessary, translating these waveforms to other frequencies or modulating carrier frequencies in order to match the transmission

media. It includes, for example, signal modulation for carrier system compatibi 1ity.

142
CONCEPT SAMPLINGI AID DIGITAL WAVE SUBCARRIER CARRIER CQUPLING

& FILTERING CONVERSION ENCODING FORMING MODULATION MULTI PLEXINGI &

SOURCE MODULATION TRANSMISSION

I l I ., '7 / \! ~. \/ )' \./ \./ \/

\ , , I ' I\.J- ..., " "

+:>

w

Information

Conversion

Functions

Signal Conversion

Functions

Media Matching

Functions

Physical

Transfer

Functions

D D D D D \. j

'V"

Multiplexing

or

Concentrating

Functions

Figure 49. Basic communications functions.
Physical Transfer

The transfer function is performed by some form of transmission medium and

the interface to it. The interface includes power amplification (e.g., a transmitter) and coupling to the link (e.g., an antenna). The medium provides the

path over which signaling information will pass. Guided wave transmission media

include wire lines, coaxial cables, optical fibers, and waveguides. Transmission

media could also include radio, optical, or acoustic radiation techniques.

There are three basic transmission modes of operation: analog, quasi-analog,

and digital. Analog transmission may be at voice band (e.g., a local telephone

loop) or with a modulated carrier (e.g., radio systems) using analog signals.

Quasi-analog transmission involves signals in digital form which modulate a carrier

and are transmitted in analog mode. Digital modes require transmission of the

digital signal directly, i.e., no carrier modulation is involved.

Multiplexing and Concentrating

These functions are the key to bus-type structures. They may occur at various

points as indicated in Figure 49. Multiplexing combines a number of signal sources

onto a single channel on a fixed allocation basis using frequency or time division

techniques. Concentrating allocates the source signals dynamically and may therefore be blocked. Only multiplexing techniques are considered here for CP/SC bus

alternatives since no blocking should occur in the transparent link.

10.2. Functional Tradeoffs

The electrical signal representing user information may undergo a number of

transformations for transmission purposes. The principal transformations are

indicated by the blocks at the top of Figure 49. In this section we indicate a

number of possible transformation functions available to the designer of a bustype link. Some bus structures may not require some of the transformations, some

may occur at different points, or they may be combined in unusual ways. For example,

voice digitizations mayor may not be used. If digitization is included the time

division multiplexing may occur after the sampling process or after the analog-todigital (A/D) conversion process. After conversion, additional digital encoding

mayor may not be used. A number of other alternative structures are apparent on

the figures given in the tradeoff summary at the end of this section.

Functional tradeoffs for each category listed across the top of Figure 49 are

described below.

144
Sampling and Filtering

Sampling converts signals which are continuous in time and amplitude into

signals which are discrete in time. The amplitude level is still continously

variable. In order to reproduce a waveform completely the samples are obtained at

points separated by 1/2B seconds where B is the bandwidth occupied by the signal.

Voice signals are norwlally filtered to a nominal 4 kHz bandwidth and therefore

8000 samples per second are required. Sampling is essential to waveform coded

systems.

Sampling may also be used as part of the process of spreading the spectrum of

digital signals. These systems are not considered here.

Comb filters and other methods of exploiting the acoustic features of speech

production are included in this functional category since they are required prior

to the A/D conversion process. Such digitizing processes are known as source

coding. Vocoders are one example.

A/D Conversion.

This involves converting the continous amplitude variation of analog signals

to discrete values. The most common method is pulse code modulation (PCM). Common

systems encode each sampled value into a 6 (tactical) or 8 (strategic) bit binary

code. Since both systems sample 8000 times per second this yields signaling rates

per voice channel of 48 kb/s and 64 kb/s respectively. Other voice digitization

techniques provide different rates. Broadband systems operating above about 20

kb/s in addition' to PCM include linear delta modulation (LDM), differential PCM,

and adaptive versions of delta modulation (ADM). Continously variable slope delta

modulation (CVSD) is operational at 16 kb/s and 32 kb/s for tactical systems.

For systems with limited channel capacity or limited bandwidth «20 kHz) more

sophisti~ated source coding techniques are used. This range includes linear predictive coding (LPC) and adaptive predicted coding (APC) as well as a number of

vocoding techniques.

Di gita1 Encod iQ.9.

Given a digital signal or a digitized analog signal the resultant digital

wavefoy'm may be encoded in many ways. The information content is not changed in

this pl:ocess. This encoding is done to match incompatible terminals, to ensure

reliable transmission, or to reduce the channel bandwidth requirements. Digitally

encodtng a binary sequence into an m-ary sequence is an example of the latter.

Parity check bits may also be added for error control. Military systems often use

cyclic redundency check (CRC) codes for this purpose. These CRC codes require

145
that additional bits be added

additional bits are required.

expense of throughput.

For secure transmissions~

to blocks of message bits. ~ypica11y 16 or 32

The use of CRe permits error detection at the

the encryption process would usually follow the

digital encoding function.

The steps involved in waveform coding are illustrated in Figure 50. As noted

above for voice frequencies of 4 kHz, a sampling rate of 8000 times per second is

required for voice. Next, the number of quantizing levels needed to obtain the

required resolution is defined. The number of quantizing levels defined is directly related to the number of bits needed. With two bits foul~ levels can be

represented, 4 bits--16 levels, 6 bits--64 levels, and 8 bits--256 levels. Six to

eight bits are normally used to encode voice signals. The figure shows a waveform

digitized with a 4~bit code as a detailed example. Amplitudes are sampled in (b).

A digital signal format is assigned in (c) and serialized in time in (d). The

resulting binary signal is shown in (e). A parity error detecting check and

signal conversion for the particular type of transmission medium used may be added

to the .bit stream before actual transmission. When the bit stream is received the

inverse operations and accuracy checks are made upon detection. The digital code

is converted back to analog form and filtered to smooth it. The resulting continuous analog waveform approximates the input waveform.

Many different digital signal forms and codes have been designed. Each has a

use or function for which it was designed. Thus, PCM is primarily used for longhaul digital trunks over cable, microwave, and satellite links.

Wave Forming

There are a number of ways to represent the digital encoded sequence of bits.

The waveform selected depends on subsequent functions to be performed. For example,

a unipolar return-to-zero (RZ) waveform may be used to pulse a light emitting

diode for transmission over an optical fiber. A bipolar non-return-to-zero waveform is more suitable for signal modulation on a radio carrier.

These and other common waveforms are shown in Figure 51. All of the waveforms result from the same binary sequence. A synchronous system (clock provided)

is envisioned where the receiver samples at the arrows to determine if the amplitude is above or below the threshold dotted line for a binary~ 1 or O.

Waveforms (a) and (b) are two basic formats where (a) has binary levels of

one polarity, and (b) was a for negative levels and 1 for positive levels. The

signal stays at that level for the entire bit period and does not return to zero

(NRZ).

146
(a) Original Signal

l'

I '-i---ri I I I I

I I i I I I ; I I . 00101011010101110101100111101

l

(e) Digitized Signal

I I I I

I I I

I ~Clock IPulsesl~ I I I

I

I I

0111

0110

0100

1011

1010

0101

0011

0000

0010

0001

Code

-.......

....,

"

,

1\

(b) S?mpling the \ l I J/

SIgnal \ / \ //

Level -

/

I

I

I

I

-'

--'

.j:::> I .. -.....J

..

-+

1000

1001

1101

1100 (d) Encoded Signa I

(c) Quantized Signal 1110

1111

Figure 50. Steps in pulse coding an analog signal.
(a) Two-level v ~:~~-- --- ----- --- ----

o I"I"'I.I.I"I.I.I~I.I.I 0110001101

(bl Polcr two-level v1D

r

-- --- -----------

-to I 01 t I i I 0I0I 0I i 11 1 , I

(c) Return-Io-zero V ..~~-- - - - ------ - - --- -

o I I" '4 1

4 1+ 1+ ,4 1+ 1-+ 1

4 I .0110001101

1.°l (d) Polar return-to-zero V 0 ,-

-to 1+0,411+11"'01+0 '+0 1+1,411+01+11

tOl

(e) Bipolar V 0 I

-1.0 1+ 1+ ,. '+ I" 1

4 ,... ,4 1+ 1+ I 0110001101

(t) oifferenlially encoded V ~l- ----------- -1.0 ... .. ... .. ... ... ... ... ... ... ... 101111101010111110111

(f,lDicoded V ~l------------------ - -1.0 4 .. .. ... + 4-

101111101010111110111

1.0

0.67

0.33

(g) Four-level V 0

-0.33

-0.67

t t t = Sampling instants -1.0

- - - =Decision thresholds

-- -- -- --- --

------ ----

I + I I + I I • I 01 10 00 11 01

Time~

Figure 51. Common digital signal formats for transmission.

148
Formats (c) and (d) are similar to (a) and (b) except that the attained level

is return-to-zero (RZ) before the end of the bit period that indicates less than

100 percent duty cycle. In (d) since a pulse, either a or 1, starts at the beginning of each bit period, the synchronization can be derived from information in

the signal (self-clocking). Note, (d) and bipolar NRZ (e) are basically threelevel signals.

Format (e) is used for T-carrier systems. The l's are alternating plus and

minus from zero, and O's are the a signal. Thus, the dc component is eliminated

allowing transformer coupling to the transmission line. The energy is concentrated

at the half-baud rate which reduces near-end crosstalk and the bandwidth required.

Another useful form not shown is partial response coding. One scheme involves

replacing each 1 with the sequence 1, 0, -1.

In (f) the information is coded in terms of the transitions (differences)

that occur in the signal. Successive pulse intervals are compared. If they are

identical, a 1 is transmitted; if a transition was made, a a is transmitte~. The

(f1) is the (f) form coded again with l's coded as a 0-to-1 transition, and O's

coded as a 1-to-0 transition to make a di-code format.

The sequence in (g) is not a binary code but an m-ary code that increases the

number of information bits per cycle. It is used when the signa1-to-noise ratio

is sufficiently high to allow multiple detection levels. It could also be considered as part of the digital encoding process and used directly to modulate a

carrier.

Subcarrier Modulation

Baseband signal waveforms may be analog or digital depending on the functions

previously performed. These waveforms may be transmitted directly or used to

modulate a carrier in order to match the transmission media. Subcarrier modulation

schemes are another functional category. The signals resulting from subcarrier

modulation may be transmitted directly, be used to modulate a higher frequency

carrier, or be translated to some other desired frequency. The translation

process is used for frequency division multiplexing several signals on a common

channel.

Analog baseband signals and digital signals may be used directly to modulate

a carrier using amplitude modulation (AM), frequency modulation (FM) or phase

modulation (PM). Examples of digitally modulated carriers are shown in Figure

52.

An example of a binary, on-off amplitude modulation (AM) is shown in Figure

52 (a). The amplitude can be varied to represent any of the signals described.

149
.0.'.1.011101011.

i I 1\1\1\ 1\ f\

AM \fUll VV Vl} t~

FM

PM

QPM

a. On-off amplitude modulation.

t~

b. Binary frequency-modulated carrier

wave.

c. Binary phase-modulated carrier

wave.

d. Quad amplitude/phase-modulated

carrier wave.

Figure 52. Common modulated carrier signals.

150
Here the carrier is turned on and off corresponding to the 0 and 1 in a binary

sequence. This intermittent carrier wave (leW) was used for sending Morse code in

earlier systems. Other amplitude shift keying (ASK) forms were also used.

An example of a binary frequency-modulated carrier, called frequency-shift

keying (FSK) , is shown in Figure 52( b) .

A binary phase-modulated (0° and 180°) carrier is shown in (c). Where a large

signal-to-noise ratio is available, multiple divisions of phase can be used to

increase the number of transmitted bits per hertz. A binary phase shift keyed

(PSK) signal contains one bit per hertz. Quadrature phase shift keying (QPSK)

contains 2 bits/hertz.

Multi-carrier modulations also can be used. The waveform in Figure 52 (d),

for example, is a combination of two phase positions and two amplitude levels for

a total of 8 logic levels. This combination illustrates how ASK and PSK can be

combined. A combination of four AM levels and four PSK phase yields 16 symbol

choices and 4 bits per hertz.

Table 25 compares several modulation schemes in terms of their error rate performance in Gaussian noise. The characteristics considered are the bits-per-hertz

efficiency and the signal-to-noise ratio (S/N) required at a system bandwidth that

will provide a bit error rate of 10-4. .

As stated below the table, practical systems may require greater SIN ratio

than those calculated. However, this can be considered the limit that can be

. achieved in this noise environment.

Analog signals may also be translated into a number of pulse modulated forms

after sampling. The series of the pulses in Figure 53 indicate ways in which the

original continuous waveform is represented. Figure 53 (a) shows an equal interval series of clock pulses used to determine when the original continuous waveform,

(b), should be sampled. Pulse series (c) is a pulse amplitude modulated (PAM)

representation of, (b), from the reference level slightly below -v, at the clock

rate and at equal intervals. The pulse series (d) is the same representation of

(b) usfng.a 0 reference level. It is known as bidirectional PA~1. Pulse series

(e) through (g) have constant amplitude pulses but use the amplitude sampling of

the original wave (b) to vary the pulse width (PWM), or pulse duration (POM), or

frequency (PFM). Series (e) shows how the pulse width varies within the limits of

the clock cycle periods, as the amplitude samples vary. Series (f) and (g) are

equal interval pulses like the rest of the pulse series, but varying in position

within the clock interval as in (f) or in repetition rate as in (g).

151
Table 25. A Comparison of Carrier Modulation Systems

Fixed Bandwidth

Type Logic Nyquist Signa1-to-Noise

Levels Bits/Hz for 10- 4 BER

(Coherent

Detection)

Amplitude 2 1 14.4 dB

FSK 2 1 11 .7 dB

Partial Response FM 4 2 21.2 dB

Partia1 Response AM 4 2 23.8 dB

2 PSK 2 1 8.4 dB

4 PSK 4 2 11.4 dB

8 PSK 8 3 16.5 dB

16 PSK 16 4 22.1 dB

QPRS AM 16 4 31.4 dB

QPRS AM + PSK 16 4 28.5 dB

o Practical systems operate at reduced performance based upon filtering, equalization, and transmitted

spectrum attenuation

152
-v

o {a} Reference signal, clock,

sampling pulse

{c} Pulse amplitude

modulation {PAM}

{undirectional} o

-v

--v -V

L...--------~-------~O {b} Modulating signal

-v

o {d} Bidirectional PAM

--v

-v

o

(e) Pulse width modulotion

(PWM) Pulse duration

modulation (PDM)

{f} Pulse position modulation

{PPM}

-v

o

{g} Pulse frequency

modulation {PFM}

Figure 53. Noncoded pulse waveform representations.

153
Carrier Multiplexing and Modulation

As noted in Figure 48 there are many points where multiplexing a number of

channels onto one channel be accomplished. The multiple wire pairs in a single

cable currently used is considered one form known as space division multiplex

(SOM) .

Alternate forms for replacing this SOM cable with a more manageable bus-type

link are frequency division multiplexing (FOM) and time division multiplexing

(TOM).

The FOM schemes are suitable for transmission over analog or quasi-analog

links. The TOM schemes can be directly coupled to digital links or after using a

modulator/demodulator (modem) to a quasi-analog channel.

Common methods for multiplexing analog terminations to analog and digital

buses are diagrammed in Figure 54. Methods for multiplexing digital terminations

onto an analog bus are shown in Figure 55.

In Figure 56 the TOM method combined with FOM allows geographically separated

terminal clusters to access the bus.

Using various levels of multiplexers a high-speed bus structure can be designed to carry traffic from terminations having different source rates. Thus,

several low-speed digital sources can be multiplexed onto a medium-speed channel

which is multiplexed with medium-speed sources for transmission on the high-speed

bus. This multilevel process is depicted in Figure 57.

An example is the frequency hierarchy levels used in the telephone network.

In this hierarchy the lowest level of multiplex equipment packs 12 telegraph

channels into one 4-kHz voice channel and the second level packs 12 voice channels

into 48-kHz groups. Five groups are combined into supergroups of 60 voice channels and 10 supergroups into a master group of 600 voice channels. Amaster group

occupies a bandwidth of approximately 2500 kHz. The L3 coaxial cable system can . handle three master groups or 1860 voice channels.

These FOM methods are accomplished by translating subcarrier modulated voice

channels to separate carrier frequencies.

Carriers may also be modulated directly using baseband or subcarrier modulated signals. Carrier modulation methods include AM, FM, and PM techniques and

variations such as double sideband (OSB) or single sideband (SSB) amplitude modulation and narrowband (NB) or wideband (WB) frequency modulation.

154
Multiplexer

~;r~~~aIS~ rOM 1__~_A_n_a_lo.....;.g_B_US --I1 FOM E

a) FREQUENCY DIVISION MULTIPLEXERS

Codec

Multiplexer

Analog

Terminals

TDM Digital

t-----=S::-"u-s---i TDM .....-----1

b) DIGITAL TIME DIVISION MULTIPLEXERS

Multiplexer

.Analog

Terminals _-i

Codec

Digital

Bus

PAM TO Mt------e

c) ANALOG TIME DIVISION MULTIPLEXERS

Figure 54. Multiplexing analog terminals on analog and digital buses.

155
Modem

Multiplexer

Digital

Terminals

FDM Analog 1----..",.-....:.----1 FDM 1------1

Bus

a) FREQUENCY DIVISION MULTIPLEXERS

Multiplexer

Modem

Digital

Terminals _-I TDM Analog

Bus

Figure 55. Multiplexing digital terminals on an analog bus.

156
---~ TOM

Digital • TOM Terminals

( Analog

Modems FDM FDM Bus

\

TOM

_._-1 TOM

Figure 56. Multiplexing digital terminals on an analog bus with separated

access.

157
Low

Speed

Terminals

First Level

NUX

NUX

Medium

Speed

Second

Level

NUX

NUX

High

Speed __---I

Third

Level

NUX High-Speed

Bus

Figure 57. Multiplexing terminal with different source rates.

158
Coupling and Transmission

Functions in this category include the power amplifications, coupling mechanism? and the transmission media itself. The power and coupling device specifications depend on the medium used and its characteristics. The medium used depends on

traffic load to be carried and the cost.

The physical transmission media that can propagate traffic mixes, either

separately or jointly, can belong to several categories:

twisted-wire pairs,

multiwire cables,

coaxial cables,

microwave radio,

waveguides,

optical fibers.

The signaling scheme used to transmit over a selected medium may be either analog,

quasi-analog or digital. Examples of each are listed below.

Analog

o voice frequencies

at baseband over

local wire pair.

o FDM/FM carrier on

coaxial cable

Quasi-Analog

o data modem over

telephone circuits

o Digital modulated

carrier on LOS microwave

Digital

o bipolar digital

signal on coaxial

cable

o Pulse modulated light source

over optical fiber.

o continuously varied

light sources over

optical fiber.

These media have different characteristics (Hoth, 1975). One important

characteristic, the attenuation in dB/km, is shown in Figure 58. Transmission

capabilities, such as data rate and bandwidth, also vary considerably. So do

other operational parameters, including cost. See Figure 59.

The power amplifier may be linear or nonlinear. Radio transmitters, for

example, must be Class A or B for AM modulation or Class C for FM modulation. The

transmission mode for cable drivers may be balanced or unbalanced, and either ac

or dc coupled.

The directivity of the transmission mode is an important concern. Transmission may use a simplex (SX) mode which is unidirectional or a duplex (OX) mode

159
60

55 Dominant Mode

Waveguide

50

45

E 40

.::eo

"- Telephone CD 35

"'0 Exchange A Cable

c: 30 0 Microwave

- t 0 Radio

::J 25 / c: Wave .S:? Guide - 20 Special « Paired

15 Cable

10 Fiber Optics1

5 Circular

~/waveguide

0

t .

103 106 109 1012 10 15

Frequency, Hz

Figure 58. Losses of current telecommunication media.

160
...- 1000

"C

Q)

"C

::J

"0

..5:

'0z

'tn0u

10K lOOK

TrendLine~

1000

Number of Circuits

100

1

10

10

c 100

c:E

'- -

.-

0"'1

--'

·S-u

.!=U

'-

Q)

a.-l/l 0U

Q)

.~

.9-

Q)

0::

Figure 59. Trend line for relative cost per circuit mile

(Abraham, 1960).
which is bidirectional. The OX mode can be either full duplex (FOX) or half

duplex (HOX). The FOX mode involves simultaneous transmissions in both directions

whereas the HOX mode uses the channel one direction at a time. The FOX circuits

normally require two channels using FOM or a 4-wire circuit.

10.3. Bus Synthesis Tradeoff Summary

Figures 60 through 63 are examples of bus type structures which might be used

for time-continuous analog signals, time-discrete analog signals, digitized

analog signals and digital signals, respectively. Several, tradeoff functions defined above are indicated under appropriate elements on these figures. Multiplexing points and methods are also shown. Each basic conceptual structure is

identified by a number. Substructures are identified by letters. The current

CP/SC links employing multiple wire-pair cable is concept lb illustrated in Figure

60.

The interface point between the bus distribution system and the existing

nodal equipments is assumed to be at the existing 26-pair hocks. This is the line

between the source and the sampling/filter function on Figures 60 through 63.

This interface point would, of course, change as nodal equipment and terminal

equipment change from analog-to-digital in the future since functions such as

sampling and A/O conversion would then take place within the node.

This aspect is considered further in Section 11 where candidate alternatives

are selected and evaluated.

The bus structures illustrated in Figures 60 through 63 identify the range of

choices faced in the selection and evaluation process. There are obviously a

number of combinations and permutations which could be selected from the sets

given in these figures.

The present CP/SC system is based entirely on the nominal 4 kHz telephone

channel for both.analog and digital signals. The transition to future switches of

the AN/TTC-39 type wi 11 introduce 32-kbit/second and 16-kbit/second CVSO as a

digital signal. These signals will require digital-to-analog conversion at the

line side of the switch in order to interface with the conventional telephone

set. If, at some time in the future, the digital-to-analog conversion is placed

at the telephone set, the existing wire pair can still be used for transmission.

However, such an approach could impact the selection of a bus structure. The

bus may have to allow for a mixture of 4-kHz analog channels and 16-kbps or

32-kbps digital signals.

In the following section we select specific bus alternatives which appear to

have potential applications in the command post network.

162
CONCEPTI SA MPLI NGI AID DIGITAL WAVE BASEBAND CARRIER

SOURCE FILT ERING CONVERSION ENCODING FORMING SUBCARRIER MULTIPLEXINGI TRANSMISSION

MODULATION MODULATION

\7 • 7 .. .. :, .. 7

' l .. 7

\. \ \ ' 7 \ \ \. \

-'

0)

w

FDM

0 /T'\ ANALOG \J.} ANALOG

AM AM/DSB

FM AM/SSB PM NBFM

WBFM

b SDM

111\ ANALOG \J7

Figure 60. Transparent bus structures for time continuous analog signals.

10

1b
WAVE BASEBAND CARRIER CONCEPTI SAMPLINGI AID DIGITAL SUBCARRIER MULTI PLEXI NGI TRANSM ISSION SOURCE FILTERING CONVERSION ENCODING FORMING MODULATION MODULATION

., , j~ ,j" , , ,J , \j' , \.j \. J j \j \j

.....

0)

.j:::o.

2

ANALOG I I 112B

TOM

o

FOM

PAM

PWM AM

PPM FM

PRM PM

I I ANALOG I 20

SOM

b PAM

PWM

PPM

PRM

I l I J I ANALOGI 2b

Figure 61. Transparent bus structures for time discrete analog signals.
WAVE 8ASE8AN~ CARRIER CONCEPTI SAMPLINGI AID DIGITAL SUBCARRI R MULTI PLEXINGI TRANSMISSION SOURCE FILTERING CONVERSION ENCODING FORMING MODULATION MODULATION

~} I

7 '7 '1 7 J l 7 '1

.I .J \) j \1 \1

ANALOG· 1128 IT\ AID f\ fT\ a fT\ QUASI-

\J..J \..J \J..../ \J..../ ANALOG

LOM Binary RZ FSK AM PCM m-ary NRZ PSK FM OPCM

AOM CRC Bipolar ASK PM

CVSO FEC Biphose

PC

4. Source Coming

ANALOG FILTI AID b DIGITAL DET -

--'

0)

Ul

3. Waveform Coding TOM

LPC

APC

VEV

CV

TOM TOM FOM

3a

40

3b

4b

Figure 62. Transparent bus structures for digitized analog signals~
AID DIGITAL WAVE SUB CARRIER CARRIER COUPLING CONCEPTI SAMPLI NGI MULTI PLEXI NGI & SOURCE FILTERING CONVERSION ENCODING FORMING MODULATION MODULATION TRANSM ISSION

\ J'7 \ J'7 \)7 , 7 , ." ,; , '7

\) \J \) \)

DIGITAL fT\ IT\ a IT\ QUASI-

\J../ \J7 \l..J ANALOG

Binary RZ FSK AM

m-ary NRZ PSK FM

PC Bipolar ASK PM

FEC Biphase

b DIGITAL

-'

O"'l

O"'l

5 TOM TOM FOM

Figure 63. Transparent bus structures for digital signals.
11. SELECTION OF PREFERRED ALTERNATIVES

The previous section has indicated that the number of candidate alternatives

for a CP/SC bus distribution system can be large. Here we reduce the number of

candidates to a manageable size for further evaluation. We then apply certain

selection criteria for choosing the preferred system.

The principal criteria used for selecting and evaluating candidate alternatives are as follows:

1. Deployment

The extent to which deployment time and manpower can be saved. This

requires a sizable reduction in weight and volume for the bus system relative to 26-wire-pair cabling.

2. F1 exibi 1ity

The design must adapt to future requirements. This includes changing

from analog to digital equipm~nt and mixes of these types of signal

sources.

3. Capacity/Range

The ability to accommodate a large number of channels on the bus. A

maximum distance of 2 km with no repeaters is assumed to be one constraint.

We also assume that the bus capacity should be capable of handling 120

full-duplex voice channels. This is equivalent to replacing ten 26-

pair cables between any two nodes.

4. Power Distribution

The capability of providing power to end instruments is an important consideration.

5. Security

The desirability for equal or improved security. This includes minimizing electromagnetic signatures of the CP/SC as well as adding encryp- tion capabilities.

6. Performance

This includes reliability and survivability. Both should be maintained

or preferrably improved over the current system. The quality of service

should also be maintained or enhanced.

7. Development Risks and Cost

The development concept should be based on proven technologies and the

cost should be minimized.

8. Modularity

The overall structure should be a transparent module requiring no external

synchronization or timing signals. The bus structure should be organized

into submodu1es which will permit adaptation to the transition from analog

to digital network elements.

167
In the following subsections we first define the existing CP/SC link structure and

then indicate alternatives to this structure. The candidate alternatives meet one

or more of the desirable features listed above but not necessarily all of them.

The relative advantages and disadvantages of each alternative are then summarized.

Preferred alternatives are selected based on the above criteria.

11.1. CP/SC Distribution System - Existing Structure

Examples of CP/SC link structures currently employed for analog and digital

source signals are depicted in Figure 64 for comparison with subsequent candidate

alternatives.

Functional tradeoffs described previously are again indicated at the top of

the figure. In this current system, the telephone voice signals are transferred

at baseband frequencies over 26-wire-pair cables. Voice channels are 4-wire circuits and each 26-pair cable usually carries 12 two-way voice channels. Separate

multipair cables are normally used to handle digital data. This is primarily teletype information which is coded in 7 bit binary form using the American Standard

Code for Information Interchange (ASCII) with 3 bits added for error control. An

FSK modem is often used with typically four TTY channels multiplexed onto a single

voice channel using FDM techniques. Transmission may use a HDX or FOX mode depending on requirements.

During one tactical field exercise called Bold Eagle conducted in 1978 and

considered typical, some 80 km of 26-pair cable were used. Thirteen C-130 aircraft

and a similar number of 2-1/2 ton trucks were required to transport the cable alone.

A 300 m spool of 26-pair cable weighs about 100 kg and requires two men to deploy

it using an A-frame despooler. See Kleekamp and Metcalf (1979).

These numbers demonstrate the obvious advantage of a bus-type link for improving transportability and for reducing deployment time. The magnitude of improvement depends on the bus design concept employed.

The existing structure of a CP/SC distribution system has a large variation

in size. The total number of telephone and teletype terminations was indicated

in Section 5 for CP sizes ranging from very small to very large. For a medium

size CP the number of telephones lines varies between 200 and 500. The number

of teletype lines for this medium CP (assuming four FOX circuits per,line) varies

between 5 and 12. Not all of this traffic is necessarily carried between any

two points. For the purpose of selecting and evaluating bus structures we assume

that the maximum number of equivalent voice channels required between any two

168
DIGITAL WAVE SUBCARRIER CARRIER COUPLING CONCEPTI SAMPLINGI AID MULTIPLEXING & & SOURCE FILTERING CONVERSION ENCODING FORMING MODULATION , MODULATION TRANSMISSION ,

~l I I \J I \1 \1 \7 \7 \1 \7

Telephone

--' TerminaI SOM

IANALOGI ED IANALOG I

TA-236 FOX with

2W, Rotary Dial SOM on

DC Pulse Multiple 2W

Pair Cable

Terminal TTY I I QUASI- I .I IBINARY I IFSK ~.ANALOG DIGITAL FDM HDX a FOX

10 Bit 4 Ch. FOX on

MGC-22 ASCII BCh.HDX 2W or 4W

Pair Cable

Figure 64. Existing CP/SC link structure.
points is 120. This would include teletype traffic and special control or network

management signals. Such a bus would replace ten 26-pair cables. If additional

channels between the two points are required (in a larger CP for example) then

additional bus systems would have to be deployed.

The following CP/SC cable runs are considered appropriate for installing bus

distribution systems during the initial improvement phase:

1. Clusters of analog telephones (4-wire) to the analog switch. An example would be from the field support area or the command headquarters to the

switch located some distance away.

2. Ditigal teletype terminals (4-wire) to the main patch panel at the

signal center.

3. Between the analog switch and the main patch panel.

4. Other 4-kHz bandwidth digital or analog terminal clusters (such as

facsimile or logistic support terminal centers) requiring real-time

connections through the analog circuit switch.

Examples of these existing types of cable runs are shown in Figure 65.

The bus distribution system would, in each case above, replace the multiple

26-pair cables at the switch wire frame or at the main patch panel with single or

dual connecting cables. Five candidate alternatives for accomplishing this are

described in the following subsections. These are evaluated and the preferred

alternative selected in Section 11.8.

11.2. CP/SC Alternative I Bus Distribution System

Alternative Ia in Figure 66 isa CP/SC link structure using separate buses

for analog and digital sources. The analog source is sampled but not digitized.

Time division multiplexing combines several voice channels for transmission. Full

duplex operation is achieved using analog transmission over 4-wire circuits. The

resulting PAM signals can be switched directly in a time division switch such as

a WECO 400. Digital data are time division multiplexed and transferred digitally

using bipolar RZ format over a 4-wire circuit.

Alternative Ib in Figure 66 combines the analog and digital TDM signals for

transmission and switching over the same 4-wire circuit. No carrier modulation is

required since band band transmission over a limited distance is achievable. Figure

67 illustrates a method for implementing Alternative Ia.

170
ANALOG

SWITCH

MAIN

PATCH

PANEL

1or More

26- Pair Cables

12 FOX ChGlnnels _ ...

per Cable

4 kHz per Channel

Ana log or Digital

\

Junction Box

Terminal

Clusters

--'

-....J

--'

Figure 65. Existing CP/SC cable run structure.
CONCEPTI

SOURCE

SAMPLINGI

FILTERING

AID

CONVERSION

DIGITAL

ENCODING

WAVE

FORMING

BASEBAND

SUBCARRIER

MODULATION

CARRIER

MULTI PLEXINGI I TRANSM ISSION

MODULATION

.....

""-J

N

Io

IANALOG I 1 1I2B I CD I PAM I IANALOG I

t FOX 00

I 4 - Wire Pairs

I Ib

I

I

I

10 I

IDIGITAL I ED IBI ~iARI IDlGITAL I

TOM· FOX on

4-Wire Pairs

Figure 66. Alternative I for CP/SC link structure.
4-Wire

Circuits·

PAM Single 4-Wire Circuit

Converter/

ANALOG

SWITCH

•••

.....J

'-l

W

TDM

DIGITAL

Single 4-Wire Circuit Bi-Polar Rz

TDM

DIGITAL

TOM = Time Division Multiplexer

PAM =Pulse Amplitude Modulator

Figure 67. CP/SC Alternative Ia bus distribution system.
11.3. CP/SC Alternative II Bus Distribution System

Alternatives IIa and lIb in Figure 68 use FDM techniques to combine analog

and digital sources after subcarrier modulation. Analog signals modulate the

subcarrier using NBFM and digital signals using FSK. Digital sources may be

multiplexed using both TOM and FDM techniques. The buses may be separated for IIa

or combined for lIb. Physical transmission is FOX using FDM on a single coaxial

cable. Another alternative is to use separate coaxial cables. Both one-way and

two-way systems are commonly used in cable television (CATV) systems using either

one or two coaxial cables. The two-way transmissions on a single cable are achieved

by FDM techniques and filters are required to separate upstream signals from

downstream signals. A single bus system could provide bidirectional service using

one half of the band for one direction and the other half for the opposite direction. Figure 69 illustrated Alternative lIb.

In a CATV system each TV channel occupies about 4.5 MHz. A 6-MHz channel is

used to allow for guard bands to prevent crosstalk. Typically 20 to 30 TV channels

are transmitted over the cable. About 500 NBFM voice channels could be transmitted

over each'TV channel. For data the number of carrier symbols per second (i.e.,

the baud rate) is roughly equal to the channel bandwidth in Hertz for FSK. This

rate is reduced by about 20% on the channel because of noise and distortion. A

4.5-MHz channel is therefore capable of transmitting digital information at a rate

given by:

4.5 MHz x 0.8 x 1 b/s/Hz = 3.6 MBPS.

Other subcarrier modulation schemes which provide 4 b/Hz to be transmitted yield

14.4 Mb/s per TV channel. A single cable could carry up to 7000 voice channels.

11.4. CP/SC Alternative III Canonical Bus Distribution System

Alternative III is illustrated in Figures 70 and 71. This bus distribution

system is described as canonical because it embodies a family of alternatives

within the same overall structure. The functional process is one of analog-todigital conversion followed by multiplexing the binary encoded voice or digital

data using TOM. Finally, transmission of the TOM signal can be over three different media; 1) T-carrier with either 4-wire pairs for short distances or dual

coaxial cables for longer distances, 2) single coaxial cable using dual carriers

modulated with PSK~ and 3) a unipolar RZ digital waveform and pulsed LEDls

driving dual fiber optical cables.

174
CONCEPTI

SOURCE

SAMPLI NGI

FILTERING

AID

CONVERSION

DIGITAL

ENCODING

WAVE

FORMING

BASEBAND

SUBCARRIER

MODULATION

CARRIER

MULTIPLEXINGI I.TRANSMISSION

MODULATION

-'

'-.l

U..,

na FOM

jANALOGI INBFM IANALOGI

I FOX Using

I FOMon

I Coaxial Coble

!JIb

I

I

no TOM I

IDIGITAL I ED IBINARY I I FSK Ki?1~~1tbGI FDM FOX Using

FOMon

Separate Coax

Figure 68. Alternative II for CP/SC link structure.
4-Wire

Analog

I

NBFM NBFM

DEMOD. MOD.

NBFM NBFM DEMOD. MOD.

DIGITAL FDM FDM DIGITAL

FSK DEMOD. DEMUX MUX FSK MOD.

4-Wire

Digital I I b- ___J •

I • ANA LOG

• SWITCH •

FDM I FDM , • .....0 Single Coaxial Cable -....J MUX DEMUX 0) DIGITAL NBFM FSK MOD. oEMOD.

DIGITAL DIGITAL FSK MO D. FSK DEMOD.

NBFM DIGITAL

MOD. FSK DEMOD.

NBFM = Narrow-Band Frequency Modulation

FS K = Frequency Shift Keying Modulator

FDM = Frequency Division Multiplexer

Figure 69. CP/SC Alternative lIb bus distribution system.
CONCEPTI

SOURCE

SAMPLINGI

FILTERING

AID

CONVERSION

DIGITAL

ENCODING

WAVE

FORMING

BASEBAND

SUBCARRIER

MODULATION

CARRIER

MULTI PLEX INGI I TRANSMISSION

MODULATION

9

01

ble

rier)

ANALOG 1/2B PCM BINARY --- 48 kb/s

TOM' ""\ BIPOLAR DIGITAL \.. ..J RZ

TOM

DIGITAL .. IT\

'-J./

-'

'-J

'-J

Figure 70. Alternative III for CP/SC link structure.
-'

-....J

c.:>

Either:

1. CVSD @ 16 kb/s or 32 kb/s

or

2. PCM @ 48 kb/s or 64 kb/s

DIA

- TDM

DEMUX • I ANALOG

TOM I SWITCH

MUX AID

DIG

Either:

1. Single Coaxial Cable PSK Carrier Modulation

for High Bit Rate

2. T-Carrier Dual Coaxial Cables Bi-Polar Rz

Waveform for Low Bit Rate

3. Unipolar Rz with Pulsed LED Dual Fiber

Optical Cables

Figure 71. CP/SC Alternative III canonical bus distribution system.
The analog to digital conversion can use either CVSD at 16 kb/s or 32 kb/s

or PCM at 48 kb/s or 64 kb/s.

The capacity of Alternative III is limited by the TDM device and the transmission media. In the CP/SC bus application with 120 voice channels, CVSD at

16 kbls would require a transmission rate of 1.92 Mb/s. Use of PCM at 64 kb/s

would necessitate a 7.68 Mb/s rate.

11.5. CP/SC Alternative IV Canonical Bus Distribution System

Alternative IV is illustrated in Figures 72 and 73. This bus distribution

system is also described as canonical because it may use a number of analog to

digital conversion processes. Functionally, this alternative includes analog to

digital conversion of voice signals followed by a modem to drive a Frequency

Division Multiplexer (FDM) for quasi-analog carrier transmission over a coaxial

cable. The FOX operation is achJeved over a single coaxial cable using FDM as in

Alternative II. Digital data can be initially combined through TDM to a 4-kHz

bandwidth equivalent rate.

11.6. CP/SC Alternative VBus Distribution System

Alternative V in Figure 74 uses LPC or APC voice digitization to achieve 2.4~

kb/s or 9.6-kb/s rates per channel. Digital data sources are combined to similar

rates and then multiplexed with the digitized voice using TDM. Physical transmission is via two-fiber optical cables driven by pulsed LED's. Such a system has

the information carrying capacity of several hundred voice channels using 16 kb/s

CVSD and several thousand voice channels using LPC at the 2.4-kb/s rate.

11.7. Summary of Assessment of Candidate Alternatives

The relative advantages and disadvantages of the five selected alternatives

are summarized in Table 26 and discussed below.

Alternative I is probably the simplest of all the alternatives to implement.

Exis"ting twisted-wire pairs and spiral-four cable can be used for the physical

link. This alternative, however, is the least compatible with the transitional

improvement plan which requires replacement of analog switches with digital

switches. The PAM signals could, however, be switched using time division matrix

as in WECO 400.

The link capacity may be limited at longer distances because of noise pickup

on the lines which restricts detectabi1ity of the PAM voice channels and the data

179
WAVE BASEBAND CARRIER CONCEPTI SAMPLINGI AID DIGITAL SUBCARRIER MULTIPLEXINGI TRANSMISSION SOURCE FILTERING CONVERSION ENCODING FORMING MODULATION MODULATION

-'

(X)

C> ANALOG 1/2B CVSD BINARY FSK I--

16 or 32

kb/s

FOM'

"' ANA&LOG

\../ Q-ANA.

TOM

DIGITAL fT\ BINARY FSK I--- \V

Figure 72. Alternative IV for CP/SC link structure.

g

x

e)
4-Wire Ana log

CVSD @ 16 kb/s or 32 kb/s

PCM @ 48 kb/s or 64 kb/s

--'

00

......

FDM

FSK AID

MUX

FSK DIA

DIG I F~ DEMUX

• I ANALOG •

• SWITCH

I ~K

Single Coaxia I Cable FSK DIG

4-Wire Digital

FSK DIG

Figure 73. CP/SC Alternative IV canonical bus distribution system.
WAVE BASEBAND CARRIER CONCEPTI SAMPLINGI AID DIGITAL SUBCARRIER MULTIPLEXI NGI TRANSMISSION SOURCE FILTERING CONVERSION ENCODING FORMING MODULATION MODULATION

1 I I U I I I I I

\. \1 \1 I ., 7 ""] J \

OJ

N

ANALOG SOURCE LPC -10 BINARY CODER OR APC

2.4 kb/s

or

9.6 kb/s

TOM'"\ UNIPOLAR PULSED PULSED

\.../ RZ LED OPTICAL

TOM

DIGITAL· fT\ BINARY - \J../

Figure 74. Alternative V for CP/SC link structure.

g

ber
4-Wire Analog

§ 4-Wire Digital

Dual Fiber Optical

PO Cable: Uni- Polar Rz

Detector

AID

D/A

LUe ANALOG

• SWITCH

DIG

DIG

LPC @ 24 kb/s

or

APC @ 9.6 kb/s

LED =Light Emitting Diode

PO = Pin Diode or Photo Diode Detector

Figure 75. CP/SC Alternative V bus distribution system.
Table 26. Evaluation of Preferred Alternatives

ALT PROCESSING TRANSMISSION ADVANTAGE DISADVANTAGE RISKS COSTS

I Analog: PAM A&D Baseband Simplest to Requires A/D Detect- Low interface

Digital: TDM Over implement. conversion abil ity &media costs.

4-Wire Pairs Uses to switch 1imits range. Higher cost

existing digitally. Requires in far term

wire pairs May be field test and may not

or spiral capacity to be

four cable. limited. High demonstrate compatible.

EM signature technical'

not secure. feasibil ity.

Useful

range

limits

fl exi bil ity.

II Analog: NBFM A&D-A FDM/FM Compatible Not compa- Special Low for near

Digital: FSK over with analog tible with voice term.

coaxial switch digita1 channel Higher for

cable. currently switch filters far term.

used. unless A/D required. Could converted. Otherwise

include Requires similar

video modems for to CATV

transmission each channel. systems.

on high Not secure.

capacity Low EM

cable. signature

requires

double

shielding.

III Analog: PCM 1) Bipolar Flexibility Requires Low risk Medium cost

or CVSD coaxial in A/D wide similar to for near

Digital: TDM T-carrier. conversion. bandwidth T-Carrier term. Lower

2) PSK Transmission per channel except for cost in

carrier options &D/A for TDM unit far term.

on coaxial range from conversion &fiber optics cable proven to for analog option.

3) Unipolar development. switch.

on fiber Low EM

optical signature.

cable.

IV . Analog: PCM Quasi-analog Fl ex i bil ity D/A Basic Medium cost

or CVSD FDM/FM in A/D conversion elements for D/A

Digital: TOM over conversion. required for have been conversion

coaxial Digital analog. demonstrated. in near term.

cable. baseband can switching. CVSD used Lower in far

be switched in tactical term.

digitally systems, and e.g., nC/39

encrypted

Low EM

signature.

V Analog: LPC Digital Maximum Sophisticated Relatively High

or APC pulses over number of terminal new processing Digital: TOM fiber voice equipment. technology. &

optical channels/link. Not tested interface

cable. Easi ly in tactical costs.

encrypted. environment

Maximum

capacity/l ink. ~linimum

weight &size.

Lowest EM

signature.
channels transmitted at baseband. The maximum useful range requires field testing.

End-to-end digital encryption is not practical and the EM signature is greater

than the other alternatives.

Alternative II" although compatible (after demodulation) with analog switches

currently in use, does not lend itself to future digital switching. Digital encryption is not feasible. The advantage is the high capacity available using the

proven technology of a CATV type system. Some risk is involved in developing

voice channel filters for the system. In the future the systems can easily be

adapted to include video circuits including television and other wideband services.

The EM signature is relatively low when double shielded coaxial cables are used.

The canonical Alternative III is compatible with digital switching but requires demultiplexing and conversion to the analog baseband voice channel for

switching with existing analog methods. The basic T-carrier concept for transmission is a proven technology which can probably be adapted for tactical use at

reasonable cost. Single coaxial cable technology is proven as well as PSK carrier

transmission. The fiber optic transmission allows incorporation of the smallest,

most advanced cable technology. A 300 mcable weights about 5 kilos. Current

fiber optical cables can provide metallic strength strands which can serve also as

power conductors. Alternative III offers considerable flexibility in choice of

the analog/digital conversion and binary encoding, and in choice of transmission

media. Digital TOM transmission is transparent to encrypted voice and could

itself be link encrypted in the future if desired. Finally, Alternative III is

compatible with future transitions to all digital operations, either with CVSD

(16 or 32 kb/s), or PCM (48 kb/s and 64 kb/s).

Alternative IV offers most of the same flexibility and advantages as found in

Alternative III with the exception of the transmission media. The FDM/FM quasianalog signal is suitable for transmission over coaxial cables.

Alternative V uses a relatively new technology and requires more sophisticated

equipment than the others. However, this system has the maximum voice-channel

capacity per link. The weight and volume reduction of the physical link is also

as great as Alternative III with the fiber optical cable. The EM signature is

negligible. The transmission properties of fiber optics eliminate many problems

inherent in wire or rf transmission such as electrical isolation, 'immunity to

lightning, EMP, EMI, and crosstalk, as well as weight, volume, and power savings.

Some field tests of fiber optics for tactical communications have been conducted by the Air Force. See Kleenkamp and Metcalf (1979). The results demonstrated the technical feasibility for handling voice (CVSD) and data traffic in

185
place of a 26-pair cable approximately 250 m long. Before operational fiber optic

systems can be implemented some refinements to components may be required to ensure

that they are suitable for use in the tactical environment. However, no new

technology breakthroughs appear to be needed. The bandwidth capacity of fiber

optics has not been fully exploited for high-traffic-density links. Combining 120

voice channels using 32 kb/s CVSD requires a data rate of about 3.8 Mb/s. This

same rate could accommodate over 1500 channels using 2.4 kb/s LPC. Rates as high

as 100 Mb/s have been achieved on fiber optical cables over short distances without

repeaters. We have assumed 2.4 kb/s LPC or 9.6 kb/s APC for comparison purposes.

The wide bandwidth of fiber optical cable, however, could easily accommodate 64

kb/s PCM in most applications and this could reduce the processing and interface

costs.

Another alternative which was not included may be of interest in applications

where the traffic to and from a node or a cluster of terminals is a mixture of

analog voice traffic and quasi-analog data traffic. These traffic types are

currently both being transmitted over wire pair circuits. Both require a nominal

bandwidth 4 kHz.

It might appear that a single codec design would be suitable for digitizing

both types of voiceband signals. Their digital representations could then be

multiplexed using time division techniques and transmitted on a digital bus. The

problem with this approach is the codec design. Quasi-analog signaling waveforms

and their spectra are statistically very different from speech waveforms even

though both occupy essentially the same bandwidths. Codecs designed for digitizing

speech signal s in an optimum manner are usually very inefficient when used to

digitize quasi-analog signals generated by a data modem. It may be possible, however l

to develop circuitry which detects the type of input signal to the codec and

switch it to an appropriate strategy. Rather then take this approach we have

assumed instead that the modems themselves should be eliminated as in Alternative

III.

11.8. Selection of Preferred Alternative

The five candidate alternatives have been evaluated in terms of the ten selection criteria introduced at the beginning of Section 11. They are: Deployment

Time, Flexibility, Capacity, Range, Power Distribution, Security, Performance,

Development Risk, Relative Cost, and Modularity. Each alternative was rated for

all criteria on a numbered basis as follows:

186
o - not practical

1 - poor

2 - fair

3 - good

4 - excellent.

The results are shown in Table 27. For Alternatives III and IV, only CVSD at 16

kb/s and PCM at 64 kb/s are shown. The differences between the other rates are

considered second order in this qualitative evaluation.

There are, of course, more sophisticated methods for choosing a preferred

alternative and many complex factors which should ultimately be considered. For

example, relative weights could be assigned to each measure of effectiveness.

Weighting procedures have been developed by panels of combat officers 'with battalion

or higher command experience by the U. S. Army Training and Doctrine Command (TRADOC).

Such weighting procedures have not been used here because of the preliminary nature

of this work and the limited time available.

While these ratings are admittedly subjective judgements by the authors they

do demons~rate a useful method for guiding the selection of the preferred alternative. Some explanations are in order for certain numerical ratings. For example,

performance is viewed from a user's standpoint. Higher voice digitization rates

normally provide a higher voice quality and are more robust (i.e., less susceptible

to errors). The nondigitized forms are rated the highest. The LPC source coding

(Alternative V) is rated low because it is more susceptible to transmission errors.

The bus capacity may impact on the deployment time since capacity depends on

the transmission media and the media affect deployment. The'number of full-duplex

4-kHz voice channels versus the transmission rate or bandwidth of the media and

parametric in voice digitization process or bandwidth requirements is shown in

Figure 76. The number of 26-pair cables which could be replaced as a function of

bus rate or bandwidth is also indicated on this figure. This number assumes each

26-pair cable normally carries 12 full-duplex voice channels. Table 28 summarizes

the number of buses required for various alternatives assuming full-duplex operation and 120 voice channels per bus link.

The deployment time is difficult to assess quantitatively. Coaxial cables

are rated fair to good depending on whether one or two are required. The fiber

optical cable is rated highest because it has the lowest weight and volume.

The flexibility ratings depend on how many changes are required to the link

structure as the nodes and terminals evolve from analog to digital. It is ass~med

187
--'

(X)

(X)

Table 27. Ranking of Five Bus Distribution System Alternatives

Alternatives I II III IV V

Selection 16 kbls CVSD 64 kb/s PCM 16 kb/s 64 kb/s LPC

Criteria PAM NBFM CVSD PCM or

T-Carrier Coaxial Fiber T-Carrier Coaxi al Fiber APC

1. Deployment Time 1 3 2 3 4 2 3 4 2 2 4

2. Fl exi bi 1ity 1 2 3 3 3 3 3 3 2 2 1

3. Capacity 1 4 3 3 3 3 3 3 4 4 3

4. Range 1 3 1 3 3 1 3 3 3 3 3

5. Power Distribution 4 4 4 4 3 4 4 3 4 4 3

6. Security 1 1 2 3 3 2 3 3 3 3 3

7. Performance 2 3 3 3 3 4 4 4 3 3 2

8. Development Risk 3 I 2 3 3 2 3 3 2 3 3 1

I 9. Relative Cost 3 I 2 3 2 2 3 2 2 2 2 a I

I

10. Modularity 1 I 1 4 4 4 4 4 4 2 2 1 I

Unweighted Total

Weighted Total

18

20

25

30

28

33

31

37

30

37

29

34

32

38

31

38

28

32

29

33

21

26
120

---

Channels

c~NBFM 12.lI.b/s

------ Ape 9.6 kb/S

Number of

36 48 60

Number of Full-Duplex

12 24

....

&

I

<D

C\l

Q)

2i

o

u

Replaced

8 I .. OJ • V v 7 8 9 10

I I I I I I I I I I I

....

o

.0 4

DO'

.!:

Q)

-ti. 3

7

N

..c:

c

6

:2-

3

"0

C

as 5

c

o

"in

l/l ·E 2 l/l

C

o

Figure 76. Estimates of bus channel capacity for various bus distribution

systems.
Tabl e 28. Channel Capacity of CP/SC Alternative Bus Distribution Systems

Bandwidth BW or Rate No. Required No. Required

Candidate Transmission for 120 FOX

Alternative or Rate for 120 HOX Media for Channels Per Channel Channels FOX Operation at 2 km Range

I (PAM) 8 kHz 970 kHz Twisted Wire 2 4

(TOM) Pairs

II (NBFM) 12 kHz 1.44 MHz Coaxial 1 1

(FOM) Cable

III (CVSO) 16 kb/s 1.9 Mb/s Coaxial 2 2

(TOM) Fiber Optical

III (CVSO) 32 kb/s 3.8 Mb/s Coaxial 2 2

(TOM) Fiber Optical 2 2

III (PCM) 48 kb/s 5.8 Mb/s Coaxi a1 2 2

(TOM) Fiber Optical 2 2 ......

1.0

0 I II I (PCM) 64 kb/s 7.7 Mb/s Coax i al 2 2

(TOM) Fiber Optical 2 2

IV (CVSO) 16 kb/s 1.9 ~lb/s Coaxial 1 1

(FOM) Cable

IV (CVSO) 32 kb/s 3.8 ~1b/s Coaxi al 1 1

(FOM) Cable

IV (PCM) 32 kb/s 5.8 Mb/s Coaxial 1 1

(FOM) Cable

IV (PCM) 64 kb/s 7.7 Mb/s Coaxial 1 1

(FOM) Cable

V (LPC) 2.4 kb/s 0.3 Mb/s Fiber Optical 2 2

(TOM) Cable

V (APC) 9.6 kb/s 1.1 Mb/s Fiber Optical 2 2

(TOM) Cable
that security by encryption requires digitization at the terminals. Development

risk and cost ratings are based on the complexity and net component developments

required. Note that a high number rating implies the lowest cost.

The two summations at the end of each column in Table 27 are unweighted and

weighted summations. For the weighted sum the deployment and flexibility criteria ratings have been increased by a factor of two because these are considered

to be the most important. The preferred alternative is Alternative III in this

subjective evaluation.

Figure 77 illustrates how Alternative III would be used as the CP/SC transition to digital switching nodes and ultimately to a structured network configuration. In 77a, the transitional improvement phase, the bus terminations at the

switch no longer require A/D and D/A conversions since the switching is accomplished on the digital format. The A/D and D/A conversion may still be required at the

remote multiplexer since many analog terminals are still in use. In the final

improvement phase at least some of these terminals would be digitized as shown in

Fi gure 77b.

An.example of the local and remoted components for a digital circuit switch

is shown in more detail in Figure 78. Here the terminals may be either analog or

digital, secure or nonsecure. Multiplexing is accomplished by assigning time

slots on a multiplexed loop. Switching is accomplished within a loop using time

slot interchange (TSI) units. Switching is accomplished between multiplexed loops

by time gating the space divided highways. This is denoted as the space switch in

Figure 78. Trunk circuits to other geographically dispersed nodes are also

di gita1.

The selection of the analog-to-digital encoding method (CVSD or PCM) and the

digitization rate to be used along with the transmission media for Alternative III

should be done during the next concept development stage. This is discussed in

greater detail in the next section.

12. FUNCTIONAL DESIGN REQUIREMENTS

The DoD procurement and development programs are normally phased through the

major activities of Concept Development, Validation, System Development, System

Implementation and System Operation. Each phase needs to be successfully completed

before proceeding to the next phase. In order to discuss functional design requirements for the preferred bus distribution system Alternative (III), the development

phase applicable must be known. While this study has clearly been part of a

concept development activity, it by no means completes concept development.

191
4-Wire Analog

4-Wire Digital

AID

&

DIA

DIG.

a) Transitional Improvement Phase

DIGITAL

SWITCH

4-Wire Digita I

b) Final Improvement Phase

DIG.

SW.

DIG.

SW.

Figure 77. Application of Alternative III to subsequent bus

distribution system improvement phases.

192
I----Remote Components --I. Switching Hub .1

Space

Switch

AVT

COMSEC

CODEC

jt'TMG

r---, r---' ~--- ......I""""f I I ~...:.I__----l

T-Trunk I: I l ---~

I I I I L __ J L __ ...J

TRU TIU

DT

r:------,

DVT :~cODEcl I L J

--'

\D

W

Legend

DSVT: Digital Secure Voice Termina I

AVT: AnalogVoice Terminal

DT:' Digital Terminal

DVT: Digital Voice Termina I

LCU: Local Concentration Unit

RCU:

TRU:

TIU:

151:

TMG:

Remote Concentration Unit

Trunk Repeater Unit

Trunk Interface ·Unit

Time Slot Interchange

lime Multiplexed Gate

Figure 78. Local and remote components of a switching hub.
In order to complete concept development for a bus distribution system, the

following R&D activities are recommended:

A. Development of "Proof of Principle" hardware for capacity, cost, risk

and field adaptability initial evaluation;

B. Final concept development study and evaluation based on quantitative

capacity, cost, and deployment time potential for analog switches and

other switches in command post table of equipment.

C. Development of a validation phase plan to produce a limited quantity

of bus distribution systems of the final version for field tests and

evaluation.

Successful completion of A through C above would finish the concept development phase and justify start of the validation phase.

Within this context, then, functional design requirements can be established

for "Proof of Principle" hardware units. Alternative III is modular, so that the

four analog-to-digital units, one TDM unit and one of each of three transmission

media can be developed. This would be sufficient and would eliminate development

of 12 separate bus systems.

This section first discusses the long-range objectives of our concept development plan. These objectives form the basis for determining the ultimate benefits.

expected when the preferred bus structure is fully implemented. Then the functional design requirements for the preferred bus distribution system (Alternative

III) are described. These descriptive parameters and the quantitative values

assigned to them are needed in order to develop proof of principal hardware for

evaluating the technical feasibility of Alternative III.

12.1. Objectives

The long-range objectives for improving CP/SC future system operations and

configurations which are specified here apply to the CP/SC at the corps level or

above. Here the overall installation capability is equivalent essentially to

replacing the dial central office and local loop plant in a small city. The

ultimate objectives are:

1. Increased speed in laying out cabling plant and making connections.

2. Increased flexibility in layout and service as technology undergoes revolutionary changes.

3; Sufficient redundancy and restoration capabilities to maintain critical communications in case of broken connection or equipment failure.

4. Minimum EM and IR signature so the CP/SC cannot be detected from

aircraft or satellite.

194
5. Enhanced security using voice digitization and end-to-end encryption. Ultimately the encryption/decryption processes would be incorporated

into each terminal.

6. Improved quality of service in terms of speaker intelligibility, speaker recognition, information bit-error rates and network outages.

With these goals in mind, the functional design requirements for proof of principle

hardware are given. These are based on Alternative III concepts developed previously.

12.2. Functional Design of Preferred Alternative

The functional design requirements outlined here include a number of optional

approaches for certain functions. These functions are: the analog channel digitization, the transmission modulation, and the physical transfer.

Following a general description, the system functional requirements are divided

into four main categories - namely the distribution system, the interfaces, the

synchronization and signaling and the end-to-end performance.

12.2.1. General requirements

An engineering test model of a transparent bus-type distribution system is

required for field test and evaluation of different development concepts. The

test results will be used to determine the optimum digitization technique, the

optimum transmission modulation, and the optimum transmission media to be used in

the final system implementation.

The test model functions defined here assume that the system will be used to

replace eight of the 26-pair cables currently used, i.e.,. 96 voice channels. The

test model, however, will be capable of handling only twelve (12) full-duplex

channels (either analog voice circuits or data modem circuits) plus any additional

control signaling information required. The system design must be expandable to

handle the 96 full-duplex channels in a fully implemented system.

The maximum transmission rate will be determined by the maximum digitization

rate employed on a per-channel basis for all 96 channels. The maximum range for

the physical transmission link is 2 km and no repeaters are to be used on this

link.

Specific functional design requirements for major system elements of the bus

structure are outlined in the following section.

195
12.2.2. Bus distribution system requirements

We define the functions to be performed as we progress through the bus dis- .

tribution structure from input to output. The system designer must recognize that

the inverse functions and operations are required for all channels to provide full

duplex transparent operations.

Analog-to-digital conversion requirements

The A/D conversion functions will be performed using four optional methods so

that a simultaneous quality performance comparison can be made. The options are

PCM at 48 kb/s and 64 kb/s and CVSD at 16 kb/s and 32 kb/s. The output of each

A/D converter will be in serial form.

Time division multiplexing requirements

The serial outputs of all of the A/D converters will be multiplexed into ,

allocated time slots for subsequent transmission over a single link. This may be

accomplished on a bit-by-bit basis or in some convenient block form. The maximum

transmission rate, excluding signaling and control bits, will be 8 times the rate

required for 12 channels digitized at the maximum per-channel rate. (i.e.,

8 x 64 x 12 =6.144 Mb/s). This will permit system tests at rates corresponding

to the ultimate 96-channel system rate.

Media matching requ"irements

Three options for the media matching functions which include waveforming and

transmission modulation are required so that three transmission media can be

evaluated. Suggested requirements are 1) bipolar NRZ waveforms and PSK carrier

modulation for transmission on coaxial cable, 2) bipolar RZ waveforms for digital

transmission on T-carrier type cable, and 3) unipolar RZ for digital pulse transmission on fiber optical cable. Alternative forms ar,e acceptable if other requirements are met.

Physical transfer requirements

The physical media will be a continuous link 2 km in length and spooled on a

cable reel for ease in deployment. Three physical media will be furnished for

alternate testing. The physical media are: coaxial cable, T-carrier type cable,

and fiber optical cable. Each cable type should be capable of withstanding the

tactical environment and normal deployment procedures including underground, on

the surface, or overhead installation. Suitable connectors for each type of cable

must be furnished so connections can be quickly accomplished at each end of the

196
link. Suitable coupling circuitry for each type of cable will be provided and

will be switch selectable for each cable type deployed.

Dual cables may be used for full duplex operations. A separate metallic wire

may be included so that either termination unit can be powered from the other when

necessary.

12.2.3. Synchronization, signaling and power requirements

Synchronization for multiplexing and demultiplexing in the time domain will

be accomplished completely independent of all external terminals and nodes. Input

signals from the AID conversion processes may be asynchronous and bit stuffing may

be necessary to achieve a synchronous link.

Control signaling waveforms, including terminal control, node control, link

control, and network management signals will be AID converted from the 4-kHz channel

and shall be transferred using inband time slots. Ring signals will be detected

by logic circuitry so that relays or gates can be operated to furnish ringing

power on the line side to terminals. See interface requirements Section 12.2.4.

Special control bits will be included to operate loop-around relays and logic

circuitry for conducting continuity and diagnostic tests on the link. Test circuitry

will be included in both link terminations and operable remotely from either end.

These special control signals can be transferred via an orderwire channel, i.e.,

using time slots especially allocated for these functions.

The power required to operate the functional elements of the bus distribution

system wi 11 be furni shed from the adjacent equ i pment node. When one 1ink termi nation is used to multiplex a number of terminals the power to this terminal element

will be obtained from the terminating unit on the opposite end of the link.

12.2.4. Interface requirements

The bus termination units will be furnished with connection panels containing

all of the 4-wire circuit terminations needed to replace one 26-pair cable. The

bus distribution system shall be easily connected to 1) 26-pair hocks on either

termination end for connecting two nodes, or 2) one 26-pair hock at one termination

and up to twelve (12) full duplex terminals at the other end.

The input and output terminations will be fully transparent to the user, i.e.,

4-kHz analog signals at any input port will appear as 4-kHz analog signals at the

corresponding output port.

The interface terminations will provide all the functions of 'BORSCHT' except

the 2-wire to 4-wire hybrid. The required functions are:

197
B Battery feed

o Overload protection

R Ringing

S Supervision and signaling

C Clocking and channel filtering

H Not applicable

T Test

These 'BORSCHT' functions are described further in the following paragraphs.

The battery feed supplies the dc current for dialing and for the microphone

on the line side. This battery voltage is typically -48 volts. A carbon microphone requires 20 rnA to 80 rnA of line current. The dc circuit impedance is nominally 400 ohms. The ac terminating impedance must match the 4-wire telephone

cable of either 600 or 900 ohms.

Overload protection is required on all incoming lines and for the bus itself

in order to protect the circuitry from high-voltage transients which may be induced.

Protection against voltage levels of 1000 volts and current surges of 1 ampere

lasting 1 millisecond is required.

Ringing power for conventional telephone instruments is a nominal 20 Hz tone

at 86 volts rms. This will be furnished from the local termination but controlled

remotely from the opposite termination using suitable signaling detection circuitry

and relays.

Supervision and signaling from a terminal is normally 15 rnA for dc hook status

control and rotary dialing of dc pulses. These inband signals will be converted

toa suitable logic level, AID converted for transmission, and reconstituted at the

other end so the link appears transparent to the user.

The clocking and channel filtering will be self-contained within the distribution system, i.e., no external synchronizing clock signals or filter banks

should be required.

The test circuitry provides a means to switch the line to a test facility for

diagnostic test purposes. Test signals may be injected at either end to insure

proper operation of the distribution system. On the 4-wire circuit a typical

2010-Hz test signal may be injected and looped back by remote control to indicate

a continuity check. This loop-back circuit should include the AID conversion processes.

198
·12.2.5. Performance requirements

The analog outputs will be evaluated by subjective means during the field

testing of this demonstration model. Voice intelligibility, and voice recognition are the crucial criteria. Here only the service performance specifications

for the digital portion of the link are given based on Interim Federal Standard

FS-1033. This data communication standard provides a uniform means of specifying

digital communication systems from the point of view of the service delivered to

the end user. In order to apply the standard here we assume an aggregate user

on the digital side of the interface. The parameter values selected are expected

to meet the requirements of an end user on the analog side of the interface.

This expectation must be verified by subjective tests using the link.

The FS-1033 performance parameters are listed in Table 29. Quantitative

values are given for those parameters which apply to the bus structure selected.

The justification for choosing specific values is given below.

Performance parameters 1 through 3 are zero since all link channels are

continuously available on a dedicated basis and access is always insured. For the

same reason items 23 through 26 are not applicable.

The bit-transfer time is essentially real time with an allowance made for bit

stuffing for synchronization. The length of the link is 2 km, and the cabling and

loading are considered to result in a propagation velocity of approximately 30

microseconds per kilometer. Additional buffer time yields the result 2 x 30 + 40 =

100 microseconds or 10-4 seconds for parameter 4.

The bit-error probability of 10-5 to 10-6 for parameter 5 is expected to

yield acceptable voice quality regardless of the digitization process. At the

same time this error rate should reproduce data modem outputs so that the 10wspeed bit-error rate of the modem itself is not degraded by the link (see parameter

10 below).

A value of 10-8 to 10-9 for bit misdelivery, bit loss, and extra bit probability

(parameters 6, 7, and 8) was selected to be an extremely low but measureab1e quantity.

This is because these parameters have an important impact when encryption is used

for security. Lost bits or extra bits could result in loss of synchronization

unless bit integrity is maintained on the link.

With the exception of the error probabilities and transfer rates, the bitoriented and block-oriented transfer parameters values are assumed to be identical.

Therefore parameter 9 is also 100 microseconds. This is true only if the information block or encoded sample crosses the digital interface in parallel and each

block represents a fixed number of bits. For our purposes here we assume that a

199
Table 29. Service Performance Specification

Part A - Primary Parameters

1. Access Time

2. Incorrect Access Probability

3. Access Denial Probability

4. Bit Transfer Time

5. Bit Error Probability

6. Bit Mi sdelivery Probabil ity

7. Bit Loss Probability

8. Extra Bit Probability

9. Block Transfer Time

10. Block Error Probability

11. Block Mi sde1i very Probabil i ty

12. Block Loss Probability

13. Extra Block Probability

14. Bit Transfer Rate

15. Block Transfer Rate

16. Bit Rate Efficiency

17; Block Rate Efficiency

18. Disengagement Time

19. Disengagement Denial Probability

o Seconds

o *

o *

10-4 Seconds

10-5 to 10-6 *

10-8 to 10-9 *

10-8 to 10-9 *

10-8 to 10-9 *

10-4 Seconds

10-5 *

10-8 *

10-8 *

10-8 *

64,000 Bits/Second

8,000 Blocks/Second

80 %

80 %

o Seconds

o *

Part B - Secondary Parameters

20. Service Time Between Outages

21. Outage Duration

22. ·Outage Probabi 1i ty

Part C - Ancillary Parameters

23. User Access Time Fraction

24. User Block Transfer Time Fraction

25. User Message Transfer Time Fraction

26. User Disengagement Time Fraction

62.5 Hours

1.0 Hours

8 x 10-4 *

N/A *

N/A *

N/A *

N/A *

*Note: The probabilities and user performance time fractions are dimensionless

numbers between zero and one.

200
block contains 8 bits (the peM case) plus 1 bit for synchronization and 1 bit for

signaling or a total of 10 bits. The block error probability of 10-5 is given for

parameter 10. Note that this yields the range of 10-5 to 10-6 for bit-error

probability (parameter 5) since one error in a single bit or in all the bits in a

block produces a single error. A similar relationship holds for parameters 11,

12, and 13.

The bit transfer rate per channel should be 64 kb/s (parameter 14) and the

block transfer rate (parameter 15) is 8000 blocks/second for each 4-kHz channel.

The bit rate efficiency and block rate efficiency (parameters 16 and 17) is

80% for the assumed 20% overhead bits. Disengagement time, parameter 18, and

denial probability, parameter 19, are zero since no switching is involved.

The secondary outage parameters, 20, 21, and 22 are based on one outage per

month where quality of service is degraded below acceptable levels because of

equipment malfunctions and two outages per year where a total failure occurs because

of equipment failures such as power supply failure, broken cab~e, etc. It is

assumed that degraded performance conditions last for 1/2 hour and the total

failures last for 4 hours. The user information time (UIT) per channel averages

two 3-minute calls per hour. Therefore there are 2 x .05 UIT hours/hour x 24

hours/day x 365 days/year = 876 UIT hours/year on each channel. The value for

parameter 20, the service time between outages or mean time between failure

(MTBF), is therefore 876 7 14 62.5 hours.

The outage duration, parameter 21, or mean time to repair (MTTR) is given by

(12 outages) (0.5 hours) + (2 outages) (4 hours) = 1 hour.

14 outages .

The outage probability, parameter 22, is determined as follows:

14 outages/year 7 (48 calls/day x 365 days/year) =8 x 10-4

The resulting availability A is given by

MTBF 62.5

A = MTBF + MTTR = 63.5 = 0.984

201
13. REFERENCES

Abraham, L. G. (1960), The complexity of the transmission network, Bell Laboratories

Record, Feb, pp. 43-48.

Army Signal Center (1978), Combat Communications within the Corps, Field Manual

FM 11-92, ATZHTD-P-L, Ft. Gordon, GA.

Hoth, D. F. (1975), Broad-band media for urban communications, IEEE Trans. on

Communications COM-23,No. 1, pp. 121-131.

Kleekamp, C. W., and B. D. Metcalf (1979), Fiber optics for tactical communications,

Mitre Rept. MTR-3723, prepared for UAF-ESD-TR-79-121, Hanscom AFB, MA.

202
14. BIBLIOGRAPHY

14.1. Military Environment

Army Command and General Staff College (1976), Control and Coordination of Division

Operations, Training Circular TC 101-5, ATSW-CD, Ft. Leavenworth, KS.

Army Signal School (1977), Combat Communications within the Division, Field Manual

FM-50, ATSN-TD-LIT, Ft. Gordon, GA.

Army Signal Center (1978), Combat Communications within the Corps, Field Manual

FM 11-92, ATIHTD-P-L, Ft. Gordon, GA.

Army Signal School (1978), Theater Communication Command (Army), Field Manual

FM 11-23, ATSN-TD-1.11, Ft. Gordon, GA.

Foyle, R. A. (1979), Here comes another came1~, Signal, Vol. 33, pp. 77-80, May/ June. --

Gravely, S. L. (1979), DCS at the crossroads, Signal, Vol. 33, pp. 53-58, May/ June. --

Hoover, J. E. (1977), TRI-TAC tactical communications for the 1980's, Signal,

pp. 92-99, August.

Howe, R. G. (1979), The integrated AUTODIN system, Signal, Vol. 33, pp. 105-110, May/~June.

Linfield, R. F. (1979), Control signaling in a military switching environment,

NTIA Report 79-13, for Army Comm. System Agency, Ft. Monmouth, NJ.

Martin Marietta (1977), Tactical communications control facilities applications guide, OT 7550 (fourth draft), for Air Force Systems Command Electronics

Systems Div., November.

Systems Engineering Office (1978), Communications zone (COMMI) transition plan, Part II and its Appendix, USACEEIA, Ft. Huachuca, AI.

14.2. Tactical Systems

. Army Tactical Communications Systems (1974), Description of Army tactical communications assemblages and equipment, ATACS, Ft. Monmouth, NJ.

Aro, E., T. K. Cheney, J. R. McMullen, and C. B. Nennerfe1t (1970), NX-1E, an

electronically controlled crossbar switching system (TTC-30), 70-CP-322-COM,

Proc, ICC-70, pp. 27-10 - 27-18.

Bird, P. J. (1973), Modular switching approach for local and remote subscribers,

IEEE, NTC-73, Vol. 2, pp. 33B-1 - 33B-4.

Blackman, J. A. (1976), Integrated switching of voice and non-voice traffic,

Proc. ICC-76, Vol. 2, Philadelphia, PA, pp. 24-1 - 24-6.

203
Dempsey, P. J., J. Roder, and A. F. Rosene (1973), A program structure for a

transportable military communication switching system, Proc. NTC-73, Vol. 2,

pp. 40B-l - 40B-7.

Dempsey, P. J., J. Roder, and A. F. Rosene (1973), Call processing in a stored

program controlled transportable military communication system (TCC-38),

Proc. NTC-71, Vol~ 2, pp. 40C-l - 40C-8.

Ellingson, C. Eo (1975), Joint Tactical Information Distribution System (JTDIS),

Proc, NTC-75, Vol. 1, pp. 14-10 - 14-14.

, I

Feltman, G. (1975), Tactical communications control facilities, P~~~. NTC-75,

Vol. 2, pp. 40-11 - 40-15.

Horner,D.W~ {1977), Command and control systems applications using DAMA technique: AFC &EA 2nd Annual Seminar, pp. 123-132, Ft. Monmouth, NJ.

McQuillan, J. M. (1978), Message addressing modes for computer networks, Proc.

Computer Comm. 78, Washington, DC, pp. 80-88.

Nejat, A. (1978), Technical aspects 'Of standardization and interoperability of

communications systems in NATO, AFC &EA 3rd Annual Seminar, Ft. Monmouth,

NJ, pp. 19-13.

Nesenbergs, M., and R. F. Linfield (1976), Parametric cost alternatives for local

digital distribution system, OT Report 76-95.

Noden, D. A. (1976), Tactical communications control facilities (CNCE-CDSE), Proc.

ICC-76, Vol. 2, pp. ~4-17 - 34-22.

Nutt, W. G., andJ.P. Savage (1978), Multipair cables for digital transmission,

Proc. of NTC-78,pp. 21.1.1. - 21.1.5.

Pagano, C. N., and A. DiGreorgo (1975), Dynamic test and measurement of tactical

communication systems, Proc. NTC-75, Vol. 2, New Orleans, LA, pp. 40-8 - 40-10.

Pollen, L. K., and E. L. Roswell (1973), A tactical military electronic central

office system organization, Proc. NTC-73, Vol. 2, pp. 40A-l - 40A-ll.

System Development Corp. (1978), Local digital distribution system (LDDS) cable

plant evaluation report, COM-RD-78-1, prepared for U. S. Army Commun. Systems Agency, Ft. Monmouth, NJ.

Thompson, R. E. G., and G. O. Dykes (1977), SB-3614automated telephone switchboard, , TCATA Test Report OT 168, TRADOC, Ft. Hood, TX.

Towle, W. C. (1976), Tactical digital interfaces (TTC-39), AFC & EA 1st Annual

Seminar, Ft. Monmouth, NJ, pp. 51-57.

Watts, J. A. (1970), NX~lE routing control complex, 70-CP-321-COM, Proc. ICC-70,

pp. 27~1 - 27-9.

204·
14.3. Bus Architectures

Abraham, L. G. (1960), The complexity of the transmission network, Bell Laboratories

Record, Feb, pp. 43-48.

Abramson, N., and F. F. Kuo (1973), Computer-Communication Networks, (PrenticeHall, Inc.).

Binder, R., N. Abramson, F. Kuo, A. Okinaka, and D. Wax (1975), ALOHA packet broadcasting - a retrospect, Proc. AFIPS Conference, Vol. 44, Montvale,

·NJ,pp. 203-215.

Blair, J. C. (1977), Preliminary evaluation of hub alternatives for access area

digital switching, prepared for CSA, Ft. Monmouth, NJ.

Bloom, L. R., A. G. Hanson, and L. G. Hause (1977), Digital transmission via

coaxial, twinaxial, and fiber optic cables, Tech. Rept.CCC-CES-XET, prepared for USACEEIA, Ft. Huachuca, AZ.

Boose, E. F. (1975), Lessons learned through a MIL-STD-1553 time division multiplex bus, NAECON Record, pp.634-641.

Boose, E. F., R. A. Costa, and B. B. Mahler (1975), Shielded twisted pair as a

transmission medium in a mu1tisubscriber time division multiplex system, NAECON Record, pp. 648-655.

Coviello, G. J., and P. A. Vena (1975), Integration of circuit/packet switching by a

SENET (~LOTTED tNVELOPE NETWORK) concept, Proc. NTC-75, Vol. 2, pp. 42-12 - 42-17.

DeMarines, V. A., and L. W. Hill (1976), The cable bus in data communications,

Datamation ?~, pp. 89-92, August.

des Jardins, R., and G. White (1978), ANSI reference model for distributed systems, Computer Communication Network Symp., Washington, DC. pp. 144-149.

0011, D. R. (1978), Data Communications: Facilities, Networks, and Systems Design (Wiley, New York, NY).

Dworkin, L., L. Coryall, and R. Dragoo (1976), The application of optical wave

guides to army communications, AFC &EA 1st Annual Seminar, pp. 10-17, Ft. r~onmouth, NJ.

Electronics Review (1978), Bell Labs develops telephone powered by lightwaves

alone, E1 ectroni cs El, pp. 39-40, November.

Everett, R. R. (1975), The information bus, Signal 29, October.

Fischer, M. J., and T. C. Harris (1975), An analysis of an integrated circuitand packet-switched telecommunications system, Proc. NTC-75, Vol. 2,

pp. 42-18 - 42-23.

Fraser, A. G. (1975), Avirtual channel network (SPIDER), Datamation ~, pp. 51-56,

February.

Gitman, I., H. Frank. B. Occhiogrosso, W. Hsieh (1977), Issues in integrated network

design, Proc. ICC-77, Vol. 3, pp. 38.1-36 - 38.1-43.

205
Gosch, J. (1979), Light-powered phone operates without an internal light source,

Electronics 52, pp. 39-40, May.

Harrington, E. A. (1977), Architectural impact of fiber optics on future military

switching systems, AFC &EA 2nd Annual Seminar, Ft. Monmouth, NJ, pp. 135-142.

Harrington, E. A. (1978), Fiber and integrated optics: a new light on switching,

Proc. NTC-78, pp. 47.4.1. - 47.4.5.

Harris, C. R. (1978), An evolution to digital local networks, International Zurich

Seminar on Digital Communication, pp. F2.1.-F2.6.

Hoth, D. F. (1975), Broad-band media for urban communications, IEEE Trans. on

Communications COM-23, No.1, pp. 121-131.

Hubbard, R. W., and R. L. Gallawa (1978), Design handbook for optical fiber

systems, CCC-CED-XED-78-01, prepared for USACEEIA, Ft. Huachuca, AZ.

Jones, J. R., and D. F. Hemmings (1978), Optical fiber T-carriertransmission

systems, Proc. NTC-78, Vol. 1, pp. 5.1.1.-5.1.6.

Kleekamp, C. W., and B. D. Metcalf (1979), Fiber optics for tactical communications,

Mitre Rept. MTR-3723, prepared for UAF-ESD-TR-79-121, Hanscom AFB, MA.

Lawrence, G. N., and A. E. Shuttleworth (1978), Digital service to the subscri~er,

Proc. of ISSLS-78,Atlanta, GA, pp. 190-194.

Linfield, R. F., and M. Nesenbergs (1978), Access area switching and signaling:

concepts, issues and alternatives, NTIA Rept. No. 78-2.

Luczak, E. C. (1978), Global bus computer communication technology, Proc. Computer

Networking Symp.-78, Gaithersburg, MD, pp. 58-71.

McCaskill, R. C. (1979), Fiber optics: the connection of the future, Data Communications, pp. 67-73, January. .

Meisner, N. B., J. L. Segal, and M. Y. Tanigawa (1977), Dual mode slotted TDMA

digital bus, 5th Data Communications Symp., Snowbird, UT, pp. 5-14 - 5-18.

Metcalf, R. M., and D. R. Boggs (1976), Ethernet: distributed packet switching for local computer networks, Commun. of the ACM~, No.7, pp. 395-403.

Nesenbergs, M., and R. F. Linfield (1976), Parametric cost alternatives for local

digital distribution systems, OT Rept. No. 76-95.

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Proc. ICC-78, Vol. 2, pp. 20.5.1.-20~5.4.

Schutz, G. C., and G. E. Clark (1974), Data communication standards, Computer, I, pp. 32-37, February.

Silcock, H. W. (1978), Digital transmission over existing subscriber cable, ISSLS,

Atlanta, GA, March, pp. 9-13. .

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on subscriber lines, International Zurich Seminar on Digital Communications,

pp. C5. 1. -C5. 4.

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Proc. of NTC-73, Vol. 2, pp. 38E~T - 38E-5.

14.4. Network Design and Survivability

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networks, IEEE Trans. Commun. Technology, COM-18, pp. 484-489.

Baran, P. (1964), On distributed communications networks, IEEE Trans. Commun.

Systems, ~S-12, pp. 1-9.

Bittel, R. H. (1978), Analysis of performance, cost and survivability for terrestrial

circuit switched voice telecommunications systems, Proc. of Computer Networking Symposium, NBS, Gaithersburg, MD, pp. 43-52.

Elias, P., A. Feinstein, and C. E. Shannon (1956), A note on the maximum flow

through a network, IRE Trans. Information Theory, IT-2, pp. 117-119.

Ford, L. R., and D. R. Fulkerson (1962), Flows in Networks (Princeton Univ. Press,

Pri nceton, NJ).

Frank, H. (1967), Vulnerability of communication networks, IEEE Trans. Commun.

Technology, COM-15, pp. 778-789.

Frank, H., and I. T. Frisch (1970), Analysis and design of survivable networks,

IEEE Trans. Commun. Technology, COM-18, pp. 501-519.

Frank, and I. T. Frisch (1971), Communication, Transmission, and Transportation

Networks (Addison-Wesley Publ. Co., Reading, MA).

Frank, H., and L. Hopewell (1974), Network reliability, Datamation, pp. 85-91.

Gomory, R. E., and T.C. Hu (1961), ~1ulti-terminal network flows, J. Soc. Indust.

Appl. Math., ~, pp. 551-570.

Gomory, R. L, and T. C. Hu (1962), An application of generalized linear programming

to network flows, J. Soc. Indust. Appl. Math., l.Q., pp. 260-283.

Kleinrock, L. (1972), Communication Nets (Dover Publications, Inc. New York, NY).

Martin, J. (1977), Future Developments in Telecommunications, 2nd edition (PrenticeHall, Inc., Englewood Cliffs, NJ).

Tainiter, M. (1976), A new deterministic network reliability measure, Networks, §.,

pp. 191-204.

Wilkov, R.S. (1972), Analysis and design of reliable computer networks, IEEE Trans.

Communications, COM-20, pp. 660-678.

207

FORM OT-29 ClI-7111

U.S. DEPARTMENT OF COMMERCE OFFICE OF TELECOMMUNICATIONS

BIBLIOGRAPHIC DATA SHEET

1. PUBLICATION OR REPORT NO 2. Gov't Accession No.3. Recipien,':;', Accession No.

NTIA Report 80-36 ... TITLE AND SUBTITLE

Command Post/Signal Center Bus Distribution, System Concept Design

7. AUTHOR(S)

R.F. Linfield, M. Nesenbergs, P.M. McManamon

I. PERFORMING ORGANIZATION NAME AND ADDRESS

U. S. Department of Commerce

NTIA/ITS-4

325 Broadway Boulder, Colorado 80303

11. Sponsorilll Orlanization Name and Address

U. S. Army Communications-Electronics

Engineering Installation Agency

CCC-SEO

Fort Huachuca, Arizona 85613

1... SUPPLEMENTARY NOTES

5. Publicatiun Date

Aoril 1980

6. PerlorminA Or,aniza,ion Code

NTIAIITS-4

'9. Project/laslt/Worlt Unit No.

10. Conllact/Grant No.

12. Type of Report snd Period Covered

13.

15. ABSTRACT (A 20o-word or less factual summary of most significant informalion. II document includes a significant

bibliOll"'plav of literature survey. mention it here.) .

The communications network structures currently used to interconnect

terminal clusters and switching nodes within an Army tactical command post and area signal center are reviewed. With this background, five alternative

structures are defined in terms of their functional requirements. These

candidate alternatives are evaluated and a preferred structure is selected

based on a number of critical issues including deployment time,f1exibi1ity, performance, and survivability. The preferred alternative is a transparent bus-type distribution system incorporating ana10g-to-digita1 conversion for

analog sources, time division multiplexing, and digital transmission facilities.

A three-phase improvement plan is also outlined. The three phases are 1)

imbedding the transparent link into the existing network structure, 2) merging these links with digital switches~ and 3) changing the topology by adding switches to enhance survivability.

16. Key Words (Alphabetical order. separated by semicolons)

17. AVAILABILITY STATEMENT

UNLIMITED.

o FOR OFFICIAL DISTRIBUTION.

'I. Securi ty Class (17tis teport)

Unclassified

19. Security Class (17tls page)

Unclassified

20. Number of pales

228

21. Price:

lISCOMM-DC 2D71t\-P73

U. S. GOVERNMENT PRINTING OFFICE 1980 - 678-297/360 Reg. 8
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