Local Area Network Feasibility

Study for the Naval Sea Systems

Command

Alan Mink

Charles 3. Siiio, Jr.

Center for Computer Systems Engineering

Institute for Computer Sciences and Technology

U.S. Department of Commerce

National Bureau of Standards

Library, t-01 Mrrrin. Bldg.

MAR i 3 1981

NBSIR 80-2187 no -

• V

• LOCAL AREA NETWORK FEASIBILITY

STUDY FOR THE NAVAL SEA SYSTEMS V

COMMAND '- ' - ' fiiC-*

Alan Mink

Charles B. Siiio, Jr.

Center for Computer Systems Engineering

Institute for Computer Sciences and Technology

U.S. Department of Commerce

National Bureau of Standards

Washington, DC 20234

\

November 1980

Issued January 1981

U.S. DEPARTMENT OF COMMERCE, Philip M. Klutznick, Secretary

Jordan J. Baruch, Assistant Secretary for ProductiviV/, Tachnaiagy, and Innovation

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

ABSTRACT

The Naval Sea Systems Command (NAVSEA) has tasked the

Institute for Computer Sciences and Technology of the

National Bureau of Standards (NBS) to perform a feasibility

study of a Local Area Networking (LAN) capability to enhance

NAVSEA' s computing facilities. This report documents that

feasibility study. In this report, NAVSEA' s environment is

established. This includes the physical and the computing

environment. After establishing the environment, a

representative set of application programs is used to

determine NAVSEA' s LAN requirements. Then a discussion of

LAN topologies is presented, and those applicable to NAVSEA

are indicated. Implementations of these applicable

topologies are discussed along with the technologies

involved and their advantages and disadvantages.

KEY WORDS: Carrier sense

analysis; feasibility

requirements analysis.

multiple access; environmental

study; local area networks;

DISCLAIMER

Certain commercial products are identified in this report.

In no case does such identification imply recommendation or

endorsement by the National Bureau of Standards, nor does it

imply that the products identified are the best available

for the purposes described.
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TABLE OF CONTENTS

EXECUTIVE SUMMARY 1

1 INTRODUCTION 3

2 ENVIRONMENT 3

2.1 Physical 3

2.2 Equipment 4

2.3 Workload 5

3 REQUIREMENTS 8

3.1 Application Areas 8

3.2 Representative Applications 10

3.3 Application Requirements 13

4 LOCAL AREA NETWORKS 16

4.1 Scope 16

4.2 Topologies 16

4.3 Suitability/Applicability of Topologies 20

5 NETWORKING OPTIONS 22

5.1 Implementing a Star 23

5.2 Implementing A Bus Network 26

6 SUMMARY 30

7 APPENDIX: REVIEW OF BUS LOCAL AREA NETWORKS 32

7.1 Concepts of Bus LANs 32

7.2 ISO Open System Reference Model 34

7.3 ETHERNET 39

7.4 NBSNET 41

8 GLOSSARY OF TERMS 45

9 BIBLIOGRAPHY 47
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EXECUTIVE SUMMARY

The Naval Sea Systems Command (NAVSEA) has tasked the

Institute for Computer Sciences and Technology (ICST) of the

National Bureau of Standards to perform a feasibility study

of a Local Area Networking (LAN) capability to enhance

NAVSEA' s computing facilities. NAVSEA' s computing equipment

and physical environment have been determined to be stable

and not expected to change prior to 1985. Due to increasing

workload and diminishing staff NAVSEA has placed increasing

emphasis on computer aided design to more efficiently

utilize valuable staff time.

In order to provide efficient as well as convenient

access to the local computing facilities, NAVSEA requires a

LAN capability which can provide communications between the

computing facilities and each terminal at rates of 9600 bits

per second (bps) . These terminals need to be dispersed

throughout the engineering design areas of NAVSEA. This is

NAVSEA' s primary requirement, high speed dispersed terminal

to computer communications. This implies the need for a flexible communication facility to handle terminal mobility

and different terminal types. In addition, NAVSEA should

consider soft-copy (CRT) terminals since hard-copy of most

sessions is not required and CRTs can operate at higher

communication rates. These terminals should be capable of

displaying text and vector (line drawing) information, and

should allow the user to point to information being

displayed on the screen.

After reviewing the technologies available to provide

NAVSEA with a LAN capability, two feasible LAN

implementations are presented. One feasible implementation

is to install a bus LAN. This requires the installation of

a coaxial cable throughout the NAVSEA complex, and bus

interface units between the cable and each device, terminal

or computer. The other feasible implementation is to run

individual point-to-point lines, using modems where

necessary, between each terminal and a concentrator located

in each building, and then run high speed lines from all the

concentrators to a port contender in the central facility

which will act as an intelligent front-end switch.

The bus LAN implementation has a number of potential

advantages over the other alternative depending on the LAN

signalling technology (baseband or RF) . An advantage both

technologies offer is inherent flexibility. Flexibility

includes such things as arbitrary locations for network

connections (i.e., additions or moves), consistent network

protocols, and personalization for different device

(terminals or computers) connections. Another advantage

both bus signalling technologies offer is ease of media

maintenance, since only a single (or two) cable (s) is
Page 2

involved. In addition, RF signalling technology offers a potentially large bandwidth that may be divided into

channels. Different priorities and speed ranges may be

associated with different channels.

The primary disadvantages of a bus LAN are the current

lack of complete high level communication protocols, the

utilization of a new technology, and the current limited

availability of bus interface units. The latter two

disadvantages will phase themselves out during the next two

years. Asynchronous terminal to computer communication does

require some level of virtual terminal protocols, and most

facilities do at least offer this minimum required level.

Intelligent interface units are just beginning to be offered

by commercial vendors. It is expected that over a dozen

vendors will have commercial units available by the time

NAVSEA is ready to procure them in 1982. Currently, the

estimating rule-of-thumb for these intelligent interface

units is approximately $1K, although LSI implementation and

mass production may reduce this by as much as 70 percent.

The individual point-to-point lines implementation

possesses two advantages. The first advantage is that all

necessary components are currently available from a number

of commercial vendors. The second advantage is the

point-to-point lines implementation is currently less

expensive than a Bus LAN, approximately $100K vs. $140K.

The point-to-point lines implementation suffers from a lack

of flexibility and more difficult media maintenance. This

lack of flexibility is felt to be a serious disadvantage.
Page 3

1.0

INTRODUCTION

The Naval Sea Systems Command (NAVSEA) has tasked the

Institute for Computer Sciences and Technology (ICST) of the

National Bureau of Standards (NBS) to perform a feasibility

study of a Local Area Networking (LAN) capability to enhance

NAVSEA' s computing facilities. This report documents that

feasibility study. In this report, NAVSEA' s environment

will first be established. This includes the physical and

the computing environment. After establishing the

environment, a representative set of application programs

will be used to determine NAVSEA' s LAN requirements.

Once the environment and requirements are established,

a discussion of LAN topologies is presented. Those LAN

topologies applicable to NAVSEA are indicated.

Implementations of these applicable topologies are discussed

along with the technologies involved and their advantages

and disadvantages. The report concludes with a brief

summary emphasizing NAVSEA' s LAN requirements and two

feasible implementation alternatives, along with their

advantages and disadvantages. A brief review is included on

Carrier Sensed Multiple Access (CSMA) bus LANs, since this

is a relatively new and emerging concept. In addition, an

overview of the International Organization for

Standardization (ISO) Communication protocol reference model

is provided, since this has become a standard framework for

discussing communications.

2.0

ENVIRONMENT

2.1

Physical

NAVSEA is physically distributed primarily among 3

adjacent buildings at the southern end of the Crystal City

complex. These buildings are all located on a single block

and, therefore, no public thoroughfares need be crossed when

going from one building to another. In addition, these

buildings are physically interconnected both on ground level

by malls and passageways, and below ground level by a multi-level parking facility.

Personnel and equipment face a rather dense working

environment. Heating, ventilation, and air conditioning

(HVA/C) in the normal working areas are generally poor.

This is due to the Federal restrictions on temperature and

also to the inconsistency/ variability of the building's

HVA/C system in maintaining a uniformly specified

environment. The centrally located computer complex has its
Page 4

own HVA/C system which adequately maintains temperature and

humidity requirements. Other intelligent devices

distributed among the working areas do not enjoy this stable

environment and, therefore, during the hot summer months are

known to malfunction.

NAVSEA is committed to remain in these three buildings

for at least the next five years. This does not mean that

the current physical arrangements will remain unchanged

during this time. Internal movement of personnel and

equipment is expected to occur due to organizational changes

and improved space allocations. This implies that any

internal communication facility must have the flexibility to

contend with the movements of personnel and equipment.

The Crystal City complex is privately owned and leased

by the Navy via GSA. This causes serious problems, since

any modifications to the building must go through a long and

complicated chain of approval (namely. Navy chain of

command, GSA, building management, contractor/craftsmen)

.

Therefore, to string wire or cable (which might be done

relatively inexpensively by Computer Operations personnel)

requires a request with justification, followed by a long

approval chain, then negotiations with an authorized

contractor, and finally the work performed by designated

craftsmen. In addition, NAVSEA feels even to access an

existing cable above the false ceiling may require this

chain of events. NAVSEA is trying to work out some

agreement to expedite this process by having risers (a

vertical cableway) installed in each building to use as

needed for communication wires or cables. In addition,

NAVSEA is trying to negotiate some level of Navy direct

handling of the cable once installed without going through

the request/approval/negotiation chain each time.

2.2 Equipment

NAVSEA' s primary computation facility has been a centralized set of large mainframe computers, and secondary

facilities have been a dispersed set of various large

mainframe machines from another manufacturer. None of these

machines are owned by NAVSEA, and all are remotely located.

The primary facilities are located at DTNSRDC in Carderock

Md, and are accessed both in an interactive (300 bits per

second (bps) dial-up) mode and a batch (RJE) mode. Batch

access is on a 50K baud leased line via a minicomputer

acting as a local RJE station with a line printer, card

reader, card punch, and an interactive graphics workstation.

The secondary facilities are accessed in a similar manner,

i.e., interactively via 300 bps dial-up lines, and for batch

on a 4800 bps leased line via a minicomputer acting as a local RJE station.
Page 5

NAVSEA has recently awarded a procurement to install a

local processing facility consisting of 4 identical

minicomputer systems. Two of these minicomputer systems

will replace the current local RJE facilities, while the

other two will provide highly responsive interactive

graphics. All of these systems will, as a secondary

function, provide local interactive and batch processing.

The configuration of this system is as follows (see Figures

la and lb)

The two processors replacing both RJE systems share

secondary memory (disk) . These systems will each have a

card reader and line printer, and will share a card punch, a

printer/plotter, and a set of 2 magnetic tape units. The

primary function of these processors will be to handle all

RJE requirements; their secondary function will be to

support local batch and interactive processing.

The other two processors will also share secondary

memory (disk), as well as sharing a line printer, card

reader, card punch, printer/plotter, and a set of 2 magnetic

tape units. In addition these processors will each support

a dynamic interactive graphics work station which is

microprocessor driven. The primary function of these

processors is to support interactive graphics, both static

and dynamic. The interactive graphics workstation equipment

will support the dynamic graphics applications. Lower cost

graphics devices will support the static graphics

applications. The current low cost graphics equipment is

mostly storage tube devices. The secondary function of

these processors is to provide local interactive processing.

Based on 1) the newly procured NAVSEA computing

facility, 2) the time required to procure additional or new

systems of the same complexity, and 3) NAVSEA' s current long

range plans, it is not expected that NAVSEA will

significantly modify or replace this computing facility

within the next 5 years.

2. 3 Workload

NAVSEA' s in-house staff has been steadily declining due

to lower personnel ceiling constraints. Simultaneously with

this diminishing staff, the workload has significantly

increased mainly due to the increasing complexity of the

various ship subsystems and their subsequent integration.

This is especially evident in combat systems,

communications, and other electronic subsystem areas. The

overflow workload is being contracted out, putting an

increasing burden on the in-house staff to monitor these

efforts in addition to accomplishing their own tasks. As a result, NAVSEA has placed an increased emphasis on computer

aided design processes to improve the productivity of its
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Page 8

staff

.

NAVSEA has made a commitment to upgrade the computing

facilities to support the ship design process. This

requires responsive, flexible, and highly available

computing facilities. As a first step, a local computing

facility was procured (see section 2.2) to provide the

required local processing capability. As a second step, a

means of providing the design engineers convenient access to

this computing facility, from their working areas, is

required. This can be accomplished by providing computer

terminals capable of displaying textual as well as graphical

information sent from the computer at high communication

rates

.

3.0 REQUIREMENTS

3.1 Application Areas

In addition to on going sowtware development, NAVSEA

has processing requirements in three major areas:

interactive graphic applications, data base query and report

applications, and scientific (engineering design)

applications

.

Interactive graphics applications can be divided into

two categories: dynamic and static. Dynamic interactive

graphics usually involves 3 dimensional objects which are

displayed in perspective views. These objects are

frequently manipulated, updated, translated and rotated.

This requires tight coupling with a processor. In today's

market this dynamic interactive graphics is generally

expensive and can not be generously supplied throughout the

engineering work areas. This type of facility is usually

supplied in limited quantities, and shared by the user

community. For NAVSEA this represents a small, but

important, percentage of its interactive graphics

applications.

Static interactive graphics applications form the

majority of NAVSEA' s graphics workload. These typically are

2 dimensional drawings, such as engineering block and wiring

diagrams, and 3 dimensional arrangement and layout diagrams.

These applications are designed to interact with the user

through CRTs that display vector information as well as text

and that permit the user to "point" to objects that are

being displayed. Currently, these applications are

implemented on storage tube terminals and the more complex

interactive graphics workstation. Commercially available

raster scan devices [cOMP 80a, COMP 80b] may provide a less

costly functional replacement. A lower cost for this class
Page 9

of device allows a greater number to be acquired and

distributed in the engineering design areas.

Data base query and report applications form a large

portion of NAVSEA's workload. Many programs produce output

consisting of report type information, such as equipment

lists, ship schedules, parts or connection lists, etc.

Currently these reports are always output on the line

printer in multiple copies and distributed for reference.

This type of output could be kept on-line and viewed on a

CRT terminal by either sequentially listing it or

selectively viewing it through the use of an interactive

editor. The authors' experience has shown that each

individual has a threshold limit to the amount of

information he/she will review on-line. This threshold is

usually a function of the amount of information that can be

displayed at one time and the speed with which the

information can be accessed..

Data base applications require additional maintenance

overhead. Program and database administrators spend a large

portion of their time reviewing, adding, and changing

verified information within the databases. Currently the

portions of these procedures that are on-line require a more

complex interaction than would be necessary if CRT terminals

and appropriate software were available. Instead of viewing

a field of information at one time, the entire record or a

large portion of it could be displayed at one time. In this

environment a more comfortable and efficient modification

procedure could also be established.

Scientific application programs encompass a large range

of input/output (I/O) interactions from a few data items of

input to a complex and lengthy input data structure;

similarly, the output may range from a few numbers to

extensive tables or reporting formats. Some of the

scientific programs are more conducive to graphical I/O.

Currently, textual input files representing graphical

information are prepared by the user and are output by the

program. The output files are then sent to either the line

printer or a hard copy plotter, whichever is appropriate.

As in the case of reports, the I/O may be accomplished

in a more efficient manner interactively on a CRT terminal

operating at high data rates. If convenient means existed

to graphically specify input and view output, this would

provide a more compatible user interface. By using CRT

terminals capable of displaying vector information (e.g.,

line drawings) , the graphical output data could easily be

displayed without the need and time delay of obtaining hard

copy. Entering information graphically is more complicated

and may require special front-end programs.
Page 10

The actual I/O to these scientific programs would still

be textual files representing graphical information. The

user would interact with the front-end program providing it

graphical information. The front-end program would check

this information and then translate it into the textual form

required by the application. The output textual files would

be translated, as before, into their vector representation

and displayed on the CRT terminal rather than drawn on

paper

.

3.2 Representative Applications

In this section we discuss a representative set of

application programs which encompass the various application

areas discussed above. These programs are mainly

electronics applications (vs. HVA/C, Hull, or Machinery

applications) , but are considered functionally

representative.

V

EDS

EDS is a static interactive graphics, as well as a database, application program. The purpose of this program

is to allow users to construct multi-level block and wiring

diagrams. A diagram is constructed from a number of layered

libraries. The lowest library layer is a template library

which defines the basic geometric shapes that the user

desires. The highest library layer is the diagram layer,

which consists of a number of multi-level diagrams.

Multi-level means that a diagram may exist at different

complexity levels; from the simplest (highest) level which

obscures detailed information, to the most complex (lowest)

level which presents every detail. The primary function of

EDS is to allow design engineers to extract "baseline"

systems, and interconnect and modify them for specific

designs. Each "baseline" system is represented by a number

of geometric shapes (e.g. a rectangle), each corresponding

to a component of that system. The components are

interconnected by a set of lines, which are the system

intraconnections. These connections may represent anything

from a logical connection (highest level) to individual

electrical connections (lowest level) . Along with each

connection is associated a textual label and attribute

information, which defines the connection function. The

user interacts with the program via a CRT terminal with

vector drawing and "pointing" capabilities.
Page 11

There are two basic user interaction modes:

constructing and viewing. In the construction mode, the

user constructs a diagram. In the viewing mode, the user

views (displays) one or more diagrams. A diagram usually

contains more information than the CRT screen is capable of

clearly displaying at one time. Therefore, only a portion

of a diagram is displayed at one time. Mechanisms are

provided through which the user can traverse to different

parts of a diagram. Due to the large amount of information

comprising a single display screen, a communication speed of

300 bps is unacceptable in the viewing mode since the time

delay is intolerable At 9600 bps the delay observed by the

user becomes negligible.

In the construction mode, the user is incrementally

building portions of the diagram. One may argue that this

incremental addition of information can be acceptably

performed at 300 bps. Due to the complexity of these

diagrams one must often "traverse” from one place to another

on the diagram, mainly to affect connections and accomplish

esthetic rearrangement of components. This traversal

requires a completely new screen of information to be

displayed. Therefore, as is the case in the viewing mode,

300 bps is unacceptable and 9600 bps is required.

The prototype of this application program is targeted

for implementation on the interactive graphics workstations

(dynamic graphics) . These workstations are located in the

central computing complex. It is generally inconvenient and

inefficient for the design engineer to reserve time in

advance and then carry all his reference and working

materials with him to these workstations. If static

interactive graphic devices, communicating at 9600 bps were

available in the design engineer's working area, the utility

of this application program would be amplified. The design

engineer might then efficiently and conveniently use the CRT

to construct, modify, and view diagrams, rather than obtain

hard copy (plotted) output. The engineers use the plotted

output in an attempt to maintain their own local collection

of diagrams, "pen-and-inked" to reflect the current status

of "minor” changes.

ELXLST

SLXLST is a set of data base oriented application

programs. Its purpose is to maintain a consistent

repository of information on all electronic equipment that

may be used in the combat system design of a ship. The data

base information consists of equipment attributes such as

space, weight, power, cooling, technical and administrative

cognizance, etc., as well as the hierarchical structure of

the equipment (i.e. its components, the subcomponents

comprising each component, etc.).
Page 12

The maintenance of the data base is carried out by a

single data base administrator, after a well defined data

verification process. The data base administrator uses both

interactive and batch processing to maintain the data base.

Interactive processing is used mainly for scanning or

modifying a few individual data fields, and is currently

performed at a data rate of 300 bps. Batch processing is

used for major modifications or additions to the data base,

and is performed via punched card input prepared from

worksheets. To view one or more complete data base records

currently requires a line printer listing.

Individual users create their own "Ship File", which is

a subset of the data base, representing an electronics

equipment list of the combat system for a specific ship

design. Once a Ship File has been created the user may then

"customize" the structure and quantity of equipments to fit

the specific design. Only certain information may be

customized, while the remaining, predominantly attribute

oriented data, may not; and this non-customizable data must

always be extracted from the data base for consistency.

Each user may have as many Ship Files as desired, usually

for different designs or trade-off studies. From these Ship

Files the user may generate a number of predefined reports.

These reports are used for reference information during the

various ship design phases and are periodically distributed

to other design engineers. Currently, the design engineers

prepare their input data to this set of applications

programs on worksheets, which they fill out by hand. These

worksheets are then transcribed to punched cards, and all

results are output on the line printer.

It would be more convenient for the users to prepare

their input data and view the resultant output on-line.

Preparing the input data at 300 bps may be acceptable based

on a typing speed argument. But entering information at

this rate does not allow for an efficient or convenient user

interaction process that could be achieved at 9600 bps.

Viewing the various outputs would not be acceptable at 300

bps, whereas at 9600 bps on a CRT it would be.

The Database Administrator does portions of the

maintenance process interactively at 300 bps. Currently the

bulk operations are more efficiently done by transcribing

the information onto worksheets and keypunching it onto

cards. At 9600 bps a more efficient user interaction

procedure could be developed and the Database Administrator

could do all the maintenance interactively.
Page 13

RADHAZ

RadHaz is an interactive scientific oriented

application program. Its purpose is to compute the on-axis

power density of microwave antennas. The results are used

to determine the hazardous areas onboard a ship caused by

microwave radiation being emitted from these antennas. The

design engineer enters about six numbers and a line or two

of descriptive text. The output is a table, consisting

mainly of radiation density values vs. on-axis distance

from the antenna.

Currently, entering the input data at 300 bps is

acceptable, although at higher speed more efficient

interaction procedures could be considered. The resultant

tabular output can get rather lengthy. At 300 bps it is not

unusual to take five or ten minutes to list the output on a

local terminal. It would be much more efficient to view

this tabular output at 9600 bps, thereby, reducing this

time.

3.3 Application Requirements

A large portion of NAVSEA''s workload on the primary

mainframe machines is RJE/punch card oriented. An attempt

to encourage design engineers to use interactive terminals

(300 bps dial-up) in the working areas, rather than punching

cards, is slowly becoming successful. The main problems are

poor response time and system unavailability, in addition to

breaking traditional usage habits.

A large portion of NAVSEA's computing output is

transient, and no permanent listing or printout is needed or

desired. Therefore, soft-copy terminals (CRTs) are

preferred to hard-copy terminals. When hard-copy is

desired, it can be sent to the local line printer. If,

however, there is an immediate need for hard-copy a printing

device can be attached to the CRT (this is expected to be a

rather rare situation) . Currently, most terminals at NAVSEA

are low speed hard-copy terminals, which means purchase of a number of soft-copy terminals should be considered. These

terminals should be capable of displaying text and vector

(line drawing) information, and should allow the user to

point to information being displayed on the screen,

depending on particular user needs.

For a large portion of the data base and scientific

applications interactive access via 300 bps dial-up is

barely acceptable. Working at these speeds has forced a mode of operation in which the design engineer minimizes the
Page 14

amount of information being displayed and, therefore, limits

the ways in which he/she may interact with this design tool

(the computer). It is clear that 9600 bps would be much

more desirable. This speed allows the design engineer to

quickly view and edit a screen full of data without becoming

bored or impatient while waiting for the desired information

to be displayed. In addition, more effective interaction

methods would become available, thereby, increasing the

capabilities and productivity of the design process.

Static interactive graphic applications form the

majority of NAVSEA's interactive graphics workload. These

typically are 2D drawings, engineering block and wiring

diagrams, and 3D arrangement and layout diagrams. These

applications require a large amount of information to be

displayed at one time. As with the other applications,

providing a low communication speed, such as 300 bps, causes

a restrictive mode of operation and impatience on the part

of the design engineer. To be more responsive to the design

engineer a communication speed of 9600 bps is required. At

this data rate reasonably complex drawings can be displayed

in a short time allowing the design engineers to interact

with the design tool on a continuous basis and in a convenient manner. Therefore, the design engineer is using

the design tool in a more compatible and synergistic manner

rather than the design tool dictating to the design

engineer, thus resulting in a less productive environment

because of user frustration.

This results in a primary requirement for a communication network that can connect a dispersed set of

terminals to the local processing facility. Such a network

must be capable of supporting communication rates of 9600

bps to each user. In addition, such a communication network

must be flexible. Flexibility includes such things as

arbitrary locations for network connections (i.e., additions

or moves), consistent network protocols, and personalization

for different device (terminals or computers) type

connections

.

Arbitrary locations for network connections are

necessary due to potential relocation of existing terminals

and acquisition of new terminals. Internal movement of

personnel and equipment is expected to occur due to

organizational changes and improved space allocations.

Changing workload and other factors may cause acquisition of

additional terminals. Different terminal types already

exist within NAVSEA. As more terminals are acquired it is

reasonable to expect that additional terminal types will

appear due to technological advances and application

requirements. The characteristics of each terminal must be

accounted for. This may be accomplished by either the

processor, the network, or both; and is sometimes referred

to as a Virtual Terminal Protocol, although at a minimal

level.
Page 15

In addition to NAVSEA's current requirements, discussed

above, there are two long range organizational goals which

will emphasize and add to these requirements. The first

goal is the introduction of Office Information Systems (OIS)

processing capabilities. This would emphasize the current

requirements for high speed communications, responsive

processing, and high availability, while adding the

requirement for a sophisticated screen (2 dimensional)

editor. This editor would also provide program developers

and design engineers a more efficient and convenient

interface to the computer. The second goal is to provide

access to Autodin II and other military networks. These

goals add inter-processor communication for dispersed

processors to the flexibility requirement. This implies the

need for consistent high level protocols well beyond the

minimun virtual terminal protocol, such as a file transfer

protocol.

NAVSEA desires to foster interactive processing by

providing interactive terminals (CRT based) distributed

throughout the engineering work areas. To successfully

accomplish this, it is necessary to provide each user with a communication speed of 9600 bps. This communication speed

will provide adequate response to the engineering community

for interactive static graphics as well as the other

applications. Since NAVSEA is currently acquiring a

completely new processing system, it is anticipated that

this will comprise the processing environment over the next

5 years. Communications facilities and terminals are

expected to be the only additions. In view of this

situation and NAVSEA's commitment to interactive processing,

the primary requirement is adequate terminal to computer

communications. A general term for such a local

communications facility is a local area network (LAN)

As a result of the above requirements the following

questions concerning LANs need to be answered. What type of

LAN is feasible to provide these communications? Are these

or will these LANs be available in the near future on a commercial basis? Will these LANs provide the services

necessary in a cost effective manner? The remainder of this

report is concerned with the LAN alternatives available to

NAVSEA can provide these communications facilities. The

architectures and technologies of each alternative are

discussed, along with their advantages, disadvantages, and

availability (over the next two years)
Page 16

4.0 LOCAL AREA NETWORKS

4.1 Scope

In this section we define LANs and their essential

elements. In order to segment the universe of possible

networks we use a taxonomy based on topology. Each

topological classification is briefly described, followed by

a discussion on the suitability/applicability of each of

these topologies to NAVSEA's requirements.

A local area network is a data communication network

limited in geographic scope. This limited geographic scope

is generally referred to as a campus. LANs are

distinguished from long haul networks in several ways.

First, LAN nodes (host computers or terminal devices paired

with communication interface units) within the campus are

seldom separated by more than a few thousand meters. This

encompasses the distance required to span a computer room,

an office building or a complex of buildings (e.g. National

Center buildings 2, 3, and 4). Second, LANs are owned and

operated by a single organization. In addition to being

cost effective, ownership allows the organization control

and flexibility in the design and operation of the LAN. The

discussion of LANs includes point to point communications

circuits (both physical and virtual) that are configured in

a star or multidrop topology, in addition to packet switched

netwo'rks of varying topologies. Arbitrary network

topologies are possible, but the star, ring, and bus forms

are the most prevalent.

Local area networks are composed of four essential

elements. The first component is a transmission medium,

often twisted-wire pair, coaxial cable, or fiber optics.

The second component is an access mechanism for controlling

transmission on the medium, such as, various forms of

polling, control token passing, or contention for

determining which node may transmit at a given time. The

third component is an interface that connects the host

computers or other devices to the network. The fourth

component is a layered family of protocols associated with

the network for transporting information successfully from

one node to another via the components of the network.

4.

2

Topologies

The topology of a network dictates the range of

possible routings (source to destination paths) between two

communicating nodes within the network. Seven topologies
Page 17

commonly occur in discussions of computer network

structures. Each of these topologies may be represented by

a graph (see figure 2) . The vertices of the graph represent

the network nodes (host computers or devices paired with

communication interface units) . The edges of the graph

represent the communication channels (links) , which may be

unidirectional or bidirectional. The seven topologies are

as follows:

1.

Mesh — characterized by a set of nodes, in which

each node may not have a direct link to every other node,

although communication can be established between any two

nodes. A node usually has a direct link to two or more

"adjacent” nodes. Each link is usually bidirectional and

control of the network is usually distributed. To

communicate with a non-adjacent node requires the

cooperation between intervening adjacent nodes along the

communications route to pass on the information. In

general, the route between source and destination nodes is

not pre-determined and alternate routes exist. Upon receipt

of the information, each node dynamically decides the next

segment of the route (i.e. which adjacent node to pass the

information to)

based on its current knowledge of the state

of the network.

2.

Star — characterized by the presence of a central

node through which, and to which, all other nodes are

connected. A communication between two nodes must pass

through the central node. Each link is usually

bidirectional and control of the network is usually handled

by the central node.

3,

Hierarchical — characterized by a tree structured

graph in which communication between two nodes not sharing

the same path from the root node must establish a communication path through a common ancestor node located at

a higher level in the tree. Each link is usually

bidirectional and control of the network is usually handled

by the root of the subtree involved in the specific

communication, or may be fully distributed.

4.

Ring — characterized by each node being connected

to exactly two adjacent nodes in a circular arrangement.

The transfer of information is unidirectional, through

active interfaces, from predecessor node to current node to

successor node. As a result, the transfer of information

from a given node to its immediate predecessor in the

circular ordering must pass through the interfaces

associated with each of this node's successors (that is,

each and every node interface) on the ring. Control of

access to the ring is usually distributed among the
Page 18

O

O 6 6 6 6

HUB BUS

Figure 2. Graph representations of network topologies.
Page 19

connected nodes. A second ring in which data travels in the

opposite direction is sometimes added for reliability. 5.

Loop — characterized by the same structure as a

ring except one master control node exists on the loop.

This master control node supervises and synchronizes the

passing of information on the loop.

6.

Bus — characterized by a straight line segment to

which all the nodes are passively attached. A bus is a shared broadcast multiaccess communications medium used by

pairs of communicating elements to transfer data according

to some predefined and mutually agreed to protocol. As in

any communications network, all parties sharing use of the

bus employ the same protocol for gaining control of the

communications medium, for identifying (addressing) the

element to be spoken to, for establishing the point-to-point

connection, and for releasing control of the communications

medium. Once the temporary connection between talker and

listener is established all other parties passively listen

to the ensuing transmission, which is part of an overall

conversation. A conversation may consist of many

transmissions, each of which independently acquires and

releases control of the bus. The conversation itself may

have meaning only to the conversing parties. While

communication actually takes place over a physical medium

(or physical circuit) , the nondedicated and timeshared use

of the physical medium causes one to view point to point

transfers of information as taking place over a virtual

circuit. To manage these virtual connections requires

appropriate buffering and necessary intelligence. This is

provided in the bus interface units which connect each node

to the medium.

7.

Hub — characterized by a multidrop line much like

a bus in which a master node controls the flow of

information. This topology implements a local circuit

switched network in which a channel is established on a time

shared basis whenever two entities connected to it need to

communicate. In this configuration nodes are operated in

polling mode under control of a master node. Several

control disciplines are possible, although two are most

common. One is roll call polling, where the master node

successively invites each node to transmit in some

pre-determined order. The other is hub-go-ahead polling

where each node that has nothing to send passes the poll

along to the next node in turn.
Page 20

4.3 Suitability/Applicability Of Topologies

In this section we discuss briefly the relationship of

each of the above topologies to NAVSEA's requirements.

1.

Mesh — this topology is best suited for long haul

networks where switching computers (or simply, switches) are

used at the nodes for forwarding messages, transactions, and

data, and is not considered suitable for satisfying NAVSEA's

requirements. While not suitable for the terminal to

computer requirements, this configuration may be a suitable

topology for maximal interconnection of the four processors

located in the NAVSEA central site.

2.

Star — this configuration could satisfy the

terminal to host computer communications requirements

typical of NAVSEA. The central node can be viewed as a

complex of four computers, each accessed through specific

port addresses. Point to point connections between the

terminals and the central site must be provided. Therefore,

communications channels must radiate out from this central

location to provide computer access for the remote

terminals. This can be accomplished by running a point to

point dedicated (nonswi tched) line from each terminal to the

central site, using switched line dial-up facilities

provided by the telephone company, or by an inhouse private

branch exchange (PBX) for both data and voice. It is not

expected that all terminals will be in use simultaneously

because the number of terminals greatly exceeds the number

of available computer ports. Therefore, a means for serving

terminal user demands on some first-come first-served

contention basis must be provided. Various devices are

available that can be used individually or in tandem for

mapping n requesting lines into m available connections

where n is greater than m. Basically these devices are a)

dial-up rotary switches and b) port selectors or intelligent

patch panels. These devices are discussed further under

networking options.

3.

Hierarchical — in the NAVSEA environment

configurations based on this topology, using multiplexers

and concentrators, actually implement only a minor variant

of the star topology. Therefore, this topology is not

considered separately, but is included in the star topology.

One could view remote multiplexers, or concentrators, on a one per floor or on a one per building basis (or both) as a hierarchically structured network. Multiplexers and

concentrators can be used to share the bandwidth of a single

wire among numerous terminals, resulting in less overall

wire and fewer wires emanating from the central site. This

bandwidth sharing is possible because the communication
Page 21

requirements of remote demand terminals are bursty in

nature. Even at peak burst rate, a single terminal does not

exhaust the channel capacity of a communications medium such

as twisted wire pair.

4.

Ring — this topology is attractive because it

reduces the numbers of cables required for point to point

connections, but in general it is not well suited for a

large number of nodes. The ring topology is not considered

suitable for meeting NAVSEA's requirements, because it poses

potential problems. The primary problem is commercial

availability in the U.S. Currenty, the majority of

operational rings are experimental. No known commercial

rings are planned for the near future. A potential problem

is related to connectivity and delay due to the sequential

topology. To implement a ring requires the use of an active

interface at each node, which incorporates a failsafe

switch. Active interfaces generally cause a delay in the

flow of information around the ring. They may remove

information, examine it, and then place it back on the next

ring segment. Depending on the duration of this delay the

overall accumulated delay may be significant. Adding nodes

to the ring requires splicing the new node into an existing

ring segment, while the ring is disabled. This may be a

problem depending on the location of the new node relative

to the nearest existing ring segment. Each node on the ring

may increase communication delays because of its active

interface as well as introducing^ additional traffic. An

other potential problem is related to maintenance and

reliability due to active interfaces. Failsafe switches

have been designed so that data and control information will

bypass an interface in the event of most failures and

continue along the ring. Failures that can disable the

entire ring are still possible (as in all other systems).

5.

Loop — although enjoying the same cost advantages

of ring networks because of the reduced numbers of

communications lines and reasonably simple interface logic,

this structure has the same problems associated with rings.

Therefore, it is considered no more suitable than the ring

for NAVSEA's requirements.

6.

Bus — The ease of interfacing to and expansion of

a coaxial cable bus strung throughout a campus make it a particularly attractive alternative for satisfying NAVSEA's

requirements. The principal characteristic of a bus is an

intelligent microprocessor controlled interface unit

typically used at each bus connection. As a result, direct

virtual circuit communication is possible between any pair

of nodes. Control of access to the bus is usually

distributed among all bus interface units on some

asynchronous contention basis, although synchronous time
Page 22

division multiplexed schemes can also be used. The main

component of this topology is the intelligent interface

unit, which is now becoming commercially available. This

unit allows existing terminals to readily access the

network.

7. Hub — the variants of this topology are not

considered applicable to NAVSEA's requirements. This

decision is based primarily on the network interface

requirements and partially on the communications overhead

incurred. Control of the network is accomplished through

the use of polling. This requires each terminal to possess

the capability of recognizing its own address, participating

in the polling protocols, and buffering information between

polls. The current NAVSEA terminals (mostly asynchronous)

do not possess these capabilities, which are normally

associated with synchronous terminals. An alternative to

requiring the terminals to possess these capabilities, is to

use an intelligent interface unit (similar to that of the

bus topology) . Currently no known appropriate interface

unit is commercially available. Considerable time is wasted

in polling nodes that have nothing to transmit, and at any

given time a large number of silent nodes is expected among

the set of asynchronous demand terminals. Contention is

likely to provide better response times for the nodes on a high bandwidth bus than would the use of centralized

control.

5.0 NETWORKING OPTIONS

Only two of the seven topologies discussed in the

previous section were considered suitable for satisfying ! NAVSEA's requirements, namely, the star and the bus ' topology. Means for implementing these two topologies are ; considered in this section. To maintain a consistent j discussion, all implementations assume 100 terminals, , uniformly distributed throughout the 3 buildings, connecting

to the central complex of 4 processors, each having 16 ports | operating at 9600 bps. i

I

I

i
Page 23

5.1 Implementing A Star

Rotary switches

Rotary switches are accessed through the telephone

company's (telco) direct dial network or through a private

branch exchange (PBX) network, thereby limiting the

communications rate to that of either the public switched

network or of the PBX. This limitation ranges from 1200 bps

to 4800 bps depending on the quality of the intervening

lines and switch gear. A telco modem or equivalent will

provide 4800 bps communications over dial up lines. Recent

introductions of rather expensive 9600 bps modems that work

over the switched network have been made by modem

manufacturers other than the telco. These sell for over

$4000.00 each, and a pair of them is needed for each

connection. In addition, modems built by different

manufacturers are not guaranteed to interoperate at 9600

bps. The cost of a dial up rotary is approximately $17.00

per month per line. Held [HELD 77] cites a telco rotary

cost of $1359 per month for a unit that handles 48 incoming

lines for 300 bps terminals and connects them on a first

come first served basis to 32 computer ports. The $1359

does not include the cost of the 80 modems that are also

needed to implement this system.

A dial-up rotary allows a remote terminal user to call

a single number and gain access to one of several auto

answer modems. The rotary scans each telephone line that is

connected to one of these modems for one that is not busy.

If all lines are in use, it generates a busy signal, thereby

forcing the terminal user to wait and try again later. At

least one rotary switch is required for each distinct

computer and/or each class of service, such as line speed,

in order to connect to the correct speed modem. Additional

dial-up rotaries are required for each computer and for each

transmission speed that the user may specificly select.

This option could meet NAVSEA's requirements. However,

it suffers from two major disadvantages which relates to its

use of the existing switched dial-up telephone network.

First, 9600 bps over dial-up facilities is not available

from the telco directly. Second, the provision of 9600 bps

service using the new microprocessor controlled digital

signal processing modems is considered too expensive. The

cost would be approximately $2800 per month for the rotaries

plus approximately $656,000 for 164 modems (assuming they

will actually work at 9600 bps in this configuration). This

is not considered to be a viable or cost effective option

for meeting NAVSEA's requirements.
Page 24

Port contenders/intelligent patch panels

The use of patch panel equipment was an early approach

to solving the inefficiency problem of each terminal user

being assigned permanently to a computer port or of having

multiple rotaries for user access to multiple computers.

This both enabled a user to manually connect to multiple

resources and, with additional cables and switches, provided

a level of system monitoring and diagnostics. Since

micro-computers can now function in add-on intelligence

roles, a new approach is possible using a micro-based

intelligent patch panel, also called a port contender. All

terminal users contend equally for the available connection

resources.

Although the range of options and facilities varies

from vendor to vendor, intelligent patch panels provide a high level of feedback to the terminal user attempting to

make a connection. This feedback eliminates the need for

intervention by computer site personnel. For example, a

port contender can generate status messages during excessive

downtime, thus diminishing the flood of phone calls to the

computer site. Typically, intelligent patch panels provide

tutorial response messages such as "wrong speed," "busy,"

"wait?" (contention) , and "unassigned", which helps minimize

the extent of operator training. Where security is an

important consideration, a response message, such as

"unauthorized", not only tells the user that he is excluded

from a particular resource but also flags the attempted

intrusion for the site manager at the system console.

Additionally the port contender can serve as a control

tool. It provides four methods of effectively managing

computer and communications resources: universal access,

contention and user feedback, statistics, and dynamic

console control. (See [VONAR 80] for further discussion of

advantages .

)

Intelligent patch panels are currently available from a number of manufacturers [COMP 80c, EVANS 80, HELD 77, VONAR

80] . Prices range from under $10,000 for a small table-top

unit with 50 interfaces to over $100,000 for a unit with

full-redundancy, options, and several hundred interfaces. A

unit capable of acommodating approximately 100 incoming

(terminal) lines for switching into approximately 64

computer port access lines can be obtained for approximately

$45,000. The intelligent patch panels are in effect private

branch exchanges for digital data, but they only provide

virtual circuit connections between two communicating

entities.

Selection of service class, where

consist of several ports operating at

a single computer, is provided by both

band signalling. Examples of this

a given class may

a particular speed on

inband and out of

type of signalling
Page 25

include escape command sequences, thumb wheel switches on

the limited distance modems, or use of separate signalling

wires. The intelligent patch panel essentially provides the

services of a rotary for each class of service and, because

of its low cost, represents an attractive means for meeting

NAVSEA's requirements.

The drawback to this configuration is the inflexibility

and expense of providing full duplex 9600 bps point to point

connections for the remote terminals. There are two ways of

stringing the necessary wires: renting the channels from

the telco, or using in-house or contracted labor. The

current telco tariff in Virginia for an 11000 series local

area data channel for passing 9600 bps at a line length of

less than three miles is approximately $6 per month. This

applies to a four-wire full duplex channel entirely in the

same building. That same channel running between buildings

on the same campus costs approximately $18 per month; or,

if it must be run through the local telco wire (local loop

switching) center costs approximately $21 per month. In all

three cases the installation charge per end is approximately

$21 (there are two ends, unless the channel is used as a multidrop line for which there are more than two ends). The

cost of leasing lines from telco, over a 5 year period, is

estimated to be approximately $89,000. The cost of leasing

lines (vs. installing your own) may increase significantly

due to potential tariff changes [BROAD 80] incited by

increased long distance competition (and lower prices) which

will be offset by increased local communication prices.

Asynchronous limited distance modems capable of speeds

up to and including 9600 bps are recommended on lines

running between buildings. They can be leased from the

telco for approximately $20 per month plus an installation

charge of approximately $100 each. Similar limited distance

modems can be purchased from other vendors for approximately

$300 each for stand alone units used at remote terminal

sites and approximately $175 each for multiple rack mounted

units used at the intelligent patch panel frontend in the

central site. Renting asynchronous limited distance modems,

over a 5 year period is estimated to cost approximately

$168,000. In comparison, the purchase cost of similar

modems is estimated to be approximately $39,000, plus any

maintenance that may be required.

This option could meet NAVSEA's requirements in a more

cost effective manner than the previous option. In

addition, this option provides extra services to the user

and the site manager, as discussed above. Assuming

purchase, rather than rental, of the modems, the

concentrators, and the port contender result in an

approximate cost of $100,000. Another advantage of this

option is that all the hardware and most (if not all) of the

software is currently available "off-the-shelf". To obtain

a customized system to perfectly fit ones' requirements may
Page 26

require "cutting and pasting" between different vendors'

products (i.e., a multi-vendor installation); although it

is possible to obtain a "turn-key" installation from a

single vendor. However, this option does have some

disadvantages which relate to the flexibility and

maintainability of the resultant implementation.

5.2 Implementing A Bus Network

The shared component of a bus LAN consists of a single

(or a pair of) coaxial cable strung throughout a building.

Individual nodes connect to the cable with the use of a CATV-style tap and a small transceiver. The transceiver is

connected at the tap, with a cable running down to an

interface located by the user's equipment. Coaxial cable

and taps can be commercially purchased from a number of

vendors. The flexible coaxial cable whose outer conductor

is made of woven copper wire mesh sells for about 21 cents

per foot, whereas the more rigid extruded aluminum shielded

lowloss cable ("broadband" cable) sells for about 33 cents

per foot [dines 80c] . The cost of installing the coaxial

cable is approximately $1.50 per foot [DINES 80c]. The use

of a passive medium (coaxial cable) and the lack of active

elements in the shared portion combine to help provide a reliable and flexible system. This approach also provides

for easy reconfiguration of nodes. Nodes can be moved by

disconnecting them at one point and reattaching them at

another without affecting the operation of the network.

Stringing the "single" cable throughout NAVSEA will be

less of a problem (cost and complexity) than stringing the

many point to point lines required by the other options. In

reality this would not be a single piece of cable, but might

be a number of segments organized in a tree structure. One

possible organization would use a cable segment as a main

"spine" connecting all buildings. In each building a vertical "riser" cable segment, spanning all floors, would

connect to the spine through a repeater. On each floor a cable segment, traversing that floor, would connect to the

riser in that building through a repeater. An advantage of

this organization is that any segment can be disconnected

(i.e. for testing, etc.) without affecting the operation on

the remaining connected segments.

Once this cable is in place devices may be easily

connected to the LAN by tapping into the cable at any

convenient location. The bulk of the cable installation

cost is attributed to labor costs. Therefore, consideration

should be given to installing a second cable at the same
Page 27

time for a marginal cost increase. This second cable could

provide future expansion or possible backup facilities to

the network.

The other component of a bus LAN is the intelligent

communications interface unit (CIU) . The CIU provides an

interface between each device and the network. The CIU is

responsible for handling the protocols associated with the

network as well as those associated with the individual

devices.

From the point of view of a device, the CIU should make

the LAN appear transparent. Devices should not be aware of

or concerned with the operation of the network. Devices

should communicate with their intended destinations (e.g. a

terminal communicating to a processor) through virtual

connections as if they were directly connected at their

normal or desired speed. This requires that the CIU buffer

information between the device and the network. In

addition, the CIU must be aware of the individual

characteristics of the device (i.e. speed, control

characters, device features and capabilities, etc.).

From the network point of view, the CIU is the

communicating entity and the devices should be transparent

to the network. This requires the CIU to participate in the

network protocols. This encompasses the electrical

interface, the type of signalling (baseband or RF)

introducing and extracting information from the cable,

recognizing its own address, formatting information,

deciding when to transmit, and possibly providing error

detection and retransmission.

Details of the individual bus LAN offerings must be

reviewed as they become available. From these details it

will be necessary to determine the impact on NAVSEA's

installation. The following information will aid in these

determinations.

1. "personalization” — devices that are to be

connected to the network require that their

individual communications characteristics be

accounted for. This function should be handled by

the CIU. The process by which this is accomplished

(i.e. who can do it, how is it done, etc.) and the

limitations involved (i.e. which parameters can be

changed, which can't, which are not considered, how

often can parameters be changed, when may these

parameters be set or changed, is special equipment

necessary, etc. ) are important to know, since they

may be costly.
Page 28

2. protocols — protocols are handled by the CIU (i.e.

signalling, sensing, data transmission, error

detection, minimal virtual terminal protocols,

etc.). These are generally sufficient for

terminals. Inter-Processor communications can

emulate terminals, but this is rather inefficient

and inconvenient for many applications. Higher

level protocols (i.e. file transport protocol,

etc.) are better suited for these purposes. Most

of these higher level protocols will be implemented

in software and reside within the various

processors. The interface between these protocols

and the CIU protocols must be considered; this

includes items such as error control, flow control,

etc. If the vendor already offers, or intends to

offer, these higher level protocols, their

capabilities should be investigated (i.e. what can

and can't be done). If the vendor doesn't offer

these higher level protocols, the facilities by

which they may be accomplished by the user should

be investigated.

3. configuration — depending on the particular

vendor's product, many different configurations are

possible. An intelligent choice can impact the

cost of the LAN and the benefits to the

organization. A CIU can handle a number of

terminals. More terminals clustered about a CIU

may result in lower cost per terminal connection.

It is expected that vendors may offer a basic

system along with options. These options should be

investigated as to the benefits that the

organization might derive from them. The selection

between baseband and RF signalling can impact the

additional applications (e.g. video, voice, and

channelization) that may utilize the LAN.

4. Technical Control Center (TCC) — although the

medium is passive and reliable, failures will

occur. A TCC provides the means to locate failures

on the cable. This usually includes a time domain

ref lactometer . The facilities offered or

recommended by the vendor to accomplish this

trouble shooting function should be evaluated.

5. Measurement Control Center (MCC) — monitors the

network operation and provides measurement reports

of the service being delivered to the user and the

utilization of the network. This can help the

organization determine heavy usage and poor

utilization. As a result, expansion or

reallocation of equipment can be initiated to

alleviate these problems. In addition,

malfunctions or other improper operations on the

network may also be determined. The facilities
Page 29

offered by the vendor to accomplish this function

should be investigated.

NAVSEA's primary requirement is to provide flexible

high speed (9600 bps) terminal to processor communications.

A bus LAN provides this. It also provides additional

flexibility and features. Processor to processor

communication will also be possible, since all processors

are connected to the cable. This can be accomplished at no

extra harware cost, since any device connected to the cable

can communicate with any other device on the cable. If the

additional processor to processor traffic is expected to be

heavy, a separate cable (baseband) or channel (RF) may be

considered. A separate cable is feasible since all four

processors are co-located within a central site. Therefore,

the installation effort and amount of cable required are

negligible.

RF signalling provides for many simultenaeous channels

through the technique of frequency division multiplexing

(FDM) . Using RF signalling each device can be assigned

individual frequency channels of different speeds. For

example, each terminal could be assigned its own 9600 bps

frequency channel and the processor to processor

communications could be assigned separate 1 Mbps channels.

This requires frequency scanning and selection capabilities

by the CIU, which could be provided by a frequency agile

modem. Other possible configurations may include designated

frequency channels for OIS applications, voice or video

information, or even a shared carrier sensed multiple access

channel (e.g. MitreBus)

Another additional feature is the possibility to

interface to other networks (e.g. AUTODIN II and other

military networks). This interface requires a gateway. A

gateway is a communications processor which translates the

protocols of one network into another. Gateways generally

handle protocol translation at or below layer 4 in the ISO

model (see section 6.2). Therefore, they do not guarantee

higher protocol layer compatibility. Gateways to other

networks can easily be connected to the LAN. This would

allow access to any of these gateways from any device on the

LAN without additional processor assistance, as would be the

case with the Star implementations.

In summary bus LANs are rapidly becoming commercially

available [3COM 80] . Within the next six months many

product announcements are expected. Currently, little is

known regarding details of these potential offerings. After

the products are announced, detailed information on their

specifications and services will be available. From this it

will be necessary to determine the impact on each customer’s

current or planned installation. The cost per terminal
Page 30

connection, exclusive of the main cable installation is

expected to range from $600 to $4000, depending on

configuration and vendor. The rule-of-thumb is currently

$1000 per terminal connection, not including installation.

This will most likely come down, with LSI implementations

and mass production, by as much as 70%.

6 . 0 SUMMARY

Given NAVSEA's stable expected environment and their

requirement to provide reliable and responsive computing

power to the engineering design areas, NAVSEA should

consider CRT based terminals distributed throughout NAVSEA's

3 adjacent buildings. These terminals must be capable of

displaying vector drawings as well as text, and provide a

convenient user pointing feature. A LAN communication

facility to the central computing complex which can sustain

rates of 9600 bps to each terminal is required to support

these terminals. Options were reviewed in this report to

provide this communications facility.

The first option centered around leasing point-to-point

lines from the telephone company and interfacing to the

computers via rotary switches (only if dial-up and modems

are used) or port contenders. This option suffers the

disadvantages of high cost and inflexibility of the

configuration. Any time an additional terminal is required

a new point-to-point wire has to be installed. If a

modification in terminal location is desired, depending on

the distance involved, this may also require a new wire to

be installed. It is not a trivial problem to maintain and

trouble-shoot this multitude of wire, especially at the

central complex where hundreds of wires are bundled

together. The cost of this option is estimated to exceed

$300K.

The main disadvantage to the first option, leased

lines, is the cost. Leasing by itself results in increased

cost (which accumulatives ) over time. In addition, future

increases in the leasing rates are expected.

Another option is for NAVSEA to run and maintain its

own lines. This second option requires a fixed initial cost

plus whatever costs are incurred over the life of the lines

for maintenance. To further minimize the problems of a large number of individual wires at the central complex and

performance problems on the wires due to speed, distance,

and variations in ground potentials between buildings.
Page 31

concentrators can be used. Wires from each building could

be run to a concentrator located in that building and then a

single high speed line could be run between buildings. This

would somewhat increase the cost of this option, but it

would be partially offset by the decrease in wire

installation and maintenance costs. The maintenance of

these concentrators would be somewhat more complex since

they would not be located at the central complex. The lines

from the concentrators would then interface to the

processing complex through a port contender. The estimated

cost of this option is $100K.

While this second option is the least cost option, it

suffers the same inflexibility as the first option, for

additions and modifications as well as potential expanded

services.

The third option is the bus LAN. This option is

feasible for four primary reasons. The first reason is it

meets all of NAVSEA's requirements mentioned above, both

current and future. The second reason is it has three

potential advantages over the other alternatives. (1) Its

inherent flexibility; devices (including intelligent

workstations) can easily be added or moved, since "tapping”

into the cable is possible anywhere. (2) Its relatively

simple media maintenance; only a single passive cable. (3)

Its potentially large bandwidth that may be channelized;

different priorities and speed ranges may be associated with

different channels. The _ third reason is that NAVSEA is

planning for installation in the 1982 time frame when

availability is expected to be sufficient. The fourth

reason is that any user can communicate directly with a new

server anywhere in the system.

The bus LAN option requires a single coaxial cable be

strung throughout the 3 buildings. Therefore, only a single

cable need be installed and maintained. The current

estimated cost of a NAVSEA implementation is approximately

$140K. The interface equipment is estimated by

rule-of-thumb to cost $1000 per terminal connection; this

may be reduced in the future by as much as 70% if LSI

implementations and mass production are taken advantage of.

The current cost of a NAVSEA inplementation is approximately

$140K. This bus LAN may be either baseband (digital) or

broadband (RF) . The main advantage of baseband is a less

complex interface (i.e. cheaper), while the main advantage

of broadband is a significantly larger overall bandwidth

that may be frequency division multiplexed into a number of

channels. As mentioned earlier in this report a number of

manufacturers are committed to commercially providing LAN

facilities [3COM 80] .
Page 32

7.0 APPENDIX: REVIEW OF BUS LOCAL AREA NETWORKS

This section provides a general review of bus LANs. A

discussion of the concepts involved is presented first.

This is followed by a discussion of the ISO model for

computer networking architecture. This model provides a

general framework for communication protocols. The

remainder of the section discusses two existing bus LANs;

their architecture, environment, and operational experience.

7.1 Concepts Of Bus LANs

Messages to be passed over a bus are usually grouped

into entities called packets, which may vary in length up to

some maximum. If parallel channels are available, such as

in a computer backplane bus, then a bus transaction may

consist of the execution of a protocol to gain control of

the medium during one or more time frames, the passing of a

parallel address during the next time frame, the passing of

parallel data for one or more additional time frames,

followed by release of the bus. This sequence of time units

for passing a packet of similar information holds also for a single channel bus over which information must be passed in

a bit serial fashion.

When extending a bus outside a computer chassis, the

cost of connectors and cableing can be minimized by using a single channel with a high enough bandwidth to support the

resulting serialized data. Coaxial cable can support high

bandwidth communications and provides excellent rejection of

electromagnetic interference. One coaxial cable can provide

a single baseband signalled channel or several RF frequency

division multiplexed channels. This can be accomplished

using off the shelf, inexpensive, and readily available

community antenna television (CATV) cable and components.

Connections can be placed in convenient locations along the

cable to provide passive taps onto the communications

medium. The cable is accessed through the taps by

intelligent node interfaces (variously called bus interface

units or modules, BIUs or BIMs, network interface units,

NIUs, or communications interface units, CIUs) . All

components are passive, in that they do not remove or hinder

the flow of information on the medium during examination or

failure. The CIUs handle all the necessary protocols and

buffering required. In this type of broadcast network all

nodes share the medium and passively listen for information

addressed to them.
Page 33

The type of signalling generally distinguishes two

variations of bus networks, those that use baseband

signalling such as ETHERNET, NBSNET, HYPERCHANNEL, and

Net/One, and those that use radio frequency (RF) modems in

distinct frequency division multiplexed channels such as

MITREbus and the General Motors Assembly Division system.

The frequency division multiplexed systems are sometimes

referred to as cable bus systems (and sometimes using the

misnomer "broadband" systems). Cable bus systems are

attractive because they provide the opportunity to support

many different services (e.g., data, voice, and television

traffic) on the same cable. This configuration may be

optimal where there are both continuous high-bandwidth users

(such as remote batch terminals and computer to computer

transfers) and bursty low speed users (such as interactive

terminals)

A single lowloss coaxial cable is capable of supporting

a bandwidth of 300 MHz [DINESSOa] . The actual transmission

speed is usually limited by the choice of interface

electronics and the degradation of signals on the cable

itself. Typically, existing local area bus network

implementations communicate in the 1 to 10 Mbps range.

HYPERchannel transfers information at 50 Mbps [THORN 80] , but it is intended for high speed computer/shared mass

storage transfers where higher speed is important. The

penalty paid for using this high speed transfer capability

is in the cost of the CIUs which range from $26,000 to

$40,000 each. In comparison, the cost of a microprocessor

controlled CIU for lower speed (1-10 Mbps) communications is

approximately $1000 per terminal or computer port connection

(the range is approximately $500 to $4000). Usually, these

CIUs are capable of handling several terminals or port

connections simultaneously. They are configured as a

cabinet with power supply and slots for a number of terminal

or port interfaces. The actual cost of a given CIU depends

on the power supply, the cabinetry overhead, and the number

of terminals or computer ports connected.

A bus LAN also requires a decentralized control

strategy be implemented by the CIUs. One very simple

control strategy that has been used and shown to work for

bus networks is contention. In a contention net, any node

wishing to transmit simply does so. Since there is no

control or priority, nothing prevents two or more nodes from

attempting to transmit simultaneously, in which case a collision occurs. This results in the messages being

garbled and received with errors, requiring retransmission

at a later time.

Collisions are the primary limitation on the number of

users and the amount of data that can be transmitted over

the channel. The ALOHA system developed at the University

of Hawaii (which uses radio communications rather than a

physical bus, and is not a LAN by our definition) was the
Page 34

first to use this contention control strategy. This

original strategy leads to relatively low channel

utilization. If the CIUs follow certain additional

protocols, significant improvements in channel utilization

result. One rule is listen before talk (LET) in which CIUs

monitor the channel before transmitting. A CIU refrains

from transmitting while any other CIU is transmitting, this

is sometimes called deference. This LET type of

communication network is referred to as carrier sense

multiple access (CSMA) . The action taken by the CIU when

the channel becomes free is referred to as persistence. The

CIU is called non-persistent if it always reschedules the

next transmission attempt for some later time. The CIU is

called p-persistent if it waits for the medium to become

free and immediately attempts to transmit with probability

p; and, with probability (1-p) it reschedules the next

transmission attempt for some later time, rather than

waiting. For example, the CIU's of NESNET have p=l (i.e.

always waits and immediately transmits) , and thus are called

1-persistent.

Another improvement in channel utilization can be

obtained by having the transmitting CIUs monitor the channel

while they are transmitting. If a collision does occur (as

might happen if two or more CIUs were waiting for the

channel to become idle) each of the CIUs must wait or

"backoff" a different period of time (typically random) to

prevent repeated collisions. The average backoff is

typically chosen as an increasing function of the number of

retry attempts, thus providing a collision moderating

mechanism when traffic is heavy. If the CIUs abort the

transmission immediately after detecting a collision, this

strategy is called "listen while talk" or simply collision

detection (CD) . Similar to the situation of two or more

people starting to talk at the same time. With CD,

colliding packets can be very rapidly truncated so as not to

waste an entire packet time on the channel. Carrier sense

multiple access with collision detection (CSMA-CD) was first

used in the experimental Xerox Corporation implementation of

ETHERNET, and is now used in most baseband signalled bus

networks including NESNET, and Net/One. Theoretical

studies, confirmed by measured data on the ETHERNET, show

that the CSMA-CD mechanism provides utilization in excess of

90% of channel capacity.

7.2 ISO Open System Reference Model

The previous section has provided a brief description

of the structure and operation of CSMA bus LANs. The rules

by which any communications system operates are also known
Page 35

as communication protocols. Several layers of communication

protocols have been identified for communication over public

packet mode networks. Standardization efforts are currently

underway for these protocols at NBS [bLANC 80] . The

following are excerpts from desJardins [deSJAR 80] which are

intended to provide an overview of the current framework of

communication protocols. This model was primarily

constructed based on experience with and requirements for

global networks. Questions have been raised as to the

applicability of this model to LANs. Work in this area is

currently being conducted and will investigate the layers

and their associated functions as they apply to LANs [NBSIR

80] . "The International Organization for Standardization

(ISO) in cooperation with other standardization bodies, have

developed and adopted an architectural reference model for

interconnecting "open” systems into distributed application

networks. These are systems which are "open" to

communication and cooperation with other systems by virtue

of their mutual support of standardized procedures. The

Reference Model of Open Systems Interconnection (RM/OSI) is

intended to provide a common basis for the coordination of

standards developments for each of the seven layers (see

figure 3) into which it is divided. It also provides for

the evaluation of existing standards and for improving these

standards to meet the needs of future distributed systems

and applications.

"The RM/OSI is based on the concept of cooperating

application activities called application-processes (AP)

An AP can be one or a cluster of activities performing a defined set of functions according to the set of procedures

established by an industrial engineer or software designer.

In a computerized system, the APs would be hosted within an

environment provided by a computer or computers and their

associated terminals or peripherals. In such an

environment, the procedures of the APs might be implemented

by computer programs.

"The purpose of OSI is to enable an AP hosted on an

"open” system which supports the OSI protocols to

communicate with any other AP located on any other open

system to which the first is interconnected by any means

whatever. As a special case, the two APs may reside in the

same open system, but they would normally have no knowledge

of this fact. It is anticipated that most open systems will

be interconnected by having acccess to the world-wide public

data networks being developed by the International Telegraph

and Telephone Consultative Committee (CCITT) member

countries, either directly or through local area networks.

"Only the portion of the AP which participates in the

open procedures — the "application-entry" as it is known

technically — is considered to be within the scope of the
APPLICATION

PROCESS

Page 36

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Page 37

open system. OSI is not intended to define either the

functions or the implementations of the end-user APs, nor

the implementations of the systems which host the APs and

provide the open interconnection facilities. Rather, OSI is

intended to provide a basis for compatible communication and

cooperation among the APs to accomplish common objectives.

"When two APs in open systems need to communicate, a

logical association called a "session-connection" between

them is first established through intervening communications

networks. The APs may then exchange messages according to

established open systems interconnection protocols.

"The architecture adopted for the RM/OSI is based on

the popular concept of layering. In this approach, a deep

complex structure is partitioned into a number of

independent functional layers.

"Each layer performs one well defined set of functions,

using only a well defined set of services provided by the

layer below. These functions implement a set of services

that can be accessed only from the layer above.

Communication among the functional entities which make up

the layer is achieved by agreed protocols of the layer

operating across connections provided as a service by the

next lower layer.

"A decision which must be made prior to implementation

of a computer network is concerned with the physical

distribution of networking functions amongst various

hardware components. To some extent this distribution will

be constrained by the existing complement of hardware which

is to be networked. There are, however, several degrees of

freedom available to the network designer. The following

paragraphs discuss each of the layers within the ISO model.

Application Layer (Layer 7) carries out the application

oriented aspects of interprocess communication between

APs in conjunction with the management functions which

support APs. Application protcols include management

protocols such as application rollback/recovery and

remote job entry, and user protocols such as

mail/message and order entry. To execute these

protocols, application-entities must accomplish the

exchange of meaningful information; this service is

provided by the Presentation Layer.

Presentation Layer (Layer 6) manages the entry,

exchange, display and control of structured data being

communicated bewteen application-entities. Each

presentation-entity provides a local "presentationimage" of the exchange data structure as a service to

its application-entity. Presentation protocols such as
Page 38

virtual terminal and virtual file accomplish the

negotiation, management and exchange of parameters and

data needed to ensure a consistent distributed data

structure. To execute the presentation-protocols,

presentation-entities need to communicate between

themselves; the service of facilitating this

communication is provided by the Session Layer.

Session Layer (Layer 5) provides services to establish

and maintain a "session-connection” or cooperative

communication channel between two presentation-entities,

and to control their orderly data exchange interactions

(e.g., control of turn to send). To implement the

transfer of data, the session-connection is mapped onto

and uses a transport-connection.

Transport Layer (Layer 4) provides reliable, costeffective transfer of control information and user data

between two session-entities. This includes

cost-effective service selection, service quality

monitoring and notification, multiplexing, and flow and

error control. To accomplish the data transfer,

transport-entities need to be able to move blocks of

data from a source open system, across an entry network,

several intermediate networks and an exit network, to a

destination open system. This network data transfer

must be provided at a known cost and quality of service,

so that the transport entities can select from

alternative avaliable network-connections those which

enable the transport-entities to meet the

session-entities quality of service requirements at

least total cost.

Network Layer (Layer 3) provides network-connections at

known cost and quality of service between any two open

systems. This includes intranetwork routing and

switching protocols for all open data communication

networks, as well as internetworking protocols which are

executed at gateways between networks. The

"connections" may be implemented in a connection

oriented network such as a CCITT X.25 or X.21 network,

or may be "sublayered" on top of a "datagram" oriented

network such as an Ethernet- type network, Alteratively,

the connection oriented part of the Network Layer

service — e.g., sequentiality of message delivery,

abbreviated addressing, low delay — may be implemented

or optional in some network-entities in order to provide

a lower quality of service at an attractive lower cost.

Data Link Layer (Layer 2) provides for reliable exchange

of a logical sequence of data blocks between equipments
Page 39

connected by a single physical link. This includes

protocols to address different logical link terminals on

the same physical link, to identify sequences of data

blocks, to detect and respond to errors, and to control

the flow of data across the link.

Physical Layer (Layer 1) provides for the physical,

mechanical, functional and procedural characteristics

required to activate, maintain and deactivate the

physical circuits between different equipment.

"Message exchanges between application-processes in

different open systems normally communicate through all

seven layers of the architecture (Figure 3) . However, some

systems will provide complete geographic "transparency" of

OSI by providing OSI facilities within the system

environment such that only the Transport Layer knows whether

the partners are located in the same system or in different

systems. And of course, two APs located in the same system

may operate entirely outside of OSI protocols. Other uses

of the architecture can be readily imagined, such as using

OSI higher layer protocols to communicate between APs in a

"closed" local network environment, or using "closed"

application-protocols across an otherwise open systems

interconnection environment."

7 . 3 ETHERNET

Ethernet is a bus LAN with distributed control based on

carrier-sense multiple-access with collision detection

(CSMA/CD) . First described in [METCA76] , this architecture

has been the subject of considerable analysis and has

inspired numerous variations. The prototype Ethernet system

developed at the Xerox Palo Alto Research Center provides a data transfer rate of 2.94 Mbps. It connects up to 255

computers, and spans a linear distance of 1 kilometer. A

piece of 75-ohm coaxial cable with terminators on each end

constitutes the bus. Transceivers are located next to the

cable and are attached to it by pressure taps. The

transceiver provides ground isolation and a high- impedance

connection to the cable for transmitting and receiving.

Twisted pair cable brings signals and power to the

transceiver from a controller in the computer.

The nodes consist mainly

other personal computers

illustration, document

communication, etc. These

sometimes with over 100 Altos

of "Alto" minicomputers and

capable of text editing,

preparation, interpersonal

machines appear in clusters,

in one campus (building or
Page 40

group of adjoining buildings). Each campus is supported by

various specialized servers providing remote access to

shared resources such as large file systems, magnetic tapes,

and high-quality printers. The campuses are interconnected

by communication facilities consisting mostly of leased

telephone circuits, but also including other networks such

as the ARPANET and the ARPA Packet Radio network. The

overall internetwork architecture in which the Ethernet

system operates is called "Pup" [BOGGS 80] . The lowest level of internet protocol is a simple

end-to-end datagram — a standardized packet (called a "Pup") which is media independent but otherwise retains the

common properties of the underlying packet networks. The

communications network and interfaces are assumed to make a "best effort" to deliver a packet from a source process at

one node to a destination process at another, possibly using

the Pup internet transport mechanism en route. Packets may

be lost, duplicated, or delivered out of order, after a

great delay, and with hidden damage. For performance

reasons the underlying networks are designed to make such

events uncommon. In the Pup/Ethernet concept it is the

responsibility of the communicating processes to provide the

level of reliability they require through suitable

end-to-end protocols. The Ethernet CIU for the Alto

computer is implemented partially in hardware, partially in

microcode, and partially in software. The hardware contains

a small (16 word) buffer, parallel-serial and

serial-parallel converters, CRC generator and checker, and

Manchester phase encoder and decoder. The microcode

performs address recognition, schedules retransmissions when

collisions occur, and provides the interface seen by the

software. The software is responsible for basic packet

formatting. Pup encapsulation and decapsulation, and

interfacing to the network-independent software. This

software distributes and collects Pups (internetwork

datagrams) to and from the communicating processes.

The prototype Ethernet system has served for several

years as the dominant local network in a nationwide Pup

internet used regularly within a number of Xerox research

and development communities. The internet presently

consists of about 25 Ethernet systems interconnected by 20

or so gateways and various long-haul transmission

facilities. Over 1000 hosts (mostly Altos and other

personal minicomputers) are connected to these networks.

Extensive measurements have been performed on one

operational Ethernet system to which approximately 120

computers are connected. These machines include personal

computers, servers, time-sharing systems, and gateways to

other parts of the Pup internet. Users of these machines

use the network regularly for file transfer, electronic

mail, bootstrap or downline loading, software distribution,

and many other purposes. In a typical 24-hour period, 2.2
Page 41

million packets are carried in this network, totalling

approximately 300 million bytes. For a 3-megabit per second

channel, this amounts to only 0.9 percent utilization of the

available bandwidth. But the utilization has high variance,

and observed utilization has been as high as 3.6 percent for

one hour, 17 percent for one minute, and 37 percent for one

second. On the average, only 0.79 percent of all packets

are delayed due to deference, and less than 0.03 percent are

involved in collisions [SHOCH79] . The analytical model of

CSMA/CD performance under heavy load and overload

conditions, first presented in [METCA76] has now been

verified experimentally. The network remains stable, its

capacity is shared fairly among the contending hosts, and

efficiency exceeds 97 per cent when traffic consists of

relatively large packets (about 4000 bits).

Failures of an entire Ethernet system have been quite

rare. For example, the 120 host network on which

measurements have been taken has suffered outages only a few

times per year, and only for a few minutes at a time while

the problem was located and corrected. Failures affecting

individual hosts or those that increase the packet error

rate have been more frequent. The usual causes of

catastrophic failure were incorrectly installed cable taps,

shorted or malfunctioning transceivers, and broken CIUs that

transmitted data indefinitely. The most serious failure

occurred when lightning struck near a pair of buildings that

had an Ethernet ca-ble strung underground between them. The

input transistors in a dozen or so transceivers became

fused. Finding all the shorted transceivers took several

hours. Partitioning the network made it apparent that there

were problems in all sections. A time domain reflactometer

was helpful in locating the damaged transceivers among the

100 or so units connected to that network. Damage such as

this has been attributed to a difference in ground potential

between the two buildings. An improved design for

preventing such problems has been proposed that includes

insulated tap blocks and connector housings as well as

current-limiting resistors in the transceiver input

circuits. Various other performance degrading malfunctions

have been identified and techniques for eliminating or at

least restricting their effects have also been proposed, and

some have even been implemented.

7 . 4 NBSNET

NBSNET is a bus LAN designed and built at the National

Bureau of Standards. It is a variant derivative of ETHERNET

in that it employs a carrier sense multiple access,

collision detection (CSMA-CD) protocol with a one megabit

per second data rate and Manchester encoding on the coaxial
Page 42

distribution cable. It has been in routine use since

October 1979 and now serves about 70 user devices in eight

different buildings. The current user devices are primarily

graphic and alphanumeric terminals, with a smaller number of

mini and microcomputers connected. Both terminal access and

file transfer protocols have been implemented. Most nodes

keep traffic and error statistics during each connection and

report the information to a central logging node when the

connection terminates.

This network is intended to serve more than a thousand

user devices at the NBS Gaithersburg, Maryland, and Boulder,

Colorado, sites. The Gaithersburg system is operational and

installation is proceeding at Boulder. The network user

devices are dispersed among a number of buildings at the NBS

Gaithersburg, Maryland, site. The network topology

(although that of a bus) has a tree structure, with a main

coaxial cable (actually in two segments) connecting all

buildings. Each individual building is served internally by

local cables connected to the main cable through a repeater.

The repeater, used between network segments, is an active

device that performs the functions of amplification and bit

regeneration, delaying the signal by one bit period. It

also contains circuitry to detect and enforce collisions on

both segments to which it is attached and contains failure

isolation circuitry to truncate transmissions greater than a maximum of two milliseconds.

NBSNET was designed to provide the following set of

required network services:

1. Full connectivity between user devices such as

terminals, microcomputers, minicomputers, and large

host computers;

2. Ability to screen each node from most

characteristics of the distant device with which it

is communicating;

3. Speed conversion over the range of at least 110 to

9600 bps;

4. Flow control to/from user must be either in-band or

out-of-band, to suit the user equipment with no

restriction on the method used at the distant user

device.

5. Ability to address over 1000 different user nodes

(however, practical electrical and protocol

considerations limit the network to a few hundred

simultaneously active devices);
Page 43

6. Cover a site 1.5 km long with 20 buildings;

7. Data encryption should be available as an option;

8. Most node failures should not affect the

communication of other nodes.

The building block of the network is a

microprocessor-based CIU called a Terminal Interface

Equipment (TIE) . The TIE connects the user device to the

coaxial distribution cable. The TIE is partitioned into

three active portions:

1. a user board (UB) that contains an MCS6512

microprocessor and all the memory serving a single

user;

2. a network board (NB) containing the serial/parallel

converters, the direct memory access controllers

for the UB buffer memory, and the sequencer to

contend for and transmit a packet onto the network

using a CSMA-CD protocol; and

3. a TAP, which contains the line driver and receiver

for the coaxial bus cable, the collision detector,

and a f ailure-disconnect system to automatically

remove "run-away" TIES from the network.

A single NB/TAP combination can support eight UBs in

the same card cage. The NB and UB circuit cards are

approximately 24 cm on a side, and each cost approximately

$400. The card cage costs about $500, the main power supply

about $400, and the TAP about $140, Each UB contains 2K to

8K of read only memory which holds all the software needed

to personalize the UB to the user device as well as to

implement the network protocol. All signals to and from the

TAP (located at the site of connection to the main bus

cable) are optically isolated at the NB, and this section of

the NB and the TAP are powered by a floating power supply.

The signal leads between the NB and TAP are coaxial cables.

The same TIE hardware design is used for both terminal and

computer connections. Only the software in the TIE is

changed to suit user characteristics. Operator commands can

be used to vary almost all of the personality

characteristics and to override others.

The cost of bringing the network to a user is composed

of six components, the distribution cable (and repeaters)

and its installation, the user's TIE and its installation,

and the cable from the TIE to the user and the cable
Page 44

installation. The interbuilding distribution cables were

installed throughout the NBS Gaithersburg site as a single

project, which represented about one-tenth of the

development cost. Cabinets were installed to contain the

repeater amplifiers to serve each building. The repeaters

are installed as required by service requests. In most

cases the TIE cabinets are installed in closets off the

corridors, and a TIE to TAP cable is run to the nearest

shared bus cable. A TIE to user cable is then run over the

corridor false ceiling and through the walls into the user's

room. The RS-232 connector for the user terminal/connection

is mounted on a cover plate similar to that used for

electrical outlet box covers. The per-user cable and

installation costs average $422 for present users with a

range of $300 to $1750. The average TIE hardware cost is

$670 per user, with four users per cabinet. This excludes

main bus cable and repeater cabinet installation costs as

well as all design and development costs.

Now that the network is successfully operational a

measurement and control center is being built to measure

network performance, identify marginal conditions, and

assist in planning for enhancements. Performance data

similar to that published for Ethernet will soon be

available.

In eight months of operation there was only one

complete failure of the network in which users system wide

could not communicate successfully. This lasted for 1.5

hours, and before the exact source of failure could be

located the problem corrected itself. Lightning caused one

partial network failure in an outlying cable segment because

of induced failure of a repeater line driver. This failure

was repaired within a few hours, and the remainder of the

system remained operational. Single TIE failures account

for the vast majority of failures, and these were

principally due to defective power supplies.

The TIE provides desirable network services. For

example, "dumb" terminals can communicate with each other

directly over the network without concern for bit rate

incompatibility, provided that flow control signals are

recognized by the sending terminal or manual typing speeds

are used. The terminal user is given control over many

parameters implemented in the node software so that they can

be instantly modified to suit various terminals. A "rotary”

is simulated in user board software so that multiple ports

of a server computer can be automatically searched when a connection is being attempted.
Page 45

8 . 0 GLOSSARY

Packet;

Datagram;

Gateway;

Host:

OF TERMS

A packet of information is a finite sequence

of bits divided into a control header part and

a data part. The header contains enough

information for the packet to be routed to its

destination. There are usually some checks on

each such packet, so that any switch (or

interface) through which the packet passes may

exercise error control. Packets are generally

associated with internal packet-network

operation and are not necessarily visible to

host computers attached to the network.

[iso 78] A group of binary digits, including

data and call control signals, switched as a

composite whole. The data, all control

signals, and possible error control

information, are arranged in a specific

format.

A finite length packet of data together with

destination host address information (and,

usually, source address) which can be

exchanged in its entirety between hosts,

independent of all other datagrams sent

through a packet switched network. Typically

the maximum length of a datagram lies between

1000 and 8000 bits.

[nbS 77] A user facility in a packet network

in which individual packets are accepted by

the network from source terminals and are

delivered independently to the destination

identified in its address field. The order of

delivery bears no fixed relationship to the

order of entry into the network.

The collection of hardware and software

required to effect the interconnection of two

or more data networks, enabling the passage of

user data from one to another.

The collection of hardware and software which

utilizes the basic packet-switching service to

support end-to-end interprocess communication

and user services.

[mcNA 77] A computer attached to a network

providing primarily services such as

computation, data base access, or special

programs, or programming languages.
Page 46

Protocol: A set of communication conventions, including

formats and procedures which allow two or more

end points to communicate. The end points may

be packet switches, hosts, terminals, people,

file systems, etc.

[nbS 80] a defined procedure or set of rules

for interactive behavior in a communications

environment.

Protocol Translator; A collection of software, and possible

hardware, required to convert the high level

protocols used in one network to those used in

another

.

Terminal: A collection of hardware and possibly software

which may be as simple as a character-mode

teletype or as complex as a full scale

computer system. As terminals increase in

capability, the distinction between "host" and

"terminal" may become a matter of nomenclature

without technical substance.

[ansi li] A point in a system or communication

network at which data can either enter or

leave.

Virtual Circuit; A logical channel between source and

destination packet switches in a packet-switched network. A virtual circuit

requires some form of "setup" which may or may

not be visible to the subscriber. Packets

sent on a virtual circuit are delivered in the

order sent, but with varying delay.
Paqe 47

9.0 BIBLIOGRAPHY

[ander 79] Anderson, R.J., "Local data networks

traditional concepts and methods," Proceedings

of the Local Area Communications Network

Symposium, Boston, MA, May 1979, pp. 127-148.

[ANSI 77] American National Standards Committee, "American

Dictionary for Information Processing", Computer

and Business Equipment Manufacturers

Association, Wash., D.C., 1977.

[BLANC 74] Blanc, R. P., Review of Computer Networking

Technology, NBS Technical Note 804, U.S.

Department of Commerce National Bureau of

Standards, January 1974.

[BLANC 80] Blanc, R. P. and Heafner, J. F. "The NBS

Program on Computer Network Protocol Standards,"

Proceedings of the Fifth ICCC, Oct. 1980, pp.

423-428.

[board 80] Board, William J., "Ma Bell Eyes New Markets",

Science, Parts 1 and 2, Vol. 209, Aug. 8 and

15, 1980, pp. 663-668 and 787-790.

[BOGGS 8 O] Boggs, David R. , Shoch, John F, , Taft, Edward

A. , Metcalfe, Robert M. , "Pup: An Internetwork

Architecture", IEEE Transactions on

Communicatons , Vol. Com-28, no. 4, Apr. 1980.

[CARPE 79] Carpenter, R. J., and J. Sokol Jr., "Serving

users with a local area network," Proceedings of

the Local Area Communications Network Symposium,

Boston, MA, May 1979, pp. 75-85.

[CERF 78] Cerf, V. G. AND P. T. Kerstein, "Issues in

packet-network interconnection," Proceedings of

the IEEE, vol. 66, no. 11, Nov. 1978,

pp. 1386-1408.

[CCITT 77] CCITT Recommendation X.25, "Interface between

data terminal equipment (DTE) and data circuit

terminating equipment (DCE) for terminals

operating in the packet switching mode public

packet switching networks," Geneva, 1977.

[CHLAM 8 O] Chlamtac, I., W. R. Franta, P. C. Patton, W.

Wells, "Performance issues in back-end storage

networks," IEEE Computer, vol. 13, no. 2, Feb.

1980, pp. 18-31.
Page 48

[CLARK 78] Clark, D.D., K.T. Pogran, and D.P. Reed, "An

introduction to local area networks,"

Proceedings of the IEEE, vol. 66, no. 11, Nov,

1978, pp. 1497-1516.

[COMP 80 a] Computer Design, Oct 1980, p. 195.

[comp 80 b] ComputerWorld, 28 July 1980, pp. 14-15.

[COMP 80 c] ComputerWorld, "Port Selector Solves Heavy

Traffic Problem for Contract House", 6 Oct 1980,

p. 21.

[COTTO 79] Cotton, I.W., "Technologies for local area

computer networks," in Proceedings of the Local

Area Communications Network Symposium, Boston,

MA, May 1979, pp. 25-44.

[DESJAR 80] desJardins, Richard "Overview and Status of the

ISO/ANSI Reference Model of Open Systems

Interconnection", Proc, of Fall CompCon 1980:

distributed processing. Wash., D.C., Sept.

1980, pp 553-557.

[dine 80a] Dineson, M. A. and J. J. Picazo, "Broadband

technology magnifies local networking

capability," Data Communications, Feb. 1980,

pp. 61-79.

[dine 80b] Dineson, M. A. , "Broadband coaxial local area

networks — part 1: concepts and comparisons,"

Computer Design, June 1980, pp. 12-21.

[dine 80c] Dineson, M. A. , "Broadband coaxial local area

networks — part 2: hardware," Computer Design,

July 1980, pp. 14-22.

[EVANS 80] Evans, R. L. , "Optimizing Computer Access in

Multi-User Systems", Mini-Micro Systems, May

1980, pp. 145-148.

[gREIT 80] Greitzer, John, "Ethernet a No-Match For IEEE

Committee", Computer Business News, Vol. 3, no.

25, June 23, 1980, pp. 1 and 6.

[held 77] Held, G., "Port selectors: trading off the

queues for lower network costs," Data

Communications, June 1977, pp. 59-63.

[held 80] Held, G. , "How much must you pay for a leased

line?" Data Communications, Feb. 1980,

pp. 83-84.
Page 49

[IEEE 78] Special Issue on Packet Communications,

Proceedings of the IEEE, vol. 66, no. 11,

November 1978.

[IEEE 80] Special Issue on Computer Network Architectures

and Protocols, IEEE Trans. on Communications,

vol. COM-28, no. 4, Apr. 1980.

[iso 78] International Organization for Standardization

(ISO) Techical Committee 97, '' Draft Proposal:

Data Communications", ISO, Geneva, Switzerland,

Doc. No. ISO/TC97/SC6 N1699, Section 9, 1978.

[ISO 79] International Organization for Standardization

(ISO) , "Reference Model of Open Systems

Interconnection", ISO/TC97/SC16 N227, Version 4

as of June 1979.

[KASS 80 a] Kass, E. M. , "'Total’ network goal nearer,"

Information Systems News, Aug. 11, 1980, pp. 1

and 28.

[KASS 80 b] Kass, E. M. , "IEEE, Ethernet Harmonize,"

Information Systems News, Aug. 25, 1980.

[lucky 73] Lucky, R.W. , "Common-carrier data

communication," Chapt. 5 in Computer

Communication Networks, N. Abramson and F.F.

Kuo, eds., Prentice Hall, Englewood Cliffs,

N.J., 1973.

[mCNA 77] McNamara, John E., "Technical Aspects of Data

Communication", DEC, Bedford, Mass., 1977.

[METCA 76] Metcalfe, R.M. , and D. R. Boggs, "Ethernet:

Distributed packet switching for local computer

networks," Communications of the ACM, vol. 19,

no. 7, July 1976, pp. 395-404.

[nBS 77] U.S. Dept. of Commerce, National Bureau of

Standards, "Computer Network Interconnecton;

Problems and Prospects", NBS SP-500-6, 1977.

[nbS 80] NBS interview (between LAN group and Promised,

Judith L.), NBS, 25 Mar 1980. NBS SP-500-6,

1977.

[nBSIR 80] NBS Report, "The NBS Computer Networking

Program", NBSIR 80-2154, NBS, Wash., D.C.

20234, Oct. 1980.
Page 50

[neSEN 76]

[SALTZ 79]

[SHOCH 79]

[SCHUL 8 O]

[thorn 80]

[VONAR 80]

[WILLA 80]

[3COM 80]

Nesenbergs, M. , and R. F. Linfield,

"Parametric cost alternatives for local digital

distribution systems". Office of

Telecommunications Report 76-95, U. S.

Department of Commerce, July 1976.

Saltzer, J. H. , and K. T. Pogran, "A

star-shaped ring network with high

maintainability," Proceedings of the Local Area

Communications Network Symposium, Boston, MA,

May 1979, pp. 179-190.

Shoch, J. F., and J. A. Hupp, "Performance of

an Ethernet local network: A preliminary

report," Proceedings of the Local Area

Communications Network Symposium, Boston, MA,

May 1979, pp. 113-125.

Schultz, B., "Exxon 'Supercontroller' weds data,

voice at up to 56K bit/sec over standard lines,"

Computerworld, May 12, 1980.

Thornton, J. E. , "Back-end network approaches,"

IEEE Computer, vol. 13, no. 2, Feb. 1980, pp.

10-17.

Vonarx, M. , "Controlling the mushrooming

communications net," Data Communications, June

1980, pp. 97-100. (Intell. Patch Panel)

Willard, D. G. , and P. E. Wagner, "RF Modem

design for broadband coaxial local area

networks," Computer Design, Aug. 1980, pp.

14-22.

3COM Corp. , "The 3COM Local Computer Network

Vendor List", 3COM corp., 3000 Sand Hill Rd.

1, Menlo Park, CA. 94025, 1980.
NBS*n4A (REV. 2-ac) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEETfSeein struct! on s)

1. PUBLICATION OR

REPORT NO.

NBSIR -80-2187

2. Performing Organ. Report No, 3. Publication Date

4. TITLE AND SUBTITLE

Local Area Network Feasibility Study for

the Naval Sea Systems Command

5. AUTHOR(S)

Alan Mink and Charles B. Silio, Jr.

6. PERFORMING ORGANIZATION (If joint or other than MBS, see instructions)

national bureau of standards

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State.

7. Contract/Grant No.

8. Type of Report 8t Period Covered

ZIP)

10. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a si gnificant

bl bliography or literature survey, mention it here)

The Naval Sea Systems Command (NAVSEA) has tasked the Institute for

Computer Sciences and Technology (ICST) of the National Bureau of Standards

(NBS) to perform a feasibility study of a Local Area Networking (LAN) capability to enhance NAVSEA' s computing facilities. This report documents that

feasibility study. In this report, NAVSEA' s environment will first be es- tablished. This includes the physical and the computing environment. After

establishing the environment, a representative set of application programs

will be used to determine NAVSEA' s LAN requirements . Then a discussion of

LAN topologies is presented, and those applicable to NAVSEA are indicated.

Implementations of these applicable topologies are discussed along with the

technologies involved and their advantages and disadvantages.

12. KEY WORDS (Six to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Carrier sense multiple access; environmental analysis; feasibility study;

local area networks; requirements analysis.

13. AVAILABILITY 14. NO. OF

PRINTED PAGES

DX I Unlimited 52

1

1 For Official Distribution, Do Not Release to NTIS

1 1 Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402. 15. Price

Order From National Technical Information Service (NTIS), Springfield, VA. 22161 $8.00

USCOMM-DC 6043-P80
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