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Computer Science and Technology
NBS
PUBLICATIONS
NBS Special (^) Publication 500-
Personal (^) Computer Networks John Barkley
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QC
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TM he National Bureau of Standards' was established by an act of Congress on March 3, 1901. The
their^ m^ effectiveBureau's applicationoverall^ goal for^ is^ publicto^ strengthen benefit.^ and To^ advancethis end,^ thethe^ nation's^ Bureau^ scienceconducts^ and^ research^ technology^ and^ provides:and^ facilitate^ (1) a basis government, for the nation's physical(3) a technical basis measurement for equity system,in trade, (2)and scientific (^) (4) technical^ and^ technological services to promote^ services publicfor^ industry safety.^ and TheEngineering Bureau's Laboratory, technical work the Instituteis performed for Computerby the National Sciences^ Measurement and Technology,^ Laboratory, and the^ the Institute^ National for Materials Science and Engineering
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The National Measurement^ Laboratory
coordinates^ Provides^ the the^ national system^ system with^ measurementof^ physical^ and^ systems^ chemical^ of^ other^ measurement;^ nations^ and chemical^ furnishes measurementessential^ services throughout^ leading^ tothe^ accurate^ Nation's^ and^ scientific^ uniform^ community,^ physical^ and^ in- dustry, Government and commerce; agencies; conductsprovides physicaladvisory and^ and chemicalresearch research;services^ to develops,^ other calibration^ produces,^ and services.^ distributes The^ LaboratoryStandard^ Reference^ consists^ ofMaterials;^ the^ following^ and^ provides^ centers:
- • (^) BasicRadiation Standards Research^2
- • (^) ChemicalAnalytical PhysicsChemistry
The National Engineering Laboratory
Provides address nationaltechnology needs and and technical to solve services national to problems;the public conductsand private research sectors in to engineering tains competence and applied in the^ sciencenecessary^ in disciplinessupport^ of requiredthese^ efforts; to carry^ builds out^ andthis^ main- research capabilities; and providestechnical engineering service; develops measurement^ engineering traceability^ data and services;^ measurement develops test and methodsproposes andnew proposesengineering engineering practices; standards and develops and codeand improveschanges; develops mechanisms Laboratory consiststo transfer of theresults following of its researchcenters: to the ultimate user. The
Applied Electronics Mathematics and Electrical Engineering Manufacturing^2 Engineering Building Fire Research Technology Chemical Engineering^2
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Conducts Federal agencies research in andthe (^) selection,provides scientificacquisition, and application,technical services and use to aid of com- puter operations technology in accordance to improve with effectiveness Public Law and 89-306 economy (40 U.S.C. in Government 759), relevant
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voluntary^ ADP^ standards standardization^ guidelines, activities;^ and^ managing provides^ Federal scientific^ participation and technological^ in^ ADP ad-
visory foundation services for and computer-related assistance to Federalpolicies agencies;of the Federal and provides Government. the technical The In- stitute consists of the following centers:
Programming Technology Science and Computer Engineering Systems
The Institute^ for Materials^ Science^ and Engineering
Conducts materials, researchquantitative and understandingprovides measurements, and other data,technical standards, information reference funda- mental addresses to thethe scientificprocessing, basis structure, for new properties advanced andmaterials performance technologies; of materials; plans research evaluation around and phase cross-country diagram scientificdevelopment; themes oversees such asBureau-wide nondestructive technical programs tion; and broadlyin nuclear disseminates reactor radiation generic researchtechnical and information nondestructive resulting evalua- from its programs. The Institute consists of the following Divisions:
Ceramics Fracture and Deformation 3 Polymers Metallurgy Reactor Radiation
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!'Located Some divisions at Boulder, within CO, the center are with some elementslocated at at Boulder, Gaithersburg, CO 80303. MD.
Reports on Computer Science and Technology
Goverment^ The^ National for^ Bureaucomputer^ of scienceStandards and^ has technology^ a^ special activities.responsibility The^ withinprograms^ the^ Federalof the
standards,^ NBS^ Institute guidelines,^ for^ Computer and technicalSciences advisoryand^ Technology services^ areto improvedesigned theto^ provideeffectiveness^ ADP
of and computer development^ utilization efforts^ in^ theas Federalfoundation^ sector, for suchand^ toactivities^ perform andappropriate programs.^ research This
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Library of Congress Catalog Card Number: 86-
National Bureau of Standards Special Publication 500-
Natl. Bur. Stand. (U.S.), Spec. Publ. 500-140, 58 pages (July 1986)
CODEN: XNBSAV
U.S. Government Washington: Printing 1986 Office
For sale (^) by the Superintendent (^) of Documents, U.S. Government Printing Office, Washington, DC 20402
ABSTRACT
Personal computers are widely used in today's office to support clerical, administrative,
and managerial functions. Because communication between individuals in a office and
between groups in an organization is vital to the organization's ability to deliver products
and services, it naturally follows that the personal computers used by the individuals in an
office need to be able to communicate. This organizational requirement for communications
is often met by networking personal computers.
Personal computer networks are grouped into those networks which are designed for
personal computers and those networks, such as those based on a telephone system, which
can connect personal computers but were designed for a different purpose. Networks
which can connect personal computers but were designed for a different purpose include:
networks which connect personal computers to personal computers, personal computers
to computer centers, and personal computers to bulletin boards by means of public and
private telephone systems; networks which connect personal computers to computer centers
by means of direct wire in the same manner that terminals are directly connected to
computer centers; and networks which connect personal computers to networks designed
for large computers.
A personal computer network model, which embodies the needs and expectations of
personal computer users, is described. Each personal computer network type is compared
to this model according to the level of service provided. The generic types of service used
for the comparison include: file and print service,^ mail, messaging and^ conferencing,^ login,
remote task execution, outside communication, and network configuration.
A discussion of options available^ to^ those^ who^ have^ an^ immediate^ need^ for^ a^ personal
computer network is presented. Personal computer networks can improve^ productivity^ in
the office.^ However,^ there^ is^ the^ possibility^ of^ installing^ a^ personal^ computer^ network^ which
in the future becomes isolated from the mainstream^ of^ networking^ technology.^ Informed
planning can prevent this isolation from happening.
iii
Contents
List of Tables
1.1 Comparison of^ networks^ designed^ for^ large^ computers^ and^ networks designed
for personal computers 5
3.1 Features of a personal^ computer^ to^ personal^ computer^ network^16
3.2 Features of a personal computer to computer center network 17
3.3 Features of a personal computer to bulletin board network 18
3.4 Features^ of^ a direct^ wire^ to^ computer^ center^ network^19
3.5 Features of a network designed for large computers 20
4.1 Features of a network designed for personal computers 22
5.1 Features of current personal computer networks 40
vi
Chapter (^1)
Introduction
Personal computers are widely used in today's office to support clerical, administrative,
and managerial functions. Because communication between individuals in a office and
between groups in an organization is vital to the organization's ability to deliver products
and services, it naturally follows that the personal computers used by the individuals in an
office need to be able to communicate. This organizational requirement for communication
is often met by networking personal computers.
This document presents a survey of personal computer network technology from the
point of view of the end user. It characterizes the capabilities of personal computer net-
works and the services which they provide the user in terms of generic features which are
available from many producers. As a result, technical management and end users will have
an understanding of how personal computer networks can fit into an overall office automa-
tion strategy. The document does not discuss or evaluate alternatives for the sharing of
data, such as the manual exchange of floppy disks between personal computers.
The information contained in this document is partially based on experience gained
from the personal computer network testbed in the Advanced Systems Laboratory of the
Institute for Computer Sciences and Technology (ICST) at the National Bureau of Stan-
dards. Additional experience was obtained from the installation and operation of two
large personal computer networks within the ICST used to support both experimental and
administrative (^) applications.
The network testbed in the Advanced Systems Laboratory consists of several different
sets of network hardware on which many different network software packages may be
run. Network hardware includes baseband CSMA/CD, broadband CSMA/CD, baseband CSMA/CA, and token ring (see Tanenbaum text cited in Appendix A for explanation of
terms). In addition to the several personal computer networks^ within^ the^ Laboratory,
access is also provided from the Laboratory to both a personal computer network and
a large computer network available throughout the ICST. The large computer network
provides access to the Department of Defense MILNET (formally^ known^ as^ the^ ARPANET)
through a minicomputer gateway. Appendix B shows the personal computer network
testbed as it is normally configured. The testbed^ at^ any^ given^ time^ may^ be^ reconfigured
1
Figure 1.1: Catagorization of personal computer networks
also provide access to other networks which may have different communications protocols.
In this case, gateways provide not only the connection but also any necessary protocol
conversion between incompatible networks. Figure 1.2 shows a floor plan of a suite of
offices belonging to a small group in which a personal computer network is used to share
data (File Server), peripherals (disk on the File Server and the Laser Printer), and provide
each user with access to other communication systems (Communication Server).
For the purposes of comparison, computer^ networks^ can^ be^ classified^ according^ to^ the
types of devices they were designed to interconnect. The first computer networks were
designed to interconnect^ large^ multi-user^ computers^ and^ their^ terminals.^ Networks^ have
been designed which are primarily for the interconnection of personal computers. In some
cases, these networks do not^ support^ the^ connection^ of^ large^ computers^ and^ terminals.
For the purposes of this document, computer networks^ are^ divided^ into^ two^ types:^ wide
area networks and local^ area^ networks.^ A^ local^ area^ network^ (LAN)^ refers^ to^ a^ network
which interconnects systems located in^ a^ small^ geographic^ area,^ such^ as^ a^ building^ or^ a
3
Staff Assistant
n Printer /^eam^^?
Communications Server File/Print Server
Manager
Figure 1.2: Example of a personal computer network in an office suite used by a small
group
complex of buildings.^ A wide^ area network (WAN) refers to a network which interconnects
systems located in a large geographic area, such as a city, a continent or several continents.
It is^ interesting^ to^ contrast how^ a computer network designed for personal comput-
ers differs from a computer network designed for large computers. These differences as
summarized in Table 1.1 include:
- Size of System at Each Node
Networks designed for large computers connect large multi-user mainframe and
minicomputer systems. Networks designed for personal computers connect personal
computers which are usually small, single user systems. The capabilities of the
computer system at each node influence the kind of services which the network
delivers. Many of the services provided to large system users are not available^ to
personal computer users. One example of this^ is print^ spooling.^ When^ mainframe
users print a file, the file is queued to a printer and users are immediately able
to continue their work without waiting for the file^ to^ be^ printed.^ In addition,^ print
spooling allows mainframe users to share expensive printers. Personal^ computer^ users
also should not have^ to^ wait^ until^ the^ printer^ is^ finished^ before^ continuing.^ Moreover,
personal computer users need to be able to share expensive printers.^ Thus,^ print
spooling is a good candidate for a service^ which^ could^ be^ provided^ by^ the^ network.
Networks designed for large computers can be either local area or wide area
networks. However, almost all networks designed^ for^ personal^ computers^ are^ local
area networks. 4
50% of the cost of the personal computer for those personal computers which have
no peripherals and rely on the network connection for access to disks and printers.
- Services Provided A user at a node of a network designed for large computers already shares in-
formation and peripherals^ with^ other^ users^ of^ that^ node^ by^ virtue^ of the fact that
the node is a large multi-user system. Consequently, networks designed for large
computers usually only provide three basic network services, i.e., login (i.e., remote
terminal connection to a host), FTP (file^ transfer),^ and^ mail. The single user per-
sonal computer may require more flexible services, such as being able to access a
remote virtual disk as though it were connected locally.
The remaining^ chapters^ cover^ the^ various^ aspects^ of^ personal^ computer^ networking^ in
more detail. Chapter 2 describes a personal computer network model which represents a
network which users can realistically and economically expect from current technology.
Chapter 3 and^ Chapter^4 discuss^ what^ is^ found^ in^ currently^ available^ personal com-
puter networks. Chapter 3 characterizes ad hoc personal computer networks i.e., those
which are^ built^ using^ communication^ systems^ already^ in^ place,^ such^ as^ telephone^ systems,
networks designed for large computers, and systems used for terminal to computer center
communications. Chapter 4 describes networks which were designed specifically for the
interconnection of personal computers.
Chapter 5 summarizes how currently available personal computer networks fall short
of users' expectations. It then provides scenarios which suggest how existing personal
computer networks may evolve into the personal computer network model of Chapter 2.
Finally, it describes how users can deal with the shortcomings of current personal computer
networks. Appendix A lists references and related reading.
Chapter 2
A Personal (^) Computer Network Model
Often, among the first things learned by personal computer users, is that having their
own local computational capability is not sufficient. They also need to be able to ex-
change information electronically with other computer systems. Users may need to obtain
data from other facilities, and they will probably want to make the results of their work
accessible (^) to others.
For example, a financial analyst needs access to an organization's financial reports kept
on a central mainframe. Such data is necessary for assessing the reasons for the current
financial state and for generating scenarios for future financial behavior. The analyst needs
to be able to download this data to the personal computer where spreadsheet software is
used for evaluation and generation of future projections. These results must be distributed
to the analyst's management and peers for their review.
This chapter describes a personal computer network model that has the capabilities
that a user might expect from a personal computer network today. The personal computer
network described could be implemented from available technology, with the installation,
connection, and usage costs consistent with the cost of personal computers. It comes as a
surprise to many that this personal computer network model is not yet available off the
shelf. The network model described in this chapter is meant to be an embodiment of a
personal computer user's needs and expectations.
2.1 File Service
File service is fundamental to any computer network. However,^ the^ file^ service^ required^ of
a personal computer^ network^ goes^ beyond^ that^ of^ being^ able^ to^ copy^ an^ entire^ file^ from
one node to another. A personal computer^ may^ have^ limited^ disk^ storage^ and^ may^ need
access to a file which is^ larger^ than^ its^ disk^ capacity.
As a result, a personal computer^ should^ to^ be^ able^ to^ attach^ to^ part^ of^ a^ remote^ mass
storage device (i.e., a virtual disk) as though it^ were^ directly^ connected^ locally.^ All^ of
2.2 Print Service
Print service on a personal computer network addresses two user needs: ongoing processing
while printing and shared use of expensive printers. Since personal computers are usually
single user, single task systems, when users want to print a file from their systems, they
must wait for the printer to finish before they are able to use the system. However, the
print service on the network accepts the file immediately and users are able to continue
work on their personal computers without delay. The network acts as a spooler for print
files. Print spooling refers to the ability of the network to queue print requests from users
to the printer of choice.
The print service on the network also provides a means for users to easily share expen-
sive high^ speed^ and/or^ high quality printers. Printers that are fast and/or can produce high
resolution text and graphics are typically too expensive to be attached to each user's per-
sonal computer.^ By^ using^ the^ network,^ the^ user^ can^ have^ easy^ access^ to^ fast,^ high^ quality
output. The use of a network print service does not preclude the use of small, inexpensive
printer directly attached to personal computers for low quality, short printouts.
2.3 Mail
Mail service^ on the network is the electronic equivalent^ of the familiar hand carried mail.
There are a number of different mail system prototypes, but in the context of this personal
computer network model, mail service functions as follows:
The network sends and receives text mail between nodes regardless of
whether the node is a personal computer or a larger system. The mail is
taken from the sender's personal computer at the time it is sent and within
a short period of time, is delivered directly to the receiver system. If the re-
ceiver's system is not turned on or^ is^ otherwise^ occupied,^ the^ network^ retains
the mail and tries periodically to deliver it. Mail is delivered^ directly to the
receiver's system if that is what the receiver wishes; otherwise, the receiver
obtains mail from a mailbox on the network. If desired, the receiver^ is^ notified
without having^ to^ interrogate^ the^ network^ that^ mail^ has^ arrived.^ If^ desired,
the sender is notified whether or not^ the^ mail^ has^ been^ delivered^ (i.e.,^ after^ a
pre-defined time, the mail is returned to the originator).
The functioning of^ mail^ described^ above^ is^ consistent^ with^ the^ manner^ in^ which^ mail
services function^ on most^ large^ multi-user^ systems^ i.e.,^ mail^ is^ delivered^ directly^ to^ the
user's disk space and the user^ can^ be^ notified^ immediately^ upon^ the^ arrival^ of^ mail^ without
having to interrogate^ a^ post^ office.
2.4 Messaging and Conferencing
Messaging refers^ to^ the^ ability^ of^ one^ user^ to^ send^ a^ short^ text^ message^ to another user and
have the message delivered immediately. One user may enter text on a personal computer
and that text is immediately^ displayed^ on^ another^ user's^ display^ if the other user wishes
to see it. Conferencing refers to the ability of one user to send a text message to several
other users simultaneously,^ i.e.,^ to^ broadcast^ a^ message.
Unlike mail, messages which cannot be delivered are not retained by the network and
the sender is informed^ of^ this^ fact.^ This^ service^ is^ the^ network^ equivalent^ of a telephone
system with a conference call capability. The network can also record for later reference
the dialogue of a message or conference session.
2.5 Login
In a network designed for large computers, login to a remote system is one of the services
almost always provided. A user at a terminal logged into one (^) of the multi-user system
nodes on the network is able to login to a remote multi-user system as though the user
were directly connected to the remote system. This personal computer network model also
supports this capability except there are no dumb terminals, i.e., a personal computer is
able to login to a remote multi-user system. In addition, the network supports the login
of one personal computer to another remote personal computer. Logging into a remote
personal computer means that the remote personal computer is being used as though the
user were sitting at the keyboard of the remote.
One application of remote login to another personal computer might be the remote
use of special hardware,^ such as a modem or an array processor installed in the remote.
Users can access the special hardware remotely from their desks without having to sit at
the personal computer to which the special hardware is attached. In addition to accessing
remote hardware, a login capability can provide users with access to special software.
Because most personal computer software is licensed for use on a single system, a login
capability means that only one copy of a software package need be purchased. A user runs
the single copy of a software package on a remote personal computer by means of the login
feature. This approach is to be distinguished from the execution of software packages by
means of a file service. When using a file service, software is not executed on the system
where it is stored but is downloaded to the user's system and is executed there. Thus,
in most cases, a license must be obtained for each system which^ executes^ the^ software
package. 2.6 Remote Task Execution
The network provides the capability of initiating the execution of a program or a job stream
on a remote system. The job stream is expressed in the command^ language^ of^ the^ remote
