Uae eae tlh
`
`zm:on
`\ —— iP 128.208
`AE|
`sis eis)a1IE
`
`=
`
`;
`
`Lia bea ke
`
`eons ag
`
`EOEaeUeAE
`
`——rectCi
`
`oT
`
`:
`
`a veinsSAE
`
`

`

` |
`
`COMPUTER NETWORKS
`
`FIFTH EDITION
`
` The Data Company Technologies Inc. v. Bright Data Ltd,
`
`ANDREW S. TANENBAUM
`
`Vrije Universiteit
`Amsterdam, The Netherlands
`
`DAVID J. WETHERALL
`University of Washington
`Seattle, WA
`
`PRENTICE HALL
`
`Boston Columbus Indianapolis New York San Francisco Upper Saddle River
`Amsterdam Cape Town Dubai London Madrid Milan Paris Montreal Toronto
`Delhi Mexico City Sao Paulo Sydney Hong Kong Seoul Singapore Tapei Tokyo
`
`=
`
`1PR2022-00135, EX. 2045
`20f6
`
`The Data Company TechnologiesInc. v. Bright Data Ltd.
`IPR2022-00138, EX. 2045
`2 of 6
`
`

`

` To Su
`
`To Ka
`
`and th
`
`Editorial Director: Marcia Horton
`Editor-in-Chief: Michael Hirsch
`Executive Editor. Tracy Dunkelberger
`Assistant Editor: Melinda Haggerty
`Editorial Assistant; Allison Michael
`Vice President, Marketing: Patrice Jones
`Marketing Manager. Yezan Alayan
`Marketing Coordinator: Kathryn Ferranti
`Vice President, Production: Vince O’Brien
`Managing Editor. Jeff Holcomb
`Senior Operations Supervisor: Alan Fischer
`Manufacturing Buyer: Lisa McDowell
`Cover Direction: Andrew 8. Tanenbaum,
`David J. Wetherall, Tracy Dunkelberger
`
`Art Director: Linda Knowles
`Cover Designer: Susan Paradise
`CoverIllustration: Jason Consalvo
`Interior Design: Andrew S. Tanenbaum
`AV Production Project Manager:
`Gregory L. Dulles
`Interior Illustrations: Laserwords, Inc.
`Media Editor: Danicl Sandin
`Composition: Andrew S.Tanenbaum
`Copyeditor: Rachel Head
`Proofreader: Joe Ruddick
`Printer/Binder: Courier Companies,Inc.
`Cover Printer: Courier Companies, Inc.
`
`Credits and acknowledgments borrowed fromother sources and reproduced, with permission,
`in this textbook appear on appropriate page within text.
`
`Manyofthe designations by manufacturersandsellers to distinguish their products are
`claimed as trademarks. Where those designations appearin this book, and the publisher was
`aware of a trademark claim, the designations have been printedin initial caps orall caps.
`
`Copyright © 2011, 2003, 1996, 1989, 1981 Pearson Education, Inc., publishing as Prentice
`Hall. All rights reserved. Manufactured in the United States of America. This publicationis
`protected by Copyright, and permission should be obtained from the publisher prior to any
`prohibited reproduction, storagein a retrieval system, or transmission in any form or by any
`means, electronic, mechanical, photocopying, recording, or likewise. To obtain permission(s)
`to use material from this work, please submit a written request to Pearson Education, Inc.,
`Permissions Department, 501 BoylstonStreet, Suite 900, Boston, Massachusetts 02116.
`
`Library of Congress Cataloging-in-Publication Data
`
`Tanenbaum, Andrew S., 1944-
`Computer networks / Andrew S. Tanenbaum, David J. Wetherall. -- 5th ed.
`p.cm.
`Includes bibliographical references and index.
`ISBN-13: 978-0-13-212695-3 (alk. paper)
`ISBN-10: 0-13-212695-8 (alk. paper)
`1. Computer networks. I. Wetherall, D. (David)I. Title.
`TK5105.5.136 2011
`004.6--dce22
`
`2010034366
`
`PEARSON
`Treeoe
`
`78910 V092 16 15 14
`
`
`
`

`

`
`
`AP.
`
`1
`
`The
`stage
`
`rence
`of the
`their
`thou-
`com-
`2d by
`2 job.
`on of
`
`acol-
`Two
`ation.
`ared,
`sizes,
`‘er to
`>of a
`
`work
`°m, a
`t sys-
`. Of-
`re, is
`buted
`mts a
`
`Users
`make
`hard-
`L user
`2 and
`
`work.
`s, the
`> (es-
`
`of ex-
`files
`user.
`
`SEC. 1.1
`
`USES OF COMPUTER NETWORKS
`
`3
`
`Although this book primarily focuses on networks, many of the topics are also im-
`portant in distributed systems. For more information about distributed systems,
`see Tanenbaum and Van Steen (2007).
`
`1.1 USES OF COMPUTER NETWORKS
`
`Before we start to examine the technical issues in detail, it is worth devoting
`some time to pointing out why people are interested in computer networks and
`what they can be used for. After all, if nobody were interested in computer net-
`works, few of them would be built. We will start with traditional uses at com-
`panies, then move on to home networking and recent developments regarding
`mobile users, and finish with social issues.
`
`1.1.1 Business Applications
`
`Most companies have a substantial number of computers. For example, a
`company may have a computer for each worker and use them to design products,
`write brochures, and do the payroll. Initially, some of these computers may have
`worked in isolation from the others, but at some point, management may have
`decided to connect them to be able to distribute information throughout the com-
`pany.
`Put in slightly more general form, the issue here is resource sharing. The
`goal is to make all programs, equipment, and especially data available to anyone
`on the network without regard to the physical location of the resource or the user.
`An obvious and widespread example is having a group of office workers share a
`commonprinter. None of the individuals really needs a private printer, and a
`high-volume networked printer is often cheaper, faster, and easier to maintain
`than a large collection of individual printers.
`However, probably even more important than sharing physical resources such
`as printers, and tape backup systems,
`is sharing information. Companies small
`and large are vitally dependent on computerized information. Most companies
`have customer records, product information, inventories, financial statements, tax
`information, and much more online. If all of its computers suddenly went down, a
`bank could not last more than five minutes. A modern manufacturing plant, with
`a computer-controlled assembly line, would not last even 5 seconds. Even a small
`travel agency or three-person law firm is now highly dependent on computernet-
`works for allowing employees to access relevant
`information and documents
`instantly.
`For smaller companies, all the computers are likely to be in a single office or
`perhaps a single building, but for larger ones, the computers and employees may
`be scattered over dozens of offices and plants in many countries. Nevertheless, a
`sales person in New York might sometimes need access to a product inventory
`
`ata Company TechnologiesInc. v. Bright Data Ltd.
`IPR2022-00135, EX. 2045
`4 of 6
`
`The Data Company TechnologiesInc. v. Bright Data Ltd.
`IPR2022-00138, EX. 2045
`4 of 6
`
`E
`E
`ES
`E
`3
`3
`‘4
`Be
`-
`z
`-
`Ee
`‘
`
`
`
`f
`
`

`

`4
`
`INTRODUCTION
`
`CHAP.
`
`1
`
`database in Singapore. Networks called VPNs (Virtual Private Networks) may
`be used to join the individual networks at different sites into one extended net-
`work.
`In other words, the mere fact that a user happens to be 15,000 km away
`from his data should not prevent him from using the data as though they were
`local. This goal may be summarized by saying that it is an attempt to end the
`“tyranny of geography.”
`In the simplest of terms, one can imagine a company’s information system as
`consisting of one or more databases with company information and some number
`of employees who need to access them remotely.
`In this model, the data are stor-
`ed on powerful computers called servers. Often these are centrally housed and
`maintained by a system administrator.
`In contrast, the employees have simpler
`machines, called clients, on their desks, with which they access remote data, for
`example, to include in spreadsheets they are constructing.
`(Sometimes we will
`refer to the human user of the client machine as the “client,” but it should be
`clear from the context whether we mean the computerorits user.) The client and
`server machines are connected by a network, asillustrated in Fig. 1-1. Note that
`we have shown the network as a simple oval, without any detail. We will use this
`form when we mean a network in the most abstract sense. When more detail is
`required, it will be provided.
`
`
`
`Figure 1-1. A network with twoclients and one server.
`
`It is widely used
`This whole arrangementis called the client-server model.
`and forms the basis of much network usage. The most popular realization is that
`of a Web application, in which the server generates Web pages basedonits data-
`base in responseto client requests that may update the database. Theclient-server
`model is applicable when the client and server are both in the same building (and
`belong to the same company), but also when they are far apart. For example,
`when a person at home accesses a page on the World Wide Web, the same model
`is employed, with the remote Web server being the server and the user’s personal
`
`SEC. 4)
`
`compute
`number
`IE w
`
`machine
`over the
`
`message
`work or
`shown mm
`
`A sex
`than infor
`commun
`two OF Bx
`ally use fi
`the water
`meaningk
`content-fz
`Telep
`instead oj
`Voice ov
`speaker at
`puter. Co
`Other,
`works. Vj
`and hear <
`eliminatin
`remote we
`easy for ty
`board or ¥
`document,
`days for a
`people eas
`remote cox
`
`
`
`

`

`
`
`1
`CHAP.
`‘Ks) may
`ded net-
`im away
`ey were
`end the
`
`ystem as
`number
`are stor-
`ised and
`simpler
`data, for
`we will
`rould be
`ent and
`fore that
`use this
`detail is
`
`ly used
`1 is that
`its data-
`server
`ag (and
`tample,
`: model
`ersonal
`
`.
`;
`4
`E
`~
`| a
`| a
`=
`3
`e
`a
`a
`a
`a
`:
`
`=.
`3
`
`5
`USES OF COMPUTER NETWORKS
`SEC. 1.1
`computer being the clicnt. Under most conditions, one server can handic a large
`number (hundredsor thousands) of clients simultaneously.
`If we look at the client-server model in detail, we see that two processes(i.e.,
`running programs) are involved, one on the client machine and one on the server
`machine. Communication takes the form of the client process sending a message
`over the network to the server process. The client process then waits for a reply
`message. When the server process gets the request, it performs the requested
`work or looks up the requested data and sends back a reply. These messages are
`shown in Fig. 1-2.
`
`Client machine
`
`Request ——_———_
`
`Server machine
`$$
`
`Server process
`Client process
`Figure 1-2. The client-server model involves requests and replies.
`
`
`
`Be
`
`
`
`Be
`-
`E
`eS
`Be
`a
`
`A second goal of setting up a computer network has to do with people rather
`than information or even computers. A computer network can provide a powerful
`communication medium among employees. Virtually every company that has
`two or more computers now has email (electronic mail), which employees gener-
`ally use for a great deal of daily communication.
`In fact, a common gripe around
`the water cooler is how much email everyone has to deal with, much ofit quite
`meaningless because bosses have discovered that they can send the same (often
`content-free) message toall their subordinates at the push of a button.
`Telephone calls between employees may be carried by the computer network
`instead of by the phone company. This technology is called IP telephony or
`Voice over IP (VoIP) when Internet technology is used. The microphone and
`speaker at each end may belong to a VolP-enabled phoue or the employee’s com-
`puter. Companies find this a wonderful way to save on their telephone bills.
`Other, richer forms of communication are made possible by computer net-
`works. Video can be added to audio so that employees at distant locations can see
`and hear each other as they hold a meeting. This technique is a powerful tool for
`eliminating the cost and time previously devoted to travel. Desktop sharing lets
`remote workers see and interact with a graphical computer screen. This makesit
`easy for two or more people who work far apart to read and write a shared black-
`board or write a report together. When one worker makes a change to an online
`document, the others can see the change immediately, instead of waiting several
`days for a letter. Such a speedup makes cooperation among far-flung groups of
`people easy where it previously had been impossible. More ambitious forms of
`remote coordination such as telemedicine are only now starting to be used (e.g.,
`
` até Company Technologies Inc. v. Bright Data Ltd.
`
`ae
`
`IPR2022-00135, EX. 2045
`6 of 6
`
`The Data Company TechnologiesInc. v. Bright Data Ltd.
`IPR2022-00138, EX. 2045
`,
`,
`6 0of6
`
`