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U.S. DEPARTMENT OF COMMERCE/ National Bureau of Standards

A Review of

Network Access Techniques

with a Case Study:

The Network Access Machine

r~-
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards 1 was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and technology

and facilitate their effective application for public benefit. To this end, the Bureau conducts

research and provides: (1) a basis for the Nation's physical measurement system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology,

the Institute for Computer Sciences and Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United

States of a complete and consistent system of physical measurement; coordinates that system

with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry,

and commerce. The Institute consists of the Office of Measurement Services, the Office of Radiation Measurement and the following Center and divisions:

Applied Mathematics — Electricity — Mechanics — Heat — Optical Physics — Center

for Radiation Research: Nuclear Sciences; Applied Radiation — Laboratory Astrophysics

" — Cryogenics " — Electromagnetics " — Time and Frequency =

. THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research leading to improved methods of measurement, standards, and data on the properties of well-characterized

materials needed by industry, commerce, educational institutions, and Government; provides

advisory and research services to other Government agencies; and develops, produces, and

distributes standard reference materials. The Institute consists of the Office of Standard

Reference Materials, the Office of Air and Water Measurement, and the following divisions:

Analytical Chemistry — Polymers — Metallurgy — Inorganic Materials — Reactor

Radiation — Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to promote

the use of available technology and to facilitate technological innovation in industry and Government; cooperates with public and private organizations leading to the development of technological standards (including mandatory safety standards), codes and methods of test; and provides technical advice and services to Government agencies upon request. The Insti- tute consists of the following divisions and Centers: Standards Application and Analysis — Electronic Technology — Center for Consumer

Product Technology: Product Systems Analysis; Product Engineering — Center for Building

Technology: Structures, Materials, and Life Safety; Building Environment; Technical Evaluation and Application — Center for Fire Research: Fire Science; Fire Safety Engineering.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts research and provides technical services designed to aid Government agencies in improving cost effec- tiveness in the conduct of their programs through the selection, acquisition, and effective utilization of automatic data processing equipment; and serves as the principal focus within

the executive branch for the development of Federal standards for automatic data processing

equipment, techniques, and computer languages. The Institute consists of the following

divisions: Computer Services — Systems and Software — Computer Systems Engineering — Information Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination and

accessibility of scientific information generated within NBS and other agencies of the Federal Government; promotes the development of the National Standard Reference Data System and

a system of information analysis centers dealing with the broader aspects of the National Measurement System; provides appropriate services to ensure that the NBS staff has optimum

accessibility to the scientific information of the world. The Office consists of the following

organizational units: Office of Standard Reference Data — Office of Information Activities — Office of Technical

Publications — Library — Office of International Relations — Office of International Standards.

1 Headquarters and Laboratories at Gaithersburg. Maryland, unless otherwise noted; mailing address Washington, D.C. 20234.

3 Located at Boulder, Colorado 80302.
.-!' .

A Review of Network Access Techniques

with a Case Study:

The Network Access Machine

OF STANDARDS

LIBRARY jut xl 1976

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no, q/j

-t. 'licJwicjfrl (UcrteL Ao,V7?

Robert Rosenthal

Institute for Computer Sciences and Technology

National Bureau of Standards

Washington, D.C. 20234

Sponsored by the National Science Foundation 1800 G Street, N. W.

Washington, D. C. 20550

Grant Number DCR 72-01206A06

<•*" °" *Q

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

U 3 NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

i J Issued July 1976
National Bureau of Standards Technical Note 917

Nat. Bur. Stand. (U.S.), Tech. Note 917, 36 pages (July 1976) CODEN: NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1976

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. 03.46:917). Price 85 cents (Add 25 percent additional for other than U.S. mailing).
CONTENTS

ABSTRACT 1

Keywords 1

INTRODUCTION 2

ASSISTANCE 3

INTERFACES and PROTOCOLS 3

TECHNIQUES 4

Basic Communications Assistance 4

Resource Identification 5

Resource Connection 6

Resource Selection 7

Service Integration 8

Distributed Assistance 9

Minicomputer Hosts 10

Other Trends 10

ARCHITECTURE 10

THE NAM 11

THE NAM FACILITY 14

Total Configuration 14

Communications Peripherals 15

Disk Peripherals 16

Other Peripherals 16

Software System 17

WORKING in the NAM ENVIRONMENT 17

APPLICATION Of the NETWORK ACCESS MACHINE 22

SUMMARY 26

REFERENCES 27

l l l
Figures

FIGURE TITLE PAGE

1

2

3

4

5

6

7

8

9

10

Example Editor Call

The NAM Configuration

Modes of NAM Operation — Normal

and Procedure

Effects of Switching Modes

Example Editor Call Using NAM

A Programmed User

Macro Language Directives

An Example Macro

Example Use of .EXT Directive

Mediated NAM Access to Retrieval

Systems

12

16

18

18

19

20

20

21

22

24

TABLE

TABLE TITLE PAGE

Selected Subset of Functions 25

IV
A REVIEW OF NETWORK ACCESS TECHNIQUES

with a Case Study: The Network Access Machine

Robert Rosenthal

Institute for Computer Sciences and TechnologyNational Bureau of Standards

Washington, D. C. , 20234

ABSTR ACT

The computer industry's ability to serve a diverse and expanding user community is evidenced

by the rapid growth of computer network services.

Computer service providers design and market their

own offerings as they deem best, given their own

market and their own set of resources. This has

led to a proliferation of similar resources

requiring different user access procedures. With

emphasis on currently operating and planned

systems that assist users in accessing available

network services, this report identifies the

techniques used in network access devices. By

examining these devices, the trend toward

improving the interface between the user and the

computer is brought more clearly into focus and up

to date.

One specific solution — A Network Access

Machine (NAM) — is described in detail. The NAM

is a minicomputer system that acts as a network

access point for a user at his terminal and

assists the user through the automatic execution

of access procedures. This minicomputer facility

allows the user to specify (or to have specified)

his own network command sequences for execution on

a specified network and host connected to that

network. Computer responses are analyzed to

assure agreement with those anticipated for

specific commands. Conditional parameterized

expansions allow the use of the same commands on

different host computers and different networks.

Key words: Access procedures; command language;

computer networks; job control language; macros;

minicomputers; protocols; teleprocessing.
INTRODUCTION

The computer industry's ability to serve a diverse and

expanding user community is evidenced by the rapid growth of

computer network services. Little over a decade ago, when

people began to interact with computers in the routine

performance of their jobs, few cared about the differences

between similar service offerings — all were eager to learn

and experiment with that new technology.

Today, with the advent and growth of computer networks,

that modest size group of scientists, engineers, and

researchers has grown to include professionals in all

sciences — mathematical, physical, health, and social — as

well as students, stock brokers, and reservation clerks from

many fields. Just as the number of users has grown so has

the number and diversity of computer services.

Computer service providers design and market their own

offerings as they deem best, given their own market and

their own set of resources. Trends in service growth,

traceable through individual families of mainframes,

operating systems, and service packages, lack direction and

consistency from the user's point of view. The reasons for

this fragmented growth might be justified considering

constraints imposed by telecommunications facilities,

peculiarities imposed by mainframes and their operating

systems, and the personal preferences of system developers.

Unfortunately, many of these services are characterized by

different implementations of the logically similar steps

that users must take in order to accomplish productive work.

Today we have a situation in which more and more users

are consuming more and more services while the services

themselves perpetuate differing user procedures for access

to the same logical services. A reasonable question to ask

is "what can be done to help the user?" Standardization of

access procedures is a possible solution. However, a procedure for access that makes one service more attractive

than another through enhanced features should not be

compromised by a premature effort to standardize such

procedures — especially if the standard settles on "lowest

common denominator" features. Encouraging competition among

network service providers can be in the user's best interest

if it leads to innovation in the amount and quality of

service received and in the reduction of costs in providing

the service. Rather than push for extensive user-oriented

uniformity, it may be desirable to continue to permit and

encourage such non-uniformity, but to compensate for it

through network access assistance to the user.
ASSISTANCE

The concept of assisting users is not new to the

computer industry. The notion of a compiler, for example

resulted from this kind of motivation. Unfortunately,

compilers were soon accompanied by complex operating system

control languages. Once again, assistance techniques in the

form of a control language macro capability or a catalogued

procedure capability were employed to help the user. With

these techniques the inexperienced user easily performed

complicated job steps and the experienced user worried less

about detail in setting up job steps.

This type of assistance, extended beyond a single

computer system and placed in the interactive computer

network environment, lessens the wearisome burden faced by

users contending with separate and different services that

accomplish logically similar tasks. In such an environment,

the user should have resources readily available from

different computers without regard for the specifics of how

to obtain them; the user should be more concerned with what

services are required.

Early attempts to provide computer network assistance

are still in use today. One interesting technique makes use

of function buttons that produce character sequences. These

sequences represent the appropriate user protocols that

identify terminals, users, and services, thus alleviating

the need for the user to key in the required protocol. The

familiar "who-are-you" drum is an example of this kind of

technique. Other devices — stunt boxes, automatic card

dialers, and paper tape loops — have been used successfully

to assist users, but all of these devices are usually

applicable only on dedicated connections to specific

computer systems and services. In a modern computer network

other more general techniques can be employed.

INTERFAC ES AND PROTOCOLS

Access assistance techniques in modern computer

networks try to improve upon the interface that exists

between a user at his terminal and a network based resource.

For the terminal user of an interactive computer network the

interface is two things. First, it is the physical

equipment — the teleprinter or CRT terminal and the

communications equipment connecting it to the computer.

Second, at a higher and more complex level, the interface is

the protocol that a user must know to communicate with the

network and its computers — to express his needs or demands
on the computer and to understand the produced results or

errors from the computer.

These user protocols, unlike the "well defined" link

protocols of computer-to-computer communications (such as

the ARPA Network IMP-IMP, HOST-IMP, or HOST-HOST protocols

[POS 74]), manifest themselves in the interactive dialog

between the user and the computer. And, these user-computer

protocols are not "well defined." They are typically machine

dependent and often installation dependent [NEU 73]

.

Interface and protocol standards groups are actively

engaged in producing outputs directly related to the issue

addressed here. At least one standards group in the Federal

Government (FIPS Task Group 20) is studying low level user

entry and exit protocols and procedures. The standards

approach to access assistance represents a technique that is

still in its infancy. With a three year projected

completion date for the development and acceptance of the

first entry and exit protocol standard for the Federal

Government, the viability of this technique is yet to be

realized. The beneficiaries of standards as an assistance

technique will be the scientists, engineers, researchers,

and those who work with them, who use, or have the potential

for using, one or more computer services.

TECHNIQUES

These approaches to solving the problem of network

access have been utilized by several groups in specific

implementations of the access function. Pyke , in a recent

paper [PYK 74] , reviews these efforts with special emphasis

on presently operating and planned access support

configurations. Categorizing these examples and other

related devices as reported in the open literature reveals

the trend that is evident in network access techniques — a trend toward improving the interface between the user and

the computer through sophisticated assistance techniques and

devices. By examining these devices — their methodology,

their purpose, and their scope — this trend is brought more

clearly into focus and up to date.

Basic Communications Assistance

Minicomputer based concentrators and packet or message

switchers are well established solutions that provide the

basic communications required of network users. Devices

like the ARPA Network TIP [ORN 72] and the TYMNET Network
TYMSAT [TYM 71] satisfy these requirements through data rate

identification, terminal compatibility transformations

including carriage delay timing functions and character set

transformations, and host computer selection specifications.

Over the last few years these devices have been

modified to reflect the needs and demands of the user

community. They utilize software packages that map

character sets and provide carriage delays to accommodate

different user terminals. These devices continue to evolve

in an attempt to follow manufacturers' terminal innovations.

In response to new terminal innovations, devices like the

TIP and TYMSAT recognize the user's terminal speed; while

default terminal characteristics for other parameters —

parity, full or half duplex, tab settings, etc. — are

assumed, provisions to specify different settings are

available. Many computer service providers and mainframe

manufacturers have followed this trend by providing

communications support for a large variety of terminals and

by utilizing front end computers with appropriate software

packages.

Resource Identification

Access techniques only start with the basic

communications assistance functions described above.

Establishing connections to network host systems, logging

into host systems, requesting resources, and initializing

services or databases can be extremely complex and

cumbersome. In one early ARPA Network attempt, a loose leaf

notebook containing information on the resources available

on the Network and the access methods to these resources has

met with only very limited success. The Network Information

Center's ARPANET Resource Notebook [ARP 73] existed in both

an on-line and printed form and contained entries for all of

the resources available at each serving host on the network.

Unfortunately, no attempt was made to facilitate access to

these resources other than listing individuals to contact.

(A more recent edition of this notebook has been published

in paperback form [ARP 75] and includes enough information

for a user to access the desired resource.) Resource

identification techniques of a more substantive nature

developed

.

The REX system, an ARPA Network based on-line user

assistance facility, provides resource-specific information

[BEN 74] . This system, designed with the eventual goal of

automating access to various network resources, finds the

location of a resource on the network, provides information
about the resource, and describes the method for acquiring

it. REX provides a facility for dealing with a heterogeneous network as a coherent entity, regardless of

the particular characteristics of the individual host.

A user language that provides commands to retrieve

information about resources and to describe specific

resources utilizes one of four keyword types — a resource

name, a resource attribute, a resource category, or a host

name — in conjunction with either a retrieval command —

FIND or DESCRIBE — or the ACQUIRE command.

An example is:

DESCRIBE FORTRAN AT MIT-MULTICS

The ACQUIRE command establishes a transparent connection to

the resource without further action on the part of the user

Resource Connection

Connections to resources that are available in computer

networks require cooperation between the connection

initiator — the user or his surrogate — and the resource

that ultimately provides the service — a coherent logical

entity that exists in order to accomplish a specific task as

viewed by the user. In a computer network environment it is

not unusual for a multi-level hierarchy of access requests

to occur to effect resource connection. Cooperation in

traversing the network hierarchy may require several

resource solicited identifications, passwords, and system or

service names.

While the solicitation of user information occurs at

the user level of interaction, many other protocols are used

by the communications discipline employed. Usually these

other disciplines are masked from the user and are

transparent. In this way, a surrogate — usually a process

knowledgeable in the protocol or line discipline employed —

acts on behalf of a user to connect him to the requested

service. For instance, users of the ARPA Network access

resources with the cooperation of a TIP. It is feasible for

the acquired resource to then request other resources on

behalf of the user. In this example, the user level of

interaction is the command language of the TIP; acting as a surrogate for the user, the TIP, knowledgeable in the

IMP-IMP protocols, completes the resource connection for the

user .
Hierarchical connections easily occur. In the ARPA

Network, many host computer resources support a service

known as FTP (File Transfer Protocol) . This service

establishes network connections to other resources on behalf

of the user for the purpose of transfer ing files between

host computers. Currently, the user need not identify

himself to the TIP; however, a user account is required for

the host system to execute the service FTP. For FTP to

access the file system of the other resource, the user level

protocols require the user identification and password for

the other resource.

Resource Selection

Evidence in the published literature indicates that a trend in the use of intelligent terminals and their close

cousins, "clustered" terminals, to assist users in the

selection of resources is developing. A research program

currently underway at the RAND Corporation aims to develop a prototype intelligent terminal system initially implemented

on a minicomputer. The system, called the RAND Intelligent

Terminal Agent (RITA) , is based on sets of condition-action

rules that encode complex sets of heuristics for handling

interactions both with users and with external systems [AND

75] . RITA is capable of interacting with remote data

systems, carrying out time-dependent tasks over extended

periods of time in a semi-autonomous manner. The

supposition that a rich set of heuristics for deciding

communications levels of remote system interaction and for

resource acquisition and graceful recovery from unexpected

failure has in part motivated this effort [AND 76]

.

At the National Bureau of Standards a minicomputer-based device called a Network Access Machine

(NAM) expands user-entered commands into command sequences

executable on specific networks and host computers connected

to that network [BLA 74] . The NAM analyzes system and

network responses to assure agreement with those anticipated

for specific commands. Conditional and parameterized

expansions of user-entered commands are capabilities being

added to the basic working NAM. This capability will allow

the use of the same commands to permit access to resources

on different host computers and different networks [ROS 75]

.

Other extensions to the NAM are currently being

implemented. One function is to predict the expected

response time of a particular computer for use in a specific
applications area — such as compute-bound FORTRAN jobs,

small BASIC jobs, interactive editing sessions, or some

other category. Good indicators of computer response time

can be calculated by the NAM in the following way. The NAM

automatically connects to the particular computer in

question in order to execute a predefined benchmark job

representative of the applications area. By having the NAM

automatically time the response for the job execution the

NAM can present to the user the results of the calculations

in the form of a prediction of expected response time.

Several benchmarks have been successfully tried — producing

excellent predictions of expected response time.

One other intriguing function being added to the NAM is

to provide the user with network wide tutorial assistance.

A profile, maintained for each NAM user, reflects the

disposition of the user with respect to any particular

computer that he might use. Data are maintained in the

profile concerning recent use of specific computers, the use

of internal indicators, and help assistance indicators.

Using this data base, the NAM acts on behalf of the computer

in assisting the user.

An example of somewhat specialized access support to a network user employing a microprocessor is the development

of a "line processor" by the Stanford Research Institute

[HAR 74] . This device interfaces a class of display

terminals together with a pointing device called a "mouse"

and a one-hand keyboard called a "key set" in such a way

that the entire configuration can provide particularly

effective access to a network-based interactive text

manipulation system. The line processor has potential,

however, for application beyond the initial intended use.

Service Integration

An important trend, motivated by the desire to

interface one user to multiple resources, is evident in the

work done in the information services community by Marcus at

MIT. He has developed a system that involves the coupling

of two bibliographic data retrieval systems in such a manner

that the user perceives a single homogeneous system [MAR

75]. Specific applications support built within the MULTICS

system at MIT includes a master index and thesaurus that

stores the vocabulary of the separate data bases along with

index term interrelationships. The user is also provided

with a common bibliographic data structure in which the data

elements for bibliographic information are organized and

interrelated among different data bases. This approach has
been demonstrated experimentally using the ARPA Network for

access to the National Library of Medicine Medline service

and the MIT Intrex retrieval system.

Another Example is the Resource Sharing Executive

(RSEXEC) for the ARPA Network [THO 73] . This executive

system provides an environment for "inter-host" user-user

interactions, for managing "multi-host" file directories,

and for controlling multiple "jobs" on several hosts. In

addition, the RSEXEC serves as a command language

interpreter for the ARPA Network TIP users. Executing in

any one of several available PDP-10 TENEX systems on the

Network, RSEXEC can maintain communications through the

Network with other TENEX systems. In this way the resources

of all of the systems to which RSEXEC connects can be

monitored and used. Facilities for monitoring status,

logged in users, and load averages are available as well as

the capability to build and create a composite file

directory incorporating files from the various computers in

the subnetwork. Provision is also available for initiating

jobs at one or more cooperating sites at which valid

accounts are maintained.

Distributed Assistance

Distributed assistance — partially in host systems and

partially in front end systems — can provide better network

response at less cost. The National Software Works (NSW)

motivated by a desire to provide users with access to a number of general or specialized software applications

packages, resides on a PDP-10, but will also be available on

a minicomputer such as the PDP-11 [IRB 76] . NSW provides

assistance in such a way so as to maintain a consistent user

interface from package to package even across host systems.

It is anticipated that heavily used common commands and

grammars can be executed in the front end systems, thus

increasing network response times and decreasing network

communications costs.

Kimbleton and Schneider emphasize that the NSW is

intended to be an environment for building software systems

[KIM 75] . It is to include program preparation tools —

cross assemblers and compilers, editors, simulators and

emulators, performance analyzers, program formatters,

flowcharters, test-data generators, and other checking tools

-- that build software systems. These systems will usually

be removed and run in a different environment, since the NSW

is not intended to support the recurring execution of

end-user applications.
Minicomputer Hosts

A minicomputer installed as a network host computer can

also perform substantial access functions for a community of

users. The ELF system provides multiple, concurrent users

with local computing and file capability including signal

processing for speech applications as well as flexible

access to ARPA Network resources [RET 75] . The ARPA Network

Terminal System (ANTS) was a mini-host designed to

facilitate use of the ARPA network by students at the

University of Illinois. Use of this system promoted Remote

Job Entry (RJE) use of the Burroughs 6700 at the University

of San Diego as well as RJE use at the Campus Computing

Network (CCN) at UCLA [BOU 73]

.

At the University of Chicago, Ashenhurst has developed

an interesting hierarchy of minicomputers and large scale

computers to assist users in laboratories [ASH 74].

Minicomputers located in science laboratories throughout the

campus are served by a larger minicomputer at a central

site. Large compute-bound applications are served when the

central minicomputer acquires resources on a large scale

computer on behalf of the laboratory mini.

Other Trends

The work of Wyatt at Harvard, in planning for an access

system to couple users to multiple serving systems and

networks, includes a call for automatic transformation of

job control statements to match those of remote systems and

for facilities to support "transparent connection" of local

terminal facilities to various communications networks [WYA

74] . Wyatt also proposes that the

"translation/communication system" perform comprehensive

accounting and billing for multiple user accounts.

ARCHITECTURE

The preceding examples suggest that alternative

solutions exist and that the access assistance functions can

reside in a process executing in a host system, in a dedicated minicomputer, or in a single user "intelligent"

terminal or terminal "cluster".

When supported on a large host computer, the access

assistance functions utilize the sophisticated and extensive

subsystems that are available — the file management

systems, the language compilers, the utility processors and

10
on and on. But, this type of application can be

accomplished with less sophisticated resources. For

instance, the ARPA Network TIP, in part motivated by a desire to move the basic communications support and low

level access functions out of the large host computers and

into smaller, less expensive minicomputers, eliminates much

of the overhead required to handle access functions in a larger host system. Minicomputers are often used

extensively for store-and-forward functions and other

applications such as remote concentrators and message

switchers; it might make good economic sense to put the

access function in a minicomputer also.

The minicomputer, placed in the communications link

between the user terminal and the serving computer network,

can allow multiple users to access different hosts on one

network or even different networks. The minicomputer seems

ideally suited for such an application especially when

several users or user groups require a moderate file storage

capability for small files and a minimum computational

capability for communications processing, signal processing

or other requirements.

Intelligent terminals can support access to multiple

hosts on a single network or to multiple networks, but file

storage and other terminal resources appear to be too

expensive at this time to dedicate to a single user

terminal. Also, intelligent terminals may require

cooperation with larger host systems for initial program

loads; such cooperation may not be available from candidate

networks or host computers. At this time, the intelligent

terminal does not have as great a potential as the "cluster"

supported minicomputer to perform the required access

functions. Based on predictions that within five to eight

years inexpensive interactive terminals will be available

with the power of todays minicomputers, the use of

intelligent terminals to support the access function will be

feasible.

THE NAM

The Network Access Machine, as pointed out earlier, is

a programmed minicomputer supporting a "cluster" of user

terminals. The NAM acts on behalf of a user at his terminal

and automatically generates the necessary interaction or

dialog that accomplishes the user's intended function. The

function might be to connect the user's terminal to a specific computer on a network, to automatically identify

the user to the computer (to log-in) , or to select and

initialize a subsystem on the computer — a language

processor such as FORTRAN or COBOL, or a data base for a

11
bibliographic search.

These functions or access procedures, requested by

users, are called macros. The NAM expands these macros to

produce the correct machine dependent (specific computer)

dialog. Complex access procedures, coded and stored on

macro files, are given simple names by the user; macros are

easily recalled by name and expanded.

At the time of the expansion, parameters can be passed

to the macro. An example use for a parameter is to identify

to the macro a particular computer, a particular user, and a particular subsystem. In this way, macros can be written

like subroutines — general in scope, but made specific by

the parameters passed to them.

The use of simple names for complex access procedures

and the ability to pass parameters to macros makes the NAM a flexible aid for any user of computers; especially when the

user accesses a variety of different computers where the

access protocols are typically machine dependent and often

are installation dependent.

Consider a simple example. Figure 1 shows the user

protocol required to access an editor on three different

computers. While the dialog is similar in all three

examples, differences in syntax, case, and editor name can

lead to confusion.

COMPUTER PROTOCOL

PDP-10 on ARPA Net E

@L 241

LOG RMR 115681

TECO

MULTICS on ARPA Net E

@L 44

enter Rosenthal CNet

teco

General Electric

Information Services

H

abcl2345, rosenthal

TEDIT (X)

Figure 1 Example Editor Call

12
A reasonable question to ask is, what can be done to

help the user?

A protocol that makes one network service appear to the

user like any other is a general answer. However, as stated

earlier, protocols that make one service more attractive

than another through enhanced features should not be

compromised by a premature effort to standardize such

protocols. Encouraging competition among network service

providers can be in the user's best interest if it leads to

innovation in the amount and quality of service received and

in the reduction of costs in providing the service. Rather

than push for extensive user-oriented uniformity at the

higher levels of user-network interaction, it may be

desirable to continue to permit and encourage such

non-uniformity, but to compensate for it through network

access assistance to the user. By focusing on the low level

user protocols like "log-in", "host selection", and "service

selection" , the user can become more concerned with the

service he requires and less concerned with how to obtain

it.

Several important user protocols can be improved upon.

First, the initial user-computer connection procedure can be

made more uniform. This starts with the physical connection

of the user terminal to the computer network. Once the

physical connection is made and the terminal's speed and

identity have been established, the access procedures which

follow are usually hierarchical, nested or even recursive.

Usually one or more of the following procedures are

performed by the user in the network environment: — host computer selection — host computer log-in — host computer service selection — service initialization — service exit request — host exit request — network exit request

These are the specific user protocols that can be improved

upon in current operational and experimental networks. The

NAM facility, designed to assist users with these protocols,

is briefly described.

13
THE NAM FACILITY

The NAM minicomputer facility gives the user the

capability to automatically access the resources of a remote

computer. This capability is made possible by the NAM's

ability to act as a surrogate both in establishing the

physical communications connection to the remote computer

and in expanding macro procedures to produce the correct

machine dependent interactive dialog for the remote

computer

.

This surrogate, acting on behalf of the user, functions

as a "programmed user" — a computer programmed to behave as

a human user ... a programmed automaton. In establishing

the physical communications connection, the programmed user

utilizes an automatic calling unit for placing dial out

calls; hard-wired connections are available for local

computer connections. In accessing resources on remote

computers, the programmed user sends requests; waits for

replies; analyzes responses; and decides to either

continue, or to seek user intervention.

While seemingly insignificant for a human to perform,

these actions — sending requests, waiting for replies,

analyzing responses, and deciding what to do next —

represent non-trivial tasks for a computer to perform. How

does the programmed user determine when the remote computer

can accept the next request; how does it know when the

remote computer has finished a reply; what is required to

analyze a response so that the next request is logical and

correct? Let us start answering these questions by stepping

way back and first discussing the total picture — the

minicomputer configuration used to support the algorithms

that execute to perform as a programmed user. Then, the

programmed user itself can be discussed revealing its

utility in the Network Access Machine.

Total Configuration

The word minicomputer is hard to "pin down" in a formal

definition — it has humorously been defined as any

processor for which the manuals are free. For the purpose

of this note, the definition of a minicomputer conjures up

the idea of a relatively small inexpensive processor to

which (often expensive) peripherals are attached. The

processor itself is usually 12 to 18 bits wide and is

usually supplied with up to 64k to 128k words of random

access memory. A complement of standard peripherals

includes disks — floppy disks, fixed head disks, or disk

14
packs — communications interface equipment, and other

miscellaneous devices such as clocks, printers, and on and

on. The term minicomputer applies to an integrated system

consisting of this type of processor and these kinds of

peripherals.

The NBS NAM is implemented on a Digital Equipment

Corporation PDP-11/45 minicomputer with 64k words of 16 bit

core. Character asynchronous communications interfaces are

used to interconnect user terminals to the NAM and the NAM

to remote computers. A special peripheral called an

automatic calling unit and line selector (ACU/LS) is used by

the NAM to place dialed telephone calls to remote computers.

A multi-programmed disk-based operating system supports the

NAM and provides for individual user directories into which

user macro files are catalogued and maintained. Other

miscellaneous devices used by the NAM system include a line-frequency clock and a printer.

Communications Peripherals

The NAM, acting as a surrogate for the user, must

interconnect the user's terminal to the remote computer. To

do this, two character asynchronous interfaces are utilized — one for the user terminal connection to the NAM, and one

for the NAM connection to the remote computer.

The physical circuits for these connections are either

dialed through the switched telephone network or directly

connected by "twisted-pairs" — wires that interconnect the

equipment. As shown in figure 2, the NAM supports directly

connected users and dial-up users. Connections to the

remote computer are supported from the NAM to directly

connected local facilities such as the NBS ARPA Network TIP,

the NBS PDP-10 in the Experimental Computer Facility (ECF)

,

and other minicomputers in the ECF, or to dialed out

networks using the automatic calling unit.

15
Directly

Connected

Users

'vwrnP*Dialup

Users

I. NBS 5 TIP

^ <-» ADDAK

H

B^S ACU to other ^^^

Networks

NAM

Figure 2 The NAM Configuration

Disk Peripherals

The disk, relatively large in storage capacity compared

to the size of core, serves a dual purpose in the NAM.

First, it supports the operating system under which the NAM

runs. The operating system requires large amounts of

storage for its state dependent information — its tables,

program modules and data — and since all of this

information will not fit into core at one time, it is

maintained on the disk — to be recalled when needed.

Second, the disk provides users of the NAM with individual

directories for cataloguing macro files. These directories

are maintained by the user — he creates new macros and he

deletes obsolete ones.

Other Peripherals

Other miscellaneous peripherals are used in the NAM

minicomputer configuration; most important is the line

frequency clock. As a multi-user system in a multi-programmed environment, the NAM must allocate its

processing power in time-slices — the amount of processor

time that a running program may utilize before another

16
program receives control. The clock controls the time slice

allocations so that each user receives an equal share of the

available processor time.

The line printer, another useful peripheral, can

produce hard-copy transcripts of the interactive dialog. At

the user's request, a disk file called the transcript file

is produced as the NAM forwards characters to and from the

terminal and remote computer. The user can request

hard-copy of all or portions of the transcript file. When

CRT display terminals are used, this printer — a shared

peripheral — is often the only hard copy available.

Software System

When viewed as an extension to the hardware, the

software system provides a foundation for building,

developing, and supporting the applications programs that

make up the NAM. The software system itself consists of two

separable entities — the operating system software and the

applications software. The applications software utilizes

the operating system software for input/output (I/O)

requests, file management requests, and other requests

including scheduling programs for execution, allocating core

for programs, and arbitrating conflicts for peripheral

requests.

The applications software is the set of programs that

execute to provide the terminal user with a network access

capability. These programs consist of the Macro File

Expander, the remote computer dialog Response Analyzer and

the terminal user Input Interpreter. These three

applications programs make up the NAM environment.

WORKING IN THE NAM ENVIRONMENT

Characters sent to the NAM are normally stored and

forwarded — user characters are forwarded to the host

system and the host system characters are forwarded to the

user's terminal. Upon receipt of the special "~" character

as the first character on a line from the user's input, the

NAM enters "procedure" mode and leaves the normal

store-and-forward mode of operation. In figure 3 these two

modes of operation are illustrated.

17
NORMAL

> N

U E

S T

E W

R

R

K

PROCEDURE

> MACRO

INTERPRETER

&

RESPONSE

ANALYZER

DISC

Figure 3 Modes of NAM Operation — Normal and Procedure

The effect of switching modes is illustrated in figure 4

where a line of text preceded by the "~" produces a macro

expansion as in the first and third lines. When the "~" is

not used, characters are simply forwarded as in the second

line of figure 4.

User Types NAM Outputs

"LOGIN 241 E

@1 241

LOG ROSENTHAL RMR 1

TECO TECO

"LOGOFF LOGOUT

@C

Figure 4 Effects of Switching Modes

18
When the "~" character is used the rest of the text on

the line containing the "~" character is treated as a NAM

macro name complete with any user supplied parameters. In

figure 5 the example editor call is again illustrated for

three host computer systems, but this time the NAM assists

the user by supplying the appropriate machine dependent

dialog

.

SYSTEM or NETWORK

BBN on ARPA Network

MULTICS on ARPA Network

GE INFORMATION SERVICES

USER DIALOG

"EDIT BBN

"EDIT MULTICS

"EDIT GE

Figure 5 Example Editor Call Using NAM

Access procedures can specify a complex series of

interactions with the remote system. In this case — the

EDIT example — each response to the NAM from the remote

system is analyzed according to information supplied by the

macro expansion. Simple Boolean combinations of character

strings describe the anticipated host computer response.

When the actual response meets this predefined criteria, the

next line of the macro expansion is transmitted to the

remote system. When the actual response fails to meet this

predefined criteria, one of two procedures is followed.

Most simply, the expansion is aborted and the offending

response is displayed on the user's terminal. In addition,

the response to the last line of the expansion is delivered

to the user to indicate that he may proceed to enter more

commands. However, the user has the option to explicitly

define an abort procedure — another macro to expand in the

event of a response failure.

Thus, as previously asserted, the NAM's macro expander

and response analyzer together form a "programmed user".

The macro expander creates machine dependent commands to be

sent to the computer network. NAM waits for the network to

respond as would a human user. The response analyzer then

decides if the network response is the anticipated response — a human user would perform this same function. If the

network response is found questionable, the decision to "try

again", or "read the manual", or "quit" must be made. If

the network response is acceptable (network response and

19
anticipated response agree) the macro expansion continues.

Figure 6 illustrates this "programmed user" concept and

equates the algorithm used by a human to accessing a network

resource with the NAM.

SEND

COMMAND

WAIT FOR

RESPONSE

NAM = Terminal + User

TRY AGAIN

READ MANUAL

ourr

YES

Figure 6 A PROGRAMMED USER

Directives employed in the macro language allow the

"programmed user" concept to be coded by real users and

interpreted by the macro expander. The major directives in

the language are shown in figure 7. Each directive in the

language relates to a function normally performed by a humar

user

.

FUNCTION DIRECTIVE

Send Command .SEND

Wait .TERM

Compare (with .MATCH

actual response)

No Match . ABORT

Figure 7 Macro Language Directives

20
These directives are illustrated in a sample dialog in

figure 8. The macro in this example is used to log into a

PDP-10 TENEX operating system at Bolt, Beranek and Newman

(BBN) using the ARPA Network TIP.

MACRO DIRECTIVES NAM SENDS/RECEIVES

.MACRO LOGIN HOST

.TERM 2' [CR LF]

' .MATCH 'HELLO'

.SEND 'E'

.TERM ' [CR LF]@

.MATCH 'OPEN'

.SEND '@L HOST'

.MATCH 'PREVIOUS'

.SEND 'LOG ROSENTHAL RMR 1 [CR]

E I

HELLO 321J,

£1 241|

LOGGER

OPEN

BBN - TENEX |

@

LOG ROSENTHAL RMR 1

JOB 24 on TTY 16

PREVIOUS LOGIN:

25-FEB-76 |

@

.ENDMACRO LOGIN

Figure 8 An Example Macro

The underlined strings in figure 8 indicate the

characters sent to the remote network by the NAM. The "I"

character indicates that the the carriage-return line-feed

sequence was received or sent. Notice that these strings

have a one-to-one correspondence to the arguments in the

macro directives. In the first directive — .MACRO — the

macro name — LOGIN — is specified and it has a formal

parameter — HOST. HOST appears again in the second .SEND

directive. The NAM output for this second .SEND directive

indicates that the ARPA host address 241 was actually sent.

This macro LOGIN was invoked and expanded by the NAM when

the user typed:

"LOGIN 2414,

The .TERM and .MATCH directives used to specify the wait and

compare states of the programmed user are specified before

21
the .SEND directive in the actual macro. While this is

seemingly inconvenient, it is necessary since the Macro

Expander facility in the NAM operates a line at a time and

consequently the NAM must know the expected response before

sending the expanded message to the remote system.

The NAM compares each character of the system response

with the predefined characters in the .TERM directive. Once

a string match occurs, the system response is considered

complete and the NAM attempts to then match the complete

response with the string in the .MATCH directive. The

strings used in the .TERM and .MATCH directives remain in

effect until they are changed or until an .ENDMACRO

directive is encountered. Notice that prior to the last

.SEND directive in figure 8, only' a .MATCH directive is

specified. The previous .TERM directive (.TERM ' [CR LF] ')

remains in effect.

APPLICATION OF THE NETWORK ACCESS MACHINE

Application of the NAM to a variety of useful access

functions has led to the development of the .EXT directive.

This directive enables the user to "penetrate" the network

to various levels using the same macro names (command names)

for different systems on the network. By appending an

extension name to the access procedure file name, the NAM

executes a macro specified for a particular host on the

network. The example in figure 9 shows how the file

extension is equated using formal macro parameters.

LOG BBN, ROSENTHAL, RMR, 1

.MACRO LOG HOST, USER, PASSWD, ACCT

.EXT = HOST

LOG USER, PASSWD, ACCT ///->

log.bbn rosenthal rmr 1

. ENDMACRO

EDIT ///->

edit.bbn

Figure 9 Example Use of .EXT Directive

22
First, an access procedure called LOG is invoked. It

has four parameters — BBN, ROSENTHAL, RMR, and 1. In the

text of the macro the extension is equated to the parameter

HOST; in this invocation, to BBN. In the third line of the

macro, the expander encounters a text line that is not a directive (not preceded by a "."); so, the expander assumes

that this line is the name of another macro to be invoked.

In this example, the text line after the .EXT directive is

to be invoked much like a subroutine — once completed,

control returns to the following macro line . This

subroutine call to macro LOG will actually be made to a macro called LOG. BBN as indicated by the expansion operator

"///->" (this symbol is only used to illustrate that this

particular expansion produces the indicated new macro name — this symbol is not part of the macro text file).

Finally, the last line in this example shows that once the

extension has been set from within a macro call, it remains

in effect for other macro invocations during the session.

(Provision to reset the macro file extension is provided.)

Using this capability, the user is able to create commands

for accessing computer networks; these commands can be

given the same name, thus providing for the user, a common

network access language.

The NBS NAM, already proven as a useful tool in the NBS

Experimental Computer Facility, is currently involved in an

experiment designed to provide convenient access to

resources likely to be found on heterogeneous computer

networks. In this experiment, the NAM is used to provide

"autonomous" access to any one of a selected set of

interactive retrieval systems. Unlike the M.I.T. work [MAR

75] on the actual "coupling" of (two) interactive retrieval

systems, the NAM has mediated but "autonomous" access to any

one of a selected set of retrieval systems. The retrieval

service selections are identified by the broad experimental

framework depicted in figure 10.

23
user terminal

NAM

intermediary

BASIS

-ORBIT

•MEDLINE

DIALOG

RECON

communication Retrieval

lines Systems

Figure 10 Mediated NAM Access to Retrieval Systems

The objective is to achieve a common command language

for only a subset of the functions that must or can be

performed in conjunction with on-line retrieval systems.

The reason for this selectivity is based on the well

established fact that some significant system differences

can render corresponding user commands irreconcilable.

Furthermore, the subset of functions to be addressed

involving those listed in Table 1 , should be realistic

enough to make the experiment productive in a reasonably

short period of time.

24
TYPE

1. Administrative

2. Substantive

3. Supportive

FUNCTI ON

a. Communication Linkup

b. Login Procedure

c. Logoff Procedure

d. System Disconnection

a. Files Identification

b. File Selection

c. Search Request

(1) Term Entry

(2) Logic Creation

d. Search Result Output

e. Search Term Display

a. Command Explanation

b. Procedural Help

c. Output Interruption

d. Input Editing

(1) Single Character

Erase

(2) Line Erase

Table 1 Selected Subset of Functions

Although the experiment is purposely limited, several

new features of the NAM are demonstrated. In addition to

the "normal" or store-and-forward character-at-a-time

transmission through the NAM a character string

store-and-forward facility proves useful. This mode allows

the NAM to selectively scan the user input data for possible

retransmission in a suitable format for the particular host

connection. This is particularly useful for correcting

simple typographical errors or for user solicited "help"

functions.

25
SUMMARY

Increased use of computer services by people in the

routine performance of their jobs continues to grow

steadily. To meet the demand, service providers design,

implement, and market their services using the technologies

and resources available to them. With the advent and growth

of computer network technology it is not uncommon for people

to use the resources of different computer systems. The

non-uniformity in access to these resources and the services

provided has led to the development of tools and techniques

to assist the user.

Some of the tools and techniques that provide users

with this access function have been described in this paper.

By examining these devices — their methodology, their

purpose, and their scope — and by discussing the current

trends in network assistance architectures, a framework has

been built for future discussions of this very important

function that can be provided to computer network users.

Within this framework, one example device, the NBS

Network Access Machine (NAM) is scrutinized to show its

applicability in solving some of the problems currently

frustrating users. The applicability of the NAM to provide

a uniform network-wide command language has been explored.

Access techniques are currently being employed to assist

users in the data retrieval community. A proposed set of

experiments that allow a user to perceive a common command

language across a heterogeneous set of retrieval services

found on different computer networks is currently in

progress.

26
REFERENCES

[AND 75] Anderson, R. H. , "Advanced Intelligent Terminals

As A User's Network Interface," How to Make Computers Easier

to Use (COMPCON 75 Digest of Papers, Sept 9-11, 1975) IEEE

N.Y., 1975. pp 180-182 (IEEE Catalog No. 75ch0988-6c)

.

[AND 76] Anderson, R. H. , and Gillogly, J. J., "The RAND

Intelligent Terminal Agent (RITA) as a Network Access Aid,"

to be published in the Proc. NCC 1976.

[ARP 73] "ARPA NETWORK Network Resources Notebook," The

Network Information Center NIC 6740, Augmentation Research

Center, Stanford Research Institute, Menlo Park, California,

1973.

[ARP 75] ARPANET RESOURCE HANDBOOK (NIC -23200) , Network

Information Center, Stanford Research Institute, Menlo Park,

California, 1975.

[ASH 74] Ashenhurst, R. L., "Hierarchical Computing," in

Greenberger, M. , et. al . , (eds.) Networks for Research and

Education The MIT Press, Cambridge, Massachusetts, 1974, pp

74-88.

[BAL 73] Balzer, R. M. , T. E. Cheatham, S. D. Crocker,

and S. War shall, National Software Works Design , USC/Information Sciences Institute, RR-73-16, November 1973.

[BEN 74] Benoit, J. W. and E. Graf-Webster, "Evolution of

Network User Services—The Network Resource Manager,"

Computer Networks ; Trends and Applications , IEEE Inc., New

York, 1974, pp. 21-24. (Proceedings of the 1974 Symposium

sponsored by the National Bureau of Standards, Gaithersburg

,

Maryland, and the IEEE Computer Society).

[BLA 74] Blanc, R. P., "Assisting Network Users with a Network Access Machine," Proc. ACM 1974, November 1974.

[BOU 73] Bouknight, W. J., G. R. Grossman and D. M.

Grothe, "The ARPA Network Terminal System—A New Approach to

Network Access," Proc. DATACOM 73, 1973 pp. 73-79.

[CAR 74] Carlson, W. E. and S. D. Crocker, "The Impact

of Networks on the Software Marketplace," EASCON '74 Record , (IEEE Electronics and Aerospace Systems Convention) IEEE

N.Y., October 1974, pp. 304-308.

[HAR 74] Hardy, M. E., Jr., "Microprocessor Technology to

27
Extend the Utility of Computer Peripherals," Proc. CQMPCON

74, February, 1974, pp. 299-302.

[IRB 76] Irby C. H. , "The Control Meta Language System," to

be published in Proc NCC , 1976.

[KIM 76] Kimbleton, S, R. , and Schneider G. M. , "Computer

Communication Networks: Approaches, Objectives, and

Performance Considerations," Computing Surveys , Vol. 7,

No. 3, Sept. 1975, ACM.

[KRI 73] Kriloff, H. Z., "A High-level Language for use

with Multicomputer Networks," Proc. NCC 1973 , pp. 149-153.

[LUT 72] Luther, W. , "Conceptual Bases of Cybernet,"

Computer Networks, ed. by Rustin and Randal, Prentice-Hall,

Inc., New Jersey, 1972, pp. 111-146.

[MAR 75] Marcus, R. S., "Network Access for the Information

Retrieval Application," Access to Computer Networks (Session

25, IEEE Intercon 75, IEEE Intercon Conference Record) IEEE

N. Y., April 1975, pp. 25/4: 1-7.

[NEU 73] Neumann, A. J., "User Procedures Standardization

for Network Access," NBS Technical Note 799, October 1973.

[ORN 72] Ornstein, S. M. , F. Heart, et. al . , The Terminal

IMP for the ARPA Computer Network," Proc. SJCC 1972, pp.

243-254.

[POS 74] Postel, J. B., et al , "ARPA Network Current

Network Protocols," Network Information Center NIC 7104,

Dec, 1974. (distributed by NTIS AD/A - 003 890).

[PYK 73] Pyke, T. N. , Jr., "Some Technical Considerations

for Improved Service to Computer Network Users," Proc.

CQMPCON 73, Feb. 1973, pp. 53-55.

[PYK 74] Pyke, T. N., Jr., "Network Access Techniques:

Some Recent Developments," Proc. Third Ann ual Texas

Conference , October 1974.

[RET 75] Retz, D. L., "ELF — A System for Network Access,"

Access to Computer Networks (Session 25, IEEE Intercon 75,

IEEE Intercon Conference Record) IEEE N. Y., April 1975,

pp. 25/2: 1-5.

[ROB 70] Roberts, L. and B. Wessler , "Computer Network

Development to Achieve Resource Sharing," Proc. SJCC 1970 , pp. 543-549.

28
[REI 74] Reintjes, J. F. and R. S. Marcus, Research in

the Coupling of Interactive Information Systems, Final

Report No. ESL-FR-556, Electronic Systems Laboratory,

Department of Electrical Engineering, MIT, June 1974.

[ROS 74] Rosenthal, R. and S. Watkins, "Automated Access

to Network Resources: A Network Access Machine," Computer

Networks—Trends and Applications, NBS-ICST and IEEE

Computer Society, May 1974.

[ROS 75] Rosenthal, R. , "Accessing Online Network Resources

with a Network Access Machine," Access to Computer Networks

(Session 25, IEEE Intercon 75, IEEE Intercon Conference

Record) IEEE N.Y. , April 1975, pp. 25/3: 1-4.

[THO 73] Thomas, R. H., "A Resource Sharing Executive for

the ARPANET," Proc. NCC 1973, June, 1973, pp. 155-163.

[TYM 71] Tymes, L. "TYMNET—A Terminal Oriented

Communications Network," Proc. SJCC 1971 , pp. 211-216.

[WYA 75] Wyatt, J. B., "Management in Applications of

Network Access," Access to Computer Networks (session 25,

IEEE Intercon 75, IEEE Intercon Conference Record) IEEE

N.Y., April 1975, pp. 25/1: 1-6.

29
NBS-114A (REV. 7-73)

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS TN-9172. Gov't Accession

No.

4. TITLE AND SUBTITLE

A Review of Network Access Techniques with a Case Study:

The Network Access Machine

3. Recipient's Accession No.

5. Publication Date July 1976

6. Performing Organization Code

7. AUTHOR(S)

Robert Rosenthal

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No. 6502372

11. Contract/Grant No. DCR-72-01206

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

National Science Foundation

1800 G Street, N.W.

Washington, D. C. 20550

13. Type of Report & Period Covered Interim

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

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

bibliography or literature survey, mention it here.) The computer industry's ability to serve a diverse and expanding user community

is evidenced by the rapid growth of computer network services. Computer service

providers design and market their own offerings as they deem best, given their own market and their own set of resources. This has led to a proliferation of similar

resources requiring different user access procedures. With emphasis on currently

operating and planned systems that assist users in accessing available network

services, this report identifies the techniques used in network access devices. By

examining these devices, the trend toward improving the interface between the user

and the computer is brought more clearly into focus and up to date.

One specific solution—A Network Access Machine (NAf^--is described in detail.

The NAM is a minicomputer system that acts as a network access point for a user at

his terminal and assists the user through the automatic execution of access procedures. This minicomputer facility allows the user to specify (or to have specified)

his own network command sequences for execution on a specified network and host

connected to that network. Computer responses are analyzed to assure agreement with

those anticipated for specific commands. Conditional parameterized expansions allow

the use of the same commands on different host computer and different networks.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons)

Access procedures; command language; computer networks; job control language; macros; minicomputers; protocols; teleprocessing

18. AVAILABILITY |

' Unlimited

_j For Official Distribution. Do Not Release to NTIS

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Springfield, Virginia 22151

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information for 5200 sets of raw data. Detailed discussions for each element, review of the

available experimental data and considerations

by which the authors arrived at final assess- ments. Complete bibliographic citations for 1658 references. Only original sources have

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Annual subscription: Domestic, $9.45; Foreign, $11.85.

NONPERIODICALS Monographs—Major contributions to the technical liter- ature on various subjects related to the Bureau's scientific and technical activities. Handbooks—Recommended codes of engineering and

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National Standard Reference Data Series—Provides

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Cryogenic Data Center Current Awareness Service A literature survey issued biweekly. Annual subscription: Domestic, $20.00; foreign, $25.00.

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