Encyclopedia of Networking P1

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

The Encyclopedia
of Networking







The Encyclopedia

of Networking
Second Edition


T
he First Edition of this 
book was published under
the title Novell’s
®
Complete 
Encyclopedia of Networking

Werner Feibel




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Paris

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Soest

Acquisitions Editor: Kristine Plachy
Developmental Editor: Guy Hart-Davis
Editors: Kristen Vanberg-Wolff and Maureen Adams
Technical Editor: Mary Madden
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Every effort has been made to supply complete and accurate information. However, SYBEX assumes no
responsibility for its use, nor for any infringement of the intellectual property rights of third parties which
would result from such use.
The first edition of this book was published under the title

Novell’s

®

Complete Encyclopedia of Networking


©1995 SYBEX Inc.
Copyright ©1996 SYBEX Inc., 2021 Challenger Drive, Alameda, CA 94501. World rights reserved. No part

of this publication may be stored in a retrieval system, transmitted, or reproduced in any way, including but
not limited to photocopy, photograph, magnetic or other record, without the prior agreement and written
permission of the publisher.
Library of Congress Card Number: 95-72476
ISBN: 0-7821-1829-1
Manufactured in the United States of America
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[In] a certain Chinese encyclopedia…it is written that animals are divided into:
(a) those belonging to the Emperor
(b) those that are embalmed
(c) tame ones
(d) suckling pigs
(e) sirens
(f) fabulous ones
(g) stray dogs
(h) those included in the present classification
(i) those that tremble as if mad
(j) innumerable ones
(k) those drawn with a very fine camelhair brush
(l) others
(m) those that have just broken the water pitcher
(n) those that look like flies from a long way off
Jorge Luis Borges

Acknowledgments

As with the first edition, this book would never have been completed without the help of

many people. These people deserve thanks for all their efforts and energy. Guy Hart-Davis
convinced me that it was time for a revision and set me to work. Several people did splen-
did work during the production process: Kris Vanberg-Wolff, a veteran of the first edition,
worked on the revision until her planned departure for the calmer (and tastier) world of
cooking school. Maureen Adams, Laura Arendal, and Nathan Johanson took over the pro-
duction chores after Kris left. They did an excellent job, especially considering the short
notice and even shorter revision schedule. My heartfelt thanks to all these folks.
Mary Madden’s technical reviews were always full of gentle, constructive corrections
and useful suggestions for improvements. Although I may not have been smart enough to
act on all of them, the suggestions have improved the book immensely—for which I’m very
grateful.
Kris Vanberg-Wolff’s eagle eyes and infallible grammatical sense found and fixed my
awkward phrasings, stylistic inconsistencies, and grammatical aberrations. I shudder to
think what the book would have looked like without the benefit of these efforts.
As always, I’m very grateful to all the people who worked between and behind the
scenes to make this book, and also to those who created the compact disc. Thanks also to
the many people who sent me information about their products and who took the time
to answer my questions.
Finally, I dedicate this book to my wife Luanne and my daughter Molly—for all the joy
and fun they provide, during both work and play hours.

Table of Contents

Introduction ix
Entries (Listed Alphabetically) 1
Appendix A: Acronyms and Abbreviations 1113
Appendix B: Bibliography and Other Resources 1235
Index 1251

Introduction

Introduction

Introduction
▼

What You’ll Find in This Book

As in the first edition, I’ve tried to make this Encyclopedia a comprehensive source of informa-
tion about matters relating to networking. I’ve also tried to present the information in a clear
and useful manner.
This book contains comprehensive, straightforward summaries of the major concepts,
issues, and approaches related to networking. Networking is defined broadly to encompass
configurations ranging from a couple of connected computers just a few feet apart to a network
of several thousand machines (of all types and sizes) scattered around the world. You’ll find
discussions of networking as it’s done by servers and clients, managers and agents, peers, and
even over the telephone.
You probably won’t find anything here that you can’t find in other places. However, I don’t
know of any other book or source that collects so much network-related information in one
place. To find all the information summarized here, you would need to check hundreds of
books, disks, articles, Web pages, or other documents.
Despite its hefty size, this encyclopedia just scratches the surface of what there is to know
about networking. After all, how complete can any book be if just the World Wide Web on the
Internet has over 10 million hypertext documents. I do think, however, that this book scratches
deeper than most other references you’ll find.
This revised edition updates entries for concepts and technologies that change rapidly or
where there have been major developments. I’ve also added considerable material about the
Internet (and especially about the World Wide Web), since interest in this networking phenom-
enon is growing at an astounding pace.
As in the first edition, I’ve tried to cover concepts rather than making this a how-to book.
Thus, you won’t learn how to install networks or run specific programs. However, you will

learn about different types of programs and what they do. For example, you can read about
browsers and how they make exploring the World Wide Web possible; you’ll also learn about
programs such as network operating systems and how they differ from ordinary operating
systems.

Concepts, Not Instructions

x

Introduction

This book was obsolete from the moment it was written. That’s because nothing changes faster
than vocabulary in a field where there is money to be made. Since major breakthroughs and
advances are still happening in the area of networking, there are new network-related words
and concepts to be found in almost every issue of every computer magazine. If you include
acronyms and abbreviations, the speed with which the vernacular expands is even faster. For
example, the first edition of this book was published under a year ago and it was no trouble
finding almost 2,000 new entries for Appendix A.
Given the futility of even trying to stay completely up-to-date, I’ve chosen to focus on the
more enduring concepts and facts—those that provide the foundations and background that
underlie the constantly changing terminology. This makes the Encyclopedia more generally
useful and enduring.
While core networking concepts change very little, the core does grow. For example, ten years
ago there was much less need to know about wireless communications because there were
fewer wireless products, as well as less public interest in the technology. Because of such
progress, the body of essential fundamentals grows with each year.
I expect to update and add to the material in the book, and hope to make the Encyclopedia
always effective, comprehensive, and useful. Fortunately, an electronic medium makes it easier
to grow in this way.
If you need to find out something about networking, look for it in this book. If you find an

entry for the topic, we hope you’ll be more informed after you’ve read it. On the other hand,
if you can’t find the information you need, didn’t understand it, or don’t think you learned
what you should have, please drop us a line and tell us.
Also, if there are concepts or terms you would like to see included, please let us know. If you
can provide references, that would be helpful. Even under the best of circumstances, there’s lit-
tle chance that you’ll get a reply to individual queries. However, we will read your comments
and suggestions and will try to use them to improve future versions of the book.

An Anchor in an Ocean of Words
Helping the Book Grow

&
&
Symbols & 
Numbers

2

& (Ampersand)

Symbols & Numbers
▼

& (Ampersand)

The ampersand is used to indicate special
characters in HTML (Hypertext Markup
Language) documents—that is, documents
for the World Wide Web. For example,

&

specifies the ampersand character
(&);

ö

specifies a lowercase o with
an umlaut, or dieresis, mark (ö).
▼

< > (Angle Brackets)

Angle brackets are used in pairs to surround

markup tags

in HTML (Hypertext Markup
Language) documents for the World Wide
Web. For example,

<P>

indicates a para-
graph break;

<B>

and

</B>

indicate the start
and end of a section that is to be displayed
in boldface.
▼

* (Asterisk)

In several operating systems, the asterisk
serves as a wildcard character: to represent
one or more characters, such as in a file
name or extension. For example,

a*

matches

act,



actor,

and

and,

but not

band.

In pattern matching involving regular
expressions, the asterisk matches the occur-
rences of the single character immediately
preceding it. For example,

ba*th

matches

bth,



bath,

and

baaaaath,

but not

bbath.

In e-mail and in other contexts that use
plain text, asterisks are sometimes used
around words or phrases to indicate em-
phasis. For example, “I *really* want
to emphasize the second word in this

sentence.”
▼

@ (At sign)

The

at sign

is used to separate the username
from domain specifiers in e-mail addresses.
For example,




would indicate someone with username

mels


on a computer named

golemxiv

at MIT.
▼

\ (Backslash)

In some operating systems, such as DOS,
OS/2, and NetWare, the backslash character
separates directory names or directory and
file names in a path statement. By itself, the
backslash represents the root directory in
these operating systems.
In various programming and editing con-
texts, the backslash is used to escape the
character that follows. For example,

\n

is an
escape code to indicate a newline character
in many operating environments.
▼

// (Double Slash)

In URLs (Uniform Resource Locators), dou-
ble slash characters separate the protocol
from the site and document names. For
example, if it existed,
/>filename.html
would refer to a file named

filename.html


residing on the

examplehost

machine at the
University of California at Santa Cruz. To
get to this file, you would use a server that
supports the HTTP (Hypertext Transport
Protocol).

4B/5B Encoding

3
▼

µ

(Mu)

Used as an abbreviation for the prefix micro,
as in

µ

sec for microsecond and

µ

m for
micrometer. This order of magnitude corre-

sponds to 2

−

20

, which is roughly 10

−

6

, or
one-millionth.

SEE ALSO

Order of Magnitude
▼

. and .. (Period and Double Period)

In hierarchically organized directory sys-
tems, such as those used by UNIX, DOS,
and OS/2, . and .. refer to the current and
the parent directories, respectively. In pat-
tern matching involving regular expressions,
the . matches any single character, except a
newline character.
▼

? (Question Mark)

In many operating systems, a question mark
serves as a wildcard character that repre-
sents a single character, such as in a file or
directory name.
▼

/ (Slash)

The slash (also known as a

forward slash

or
a

virgule

) separates directory levels in some
operating systems (most notably UNIX), in
addresses for gopher, and in

URLs

(Uniform
Resource Locators). For example, the fol-
lowing URL specifies the name and location
of a hypertext version of the jargon file,

which contains definitions for terms and
events that have helped define the computer
culture:

index.html
In this URL, the file is named

index.html,

and it is located in the

/fun/jargon

directory
on a machine in Germany (

de

).
In other operating systems, such as DOS,
OS/2, and NetWare, a slash is sometimes
used to indicate or separate command line
switches or options for a command.
▼

1Base5

The IEEE 802.3 committee’s designation
for an Ethernet network that operates at
1 megabit per second (Mbps) and that

uses unshielded twisted-pair (UTP) cable.
This configuration uses a physical bus,
with nodes attached to a common cable.
AT&T’s StarLAN is an example of a 1Base5
network.

SEE ALSO

10BaseX; 10Broad36
▼

4B/5B Encoding

4B/5B encoding is a data-translation scheme
that serves as a preliminary to signal encod-
ing in FDDI (Fiber Distributed Data Inter-
face) networks. In 4B/5B, every group of
four bits is represented as a five-bit symbol.
This symbol is associated with a bit pattern
that is then encoded using a standard signal-
encoding method, usually NRZI (non-return
to zero inverted).
This preprocessing makes the subsequent
electrical encoding 80 percent efficient. For

4

5B/6B Encoding

example, using 4B/5B encoding, you can

achieve a 100 megabit per second (Mbps)
transmission rate with a clock speed of only
125 megahertz (MHz).
In contrast, the Manchester signal-
encoding method, which is used in Ethernet
and other types of networks, is only 50 per-
cent efficient. For example, to achieve a 100
Mbps rate with Manchester encoding, you
need a 200 MHz clock speed.
▼

5B/6B Encoding

A data-translation scheme that serves
as a preliminary to signal encoding in
100BaseVG networks. In 5B/6B, every
group of five bits is represented as a six-bit
symbol. This symbol is associated with a bit
pattern that is then encoded using a stan-
dard signal-encoding method, such as NRZ
(non-return to zero).
▼

8B/10B Encoding

A data-translation scheme related to 4B/5B
encoding that recodes eight-bit patterns into
10-bit symbols. 8B/10B encoding is used, for
example, in IBM’s SNA (Systems Network
Architecture) networks.

▼

9-Track Tape

A tape storage format that uses nine parallel

tracks on

1

/

2

-inch, reel-to-reel magnetic
tape. Eight tracks are used for data, and one
track is used for parity information. These
tapes are often used as backup systems on
minicomputer and mainframe systems; digi-
tal audio tapes (DATs) are more common on
networks.
▼

10BaseX

The designations 10Base2, 10Base5,
10BaseF, and 10BaseT refer to various
types of baseband Ethernet networks.
10Base2 uses thin coaxial cable. This ver-
sion can operate at up to 10 megabits per

second (Mbps) and can support cable seg-
ments of up to 185 meters (607 feet). It is
also known as

thin Ethernet, ThinNet,

or

CheaperNet,

because thin coaxial cable is
considerably less expensive than the thick
coaxial cable used in 10Base5 networks.
10Base5 uses thick coaxial cable. This ver-
sion is the original Ethernet. It can operate
at up to 10 Mbps and support cable seg-
ments of up to 500 meters (1,640 feet). It is
also known as

thick Ethernet

or

ThickNet.

10BaseF is a baseband 802.3-based Ethernet
network that uses fiber-optic cable. This
version can operate at up to 10 Mbps.
Standards for the following special-
purpose versions of 10BaseF are being

formulated by the IEEE 802.3:

10BaseFP (fiber passive):

For desktops

10BaseFL (fiber link):

For intermediate

hubs

and workgroups

10BaseFB (fiber backbone):

For central
facility lines between buildings

10Base2
10Base5
10BaseF