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CONTINUED DEVELOPMENT AND IMPLEMENTATIONOF THE PROTOCOLS FOR THE

DIGITAL ENGINEERING LABORATORY NETWORK

THESIS

AFIT/GE/EE/82D-37 Craig H. HazeltonCapt USAF

DTICELECTE

FEB 2 51983

6 DEPARTMENT OF THE AIR FORCE DAIR UNIVERSITY (ATC)

. AIR FORCE INSTITUTE OF TECHNOLOGY

Wright- Patterson Air Force Base, Ohio

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CONTINUED DEVELOPMENT AND IMPLEMENTATIONOF THE PROTOCOLS FOR THE


THESIS

AFIT/GE/EE/82D-37 Craig H. HazeltonCapt USAF

A-.s

Approved for public release; distribution unlimited.

4. -

AFIT/GE/EE/82D-37

CONTINUED DEVELOPMENT AND IMPLEMENTATION

OF THE PROTOCOLS FOR THE


THESIS

Presented to the Faculty of the School of Engineering

of the Air Force Institute of Technology

Air University

in Partial Fulfillment of the

Requirements for the Degree of

Master of Science

by

Craig H. Hazelton, B.S.

Capt USAF

Graduate Electrical Enginegring

December 1982

Approved for public release; distribution unlimited.

- - Preface

This report presents further design and implementation

of the Air Force Institute of Technology's Digital

Engineering Laboratory Network (DELNET) operating system

protocols. It is hoped that the protocol designs, of this

thesis effort, will provide a firm base on which future and

continued research can depend.

I would like to take this opportunity to express my

sincere appreciation to Dr. Gary Lamont, my thesis advisor,

for his guidance and patience during this effort. Dr.

Lamont's philosophy of the thesis effort focusing on the

aspects of learning and quality rather than mere quantity

has made this thesis effort a truly rewarding experience. I

q- would also like to thank Capt. Geno Cuomo whose concurrent

thesis efforts provided me with assistance and insight into

the hardware aspects of this project. I would like to thank

the personnel of the DEL, especially Capt. Lee Baker and

Mr. Dan Zambon, for their assistance and enthusiasm in all

matters relating to this project. I would like to extend my

appreciation and best wishes to my fellow students whose

support and humor have made this project an enjoyable

experience.

Foremost, I would like to dedicate this thesis to my

wife, Karen. She has provided me with love and support for

over fourteen years. For this, I will be eternally

- grateful.

Page

Preface . . . . . . . . . . . . . . .. . .. . . . . ii

List of Figures . . . . . . . . . . . ... . v

List of Tables . . . . . . . . . . . . . . . . . . .. vi

Abstract .. . . . . . . . . . . vii

I. Introduction . . . . .1 . .. . . - 1

Historical Perspective .. . . . . . . . . . . 1- 2Background . . . . . . . . . . . . a 0 . . * . 1- 4Problem and Scope . . . . . . . .. . 1- 6Approach/Objectives . ............. 1- 6Overview of the Thesis . . . . .. . . . . . . 1-11

II. Functional Requirements and Standards ...... 2- 1

Introduction ............ ... 2- 1Global Requirements . . . . . . . . . . . . . . 2- 1Fibility .... ee2

Virtual Operation ........... 2- 2Performance Monitoring . . . . . . . . . . . 2- 3

Global Standards . .... . . . . . 2- 3Physical Layer. .. . ..... .... 2- 6Data Link Layer .............. 2- 6Network Layer ............... 2- 6Transport Layer . . . . . . . * . 6 . . * . 2- 6Session Layer . . . . . . . . . . . . . o . 2- 7Presentation Layer ............ . 2-7Application Layer . . . ........ . 2- 7

System Requirements. .......... 2- 7Packet Switching Protocol o . . . . . . . . 2- 8Routing Techniques . . . . o . . . . . . . . 2- 8

System Standards . , *....... , .. ..... ..... 2- 9Detailed Requirements . . . . . . . . . . . * * 2-10

Network Operating System . . . . . o . . . . 2-10Detailed Standards v * .*. . .. . . . . . . . 2-13

Physical Layer . . .... ......... 2-134 Data Link Layer . . .. * e v o * . . 2-15

Network Layer . . ............. 2-15Summary . . . . . . . . . . . . . . . . . . .. 2-18

Nb iii

Page

III. The Physical Layer 3- 1

Introduction .... 3- 1Theoryctn . . . . . . . . . . . . . . . . . 3- 1

Twisted Wire Pair . . . . . . ....... 3- 2Coaxial-Cable ............... 3- 3Fiber Optics . . . . . . . . . . . . . . . . 3- 3

DELNET Implementation . . ........... 3- 5Summary . . . o . . 3- 6

IV. Data Link Layer . . . 4- 1

Introduction ................. 4- 1Design Considerations 9 . .. . . 4- 1DELNET Design and Implementation ....... 4- 4Summary . . . . . . . . . . . . . . . . . . . . 4-16

V. The Network Layer . . . . . .. .. ....... 5- 1

Introduction ............. 5- 1Design Considerations. . . . . ........ 5- 1DELNET Design and Implementation . . . . ... 5- 3Summary . . . . . . . . . . . . . . . . . . 5-13

VI Software Configuration and Validation ...... 6- 1

Introduction .... 6- 1Test Environment and Software Configuration . . 6- 1DELNET Software Configuration . . . . ..... 6- 3Software Test and Validation . . . . . . . . . 6- 9Summary . . . . . . . . . . . * * 6-15

VII. Conclusions and Recommendations . o . . . . . . . 7- 1

Conclusions . . . . . . . . . . . . . . . . . 7- 1Recommendations ................ 7- 4

Bibliography . . . . . Bib- I

Appendix A: Data Dictionary . . . . . . . . . . . . . A- 1

Appendix B: Data Dictionary Cross Reference . . . . . . B- 1

Appendix C: Software Listings . . . . . . . . . . .. C- 1

Section I - Local Operating System ..... C- 2Section II - Network Operating System ..... C-50Section III- Shared Compnents . . . . . . . . C-87

Vita . . . . . . V-i

iv

LFigures

Figure Page

1 Initial DELNET Configuration . . . . . . . . . . . . 1-10

2 ISO Protocol Model with UNID . . . . . . . . . . . . 2- 5

3 Protocol Hierarchy at the Systems Level . . . . . . 2-11

4 Link Access Procedure Frame Format . . . . . . . . . 2-16

5 Hierarchy of DELNET Standards . . . . . . . . . . . 2-17

6 DELNET Frame Format Scheme . . . . . . . . . . . . . 4- 6

7 Main Driver for Network Operating System . . . . . . 4- 9

8 RouteIn Procedure for Network Opertirig System . . . 4-10

9 Routeout Procedure for Network Operating System . . 4-11

10 Subordinate Procedures for Network Operating System. 4-12

11 Network Layer's View of Data Packet . . . . . . . . 5- 5

12 Local and Network Operating Systems' Table Buffers . 5- 6

13 Main Driver for Local Operating System ....... 5- 8

14 RouteIn Procedure for Local Operating System . . . 5- 9

15 Routeout Procedure for Local Operating System . . . 5-10

16 Subordinate Procedures for Local Operating System . 5-11

17 UNID Memory and Processor Configuration . . . . . . 6- 4

U| V

L±LL ps

Table Page

2 Hierarchy of DELNET Requirements . . . . . . . . . . 2-14

1 Software Modules Implementing DELNET Operating System 6- 6

vi

"° Abstract

Development of the Air Force Institute of Technology's

Digital Engineering Laboratory Network (DELNET) was

continued with the design and implementation of the first

three layers of the DELNET's Operating System protocol

structure. This effort centered on the actual software

module development and their relationships to established

standards for local area network protocol structures. The

overall system organization and protocol structure followed

the recommendations of the International Standards

Organization's (ISO) Reference Model for Open Systems

Interconnections. Within these guidelines, the Data Link

Layer was developed utilizing a selected subset of the Link

Access Procedure Protocol (LAP) adapted by the Consultive

Committee for International Telephone and Telegraph

(CCITT). The third protocol layer was developed utilizing

an appropriate subset of the X.25 Packet Switching Protocol

standards which were also adapted by of the CCITT. This

study formulates the specific requirements, designs, and

implementations of these protocol layers and presents

recommendations for future research and development.

vi

6| vii

-.- w - . - . ..

\I INTRODUCTION

The purpose of this thesis investigation is to continue

the design and implementation of the software necessary to

perform intercommunications between host-to-host computer

devices and host-to-node computer devices for the Air Force

Institute of Technology's (AFIT) Digital Engineering

Laboratory Network (DELNET). AFIT's DELNET is a proposed

local computer network (LCN) whidh will interconnect a

series of independent stand alone minicomputers and

microcomputers confined within a local area of the Digital

Engineering Laboratory (DEL). The DELNET in'turn will

eventually connect to the AFIT Local Area Network (ALAN).

Much of the research for this thesis effort is sponsored by

the Rome Air Development Center (RADC) located at Griffis

AFB, NY. under AFIT's post doctorial reseach program.

A tremendous concentration of research has been spawned

by industry to place computers and their peripheral devices

into LCNs (Ref 11) . The driving force for this intense

research is two fold. First is the tremendous power gained

by combining several processors to accomplish a single task

or multiplicity of tasks. And the second is the tremendous

savings involved in sharing both software and hardware

resources by reducing duplication of effort. The initial

dominant influences for network design has evolved from

private vendors whose designs were implemented with vendor

unique hardware and software (Ref 19). Fortunately, much of

the software design occured during the same -time period as

4[' 1-1

the general computer software community was transitioning to

modularized design and top down analysis. For this reason,

throughout industry there has been a general acceptance of

structured design levels or rules called 'protocols'. It is

through this philosophy of strictly detined levels of

protocols that this investigation is based.

Since the advent of modern 'computers in the late

1940's, researchers have continually attempted to reduce the

physical size and increase the speed of computers. As these

goals are achieved, computers generally become more

accessible and flexible in their applications. Several

milestones in recent electronic history have made this goal

a reality. The first was the development of the transistor

and solid state electronics. The second was the development

of integrated circuits and their large scale integration

(Ref 6). Additional developments include the advancements

in transmission line technology using broadband techniques

rather than the more conventional baseband (Ref 12).

Computers have become so diversified and relatively

inexpensive that their availability is well within the reach

of practically all institutions and many individuals.

But even with the greatly improved accessability and

reduced size and cost of computers, many limitations still

exist. For example, large main frame computers are required

for a wide variety of applications. These computers remain

large, expensive, and often out of reach of many potential

1-2

users. Additionally, small minicomputers and microcomputers

have limitations such as relatively small memories and slow

computational speeds. Peripheral equipment such as

secondary storage devices are costly and are only used a

fraction of the time when they are connected to dedicated

small computers. Large data bases are not only costly but

must be shared by many users simultaneously in order to be

effective and cost efficient. These are just a few reasons

why networking has become a necessity. By interconnecting

computers into a network, each computer's capability can be

greatly increased and the costs of both hardware and

software can be significantly reduced by sharing valuable

resources.

Often when new technology is developed, additional

forms of technology must be developed to function as a

technological buffer or bridge before the new technology can

be appli' d. The time span from first conception to actual

application may be several years. Fortunately this is not

the case for the development of LCNs. The phenominal

advances in large scale integration which have made the

advent of minicomputers and microcomputers a reality are

also the vehicle which makes it possible to develop the

interfaces for placing these computers into networks. These

network interface units (NIt]) are normally microprocessor

controlled devices with inputs, outputs, and memory; the

same components which compose the computers themselves. In

fact, the NIUs may be thought of as special purpos.

01 -3

computers which are architecturally designed for interfacing

with other computers for the purpose of routing information

into and out of the network.

It became readily apparent to the military that the

distributed processing and resource sharing of the LCNs were

of great importance from both an economical and operational

viewpoint. In 1977 a technical report was produced by the

1842 Electrical Engineering Group at Scott AFBr Ill (Ref

23). This report stated the necessity fo r

compute r/communi cations networks and presented assessments

on the feasibility and economics concerning such a network.

This report included a scenario for a typical military

lw facility communications network which incorporates a

multi-ring topology. The report specified five distinct

types of NIUs to be used as the distributed communication

concentrators. A 1980 AFIT thesis concluded that these five

NIU types could be combined into a single universal WIU (Ref

3) . Later that same year, another AFIT MS student designed

a prototype Universal Network Interface Device (UNID) as his

AFIT MS thesis (Ref 2). In late 1981, an upgraded prototype

UNID was constructed and partially demonstrated as part of

4 another AFIT MS thesis effort (Ref 17) . Although the UNID

was successfully demonstrated in part, it had several

hardware design problems which required upgrading before its

4 full capabilities could be demonstrated. Concurrent with

this thesis effort, a continuation of the upgrade to the

1-4

UNID is being conducted (Ref 4).

As the UNID development progressed, the AFIT DEL became

interested in using the UNID as the DELNET's interface

medium (Ref 11). With its abundance of minicomputers and

microcomputers, the DEL was an ideal environment to test

both the UNID's suitability as a NIU and the feasibility of

interconnecting the DEL's varied population into a LCN.

There were three basic advantages of- placing the DEL into a

network. The first two of resource sharing and distributed

processing were previously discussed. The third reason is

that the DELNET would provide an ideal vehicle for state of

the art research and study by AFIT students and faculty.

As a result of this interest, AFIT sponsored another

thesis project to identify requirements and specify an

initial design for the DELNET. That thesis included in the

performance capabilities: virtual system transparency,

software tool sharing, peripheral device sharing, file

, transfer, potential for additional network interface, and a

distributed data base applications (Ref 11). The thesis

4 included in its hardware specifications: loop network

topology, a two UNID system connected by a fiber optic link

for the network bus, and three host computers (Ref 11).

4d Another AFIT MS thesis effort continued the design of

the DELNET from a software viewpoint (Ref 9). That

investigation determined the overall structure of the DELNET

protocols and partially implemented and successfully

demonstrated several modules of software from .both the local

1-5

-. . .. . - -. .. . , , . ,

and network side of the UNID.

Problem And Scope

This study focused on the areas necessary that would

make the UNID functional at its minimum level. A minimum of

operations should consist of being able to have one host

computer interject a message packet through its UNID and

onto the network. A second UNID should be able to sieze the

packet and properly route it to its appropriate host.

The purpose of this study was to continue the

development of the host-to-host and host-to-node protocols

required for DELNET implementation. It included

continuation of development and implementation of the UNID

operations, the implementation of a local and network

operating systems for the UNID, and a generalized

methodology for the host computer implementation.

ARoroach/Obiectives

The intial approach in solving the problem of network

design consisted of performing an extensive literature

search to gather as much of the available information as

possible. The enormous volumes of information was

indicative of the attention focused on computer and

communication networks in recent years. In addition to this

information, all previous theses from AFIT that pertained to

the DELNET and UNID were studied.

It is the objective of this investigation to build upon

these previous thesis efforts and continue the protocol

Fi i-6

implementation and software development. As in the previous

I research, the main framework for the protocol structures is

a modularized structure using a top down approach. It is

also important to use established documented standards

within this framework. This effort enables follow on

development to continue with a minimum of rework; it enables

modifications and revisions easily and efficiently; and it

reduces the cost of additions.

The philosophy of top down design is sound and although

it is seldom used, it is the accepted standard throughout

industry (Ref 14). However, for actual implementation it

has several drawbacks. For example, if the design begins at

the highest level and sequences downward to smaller

sub-modules, the proper perspective is maintained but the

overall structure cannot be exercised until the bottom most

module is complete. This is especially true if the top

modules must use the lower modules to perform their tasks.

The development of the DELNET's operating system combines

the hierarchial structure of the protocol and structured

programming which comprise the software for developing this

protocol. This development is analogous to the construction

of a high rise building. The design begins from the

architectural view of the entire building and gradually

becomes more specific and narrow in scope until finally the

intricate details are designed. The actual construction of

the building on the other hand, must begin on the ground

level and slowly move toward the larger final product. The

1-7

protocol hierarchy of the DELNET operating system is similar

to that of a high rise building. Each protocol layer is

like a level of the building of which the lower levels must

be climbed before reaching the top. A similar analogy can

be drawn between the hierarchial structure of the protocol

levels and that of the top down design of structured

programming. This comparison is not subtle, however. It is

through the new Systems Engineering philosophy of structured

analysis that both were derived.

While the overall framework and global design of the

DELNET operting system is based on the top down approach,

the actual implementation will be based on a bottom up

approach. The lower levels of protocol are established,

tested, and built upon. In this manner, the basic network

functions can be used until the higher levels can be

developed. Additionally, the lower levels can be used to

help test and verify the upper levels during

implementation. In using this approach two important points

must be continually addressed. The first is that even

though the levels are being implemented from the bottom,

they must conform to the overall framework established in

the top down design. And secondly, each protocol level in

itself is treated as a complete entity and is designed in

the top down fashion. Keeping these facts foremost, the

design of the network began.

It was not feasable to attempt to incorporate all the

minicomputers and microcomputers in the DEL for current

4€ 1-8

thesis efforts. For this reason a small subset was chosen.

The most logical choice was the Zilog MCZ 1/25 microcomputer

which was used as the software development system for the

DELNET. The most attractive aspect of this system is that

it is dedicated to this thesis effort and was available at

any time. The additional choices for implementation

included the DEC LSI-ll, DEC Vax 11/780, and Data General

Eclipse S/250. These latter choices were made because each

uses the Pascal programming language and support a variety

of highly desirable peripheral equipment. The primary

reasons for selecting Pascal as the programming language

were due to its modularized structured design, and its

availability to APIT students both in hardware and detailed

instruction. The proposed initial DELNET configuration is

shown in Figure 1.

The initial plan was to incorporate the MCZ 1/25 and

LSI-11 microcomputers into the network. The MCZ was chosen

because of its availability and dedication to this project.

The LSI-11 was chosen due to the familiarization to the

personnel involved with this project and its availaility

during the time period of this investigation. As the

software for succesive levels of protocol was developed, it

was to be tested and validated. When the system was able to

properly transmit, route, and receive message packets from

one host to the next, the additional computers were to be

incorporated into the network.

1-9

LSI -,.1 VAX ECLIPSE

11/780 S/250

HOST 2 HOST 3HOST 4

LOCAL BUSSES

NETWOR~K BUS

MCZ 1/25

Figure 1. Initial Delnet Configuration

1-10

Ovgriaw l Thesais

The overall structure of this thesis parallels the

developmental structure of the DELNET protocols. Chapter II

presents the overall network structure which discusses the

functional requirements and standards used in the protocol

development. Subsequent chapters present a single level of

protocol and its design and implementation. Chapter VI

describes the software configuration, testing, and

validation of the DELNET operating system. The final

chapter summarizes the report and makes recommendations for

future research and development. The appendices contain

software and supporting documentation for the main portions

of this thesis effort.

u. tional Reguirements And StandArds

Introduction

This chapter introduces the functional requirements

which are applicable to this project and the standards which

govern it. These requirements and standards result from the

initial design of the UNID and DELNET which were addressed

in Chapter I. This chapter is separated into three sections:

global requirements, system requirements, and detailed

requirements.

The global level requirements are those which apply in

general to all phases of the project. System level

requirements are those which have multiple influences

including the global requirements, technical aspects of the

LCNs, and constraints of initial DELNET configuration. The

detailed level requirements are those network functions

which specifically apply to the operation and application of

the DELNET. The standards which govern these requirements

are presented in each section.

Global Reuirements

Global requirements are basically abstractions and deal

with the characteristics of an idealized system. They were

initially defined by a 1980 AFIT Thesis (Ref 11) as the

wDesign-Oriented Functional Requirements". They include

flexibility, virtual operation, and network performance

monitoring.

Flexibilitf. Flexibility is a term which has become

S2-1

increasingly used in recent years whenever discussing new

technology and designs. Because of growing costs,

specifically in the area of new system design and

development, it has become necessary to build in

'flexibility' so that a product can be used for a variety of

tasks with little or no modifications. This philosophy is

sound and has often been proven to save both time and

money. Care must be taken, however, not to over design a

new system or else it may become too universal in nature

(Ref 8). In doing so, the system may not function optimally

in any application and the cost may exceed the combined cost

of individual nonflexible specific designs.

The design of the DELNET protocols must be such as to

accomplish the specific objectives of the DELNET, but

flexible enough to allow for expansion and reconfiguration.

Just because the UNID is the device for interfacing the

hosts into the DELNET, this does not imply that the

protocols for the DELNET will necessarily function on a

universal basis for all applications where the UNID is

used. The flexibility, as it applies to the DELNET,

specifically addresses the ease in which hardware, software,

topologies, and network concepts can be modified. This is

especially true in relation to the continual changes and

upgrading of minicomputers and microcomputers which are

presently being used in the DEL.

.Virtua1 O.De.ati2n. Virtual operation implies that

within the DELNET, one host can communicate with another

4 2-2

host on the same level of protocol. For example, in

transferring files, the user only generates the proper

command and the transfer takes place. The formatting of the

file into packets, tagging the packet with the headers and

trailers, and routing the the packet are all transparent to

the user. These services take place at various levels

throughout the protocol hierarchy. The user simply

communicates at the user interface level. The transparency

or virtual operation is an essential element of an efficient

and effective network. Tradeoffs may be made to develop

workable systems within the scope of this project.

Performance Mjj.riji g. The ability to monitor the

performance of the DELNET would be of great benefit for a

variety of reasons. First, it would provide a means of

testing and verifying proper system performance during its

development. Secondly, it would provide a means of

collecting data on the system for the purpose of real time

evaluations and fault analysis, or more simply to insure

proper operation once the DELNET becomes operational.

Thirdly, future modifications can use the monitor to insure

proper integration into the DELNET.

~1~kAStandards

Many of the specific protocols for the DELNET are not

directly transferable to other networks which use the UNID.

This is because many of the services that the DELNET

4 -operating system provides pertain only to networks with

similar characteristics such as topology, routing schemes,

42-3

- .. •I--.-..------..---------------------.-

and flow control. The general framework for developing

these protocols, however, can be used to develop or modify

the specific protocols for other applications. There are

many global schemes or standards used by industry for

* developing their protocol frameworks for LCNs. Most of

these standards are derived from the Consultive Committee

for International Telephone and Telegraph (CCITT), the

International Standards Organization (ISO) , the American

National Standards Institute (ANSI), the Electronic

Industries Association (EIA), or a proprietary standard

design from a particular vendor (Ref 7).

At the present, most of these standards do not address

the global aspect of protocol design, but rather concentrate

on specific levels of protocol. The ISO has, however,

developed one of the first complete global models for

general LCN applications. It is called the Reference Model

of Open Systems Interconnection (OSI). The ISO is a seven

layer protocol model. Each layer in turn is governed by

additional more specific standards (Ref 33). Figure 2 shows

a pictorial representation of .the ISO model.

In developing this model the ISO considered several

important points. First, each abstraction of communication

should be placed into its own protocol level. Second, this

communication level should perform a specific function.

Third, these functions should minimize flow across the

protocol layer boundry. Fourth, the protocol layer

boundries should be chosen to minimize data flow across

4. 2-4

-

interfaces. And lastly, each layer should be manageable and

yet be able to support its function (Ref 33).

The following is a global description of the ISO seven

layer protocol model (Ref 22).

The Phy L . This is the lowest and most basic

link in the network. It deals with the physical realities

of the network and is concerned with the transmitting of raw

bits over a channel. It deals with connections, voltage

levels, and transmission rates.

.The Data Link Layer. This level creates, recognizes,

and governs the flow of the logical bits created in the

physical layer. This is generally accomplished by creating

frames or packets of data. The effort placed into this

layer will allow the next level (Network Layer) to

accomplish its task in a more efficient manner.

RIe.tok Laya. This layer is concerned with the

routing and management of the data packets. It largely

determines the host-to-node interface and is subject to

substantial design attention with concerns over the division

of labor between the host and the node.

xaDna.QL~l.. . This layer is concerned with

establishing communication paths between hosts. It is

sometimes referred to as the host-to-host layer. It manages"4buffer space and controls data flow. This is the highest

layer concerned with the transport services and normally

functions with communications taking place from a source

host to a destination host with the NIU being transparent to

2-6

VIRTUALLEVEL 7 APPLICATION LAYER HOST TO HOST

COMMUNICATION

VIRTUALLEVEL 6 PRESENTATION LAYER HOST TO HOST

COMMUNICATION

VIRTUALLEVEL 5 SESSION LAYER HOST TO HOST

COMMUNICATION

VIRTUALLEVEL 4 TRANSPORT LAYER HOST TO HOST

COMMUNICATION

VIRTUALLEVEL 3 NETWORK LAYER NODE TO NODE

COMMUNICATION

VIRTUALLEVEL 2 DATA LINK LAYER NODE TO NODE

COMMUNICATION

I PHYSICALLEVEL 1 PHYSICAL LAYER f--e-NODE TO NODE

COMMUNICATIONa

* Fiue2.IOPrtcl oe

Pr

the service.

Session Lay r. This layer is the user's interface into

the network by establishing a connection or session to

manage the dialoque in an orderly fashion. An example may

be time sharing or the transferring of a file from one host

to another. The service includes setting up the connection,

establishing agreement on the session options (called

binding) , managing the session, and disconnecting the

session upon task completion.

PU esntation Lyaxer. This layer performs library

functions for the network such as the transfer of files,

format configuration, text compression, encryption, etc.

The presentation layer attempts to alleviate inconsistencies

in the network faced by different host users.

AD~icatLiofl aer The content of this layeL is

determined by the users. They are normally application

dependent but many services are common in nature such as

file transfer and remote job execution.

Depending upon the size, complexity, and general

application of the network, the three top levels of protocol

may become blurred as to their specific tasks. In fact, in

small special purpose systems, the three top levels may be

grouped together into a single protocol layer called the

'Applications Layer" (Ref 22).

Syste Requirements

The global requirements specified in the previous

sectiun dealt with the rather abstract qualites of the

2-7

system such as virtual operation, flexibility, and

performance monitoring. At the systems level these

requirements become more specific. At the lower levels of

the ISO seven layer model the system requirementsare quite

explicit. But as the levels increase so does their

complexity. In fact, the complexity evolves into

abstraction as the upper protocol levels are reached. This

is due to the application dependence .of the upper levels and

inability to fix requirements and standards to systems that

are application variant. For this reason, this section

concentrates on the lower levels of protocol where the

system requirements are well defined and yet femain under

the requirements defined at the global level.

Packet i inq Protocol. The global requirement of

flexibility establishes the necessity for a packet switching

data transfer technique rather than that of dedicated

physical connections. Additionally, the transparency

requires all forms of data to be processed similarly.

Efficiency requires the potential for parallel processing

with time division multiplexing of message portions. Again,

packet switching meets these requirements while meeting the

transmission bandwidth (Ref 9). For these reasons the

DELNET will use packet switching, store-and-foward

protocol.

RouDing Tchnigurl. Routing algorithms can greatly

influence the effectiveness of a network. This is

especially true for multipath networks which use dynamic

2-8

routing schemes (Ref 20). One advantage of implementing the

DELNET with a loop or ring topology and store-and-foward

packet switching is that the routing technique is relatively

simple. It simply enables the UNID to interface a data

packet into the normal traffic of the network. The more

important aspect of this issue relates to the flexibility

requirement of the network. The protocols developed for

this investigation should be capable of absorbing additional

nodes and host into the network.

Using the ISO seven layer model as the global framework

for the network standards, many specific standards exist for

implementation of the bottom three levels of the protocol

model (Ref 22). Few specific standards exist, however, for

the top four levels since they are abstract in nature and

tend to pertain to the specfic system and its applications.

For this reason, this section will focus on the system

requirements for the bottom three layers of protocol.

The (CCITT) has developed an international standard

protocol for the bottom three layers of the ISO model. This

standard is known as the X.25 standard (Ref 7)

Investigation of other commercially available protocols

found serious deficiencies including vendor dependent

equipment, lack of technical sophistication, and the

overdependence of specific hardware. The versatility of the

X.25 standard and its endorsement by the CCITT led to its

acceptance as the access protocol for the DELNET (Ref 11).

4 2-9

The X.25 recommendation defines the three layers of

protocol through references to the X.21 standard for the

Physical Layer, Link Access Procedure (LAP) for the Data

Link Layer, and packet control at the Network Layer (Ref

22). Figure 3 shows the protocol structure at the systems

level.

~Detailed Reguirements

At the detailed requirements level, the specific

network functions to be encountered by this project are well

defined. They include the operating system for the network

and the application functions.

02grjatng Syse fr ±he Network. There are two basic

approaches available for implementing an operating system

within the DELNET. The first is to have one host which

functions as a central node and control for the entire

ring. Each host would route its message to this central

host which in turn would perform any necessary conversions

or network control functions and route the packet to the

original destination. The central control node would thus

have the majority of the network operating system contained

within its memory. It would control all access commands and

control the network functions. The second method that could

be employed to implement the operating system for a network

is to have each host within the ring function independently

and on the same level. In this case the network operating

system would be stored within the memory of each system

host. Either method satisfies the requirement of a network

2-10

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operating system that would provide certain user services.

These services should include, but should not be limited to,

commands to LOGIN, LOGOUT, and HELP. Following is a brief

discussion of these commands as well as several special

application functions which should be included as services.

When a user wishes to use the network, the LOGIN

command will be used. This command will verify access

authorization, identify the user to the network for data

routing and status, and initializes the host for DELNET

processing.

The LOGOUT command will perform the opposite process.

The user is removed from the network configuration at the

network operating system level, and the host dependent

interface to the network is terminated.

The HELP command is required to provide any user with

convenient information about the network. The information

available must include network overview, current network

status, network map for routing, and command syntax

instructions (Ref 9).

The application functions are a minimum set of

instructions required to perform network operations. They

should include user messages for real time internetwork

communications, file transfer, and remote job execution.eThe message transfer is to allow for direct communication

from host to host (electronic mail). The file transfer

requirement is included to enable data identified as a file

on one host to be transfered to any other network host.

2-12

Finally, the remote job execution will allow command files

on any host to be executed by any other network user (Ref

9).

Table 1 shows the relationships of the global, system,

and detailed levels of requirements and how they apply to

the DELNET.

SDe ailedStnad

As with the system level, specific standards for the

upper levels of protocol do not exist due to their

abstractions. In fact, future research on the DELNET

protocols may elect to combine several of the higher levels

of the ISO Model into a single Applicationns Layer (Ref

22).

Physic J. The standards for this layer at a

detailed level are contained within the standards at the

systems and global level peviously presented. The

justification for these standards can be found in Reference

7. On the local side of the UNID the data link uses the

RS-232C standard for twisted wire pairs and connectors.

Only 9 out of the available 25 pins are used (Ref 17) . The

data transfer from host to UNID is in serial at a maximum

rate of 19.2 kbps. On the network side, the data flow is

again serial using a modified RS-449 standard and a fiber

optic link at a maximum data rate of 2 mbps for the network

bus. Future research may explore various data rates. If

the maximums listed are exceeded, either the standards must

"* be changed or modifications must be made to the established

* 2-13

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4 2-14

standards. It must be emphasized that standard

modifications should not be taken lightly. A subtle change

at an early stage in development could substantially effect

modifications or interfaces in the future.

Data Link Lar. As specified at the systems level,

the data link access is governed specifically by the CCITT

standard for Link Access Procedures (LAP). This LAP is very

similar to the ISO standard for th.e High Level Data Link

Control (HDLC). This standard specifies the packet frame

format as shown in Figure 4.

ketwoxr Layer. The specific detail of the standards

for this layer are basically the same as for the systems

level. The routing for the DELNET is simple and does not

require a great deal of attention. Frames simply travel

unidirectional within the ring. The source and destination

information is contained in the frame's header information.

As the frame in injected into the ring, it proceeds from

UNID to UNID until the address of the host is recognized by

its connected UNID. At this point the packet is seized and

routed to the proper host on the UNID's local side.

Figure 5 presents a hierarchy of all the DELNET

standards. Figure 5, in conjunction with Table 1, should

present the reader with a graphical representation of the

functional requirements and standards, at each level, which

govern the DELNET.

2-15

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I

PXOTC COL LCCAL N LT'0 Sv TANEARKLLVEL5 SIDE INTERFACE SIDE STANDARDS

Data Packet aStandards for the Application

128 byes Layer are governed by the ISOLE~d ? 18 byes ifo7 layer model.

APPLICATION Initial implementation of DELNETLATER combines layer 5,6, and ? into a

single Applications Layer.

Host The UNID is transparent at this, level.

Data Packet =

LEVEL 6 128 bytes info

PRESENTATION ( Same as Level 7LAYER

Host

Data Packet =

LEVEL 5 128 bytes info

SESSION ( Same as Level 7LAYER

Host

Data Fack.et u Standards for the Transport

LEVEL 4 128 bytes + Layer are governed by the ISO5 bytes for 7 layer model and specific

TRANSPORT 40st-to-Ifost Host-to-Host DaLflLT standardsLAYUR protocol to be determined.

'he UNlID is transparent at thisH' fost Elevel.

Data Frame x Standards for the NetworkLEVEL 3 Data Packet + Layer are governed by the ISOLV 6 bytes for 7 layer model, CCITT StandardsN-TORK LAP protocol for X.25 and LAP, and specific

LAYER UNID DELNET Standards to be determined

Data Frame =

LEVEL 2 total 139bytes

DATA LINK UNID C Same as Level 3LAYER

Host D -"tan'ards for the ihysical

LEVEL 1 Layer are governed by the ISO7 layer model, CCITT Standards

PHYSICAL for X.21, and EIA Standards formUNID RS-232C RS-422, RS-423, andLAYER _ Modem S- 449.

b a a a Loal bus lines use 19.2 kbpa.Hos . otaork bus lines use 2 mbps.

Notes: a. RS-232C Connectors d. 2651 USARTb. RS-232C Data lines O. Z-80 SIO

c. RS-449 Data Line (Fiber Optic)

Figure 5. Hierarchy of DELNET Standards

2-17

Summar

The purpose of this chapter is to identify the functional

requirements and standards for the DELNET from a global,

systems, and detailed viewpoint. The global level focused

on the flexibility, virtual operation, and performance

monitoring. The framework for the global standards is the

ISO seven layer protocol model. At the systems level, the

focus was on the techniques required for packet switching

and routing using the store-and-foward method. The system

level standards are governed by the X.25 standard developed

by the CCITT. The scope of the investigation limits the

detailed requirements to those which pertain to DELNET

operations. These include the network operating system

functions for access control and user help services, and

application functions for message transfer, file transfer,

and remote job execution. Lastly, the standards that govern

the detailed requirements are specific for the bottom two

layers of protocol. The Physical Layer uses RS-232C and

RS-449 standards whereas the Data Link Layer uses LAP. The

third and forth levels at the detailed level are the same as.4

at the systems level. Also at the detailed level, the top

three levels are combined to make a single applications

layer. There have been several minor design considerations

mentioned in this chapter so that the detailed requirements

could be more specifically defined. The folk¢ ing chapters

define the actual designs of the first three protocol levels

and the implementations to support them.

2-18

Phscl ae

Introduction

This chapter presents the rationale used to determine

the specific hardware necessary for designing and

implementing the lowest level of the ISO seven layer model

for protocol development. The chapter begins with a general

theoretical discussion of various Physical Layer

implementaion techniques. It then discusses the specific

designs and implementations of the DELNET and how these

designs relate to previous research for this project. All

the actual implementations for the Physical Layer of the

DELNET are governed by the standards set forth in Chapter II

as shown.

Theo

The initial perception of the Physical Layer is one of

fulfilling a rather simplistic requirement to insure a

complete overview of all areas pertaining to data transfer

within a network. In contrast, however, the actual

theoretical considerations pertaining to this subject can

become quite complex. In fact, a comprehensive analysis

must consider the data bit stream as a periodic waveform and

is therefore subject to the bandwidth limitations determined

through complex Fourier Analysis.: It is imperative that the

bandwidth of the transfer medium be broad enough to support

a sufficient number of harmonics of the basic frequency to

successfully reproduce the square wave type bit stream.

3-1

.- - - - - - - - - -

Chapter 3 of Reference 22 presents a detailed description of

this analysis. The results of this analysis contain several

important points. For example, given a particular type of

transfer medium or channel there exists a maximum data rate

that can be transmitted on that type of medium due to

bandwidth limitations.

The data rate is not the only factor used in

determining the type of channel used for a LCN. Additional

variables include length of channel, topology,

troubleshooting and maintenance, availablity of channel

interface equipment, susceptibility to electromagnetic

interference (EMI), and cost. The types of transfer mediums

most often used for LCNs are twisted-wire pair, coaxial

cable, and fiber-optics. Each has definite limitations and

advantages over the others as described in the following

sections (Ref 13).

Twisted-wire Pair. Twisted-wire pairs are the most

commonly used channel medium between conventional data

communications equipment (DCE) and data termination

equipment (DTE). The primary reasons are low cost and

availability of the wire as well as its connectors. This

type of channel is highly acceptable for normal

communications between DCE and DTE especially for short runs

of the cable (Ref 13). At the present time, 19.2 kbps and

9.6 kbps are the most widely implemented data rates due to

the RS-232C standard. Twisted-wire pairs can even handleI

data rates up to 10 Mbps for short distances of less than

3-2

100 feet. One disadvantage of this type channel is its

susceptibility to EMI and its inadvertant broadcasting of

its own electromagnetic fields (Ref 8).

Within some networks one of the major disadvantages of

twisted-wire pairs is its limitation to function as a

baseband medium. Both fiber-optics and coaxial cable have

the capability to be used as both baseband or broadband

channel mediums. Baseband refers to the method of data

transfer of placing the bit stream directly onto the

channel; whereas, broadband refers to the method of

modulating the data onto an RF carrier frequency. Using

broadband channels, several customers have access to the

same channel simultaneously by modulating their data streams

at different rates (Ref 12 and 13).

Coaxial-cable. In LCNs, coaxial-cable is the most

attractive medium for implementation due to its advantages

over twisted-wire pairs and few real disadvantages. Not

only can it support RF transmission for broadband

capabilities, but it is relatively inexpensive and easily

tapped, thus allowing easy additions to the network. It has

a broad bandwidth and can support data rates of 10 Mbps for

over 1000 feet or up to several miles for lower

frequencies. The only real disadvantages are its small

increase in cost over twisted-wire pairs, slight complexity,

and nonavailability and nonconformaty of connectors for the

DCE/DTE interface (Ref 13).

-iber=otics. The use of fiber-optic channels is

3-3

increasing proportionally as the technology of the subject

increases. At the present time there are several large

drawbacks to using fiber-optics within an LCN. The two

predominant limitations are cost and complexity of

installation. The fiber-optic modem which is used to

interface the NIUs to the network bus, is considerally more

expensive than the simple connectors used for twisted-wire

or coaxial cable. Additionally, any breaks in the

fiber-optic bus for the reasons of maintenance or additional

hookups must be precise and often become very complicated.

Once these obstacles are overcome, the fiber-optic channel

is the 'most efficient' and versatile channel of the three.

The primary benefits to using fiber-optics is that it is

practically impervious to EMI (Ref 13) and it can transfer

data at rates of over several hundred Mbps for distances ten

times greater than coaxial cable (Ref 8).

Many of the larger and newer LCNs are using various

combinations of the channel mediums mentioned. For example,

an inter-office network might be connected by a baseband bus

composed of either twisted-wire pairs or coaxial cable.

These small LCNs might join into a larger network being

supported by a broadband coaxial bus. This secondary

network might interconnect offices over several city blocks

from several different buildings. Finally, these secondary

networks might be connected to other secondary networks on

the other side of a large city via a fiber-optics channel.

It is easy to visualize that the type channel implemented

3-4

depends on a great many variables which are primarily

determined by the use and size of the network (Ref 12).

DELNET Implementation

As stated in Chapter I, the role of the DELNET will

have many purposes. It will greatly aid to increase the

productivity of the DEL as well as providing a highly

pedagogical platform for student and faculty research and

study. For this reason, several decisions for the original

design of the DELNET departed from the typical operational

design considerations (Ref 9).

For example, in one of the original AFIT sponsored

thesis projects, the design specified a fiber-optic link to

be used as the network bus channel between the UNIDs (Ref

3). This design has carried foward and was incorporated as

part of the DELNET. It was determined that the fiber-optic

link would provide a vehicle for students to receive first

hand experience with this system.

Although the DELNET's main network link is implemented

by a fiber-optic bus, the UNID itself does not incorporate a

4fiber-optic modem nor connectors. For this reason, the UNID

connections on the network side begin with an RS-232C

connection and cable and lead into a fiber-optic modem

(Fibronics Model TTK) for network bus interface. By

connecting the network bus in this manner, it provides the

pedagogical requirements or the original design yet

minimized the cost and complexity of the UNID.

Additionally, a very short run of twisted-wire pairs will

3-5

not degrade the network link when working with data ratesbelow 10 Mbps (Ref 13). For this and all preceeding DELNET

research, the network bus has functioned as a baseband

channel. With the fiber-optic cable functioning as its

channel medium, the possibility exits for an upgrade to a

broadband channel. The upgrade to a broadband channel would

allow for a greater number of UNIDS to be connected to the

DELNET without the adverse effects of increased traffic.

Additionally, the DELNET could support analog types of data

such as video and voice.

On the local side of the UNID, the four hosts are

connected to the UNID on standard RS-232C serial links. The

data rate between the hosts and the UNID is 19.2 Kbps.

Reference 17 provides a complete schematic breakdown of

these links, connectors, and pin assignments. There are no

future plans to change the local side bus configuration.

Summar

Within the LCN community, the three basic types of

channel mediums being used for the physical layer of

4protocol are the twisted-wire pairs, coaxial cable, and

fiber-optics. Under the standards set forth in Chapter II,

the DELNET incorporates a combination of twisted-wire pairs

4 for the local side data link at 19.2 Kbps. The network side

uses a fiber-optic link at 2 Mbps. All channels of the

DELNET operate in the baseband configuration but could be

4I expanded to broadband in the future.

d3-6

*v Data Link L ~

Introduction

This chapter presents the design considerations

necessary for implementation of the second level of the ISO

seven layer model for protocol development. The chapter

begins with a discussion of various techniques that may be

employed to design a network's Data Link Layer. It then

discusses the specific design and 'implementation of the

DELNET's data link protocol scheme and how this thesis

effort integrated its findings into the design of the

previous thesis efforts. All the actual implementations for

the Data Link Layer of the DELNET are governed by the

standards set forth in Chapter II as shown.

flaijg Considerations

The role of the Data Link Layer is to perform a variety

of tasks which are totally transparent to the users. The

tasks themselves vary widely in complexity in both concept

as well as in actual implementation. The main task of this

protocol level is to consider a raw transmission medium

between NIUs and transform it into a sophisticated channel

that appears free of errors to the next higher level of

protocol. It normally accomplishes this task by placing the

data packets into frames, transmitting the frames

sequentially, and then processing the acknowledgement frames

sent back from the receiving NIU (Ref 22).

The concept of the Data Link Layer is rather basic;

S4-1

however, depending upon the number of protocol enhancements

provided by a particular network, the design can become

quite complex. These enhancements may include flow control,

error detection, error correction, sequence management, and

automatic reset and restart capabilities. The degree of

effort spent in developing this layer of protocol is

directly reflected in the higher protocol layers. That is,

as many housekeeping tasks as possible should be implemented

within the lower levels of the protocol structure thus

freeing the higher levels to be used in a more efficient

effective manner (Ref 22).

There are as many variations for developing the Data

Link Layer as there are vendors and regulatory agencies

which control standards. Even when two seperate networks

are designed under the same identical standards, slight

variations exist due to the changes in topology and

utilization (Ref 18).

There are several major procedures used in industry for

implementing the Data Link Layer of a LCN. Fortunately,

most of these procedures are all very much alike, LAP (Ref

7) , HDLC (Ref 7) , SDLC (Ref 18). In fact, they are so

common, many hardware devices incorporate modes of operation

specifically designed to automatically accomplish many of

the tasks of this protocol layer. One such device is the

new Intel 8272 Programmable HDLC/SDLC Protocol Controller.

Many other such devices are now in production (Ref 8). In

fact, in the same time period as this thesis report was

4 4-2

being prepared, the Digital Equipment Corporation (DEC)

developed an NIU on a single LSI chip (Ref 8). In the past

and until such hardware devices are commonly used, most of

the tasks performed by the Data Link Layer will be

accomplished through software realization.

The fundamental building block of the Data Link Layer

is the data frame. As a packet of data is processed for

transmission from node A to node B, *a frame is built around

the packet. Figure 3 of Chapter II shows a typical frame.

The flag bits are normally set to 01111110 but may vary if

protocols agree. These flag bits are appended onto the

original data packet as are the address, control, and

checksum fields. The address bits are for routing and flow

control. The control bits provide information as to the

type, purpose, sequence number, and acknowledgement of

frames. The checksum bits are for error detection and in

some cases for error correction. The schemes themselves may

be as simple or complex as the networks which they control.

The Data Link Layer is only concerned with the appending

fields and normally has nothing to do with the data packet

field. Reference 7 presents a detailed description of how

these frame headers are formatted and used.

The overall throughput efficiency of a data frame from

one node to another is proportional to the time spent on the

analysis of the header information (Ref 1). For example,

" consider routing a frame from node A to node B through node

'- C. The designer of the network must decide if there should

4. 4-3

be an acknowledgement between A and C and then C and B or

just between A and B. Additionally, the designer must decide

if error checking should be performed at every intermediate

node or just at the destination node. other decisions that

the designer must make includes the numerical sequencing of

the frames known as the 'modulo number' and the maximum

number of frames that can be transmitted before an

acknowledgement is required (Ref 22) .Also, if an

acknowledgement is not received, the designer must

incorporate the time interval before retransmission occurs.

As with most design problems, there are many

considerations that effect the performance of the network.

These include the topology, the amount of traffic on the

network, and perhaps the most important, the applications of

the network (Ref 22) . It is very possible to incorporate so

many overhead enhancement features into the Data Link Layer

that the throughput is actually reduced (Ref 1) *The

designer of the network protocol scheme must address these

specific performance considerations.

DELLE~ Desaign Aa Implementation

Although there were many design decisions in regard to

the DELNET protocol scheme, there was one consideration that

would not normally affect a typical design environment.

This was the fact that this project would be used in a

continuing academic environment and would be passed from

student to student over several thesis efforts.

Additionallyp in an acedemic environment a primary conc~ern

4-4

is flexibility which fosters continuing research

investigations. Because of this, the overall design

concepts used did not only incorporate the modularized

approach as specified in Chapter I, but they have been kept

as basic as possible while maintaining the ability to

perform all the functions of the original design.

The network topology of a ring structured system

creates an ideal environment for a very simple yet effective

store-and-foward routing philosophy (Ref 22). While still

under the standard of the LAP, this philosophy actually

eliminates much of the data link control overhead and

greatly reduces others. Additionally, the store-and-foward

concept treats all UNIDs equally and independently and

eliminates the master-slave relationships normally designed

into an HDLC/SDLC type protocol scheme such as the LAP (Ref

22). Although the ring topology is not suited for all

applications of networks, it is an ideal first step or

starting point for the DELNET to build upon.

The data frame shown in Figure 4 was modified slightly

for the DELNET scheme development as shown in Figure 6.

There are two types of data frames ustd within the DELNET

design. Both types have a fixed length of 139 bytes. The

first is the information or I-frame and is used for

transfering data between two UNIDs. The second is the

supervisory or S-frame and is used for acknowledging the

receipt of a good I-frame. As the formatting information of

Figure 6 shows, the possibility of expanding the role of

'I 4-5

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supervisory functions is open for future development. All

the procedures and tasks pertaining to this level of

protocol strictly function on the five appended fields of

the frame. The information contained in the packet field is

of no use at this level of protocol.

The software developed in the previous thesis effort

(Ref 9) defined the basic framework of the procedures

required to support the Data Link Layer under the basic

guidelines of the LAP and X.25 standards. This software

established the buffer tables and pointers to maintain the

various routing of the frames, but made little or no

analysis of the appended header information. The primary

concern of this thesis effort, in relation to the Data Link

Layer, was to incorporate this analysis into the framework

previously designed.

The remainder of this section discusses the sequence of

events for the Data Link Layer scheme. Reference 9 should

be reviewed in order to understand the buffer table

structures previously developed. The algorithms of this

project were developed with the following philosophy of

operation:

- Fixed length frames

- one directional communication on network bus

- Frame sequence numbering is modulo 2 (1 or 0)

- Frames received are physically moved to

- their appropriate tables in shared memory

-No attempt is made at error correction

4-7

- All frames are independent of each other

- The network does not approach saturation

- The percentage of network errors is low

The algorithms used to perform the services of the Data

Link Layer, were developed using a three tier scheme which

consisted of Data Plow Diagrams, Structure Charts, and

Pseudo English. The Data Flow Diagrams provide a means of

identifying the modularity of processing that is required to

transform the input data into the final form of processing.

The Structure Charts transform the Data Flow Diagrams into a

physical structure of procedures which will accomplish the

processing shown in the Data Flow Diagrams. Lastly, the

Pseudo English is used to bridge the gap between the

Structure Charts and actual code by combining understandable

English statements and computer code. If performed

correctly the transition between Pseudo English and actual

code is straight foward.

The Data Flow Diagrams were developed during the

initial phases of the DELNET design and are presented in

* Reference 9. The Structure Charts for the Data Link Layer

are presented in Figure 7 through 10. The following

paragraphs contain the Pseudo English description. In order

to assist in the understanding of both the Structure Charts

and Pseudo English constructs, Appendices A-C provide a

comprehensive description of all descriptors and processing

if pertaining to this software.

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K After completing the initialization of the table

Sbuffers and their pointers, the processing enters an endless

loop of calling procedure ROUTEIN and ROUTEOUT. Note that

actual variable and procedure names are presented in all

capital letters.

Enter Procdure ROUTE_IN

If a frame is present in NT01TB then

Determine its DESTINATION

If DESTINATION = NTNTTB then

MOVE frame to NTNTTB

Update the NTNTTB pointers

End If

If DESTINATION = NTLCTB then

If the frame is an S-frame then

Determine if the S-frame is a positive

ACKNOWLEDGEment of last transmitted I-frame

Else ( must be I-frame

Determine the INPUTSEQBIT

Call BUILD_S_FRAME to transmit ACKNOWLEDGEment

MOVE frame to NTLCTB

Update the NTLCTB pointers

End If

End If

Update the NT01TB pointers

End If

End Procedure ROUTE_IN.I

Enter Procedure ROUTE_OUT

4-13

If a frame is present in NTNTTB then

LIf the DESTINATION address < MAX_UNIDS then

Call TRNMIT


Else ( address out of limits

Increment status table, STATTB


End If

If a frame is present in LCNTTB then

If it is an S-frame then

If the DESTINATION address < MAX_UNIDS then

Call TRNMIT

Update the LCNTTB pointers

Else ( address out of limits



End If

Else ( it was an I-frame )

Place proper SEQBIT in control byte of frame

If the DESTINATION address < MAX_UNIDS then

If the TIMEDELAY is COMPLT then

Call TIME_DELAY

End If

If ACKNOWLEDGE = FALSE 'AND' COMPLT - TRUE then

Call TRNMIT

Force ACKNOWLEDGE to FALSE until the reception

of a good S-frame makes it TRUE

4-14

Call TIME_DELAY to start timing sequence

End If

If ACKNOWLEDGE - TRUE then


Compliment SEQBIT for next usage

End If

Else ( address out of limits.)



End If

End If

End If

End Procedure ROUTEOUT.

The method of positive acknowledgement and

retransmission of I-frames and the discarding of any frame

where an error may have occured has both advantages and

disadvantages. It is relatively easy to implement, has

little overhead, and gets the job done quite well and

efficiently when few errors occur on the network. If the

error rate is high, the throughput of the system will be

reduced considerably (Ref 1). This general philosophy is

often used in even large sophisticated networks although

often network monitoring techniques are employed to guard

against bottlenecks and breakdowns (Ref 18). Appendices A-C

contain documentation of the software used to implement the

Data Link Layer protocol.

The method employed to design and implement the actual

4-15

DELNET services provided by the Data Link Layer can actuallybe described as 'datagram' service. Each frame is

transmitted independently of other frames. It will be the

responsibility of the Transport Layer of protocol to place

the data packets in proper order if required. Reference 22

has a good description of datagram service and how this

relatively simple concept relates to the data link protocol

layer using the store-and-foward concept.

Sumar

The majority of the various protocol schemes present a

framework from which very sophisticated and complex network

services can be provided. Man of these services can be

reduced or eliminated for simpler networks such as the

initial DELNET implementation. In fact, the ring topology

of the DELNET further relaxes the routing portions of the

protocol scheme to an easily designed and implemented

store-and-foward concept. This concept is consistent with

the general philosophy of the DELNET to be a modularized and

maintainable network. The data link protocol layer designed

.for the DELNET incorporates communications between UNIDs

while maintaining the flow control, error detection, and

virtual addressing. This datagram service, as it is

4 sometimes called, is implemented through hardware using the

Z-80 SIO and through software.

-

4-16

Ntke.twrk Layer

Introduction

This chapter presents the design considerations

necessary for implementation of the third level of the ISO

seven layer model for protocol development. The chapter

begins with a discussion of the Network Layer philosophy and

how this layer might be implemented. It then discusses the

specific design and implementation of the DELNET's Network

Layer protocol scheme and how this thesis effort was

integrated into previous designs. All the actual

implementations for the Network Layer of the DELNET are

governed by the standards set forth in Chapter II as shown.

Dlesign Considerations

The role of the Network Protocol Layer is to interface

the Data Link Layer discussed in Chapter IV with the

Transport Layer which has direct virtual communication with

the Transport Layers of additional host computers (Ref 22).

In simple terms, it transforms a frame of data from the

network side of a NIU to a packet of data on the local side

of a NIU. It is also up to the Network Layer to determine

the actual routing of the data packet and pass this

information to the Data Link Layer for transmission.

Additionally, it is the task of the Network Layer to insure

that messages are properly sequenced before delivery and

upon arrival to the Data Link Layer (Ref 5).

* The Network Layer is often called the packet or

5-1

communications subnet layer (Ref 5). In either case, it

refers to the Network Layer and its two subordinate layers

in providing the actual communication transmissions between

the NIUs and their host computers. This communication takes

place by the routing of packets from the network layer to

the subordinate layers and then over the physical channel to

the destination NIU. From there it proceeds up the

hierarchy to the Network Layer of the designated host.

As with the Data Link Layer, the Network Layer may be

quite complex or rather simple depending on the complexity

of the routing and control schemes of the network. In fact,

the X.25 standard has five different packet types defined

for full implementation if all services of this layer are

required. For lesser services, a subset of these types may

be used. This layer not only concerns itself with routing

and sequencing as previously mentioned, but may control such

areas as establishing virtual circuits, controlling

collisions, preventing deadlocks, call confirmations andclears (Ref 22). This is what makes the X.25 standard

universal in concept. It has services to control

practically every situation that might arise.

If the Network Layer supports or does not support

datagram services is perhaps one of the most critical

questions the designer must ask. If no virtual circuit has

to be established prior to transmission, the type of packet

that sets up the virtual call may be disgarded. As in theDData Link Layer, using the loop topology, simplex

* 5-2

communications, and store-and-foward routing philosophy, the

complexity of the Network Layer is reduced considerably.

D LNET Design nd Implementation

In developing the DELNET's layer scheme, the X.25

packet switching guidelines set forth by the CCITT were

adhered to in philosophy, but varied slightly in actual

format implementation. Since the design scheme incorporated

the simple store-and-foward routing algorithm and the

transmit-and-wait positive acknowledgement technique in the

Data Link Layer, it was not necessry for the DELNET to

establish a virtual circuit before transmission. For this

reason, the 'Call Request' and 'Incoming Call' packet types

were not needed. The source and destination DTE address

fields were incorporated into a modified data type packet.

This allowed the DELNET to utilize a single type of packet

(called the data packet) and yet provide all the information

necessary for virtual communications.

In addition to the actual data, this modified data

packet contains five header fields of a single byte each.

Bytes one and two are the destination and source host

addresses respectively. Each contains both the UNID number

and local channel number. Byte three contains the sequence

number of the packet and will be used by a higher layer of

protocol to sort the data. Bytes four and five are left

blank for future development. Future efforts might use

these bytes to incorporate an error checking scheme (CRC) at

the network level or a word count for variable size

o| 5-3

.. kets. A wide variety of choices exit (Ref 22). The

reader should keep in mind that since a hierarchial protocol

scheme is being used, the data field from the Data Link

Layer contains the five header bytes plus the data field of

the Network Layer. Likewise, the data field of the network

layer will contain some header fields from its higher

Transport Layer. Figure 11 shows the complete data frame as

viewed from the Network Layer.

The software development in the previous thesis effort

(Ref 9) prepared the basic framework of most of the

procedures required to support the Network Layer software

for the UNID. This software established the buffer tables

and pointers required to maintain the various UNID internal

routings of the packets, but did not consider the appended

header information. The primary task of this thesis effort

was to implement the previously designed software by

augmenting the header information scheme and processing the

data flow accordingly.

The remainder of this section discusses the sequence of

processing to control the Network Layer. As with the Data

Link Layer, Reference 9, Chapter VII should be consulted to

obtain an understanding of the buffer tables and pointers

and how they are used to enhance the packet flow and4

processing. Figure 12 encapsultes these tables and the

types of data contained in each.

The algorithms used to perform the services of the

Network Layer were developed using the same three tier

4| 5-4

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5-64

approach used for the Data Link Layer. The Data Flow

*Diagrams are presented in Reference 9. Figures 13 through 16

present the Structure Charts and the following paragraphs

descibe the processing using Pseudo English.

As in the Data Link Layer, the processing begins with

the initialization of the table buffers and pointers and

then enters an endless loop of calling procedures ROUTEIN

and ROUTE_OUT. Note that the actual variable and procedure

names are presented in all capital letters.

Enter Procedure ROUTE_IN

If a packet is present in LCO1TB then


If the DESTINATION is a Case of

LCLCTB then

MOVE packet to LCLCTB

Update the LCLCTB pointers

LCNTTB then

Call BUILD_IFRAME

MOVE the new frame to LCNTTB

Update the LCNTTN pointers

Else ( improper DESTINATION address )

Increment status tableSTATTB

End If

Update the LCO1TB pointers

End If

Repeat this sequence for LC02TB through LC04TB

End Procedure ROUTE_IN

5-7

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Enter Procedure ROUTE-OUT

If a packet is present in LCLCTB then


If DESTINATION is a Case of

Channel No. 1 then

Call TRNMITPKT (To send to channel 1)


Repeat this sequence for all Cases of

Channel No. 2 through Channel No. 4

Else ( Improper channel number )

Increment status table,STATTB


End If

End If

If a frame is present in the NTLCTB then


If the DESTINATION is a Case of

Channel No. 1 then

Call TRNMITPKT (To send to channel 1)

Update the NTLCTB pointers

Repeat this sequence for all Cases of

Channel No. 2 through Channel No. 4"0Else ( Improper channel number )

Increment status table,STATTB

Update the NTLCTB pointers0End If

5-12

End If

End Procedure ROUTE-OUT

The processing for the Network Layer will transmit and

receive packets of data between the UNID and its hosts.

Additional services may be provided when the design of the

Transport Layer is completed and the Network/Transport Layer

interface is completed.

Summarx

The Network Layer of protocol is the interface between

the transport services layer and the basic Data Link Layer.

For a rather complex network, it can use a wide variety of

packet types to accomplish a multitude of tasks. But for a

simple network such as the DELNET, these types can be

combined into a single packet type. Within the scheme of

the DELNET, the Network Layer simply transforms a data link

frame, which is transmitted on the network bus, to a data

packet, which is used for local processing. This

transformation is accomplished by evaluating the packet

headers and moving the packet to the proper location. With

the completion of this layer of protocol, the UNIDs are

capable to transmit and receive data frames from the network

ports, route the frames internally, and receive and transmit

the packets to the appropriate ports of their connected

hosts.

0 5-13

V.Software Configuration AValiato

Introduction

This chapter presents the procedures for configuring

and testing the software developed during this thesis

effort. The chapter begins with a discussion of the MCZ

1/25 software development system and the UNID environments

and concludes with the actual test procedures conducted

utilizing this environment to test the DELNET software.

This chapter presents examples of the actual commands that

were used to process the software under test. A working

understanding of References 26, 29 and 30 would be helpful

to fully comprehend the following text; however, a general

knowledge of minicomputer operating systems will be

sufficient.

SEnvironment Test S Configuration

The Zilog MCZ 1/25 minicomputer, Zilog RIO operating

system, and the PLZ programming language present an 'ideal'

environment for the development and testing of an operating

system such as the one for the DELNET. The PLZ language is

primarily based on the concept of combining structured

modules of software written in either the PLZ higher order

language or Z-80 assembly level language. It is this

diversification of combining and linking these modules

together that create the flexibility desired for new

operating system development. A second and perhaps equally

important feature of this environment is that the modules

6-1

are relocatable and may be placed into specific memory

locations with simple linking commands (Ref 26).

For example, suppose we have two source code modules of

software. The first module, Testl.S, is written in PLZ and

the other, Test_2.S, is written in Z-80 assembly language.

Note that the RIO Operating System rules require the suffix

l.Ss for source code modules. *The Test-l.S module must

first be compiled using the 'PLZSYS' command.

%PLZSYS TEST_1.S

The result of this compilation is a Test_l.L listing file

and a Test-l.Z intermediate code file. The 'Z' code files

are actually executable code which can be run by using the

ZINTERP interpreter (Ref 26). The code is more efficient,

however, if it is assembled by the PLZ Code Generator with

the following command:

%PLZCG TEST_1.Z

The result of this assembly is an object code file,

Testl.OBJ. It is recommended that for the DELNET operating

systems, the latter method of generating an object code file

be used. The execution time of the interpreted 'Z' code is

much slower.

The Test_2.S assembly language module is simply

4 assembled using the command:

%ASM TEST_2.S

The result is an object code file, Test_2.OBJ. Once all the

modules have been assembled and each has an object file

attached, they are linked together and placed into memory

6-2

using the 'PLINK' command:

%PLINK $=5000 TEST_1 $-8000 TEST_2

This command places the TestlI.OBJ code into memory

beginning at location 5000 Hex and the Test_2.OBJ code

beginning at location 8000 Hex. The linking information is

placed directly following the last used memory location. If

only a single address is specified, then each module is

attached in sequential locations. For example:

%PLINK $=5000 TEST_1 TEST_2

After the linking is completed, the executable code is

referenced by the name of the first module in the linking

string. In the above example, Test_l would be the programs

name. To execute this program on the MCZ 1/25, it would be

necessary to simply type 'TESTI'. To obtain a memory map

of the program, a '.MAP' suffix is attached following the

linking process. To print a memory map just type:

%PRINT TEST_1.MAP

DELNET Stwa Configuration

The DELNET software for protocol layers two and three

is located in the UNID's memories. Figure 17 shows the

configuration of these memories and the Z-80 processors

which controll them. Basically, the network operating

system implements the Data Link Layer and the local

operating system implements the Network Layer. The local

processor has access to its 32 K (8000 Hex) of its local

system memory and the 32 K of the shared memory. In the

same manner, the network processor has access to its 32 K of

6-3

UNDER CONTROL UNDER CONTROL

MEMORY OF LOCAL OF NETWORK MEMORY

(HEX) Z-80 PROCESSOR Z-80 PROCESSOR (HEX)

0000 0000

LOCAL NETWORKSYSTEM SYSTEMROM ROM

oFFF 0FFF1000 1000

LOCAL NETWORKSYSTEM SYTEMRAM RAM1FFF IFFF

2000 LOCAL NETWORK 2000

OPERATING OPERATINGSYSTEM AND SYSTEM ANDTABLE TABLE

7FFF BUFFERS BUFFERS 7FFF

8000 8000

SHARED MEMORY

TABLE BUFFERS FOR ACCESS BYBOTH THE LOCAL AND NETWORKZ-80 PROCESSORS

14

FFFF FFFF

Figure 17. UNID Memory and Processor Configuration

6-4

._ _ .. _.:.... , ,. ..=. 2

network system memory and the 32 K of the shared memory (Ref

4). In refering back to Figure 12, the reader can see why

the NTNTTB and NTO1TB are located in the netwcrk system

memory, the LCLCTB and LCOlTB-LC04TB are located in the

local system memory, and the LCNTTB and NTLCTB are located

in the shared memory.

There are a total of eight-software modules presently

being used to implement the DELN4T operating system and

which reside in the UNID memories. They were first

presented in Chapters IV and V, but are condensed in Table

II for continuity and clarity. After studying Table II, it

should become clear to the reader why the relocatable

options of PLZ are ideal for such software development.

In addition to the MCZ 1/25 environment, the UNID

itself has several features which were previously developed

to enhance its capabilities (Ref 2). The UNID incorporates

1 K of ROM and 1 K of RAM in each of the system memories

which are used for the basic bootstrapping operations of the

UNID and serve several monitoring functions as well. This

monitoring program together with a video monitor enable the

loading, filling, displaying, and moving of memory locations

throughout the UNID. Reference 2 contains a complete

desciption of the monitor options and procedures.

Each of the DELNET operating system software modules

are compiled and/or assembled to produce the object codes

for the modules. To place the modules in their correctI

locations in UNID memory, the following linking commands are

6-5

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envolked on the MCZ:

1). %PLINK $=5000 L.VINT L.TAB L.MAIN $=7000

ZINTERP.DATA $=8000 U.LIB U.SHTAB

2). %PLINK $=5000 N.INSIO N.TAB N.MAIN $=7000

ZINTERP.DATA $=8000 U.LIB U.SHTAB

First, note that ZINTERP.DATA is the linking information and

is placed in each of the system memories. This prevents the

local or network linking information from writing over each

other. If it was left to the operating system, it would

place the linking information at the end of the shared

memory modules each time it loaded a different operating

system, thus writing over each other. Both the local and

network modules must each be linked with the shared memory

wmodules since each must contain unique linking information.

Once all the modules of each operating system are

properly linked together, they are ready to be placed into

the UNID memories. First, the network operating system is

loaded. Since the network monitor cannot interface the MCZ

1/25 directly (network side of UNID), the network operating

system is initially loaded into the local side of the UNID.

This is accomplished with the command on the UNID local

monitor:

0 >L N.INSIO

At this point, the network operating system is loaded into

the UNID's local and shared memory locations according to

the previous linking information. The portion of the

network operating system in local memory is then moved to

6-7

4

shared memory by the following move command:

M A000 5000 2FFF

This command moves to location AOOO Hex from location 5000

Hex a total of 2FFF Hex bytes. Now that the network

operating system is located in shared memory, it is moved

down into the network system memory with the following

command envolked on the network monitor console:

M 5000 A000 2FFF

The local operating system is then simply placed into its

system and shared memory by its load command. Upon the

loading of the local operating system, the shared memory

modules are written over in a one to one correspondence so

both operating systems are linked to it independently. Once

both these operating systems are loaded into their correct

memory partitions, the processing can begin.

First, the memory maps of each operating system are

checked to identify the starting addresses of each system.

The starting address of the local operating system is set

into the program counter (PC) and the stack pointer (SP) is

set to a value away from used memory (3000 Hex). The local

processing is begun with the 'go' command on the local

Smonitor. This process is repeated for the network

processing. Both the network and local processing enters

enless loops of routing in and routing out of frames and

packets of data respectively and uses the shared memory

buffer tables to interchange the data.6

21_ 6- 8

Software Test and Vlidaion

Perhaps the most challenging efforts of this thesis

investigation was to develop and conduct a test plan that

would adequately test and validate proper operation of the

network and local operating systems. Since one of the

constraints of the original software implementation was to

design the software in a structured fashion, there were not

a great many warnings and pr.ohibited constraints

incorporated into the original design. For this reason, the

majority of the testing focused on those aspects of the

DELNET operation that were suppose to occcur rather than on

the endless permutations pertaining to Murphy's Law of 'What

If' anomallies. All the safeguards that were built into the

system were tested, however.

There was one significant obstacle in testing the

DELNET's software. The UNIDs which were being upgraded

during a concurrent thesis effort (Ref 4) were only

completed during the final week of the testing period. For

this reason, much of the software was tested using the MCZ

1/25 computer rather on the Z-80 processors inside the

UNID. Since the MCZ utilizes the same Z-80 processor and

the UNID processor scheme was designed under the framework

of the MCZ, the differences were small. In fact, the RIO

Operating System of the MCZ was much superior to the small

monitor program of the UNID and it actually expedited

development with its robust environment of memory

manipulations and troubleshooting tools. The only real

6-9

drawback was that the MCZ used only a single processor and

*the local and network operating systems had to be tested

independenly without the capability of handshaking.

Additionally, the MCZ could not actually transmit or receive

frames of data on the network side or packets of data on the

local side. The MCZ was used, however, to checkout the

internal processing of each of the operating systems when

certain conditions were intiated thr.ough manual manipulation

of variables, table buffers, and pointers.

The global approach for testing the DELNET software was

analogous to that of structured design. Each module or

service was tested and validated to insure proper operation

at the bottom most level. Next, the higher modules were

tested which used the already validated sub-modules.

Unfortunately, the complete end-to-end test of the DELNET at

the global level could not be performed due to the

previously mentioned problems encountered with the UNID

development. Each internal module was tested; however, and

provided confidence that the overall system would function

-. properly if provided with a fully opertional set of UNIDs.

The following paragraphs describe the tests conducted

* using the MCZ 1/25 to simulate the UNID processing. Each

test describes the setup and results. Appendix A may be

refered to along with the many figures of preceeding

chapters in order to follow the processing flow required and

to obtain the results listed. In order to simplify the

manipulations of the frames and packets for these tests, the

6-10

packets contained a total of 30 bytes and the frames 32

bytes. In both cases the header fields were complete.

Each test performed validates specific servies provided

by the DELNET operating system. Each service is identified

along with the setup and results for the specific test.

.Test 1- Reception of Local-to-Local Packet

a). Place 30 byte packet into LC01TB; all bytes = BB.

b). Set byte 1 to 03 (to UNID No.0, Channel No.3).

c). Set byte 2 to 01 (From UNID No.0, Channel No.1).

4 d). Set LCO1NE to IE Hex (30 bytes in table).

e). Jump around Init_L_Tab and Init_U_Shtab (this would

reinitialize the LCO1NE pointer to zero).

17- f). Set PC and SP

g). Go

The packet was properly routed to the LCLCTB and the

LCLCNE pointer was updated to 1E Hex. All combinations of

the addresses were then placed into the destination address

4 byte 1. The destination address was then changed to an

incorrect channel number. The error was properly noted and

the STATTB was incremented accordingly. In all cases this

software functioned correctly.

Test 2 - Reception of Local-to-Network Packet

a). Place 30 byte packet into LCOlTB; all bytes = BB.

4 6-11

b). Set byte 1 to 13 (to UNID No.1, Channel No.3).

c). Set byte 2 to 01 (From UNID No.0, Channel No.1).

d). Set LCO1NE to 1E Hex (30 bytes in table).

e). Jump around InitLTab and InitUShtab (this would


f). Set PC and SP

g). Go

Results f Test.2

The packet was properly routed to the LCNTTB and the

frame headers for the Data Link Layer were added correctly,

thus transforming the packet (30 bytes) to a frame (32

bytes). The new frame header byte 1 was set to 10 and the

byte 2 was set to 00. All pointers were properly changed

after transfer; LCNTNE was changed to 20 Hex and LC03NS was

changed to 1E Hex. All combinations were checked and the

system performed in the correct manner. In all cases this

software functioned correctly.

Test 3 - Reception of Network-to-Network Frame

OG a). Place 32 byte frame into NTOlTB; all bytes = BB.

b). Set byte 1 to 10 (To UNID No.1 From UNID No.0)

c). Set byte 2 to 00 (I-Frame, Sequence No.0)

d). Set NT01NE to 20 Hex (32 bytes in table).

e). Jump around InitL_Tab and Init_U_Shtab (this would

reinitialize the NTO1NE pointer to zero).

_ -f). Set PC and SP

g). Go

[0 6-12

fResults of Test

The frame was routed to the NTNTTB properly. All

pointers were properly updated; the NT01NS was set to 20 Hex

and the NTNTNE was set to 20 Hex. The test was repeated

with the destination address changed to UNID No.3. This

value exceeded the variable MaxUNIDS and the SHATTB was

properly incremented. In all cases the software functioned

correctly.

Test A - Reception of Network-to-Local I-Frame

a). Place 32 byte frame into NTOlTB; all bytes = BB.






f). Set PC and SP

g). Go

Results f Test A

The frame was properly placed into the NTLCTB with the

pointers being updated correctly; NTLCNE was set to 20 Hex

and NT01NS was set to 20 Hex. An S-Frame was created andplaced into the LCNTTB. The proper headers were placed on

the S-Frame; byte 1 was set to 10 and byte 2 was set to 00.

The LCNTNE was correctly set to 20 Hex with the addition of

the S-Frame. In all cases the software functioned

correctly.

6-13

s 5- Reception of Network-to-Local S-Frame

a). Place 32 byte frame into NTOlTB; all bytes = BB.

b). Set byte I to 10 (To UNID No.1 From UNID No.0)

c). Set byte 2 to AO (S-Frame, Sequence No.1)




f). Set PC and SP

g). Go

~Results of1 Test5

The results were correct. The only action taken was

that the pointer NT01NS was set to 20 Hex. The varialble

'acknowledge' should have been complimented during actual

operation. But since the varialble is not global, its

values could not be confirmed during this test. Both

combinations of sequence numbers were tested. In all cases

the software functioned correctly.

Test - Transmission to Network of I-Frame and S-Frame

a). Place 32 byte frame into LCNTTB; all bytes = BB.



d). Set LCNTNE to 20 Hex (32 bytes in table).


reinitialize the LCO1NE pointer to zero)

f). Set variable MAXNUM to 100 (allow 2.7 secs. between

6-14

transmissions).

g). Set PC and SP

h). Go

The I-Frame was transmitted to the network once every

2.7 seconds. The painter LCNTNS was never updated because

the varialble 'ackncwledge' could not be complimented by the

arrival of an S-Frame. Between the successive transmissions

of I-Frames, the normal processing of routing in and out

data continued. Byte 2 of the frame in the LCNTTB was

* changed to AO Hex to indicate an S-Frame. The S-Frame was

transmitted once to the network and pointer LCNTNS was set

to 20 Hex correctly. In all cases the software functioned

correctly.

The Zilog MCZ 1/25 microcomputer and its supporting

software were used to develop and support the testing of all

software modules for this thesis effort. This system which

supports the philosophy of structured software modules,

relocatable code, and the combination of higher order and

assembly language programming, provides a robust environment

for the development of operating systems.

* The DELNET operating system is composed of two basic

components. The first is the network operating system which

is controlled by a Z-80 processor within the network side of

_ the UNID. It controls the operations pertaining to the Data

Link protocol layer for frame traffic between UNIDs on the

6-15

network bus. The second is the local operating system which

is also controlled by a Z-80 processor but located on the

local side of the UNID. It controls the local packet

traffic of the Network protocol layer between the hosts and

the UNID.

Both the local and network operating systems have

access to their own memory partitions for unique system

operations as well as to, shared memory for

intercommunications and packet/frame sharing. There are a

total of eight software modules; three for the local side,

three for the network side, and two for shared memory. Each

software module was tested and validated to perform properly

for all operations pertaining too inter-UNID processing and

communication.

6

I

6 6-16

.Ya. Concluions Aad Recommendations

The purpose of this investigation was to continue the

initial design of the DELNET operating system and to

implement it in such a manner as to make the UNID minimally

functional. The majority of the specific objectives were

accomplished. The continuing problems encountered with the

UNID hardware, however, greatly hampered the testing and

overall developmental efforts of this project. This report

provides a firm foundation for continued development for the

DELNET and its operating system.

Although the software is minimal in scope, it is based

on accepted standards and has been developed in such a

manner as to allow for expansion within these standards.

The foremost conclusion of this thesis effort pertains

to the validity of the DELNET operating system which was

initially designed by the previous AFIT MS student (Ref 9).

This study confirms that the software and data structures

initially designed into the operating system are sufficient

to perform the tasks required for DELNET operation.

Although perhaps not optimal in structure, they provide for

4 an easily understandable and maintainable software system

which can be extended.

Within the limitations of the test equipment available,

4the local and network operating system modules functioned

properly. It is regrettable that the hardware limitations

7-1

of the UNID (Ref 6) did not allow a more complete

demonstration of the DELNET with true inter-UNID

communications. Due to the UNID anomalies, the actual

routing of the frames into and out of the UNID was not

accomplished. This was demonstrated, however, during the

previous thesis effort (Ref 9).

The designs and techniques used to implement the

Physical Layer of protocol (layer 1) were demonstrated and

found valid in the previous thesis effort (Ref 9). the

RS-232C and RS-449 standards provide for all the services

necessary for complete communications on the channels for

both local and network traffic within the DELNET.

The designs and techniques used to implement the Data

Link Layer of protocol (layer 2) were much more complicated

than the Physical Layer due to the large variety of options

for available services. Since the standards which govern

this layer are truely universal in scope, great care was

exercised to select a methology which did not violate

standards yet allowed a simplified appraoch. Using a ring

topology and store-and-foward simplex (unidirectional)

routing approach, a protocol subset was chosen. The subset

chosen was complete in that it provided for a minimum of

services that would insure proper data link operation.

These included such services as flow control, error

detection, and virtual addressing. It accomplishes this by

using a modulo 2 sequencing scheme, two types of frames

(information and supervisory), and a 'transmit- wait for

7-2

reply -retransmit if no reply' acknowledgement philosop! y.

- " Much of the difficult flow control and error detection

services were performed by the Z-80 SIO (Ref 16)

The designs and techniques used to implement the

Network Layer of protocol (layer 3) were perhaps the most

ambiguous. Athough Reference 7 contains the standards for'

this layer, the actual implementation is quite complex.

This is because the standards allow for a wide variety of

services, many of which the DELNET does not require. For a

rather uncomplicated network such as the DELNET, a subset of

services was selected.

A single packet type was chosen to incorporate this

protocol level in its present configuration. Once the

Transport Layer protocol services are defined, the

Network/Transport Layer interface will probably require

additional services and therefore the addition of various

other types of packets. The present single packet type

contains specific header fields which are used to insure

correct packet routing and packet sequencing. Additional

fields were left blank so that additional services could be

provided under the existing standards.

When these three layers are combined, they provide for

a minimally operational system. If provided with a set of

fuctional UNIDs they can receive/transmit packets between

the UNID and host computers, transform the packets into

frames, and receive/transmit frames between UNIDs. Thus,

the virtual information transfer for host to host has been

6 7-3

achieved.

Recommendations

Because this thesis effort is a continuation of

previoug' research, the overall recommendation is to continue

with the DELNET development project. The specific

objectives for future efforts fall into three major areas.

The first is to improve upon the initial three levels of

protocol thus far developed. The second is to continue to

develop the successive higher levels of protocol. And the

third is to develop a network monitoring system that can

provide real time network monitoring and evaluation. In

either case, the guidelines of standards set forth in

Chapter II must be carefully followed. In particular, the

future projects must pay close attention to the seven layer

model of the ISO.

There are enough additional services or enhancements

that could be incorporated into either the Data Link Layer

or Network Layer that would require several dedicated thesis

projects. The following recommendations, however, pertain

only to those additional services and tasks that would be of

benefit to the DELNET as it is viewed for use in the

foreseeable future.

*O The first recommendation pertains to the mode of the

communications. Complete LAP and HDLC protocols utilize

full duplex communications rather than the DELNET's present

* ~ simplex method. The DELNET should be upgraded to at least a

half duplex if not full duplex capability. The second

0 7-4

recommendation is to increase the sequence numbering scheme

from the present modulo 2 to either modulo 8 or modulo 128.

This would increase the I-frame traffic and greatly reduce

the overhead of the S-frame traffic. Thirdly, the data link

frames should be made of variable length. Under the present

scheme of fixed buffers and pointers, this would require

substantial rework of the data strctures. Next, the

acknowledgement of I-frames should be made point to point

(UNID to UNID) around the network instead of just from the

destination UNID to the source UNID. Lastly, a new 'Request

To Send' S-frame should be incorporated between adjacent

UNIDs to reduce errors and increase flow control. The

incorporation of each of these recommendations would widen

the subset of services that the AP protocol is suppose to

provide for the Data Link Layer and bring the DELNET closer

to full standard compliance.

The recommendations for the Network Layer of protocol

basically parallels those recommendations fcr the Data Link

Layer. The X.25 standard incorporates numerous packet types

that provide a wide variety of services. The Network Layer

for the DELNET should incorporate a packet numbering scheme

that is similar to that of frames of the Data Link Layer.

Additionally, the size of the packets should be made of

variable length. Thirdly, the X.25 acknowlegement scheme

should be developed between the UNID and its hosts. Next, a

variety of Network Layer supervisory tasks should be

incorporated according to the X.25 standard to allow for

7-5

error detection and flow control.

While improvements to the present DELNET protocol

levels are important, continued development of the higher

levels of protocol is essential in order to obtain a working

DELNET in the foreseeable future. In doing so, the DELNET

will sacrifice some quality but will realize an actual

operational network. If follow-on research focuses on the

continued development of higher protocol levels, it is

essential that the ISO model be maintained as the overall

framework for future development. It is imperative that if

a subset of a higher protocol level is selected for DELNET

operation, it must be implemented in such a manner as to

allow for future enhancements to the full set of allocated

serivces of the particular protocol.

The third major area of recommended future research

deals with the development of a network monitor. The

ability to monitor network operations would provide a means

of testing and validating proper system performance. It

would also provide the DEL with a pedagogical tool for

network research.

Whichever choices are selected for future research, the

central theme of the DELNET operating system development is

'quality'. The undbrlying theme is modularity and

structured programming. This software engineering approach

together with the established standards described in Chapter

II, provide a firm foundation on which the DELNET can be

developed. A fully operational network which implements

7-6

full HDLC and X.25 standards is a tremendously complex

system of enormous proportions. Full in-house development

which attempts to include all the possible services is

- perhaps a unrealistic objective. But a fully operational

network for the DEL is obtainable using carefully selected

subsets of the services from those available.

7

01

I7-7

D-R124 874 CONTINUED DEVEI40PRENT AND IMPLEMENTATION OF THE2/PROTOCOLS FOR THE DIGITAL..(U) RIR FORCE INST OF TECHMRIGHT-PATTERSON AFB OH SCHOOL OF END!. C H HAZELTON

UNCLASSIFIED DEC 82 AFIT/GE/EE/82D-37 F/G 9/2 M

..

L6L

11111 *r1 50

t!

k i++ .... -

11111L2 1 1. lAO 520

, 1' U t!!i:

MICROCOPY RESOLUTION TEST CHART

NATIONAL BUREAU OF STANDARDS 963-A

'4

.4.

Bibliography

1. Abrams,Marshal Dr. and Blanc, Bobert P. and Cotton,Ira W., "Computer Networks: A Tutorial (JH 3100-5C),"

oLQeinU f tI j] , New York, 1978.

2. Baker, Capt Lee R., "Prototype and Software Developmentfor Universal Network Interface Device," Unpublished MSThesis. School of Engineering, Air Force Institute ofTechnology, Wright-Patterson AFB, 1980.

3. Brown, Capt Eric F. "Prototype Universal NetworkInterface Device," Unpublished MS Thesis. School ofEngineering, Air Force Institute of Technology,Wright-Patterson AFB, 1980.

4. Cuomo, Capt Gennaro. "Continuation of UNID HardwareDesign," Unpublished MS Thesis. School of Engineering,Air Force Institute of Technology, Wright-PattersonAFB, 1982.

5. Davies, D.W., and Barber, D.L.A., and Price, W.L., andSolomondies, C.M. .CmrIuter Networks and Their.ooo. Chichester, Great Britain: John Wiley andSons, 1979.

6. de Sousa, Paulo J.T. and Ingle, Ashok D. and Sharma,Roshan Lal. Network Syste . New York, New York: VonNostrand Reinhold Co., 1982.

7. Folts, Harold C. and Harry R. Carp (Editors). DataCommunications S. New York: McGraw-HillPublications Co.,1978.

8. Freeman, Harvey A. "Local Computer Networks," 26thAnnual Symposium of the Central Ohio Chapter of theAssociation for Computing Machines. Columbus, Ohio, 12May 1982.

9. Geist,Capt John W."Development of the Digital. Engineering Laboratory Computer Network: Host-to-Node/

Host-to-Host Protocols," Unpublished MS Thesis. Schoolof Engineering, Air Force Institute of Technology,Wright-Patterson AFB, 1981.

10. Graube, Maris. "Local Area Nets: A pair of Standards,"" ectru , Vol. 19 No.5: 60-64, New York, 1982.

11. Hobart, Capt William C. Jr. "Design of a LocalComputer Network for the Air Force Institute ofTechnology Digital Engineering Laboratory," UnpublishedMS Thesis. School of Engineering, Air Force Instituteof Technology, Wright-Patterson AFB, 1981.

6Q Bib-l

12. Hoskins, Gregory T. and Meisner, Norman B. "ChoosingBetween Broadband and Baseband Local Networks,"Mini-icro S , Vol XV : 265-274, (June 1982).

13. Karp, Peggy M. and Socher, Ivan D. "DesigningLocal-Area Networks," Mini-Miro Sy , Vol XV :219-231, (April 1982).

14. Koffman, Elliot B. P-roblem Solvig and StructuredProgramming in Pascal. Philippines: Addison-WesleyPublishing Co., 1981.

15. Leventhal, Lance A. Z0 As_ l Language P rgrmig.Berkeley, Ca.: Adam Osborne & Associates Inc., 1979.

16. Osborne, Adam et al. An Introduction to MicrocomputersL11=.U, Berkeley Ca.: Osborne & Associates, Inc.,197 9.

17. Papp, Charles E. "Prototype DELNET Using the UniversalNetwork Interface Device," Unpublished MS Thesis.School of Engineering, Air Force Institute ofTechnology, Wright-Patterson AFB, 1981.

18. Randesi, Stephen J. "Interfacing Minis and Micros toIBM networks," Miiir Systems, Vol XV, No 3:159-168, (Mar 1982).

19. Roberts, Michael. "Multiprocessing Networks VersusMain Frames," Mini-Micro S Vol XIII No. 10:121-128, (Oct 1980).

20. Schwartz, Mischa. Computer-Communication NetworkDaegn Ad Analysis. Englewood Cliffs, N.J.:Prentice-Hall, Inc., 1977.

21. Sluzevich, Capt Sam C. "Preliminary Design of aUniversal Network Interface Device," Unpublished MSThesis. School of Engineering, Air Force Institute ofTechnology, Wright-Patterson AFB, 1978.

22. Tanenbaum, Andrew S. Computer Netwrks. EnglewoodCliffs, N.J.: Prentice-Hall Inc., 1981.

23. Weaver, Thomas H. "An Engineering Assessment TowardEconomic, Feasible, and Responsive Base-LevelTelecommunications Through the 1980's", TechnicalReport 1842EEG/EEIC TR 78-5, 1842 Electonic EngineeringGroup, Richards-Gebaur AFB, Mo, 31 Oct 77.

24. Yourdan, Edward and Larry Constantine. Strucuredlesign. New York: Yourdan Press, 1978.

25. Zilog, Inc. MCZ-I/2Q,25 Hardware User's Manual,

I Bib-2

Manufacturer's data. Cupertino, Ca.: Zilog, Inc.,1977.

S26.• Zilog, Inc. Lzu User Guide ( 03-3096-011,

Manufacturer's data. Cupertino, Ca.: Zilog, Inc., July1979.

;27. Zilog, Inc. Z80MC Hardware User's Manual,Manufacturer's data. Cupertino, Ca.: Zilog, Inc.,1977.

28. Zilog, Inc. Z80-_CD Sofki.re. User's Manual(03-3004-01), Manufacturer's data. Cupertino, Ca.:Zilog, Inc., May 1978.

S29. Zilog, Inc. Z80-RIO Qprtn! Syt User's Manga(03-0072-01), Manufacturer's data. Cupertino, Ca.:Zilog, Inc., Sept 1978.

30. Zilog, Inc. Z80-RT eI n Asemb er an d LinkerUser's Manual, Manufacturer's data. Cupertino, Ca.:Zilog, Inc., 1978.

31. Zilog, Inc. Z80-SIB User's Maual (03-0051-00),Manufacturer's data. Cupertino,-Ca.: Zilog, Inc., July197 8.

32. Zilog, Inc. Z80-STO Tecnical Manual (03-3033-01),Manufacturer's data. Cupertino, Ca.: Zilog, Inc., Aug197 8.

33. Zimmermann, Hubert. "OSI Reference Model - The ISOModel of Architecture Open Systems Interconnection,"1= Transactions on Communication, Vol COM 28(4):425-432, (Apr 1980).

Bib-3

Data Dictionary

This appendix contains the data dictionary for theeight modules which compose the DELNET operating system inits present configuration. This data dictionary isorganized by modules which are presented in alphabeticalorder. Each module contains a section for constants,variables, and procedures which are in turn listed inalphabetical order. Appendix B contains a cross referencelist for all constants, variables, and procedures and themodules where they are located.

• Table of Contents

ModulePage

L. MAIN e. . . . ... . . . . . A- 2L.TAB 0A- 4

!LVN *. . . . . . . . . . . A-6

N. INSIO e. . . . . . . . . . . . . . . . . . . . . . A-11U.SHTAB 9ee9*9o**. A-I12

!iUoLIB . . . . . . . .. . . . A-13

A-1

The purpose of this module is to provide the localoperating system with the main line of processing. Thelocal operating system is required to input/output data fromthe four local channels or hand off and receive data fromthe network operating system.

Consants

CONCMD - Command port address for the USART on the localmonitor console.

CONDAT - Data port address for the USART on the localmonitor console.

F_TABLE_SIZE - Number of bytes in a frame table buffer.

FRAME-SIZE - Number of bytes in a frame.

LRIDESTERR - Local route in destination error.

IR..L_RODEST_ERR- Local route out destination error.

P_TABLESIZE - Number of bytes in a packet table buffer.

PACKET_SIZE - Number of bytes in a packet.

PACKETS_ IN_TABLE - Number of packets in a packet tablebuffer.

STAT_NBR - Number of the status entries to be included inthe status table buffer.

********** NOTE **********

The next constant, UNID_NBR, must be unique for eachcopy of the module L.lMain placed within each UNID orincorrect processing will result.

********** NOTE **********

UNIDNBR - Unique UNID number for the UNID performing theevaluation. See above note!

U01DAT - Local channel 1 USART data port address.




A-2

77-7-7-7-

TDAADD - Global, type Pbyte - Starting address of data forto be transmitted out the USARTS.

TPRADD - Global, type byte - Data port address for theUSARTS.

DESTINATION - Internal, type word - The destination addressof a data packet or frame.

STARTUPHDR - Internal, type array - A message to theconsole indicating proper operating system operation.

BUILD_I_FRAME - A procedure which transforms a packet into aframe.

DETDEST - 'Determine Destination' - Determines thedestination of a packet or frame by evaluating itsheaders.

LDTABHSKP - 'Load Table Housekeep' - Housekeeps aspecified table after a new packet or frame has beenloaded.

MAIN - This is the main procedure which drives otherprocedures through their proper sequencing.

ROUTEIN - Routes in packets from their correct input tablebuffers and places them into their correct output tablebuffers for transmit.

ROUTEOUT - Routes out packets from their correct outputtable buffers to their correct output channels.

SRVC_TAB_HSKP - 'Service Table Housekeep' --Housekeeps aspecified table buffer whenever a packet or frame isremoved.

TRNMIT_PKT - 'Transmit a Packet' - Transmits a packet out ofone of the two output table buffers to one of the localchannels.

A

A- 3

ODL.

U The purpose of this module is to provide the localoperating system with the table buffers necessary forstoring the packets of data after reception and before

V" transmission to the local hosts.

F_TABLESIZE - Number of bytes in a frame table buffer.

FRAMESIZE - Number of bytes in a frame.

P_TABLE_SIZE - Number of bytes in a packet table buffer.



.EVaables

LC01TB - Global, type array - Local input table buffer fromthat interfaces with channel number 1.

LC01NE - Global, type integer - Pointer for the nextavailable position within LCOlTB.

LC01NS - Global, type integer - Pointer for the next byte tobe serviced within LCO1TB.

LC01SZ - Global, type integer - Size of the LC01TB tablebuffer.

K LC02TB - Global, type array - Local input table buffer fromthat interfaces with channel number 2.

LC02NE - Global, type integer - Pointer for the nextavailable position within LCO2TB.

LC02NS - Global, type integer - Pointer for the next byte tobe serviced within LC02TB.


VLC03TB - Global, type array - Local input table buffer from

that interfaces with channel number 3.

LC03NE - Global, type integer - Pointer for the nextavailable position within LC03TB.

A-4

LC03NS - Global, type integer Pointer for the next byte to: :be serviced w thiLC3B


LC04TB - Global, type array - Local input table buffer fromthat interfaces with channel number 4.

LC04NE - Global, type integer - Pointer for the nextavailable position within LC04TB.

LC04NS - Global, type integer - Pointer for the next byte tobe serviced within LC04TB.


LCLCTB - Global, type array - Local-to-local table bufferthat receives packets from local hosts that aredestined for other local hosts.

LCLCNE - Global, type integer - Pointer for the nextavailable position within LCLCTB.

LCLCNS - Global, type integer - Pointer for the next byte tobe serviced within LCLCTB.

LCLCSZ - Global, type integer - Size of the LCLCTB tablebuffer.

INIT_L_TAB - 'Initialize Local Table Buffers' - Sets up thelocal table buffers and initializes the pointers tozero.

A

I A-5

t"DIUL L.VINT

The purpose of this module is to support the localoperating system and its processing. L.VINT is anassembly language module and does not have any declaredconstants or varialbes.

INVINT - 'Intialize Vector Interrupt Mode' - The purpose ofthis procedure is to initialize the vector interruptprocess through the use of the Priority InterruptController (PIC).

INIURT - 'Initialize Local Card USARTS' - Initializes the2651 USARTS on the UNID local board.

TRNMIT - 'Transmit' - The purpose of this procedure is toenable a transmit interrupt from a PLZ module.

URTR01 - 'I/O Receive Interrupt Controller' - The purpose ofthis procedure is to service local channel 01interrupts.




URTTRN - 'I/O Transmit Interrupt' - The purpose of thisprocedure is to service the local channel transmitinterrupts.

A-6

• .;MODULE Nl.MAIN

The purpose of this module is to provide thenetwork operating system with the main line ofprocessing. The network operating system is requiredto input/output data from the network channel or handoff and receive data from the local operating system.

Consants

CONCMD - Command port address for the USART on the localmonitor console.

CONDAT - Data port address for the USART on the localmonitor console.

F_TABLESIZE - Number of bytes in a frame table buffer.

FALSE - Boolean word use for high order control.

FRAME_SIZE - Number of bytes in a frame.

FRAMES_IN_TABLE - Number of frames in a frame table buffer.

HDROO - Frame header byte 00, address word.

HDR01 - Frame header byte 01, control word.

NET_RI_DESTERR- Network route in destination error.

NETRODESTERR- Network route out destination error.

PACKETSIZE - Number of bytes in a packet.


STAT_NBR - Number of the status entries to be included inthe status table buffer.

********** NOTE **********

The next constant, UNID_NBR, must be unique for eachcopy of the module L.Main placed within each UNID orincorrect processing will result.

********** NOTE **********

UNID_N V U que UNID number for the UNID performing theeva iti4,n. See above note!

Variables

A-7

ACKNOWLEDGE - Internal, type byte - Indicates either true orfalse if a good acknowledgement frame has beenreceived.

COMPLT - Global, type byte - Indicates either true or falseif the TIMEDELAY procedure is complete.

CTCCNT - Global, type byte - Counter for CTC. Incrementedonce each timeout of CTC.

DESTINATION - Internal, type word - Destination of datapacket.

INPUTSEQBIT - Internal, type byte - Sequence bit (modulo2) to be entered into new frame.

********** NOTE **********

The next variable, MAX_UNIDS, must be set to the exactnumber of UNIDs in operation on the DELNET or improperprocessing will result.

********** NOTE **********

MAX_UNIDS - Internal, type byte - The maximum number ofUNIDs connected to the DELNET. The number must bechanged if UNIDs are added or removed or inproperprocessing will result. See note above.

MAXNUM - Global, type byte - The maximum number of times theCTC will cycle through its counting routine.

S_FRAMETB - Internal, type array - Supervisory frame tableused to build up an S-frame.

SEQBIT - Internal, type byte - Sequence bit (modulo 2) ofan active I-frame.

STARTUPHDR - Internal, type array - A message to theconsole indicating proper operating system opertion.

THISSEQBIT - Internal, type byte - Sequence bit that is4d presently under examination.

BUILDS_FRAME - A procedure which builds an S-frame andplaces it into the proper location for networktransmission.

DETDEST - 'Determine Destination' - Determines thedestination of a packet or frame by evaluating its

A- 8

headers.

LDTABHSKP - 'Load Table Housekeep' - Housekeeps aspecified table after a new packet or frame has beenloaded.

MAIN - This is the main procedure which drives otherprocedures through their proper sequencing.

ROUTEIN - Routes in frames from the network bus and placesthem into their correct table buffers for evaluation.

ROUTE_OUT - Routes out frames from their correct output,table buffers to the network bus..

SRVC_TABHSKP - 'Service Table Housekeep' - Housekeeps aspecified table buffer whenever a packet or frame isremoved.

TIMEDELAY - Creates a time delay between succesivetransmissions if I-frames.

A

A- 9

. ::: MODULE .A

The purpose of this module is to provide thenetwork operating system with the table buffersnecessary for storing the frames of data afterreception and before transmission to the network bus.

Constants



FRAMES_IN_TABLE - Number of Frames in a frame table buffer.


PACKETS_IN_TABLE - Number of packets in a packet tablebuffer.

VaLriable

NT01TB - Global, type array - Network input table bufferfrom network bus.

NT01NE - Global, type integer - Pointer for the nextavailable position within NTO1TB.

NT01NS - Global, type integer - Pointer for the next byte tobe serviced within NTO1TB.

NT01SZ - Global, type integer - Size of the NTO1TB tablebuffer.

NTNTTB - Global, type array - Network output table bufferfor the network bus.

NTNTNE - Global, type integer - Pointer for the nextavailable position within NTNTTB.

NTNTNS - Global, type integer - Pointer for the next byte tobe serviced within NTNTTB.

NTNTSZ - Global, type integer - Size of the NTNTTB tablebuffer.

INIT_N_TAB - 'Initialize the network table buffers' - Setsup the network table buffers and initializes thepointers to zero.

6e A-10

.'-DU HtoINSIO

The purpose of this module is to support thenetwork operating system and its processing. N.INSIOis an assembly language module and does not have anydeclared constants or variables.

INSIO - 'Initialize SIO' - The purpose of this procedure isto initialize the I/O process for frames transmittedand received on the network bus.

SIOREC - 'SIO Receive Interrupt Cntroller' - This procedureservices the receive interrupt requests for framescoming into the UNID for the network bus.

STCTC3 - 'Start CTC Channel 3' - This procedure sets up theCTC 3 for proper operation.

TRNMIT - 'Transmit' - This procedure transmits a frame outon the network bus.

A-1l

..........

The purpose of this module is to provide both thelocal and network operating system with a sharedinterface for which they can exchange information. Inthe present form this interface is a pair of tablebuffers which will be located in the shared memorypartition of the UNID memory.



P_TABLE_SIZE - Number of bytes in a packet table buffer.



STATNBR - Number of the status entries to be included inthe status table buffer.

Variables

LCNTTB - Global, type array - Table buffer for transferringpackets from local side to the network bus.

LCNTNE - Global, type integer - Pointer for the nextavailable position within LCNTTB.

LCNTNS - Global, type integer - Pointer for the next byte tobe serviced within LCNTTB.

LCNTSZ - Global, type integer - Size of the LCNTTB tablebuffer.

NTLCTB - Global, type array - Table buffer used for storingframes received from network side and going to localhosts.

4 NTLCNE - Global, type integer - Pointer for the nextavailable position within NTLCTB.

NTLCNS - Global, type integer - Pointer for the next byte tobe serviced within NTLCTB.

NTLCSZ - Global, type integer - Size of the NTLCTB tablebuffer.

A-1 2

ODULE U.LIB

The purpose of this module is to support both thelocal and network operating system with a series ofassembly laguage library routines. Because it is anassembly language routine, it does not have declaredconstants or variables.

MOVSEQ - 'Move Sequence' - This is a procedure to move ablock of data from one area of memory to the next.

RECSEQ - 'Receive Sequence' - This is a procedure to receivea squence of bytes from an identified port.

SNDSEQ - 'Send Sequence' - This is a procedure to send asequence of data out of an identified port.

A-13

Apedi4

Data Dictionary Cross Reference

This appendix contains all the constants, variables,and procedures used in all eight modules of the softwarewhich compose the DELNET operating system. The identifiersare arranged in alphabetical order and list the specificmodules from Appendix A where a full description may befound.

I B-i

Identifietr Modules~

ACKNOW~LEDGE N.*MAINBUILD_I_FRAME L.MAINBUILD_S_FRAME N.MAINCOMPLT N. MAINCONCMD L.MAIN, N.M1A INCONDAT L.MAIN, N.MAINCTCCNT N.MAINDESTINATION L.MAINDET _DEST L.MAINI N.MAINFTABLESIZE L.MAINr L.TAB, N.MAIN, N.TABF U.SHTABFALSE N.MAINFRAMESIZE L.MAIN, L.TAB, N.MAIN, N.TAB, U.SHTABFRAMES_IN_TABLE L.MAIN, L.TAB, N.MAIN, N.TABHDROO N.MAINHDR01 N.MAININITL-TAB L.TABINIT_-N.TAB N.TABINPUT..SEQ_..BIT N.*MAININSIO N. INSIO,INVINT L.VINTLCLCTB L.TABLCLCNE L.TABLCLCNS L.TABLCLCSZ L.TABLCNTTB U.SHTABLCNTNE U.SHTABLCNTNS U.SHTABLCNTSZ U.SHTABLCOMT L.TABLCOINE L.TABLC01NS L.TABLCOISZ L.TABLC02TB L.TABLC02NE L.TABLC02NS L.TABLC02SZ L.TAB

=LC03TB L.TABLC03NE L.TABLC03NS L.TABLC03SZ L.TABLC04TB L.TABLC04NE L.TABLC04NS L.TABLC04SZ L.TABk.RIDESTERR L.MAINL...RODEST_-ERR L.MAINLD_TAB_.HSKP L.MAIN, N.MAINMAIN L. MAIN, N.MAINMAX-UJNIDS N.KAINMAXNUM N.MAINMOVSEQ U.LIBNET...RIDEST _ERR N.MKAIN

o B-2

NET-RODEST-ERR N.KAINNTLCTB U.SHTABNTLCNE U.SHTABNTLCNS U.SHTABkTLCSZ U. SHTAB

*NTNTTB N.TABNTNTNE N.TABNTNTNS N.TABNTNTSZ N.TABNTOITB N.TABNT01NE N.TABNT01NS N.TABNTOISZ N.TABPTABLESIZE L.MAIN, L.TAB, N.MAIN, N.TAB, U.SHTABPACKETSIZE L.MAIN, L.TAB? N.MAIN, N.TAB, U.SHTABPACKETS_INTABLE L.MAIN, L.TAB, N.MAIN, N.TAB, U.SHTABRECSEQ U.LIBROUTEIN L.MAIN, N.MAINROUTEOUT L.MAIN, N.MAINS_-FRAMETB N.MAINSEQ-BIT N.MAINSIOREC N.INSIOSNDSEQ U.LIBSRVCTABRSKP L.t4AIN, N. MA INSTARTUP_-HDR L.MAIN, N.MAINSTAT_-NBR L.MAIN, L.TAB, N.MAIN, N.TAB, U.SHTABSTCTC3 N.INSIOTDAADD L.I4AINTHIS-..SEQBIT N.M1AINTIMEDELAY N.MAINTPRADD L. MAINTRN14IT L.VINT, N.INSIOTRNMITPKT L.MAINTRUE N.MAINUNIDNBR L.MAIN, N.MAINURTR01 L.VINT

*URTRO2 L.VINTURTRO3 L.VINTURTRO4 L.VINTURTTRN L.VINTU01DAT L.MAINU02DAT L.MAINU03DAT L.MAINU04DAT L.MAIN

B-3

Append~ix .

DELNET Operating System Software Components

This appendix contains the actual software listingswhich compose the DELNET operating system. The modules arebroken up into three major sections. Section I containsthose modules which comprise the local operating system.Section II contains those modules which comprise the networkoperting system. Section III contains the modules whichcomprise the shared components of the DELNET operatingsystem.

Section I C- 2L MAIN o 9 * & o a o C- 3L.TAB 0 0 * * * * . . . . . . . . . . C-27L*VINT o o 9 o o 9 o * 9 e * e o 9 e o* @ oC-3 0

Section II . . . . . . . . . . . . . . . . . . C-49NMAIN"000000oo9* C-50

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This section of Appendix C contains the softwarelistings which comprise the local operating sysstem.

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This section of Appendix C contains the softwarelistings which comprise the network operating system.

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A eni CSectionII

This section of Appendix C contains the softwarelistings which comprise the shared components of the DELNEToperating system.

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: Vita

Captain Craig H. Hazelton was born on 10 January, 1949

in New York City. In 1952 he moved to Atlanta, Georgia andlater to Bradenton, Florida where he graduated from high

school in 1967. In 1968 he enlisted in the United States

Air Force and served as a missile electronics technician

until 1978 when he entered the University of Central Florida

under the Air Force's Airman Education and Commissioning

Program. After graduating with a Bachelor of Science degree

in Electrical Engineering, he received his commission and

was assigned to Eglin AFB, Florida where he served as lead

test engineer for the F-15 electronic warfare system. He

entered the Air Force Institute of Technology in June 1981.

Permanent Address: 3316 32nd Street West

Bradenton, Florida 33505

V-i

UNCLASSIFIED

SECURITY CLASSIFICATION OF THIS PAGE (hen Dsta i[nteredj READ INTRUCTIONS

REPORT DOCUMENTATION PAGE BEF-RE MrLoRMBEFORE COMPLETMnG FORM1. RPORT NUMNER 2. GOVT ACCESSION NO a. RECIPIENTs CATALOG NUMSE@R

APIT/GE/EE/82D-37 p ____"/_/______"___"

4. TITLE (and Subtille) S. TYPE OF REPORT & PE000 COVEREDCONTINUED DEVELOPMENT AND IMPLEMENTATION MS Thesis

* OF THE PROTOCOLS FOR THEDIGITAL ENGINEERING LABORATORY NETWORK s. PERFOMING ORG. RXPORT NUMBER

' '7. AUTHOR(@) 8. CONTRACT OR GRqANT NUMSEa(s)

Craig H, Hazelton, Capt, US"F

S. PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT, PROJECT. TA"

Air Force Institute of Technology(AFIT/EN) AREA & WORK UNIT NUMiERS

Wright-Patterson APB, OH 45433

II. CONTROLLING OFFICE NAME AND ADDRESS 12. REPORT DATE

Air Force Institute of Technology(APIT/EN) December 1982Wright-Patterson APB, OH 45433 IS. NUMBER OF PAGES

r. 21314. MONITORING AGENCY NAME & AOORErSS(l dlibmeto fi Con"utc.I Offiee) IS. SECURITY CLASS (fg dle t)

"S.. OECLASSIFICATION/DOWNGRADING

SCHEOULE

I. DISTRIBUTION STATEMENT (of this Roped)

Approval for public releasel,distribution unlimited

'7. DISTRIBUTION STATEMENT (*I Me sbe.oat entere t1olek 2. it difgea ten Ripeo)

I SUPPLEMENTARY NOTESo ,

'ad I~o b VOW A'. IW D T.pe

Af~~l.t r u oj I LLnn4 qV (AIC.) 0

I. KEY WORDS (Centtum an meveo side It ne..emy mid Id*a.U by &eek nmnber)

Local Computer NetworksLocal Area NetworksComputer Network ProtocolsComputer Interfaces

20. A STRACT (Centiu. an e ere eide iI meoesmy and Identi y by Wloek mundr)

Development of the Air Force Institute of Technology DigitalEngineering Laboratory's local computer network (DEWLET operatingsystem was continued. The DELNET operating system was developedunder the standards of the International Standards Organization's7 layer protocol model. This report contains the design andimplementation of the protocol layers l,2,and 3. This report alsopresents the tests and validations conducted to verify proper-- re development. Conclusions and recommendations are also ps,

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lmhhsohmohmoiI onhhhhhhhonh1honhI - DTIC · Laboratory Network (DELNET). AFIT's DELNET is a proposed local computer network (LCN) whidh will interconnect a series of independent stand