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`Exhibit 4
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`COMPUTER NETWORKS
`
`FIFTH EDITION
`
`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
`
`

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`Case 4:18-cv-07229-YGR Document 59-6 Filed 04/06/20 Page 3 of 74
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`
`
`
`Editorial Director: Marcia Horton
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`
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`Hagerstown
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`
`
`
`Credits and acknowledgments borrowed from other sources and reproduced, with permission,
`in this textbook appear on appropriate page within text.
`
`Many of the designations by manufacturers and sellers to distinguish their products are
`claimed as trademarks. Where those designations appear in this book, and the publisher was
`aware of a trademark claim, the designations have been printed in initial caps or all 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 publication is
`protected by Copyright, and permission should be obtained from the publisher prior to any
`prohibited reproduction, storage in 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 Boylston Street, 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) II. Title.
` TK5105.5.T36 2011
` 004.6--dc22
` 2010034366
`
`10 9 8 7 6 5 4 3 2 1—CRW—14 13 12 11 10
`
`
`
`
`

`

`Case 4:18-cv-07229-YGR Document 59-6 Filed 04/06/20 Page 4 of 74
`
`1
`
`INTRODUCTION
`
`Each of the past three centuries was dominated by a single new technology.
`The 18th century was the era of the great mechanical systems accompanying the
`Industrial Revolution. The 19th century was the age of the steam engine. During
`the 20th century, the key technology was information gathering, processing, and
`distribution. Among other developments, we saw the installation of worldwide
`telephone networks, the invention of radio and television, the birth and unpre-
`cedented growth of the computer industry, the launching of communication satel-
`lites, and, of course, the Internet.
`As a result of rapid technological progress, these areas are rapidly converging
`in the 21st century and the differences between collecting, transporting, storing,
`and processing information are quickly disappearing. Organizations with hun-
`dreds of offices spread over a wide geographical area routinely expect to be able
`to examine the current status of even their most remote outpost at the push of a
`button. As our ability to gather, process, and distribute information grows, the de-
`mand for ever more sophisticated information processing grows even faster.
`Although the computer industry is still young compared to other industries
`(e.g., automobiles and air transportation), computers have made spectacular pro-
`gress in a short time. During the first two decades of their existence, computer
`systems were highly centralized, usually within a single large room. Not infre-
`quently, this room had glass walls, through which visitors could gawk at the great
`electronic wonder inside. A medium-sized company or university might have had
`
`1
`
`

`

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`2
`
`INTRODUCTION
`
`CHAP. 1
`
`one or two computers, while very large institutions had at most a few dozen. The
`idea that within forty years vastly more powerful computers smaller than postage
`stamps would be mass produced by the billions was pure science fiction.
`The merging of computers and communications has had a profound influence
`on the way computer systems are organized. The once-dominant concept of the
`‘‘computer center’’ as a room with a large computer to which users bring their
`work for processing is now totally obsolete (although data centers holding thou-
`sands of Internet servers are becoming common). The old model of a single com-
`puter serving all of the organization’s computational needs has been replaced by
`one in which a large number of separate but interconnected computers do the job.
`These systems are called computer networks. The design and organization of
`these networks are the subjects of this book.
`Throughout the book we will use the term ‘‘computer network’’ to mean a col-
`lection of autonomous computers interconnected by a single technology. Two
`computers are said to be interconnected if they are able to exchange information.
`The connection need not be via a copper wire; fiber optics, microwaves, infrared,
`and communication satellites can also be used. Networks come in many sizes,
`shapes and forms, as we will see later. They are usually connected together to
`make larger networks, with the Internet being the most well-known example of a
`network of networks.
`There is considerable confusion in the literature between a computer network
`and a distributed system. The key distinction is that in a distributed system, a
`collection of independent computers appears to its users as a single coherent sys-
`tem. Usually, it has a single model or paradigm that it presents to the users. Of-
`ten a layer of software on top of the operating system, called middleware, is
`responsible for implementing this model. A well-known example of a distributed
`system is the World Wide Web. It runs on top of the Internet and presents a
`model in which everything looks like a document (Web page).
`In a computer network, this coherence, model, and software are absent. Users
`are exposed to the actual machines, without any attempt by the system to make
`the machines look and act in a coherent way. If the machines have different hard-
`ware and different operating systems, that is fully visible to the users. If a user
`wants to run a program on a remote machine, he† has to log onto that machine and
`run it there.
`In effect, a distributed system is a software system built on top of a network.
`The software gives it a high degree of cohesiveness and transparency. Thus, the
`distinction between a network and a distributed system lies with the software (es-
`pecially the operating system), rather than with the hardware.
`Nevertheless, there is considerable overlap between the two subjects. For ex-
`ample, both distributed systems and computer networks need to move files
`around. The difference lies in who invokes the movement, the system or the user.
`
`† ‘‘He’’ should be read as ‘‘he or she’’ throughout this book.
`
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`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
`common printer. 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 computer net-
`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
`
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`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 computer or its user.) The client and
`server machines are connected by a network, as illustrated 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.
`
`Client
`
`Server
`
`Network
`
`Figure 1-1. A network with two clients and one server.
`
`This whole arrangement is called the client-server model. It is widely used
`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 based on its data-
`base in response to client requests that may update the database. The client-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
`
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`SEC. 1.1
`
`USES OF COMPUTER NETWORKS
`
`5
`
`computer being the client. Under most conditions, one server can handle a large
`number (hundreds or 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
`
`Network
`
`Reply
`
`Client process
`
`Server process
`
`Figure 1-2. The client-server model involves requests and replies.
`
`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 of it quite
`meaningless because bosses have discovered that they can send the same (often
`content-free) message to all 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 VoIP-enabled phone 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 makes it
`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.,
`
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`6
`
`INTRODUCTION
`
`CHAP. 1
`
`It is some-
`remote patient monitoring) but may become much more important.
`times said that communication and transportation are having a race, and which-
`ever wins will make the other obsolete.
`A third goal for many companies is doing business electronically, especially
`with customers and suppliers. This new model is called e-commerce (electronic
`commerce) and it has grown rapidly in recent years. Airlines, bookstores, and
`other retailers have discovered that many customers like the convenience of shop-
`ping from home. Consequently, many companies provide catalogs of their goods
`and services online and take orders online. Manufacturers of automobiles, air-
`craft, and computers, among others, buy subsystems from a variety of suppliers
`and then assemble the parts. Using computer networks, manufacturers can place
`orders electronically as needed. This reduces the need for large inventories and
`enhances efficiency.
`
`1.1.2 Home Applications
`
`In 1977, Ken Olsen was president of the Digital Equipment Corporation, then
`the number two computer vendor in the world (after IBM). When asked why Dig-
`ital was not going after the personal computer market in a big way, he said:
`‘‘There is no reason for any individual to have a computer in his home.’’ History
`showed otherwise and Digital no longer exists. People initially bought computers
`for word processing and games. Recently, the biggest reason to buy a home com-
`puter was probably for Internet access. Now, many consumer electronic devices,
`such as set-top boxes, game consoles, and clock radios, come with embedded
`computers and computer networks, especially wireless networks, and home net-
`works are broadly used for entertainment, including listening to, looking at, and
`creating music, photos, and videos.
`Internet access provides home users with connectivity to remote computers.
`As with companies, home users can access information, communicate with other
`people, and buy products and services with e-commerce. The main benefit now
`comes from connecting outside of the home. Bob Metcalfe, the inventor of Ether-
`net, hypothesized that the value of a network is proportional to the square of the
`number of users because this is roughly the number of different connections that
`may be made (Gilder, 1993). This hypothesis is known as ‘‘Metcalfe’s law.’’ It
`helps to explain how the tremendous popularity of the Internet comes from its
`size.
`It can be surfing the
`Access to remote information comes in many forms.
`World Wide Web for information or just for fun. Information available includes
`the arts, business, cooking, government, health, history, hobbies, recreation, sci-
`ence, sports, travel, and many others. Fun comes in too many ways to mention,
`plus some ways that are better left unmentioned.
`Many newspapers have gone online and can be personalized. For example, it
`is sometimes possible to tell a newspaper that you want everything about corrupt
`
`

`

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`
`SEC. 1.1
`
`USES OF COMPUTER NETWORKS
`
`7
`
`politicians, big fires, scandals involving celebrities, and epidemics, but no foot-
`ball, thank you. Sometimes it is possible to have the selected articles downloaded
`to your computer while you sleep. As this trend continues, it will cause massive
`unemployment among 12-year-old paperboys, but newspapers like it because dis-
`tribution has always been the weakest link in the whole production chain. Of
`course, to make this model work, they will first have to figure out how to make
`money in this new world, something not entirely obvious since Internet users
`expect everything to be free.
`The next step beyond newspapers (plus magazines and scientific journals) is
`the online digital library. Many professional organizations, such as the ACM
`(www.acm.org) and the IEEE Computer Society (www.computer.org), already
`have all their journals and conference proceedings online. Electronic book read-
`ers and online libraries may make printed books obsolete. Skeptics should take
`note of the effect the printing press had on the medieval illuminated manuscript.
`Much of this information is accessed using the client-server model, but there
`is different, popular model for accessing information that goes by the name of
`peer-to-peer communication (Parameswaran et al., 2001). In this form, individu-
`als who form a loose group can communicate with others in the group, as shown
`in Fig. 1-3. Every person can, in principle, communicate with one or more other
`people; there is no fixed division into clients and servers.
`
`Figure 1-3. In a peer-to-peer system there are no fixed clients and servers.
`
`Many peer-to-peer systems, such BitTorrent (Cohen, 2003), do not have any
`central database of content. Instead, each user maintains his own database locally
`and provides a list of other nearby people who are members of the system. A new
`user can then go to any existing member to see what he has and get the names of
`other members to inspect for more content and more names. This lookup process
`can be repeated indefinitely to build up a large local database of what is out there.
`It is an activity that would get tedious for people but computers excel at it.
`
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`
`8
`
`INTRODUCTION
`
`CHAP. 1
`
`Peer-to-peer communication is often used to share music and videos. It really
`hit the big time around 2000 with a music sharing service called Napster that was
`shut down after what was probably the biggest copyright infringement case in all
`of recorded history (Lam and Tan, 2001; and Macedonia, 2000). Legal applica-
`tions for peer-to-peer communication also exist. These include fans sharing pub-
`lic domain music, families sharing photos and movies, and users downloading
`public software packages.
`In fact, one of the most popular Internet applications
`of all, email, is inherently peer-to-peer. This form of communication is likely to
`grow considerably in the future.
`All of the above applications involve interactions between a person and a re-
`mote database full of information. The second broad category of network use is
`person-to-person communication, basically the 21st century’s answer to the 19th
`century’s telephone. E-mail is already used on a daily basis by millions of people
`all over the world and its use is growing rapidly.
`It already routinely contains
`audio and video as well as text and pictures. Smell may take a while.
`Any teenager worth his or her salt is addicted to instant messaging. This
`facility, derived from the UNIX talk program in use since around 1970, allows two
`people to type messages at each other in real time. There are multi-person mes-
`saging services too, such as the Twitter service that lets people send short text
`messages called ‘‘tweets’’ to their circle of friends or other willing audiences.
`The Internet can be used by applications to carry audio (e.g., Internet radio
`stations) and video (e.g., YouTube). Besides being a cheap way to call to distant
`friends, these applications can provide rich experiences such as telelearning,
`meaning attending 8 A.M. classes without the inconvenience of having to get out
`of bed first.
`In the long run, the use of networks to enhance human-to-human
`communication may prove more important than any of the others. It may become
`hugely important to people who are geographically challenged, giving them the
`same access to services as people living in the middle of a big city.
`Between person-to-person communications and accessing information are
`social network applications. Here, the flow of information is driven by the rela-
`tionships that people declare between each other. One of the most popular social
`networking sites is Facebook. It lets people update their personal profiles and
`shares the updates with other people who they have declared to be their friends.
`Other social networking applications can make introductions via friends of
`friends, send news messages to friends such as Twitter above, and much more.
`Even more loosely, groups of people can work together to create content. A
`wiki, for example, is a collaborative Web site that the members of a community
`edit. The most famous wiki is the Wikipedia, an encyclopedia anyone can edit,
`but there are thousands of other wikis.
`Our third category is electronic commerce in the broadest sense of the term.
`Home shopping is already popular and enables users to inspect the online catalogs
`of thousands of companies. Some of these catalogs are interactive, showing pro-
`ducts from different viewpoints and in configurations that can be personalized.
`
`

`

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`
`SEC. 1.1
`
`USES OF COMPUTER NETWORKS
`
`9
`
`After the customer buys a product electronically but cannot figure out how to use
`it, online technical support may be consulted.
`Another area in which e-commerce is widely used is access to financial insti-
`tutions. Many people already pay their bills, manage their bank accounts, and
`handle their investments electronically. This trend will surely continue as net-
`works become more secure.
`One area that virtually nobody foresaw is electronic flea markets (e-flea?).
`Online auctions of second-hand goods have become a massive industry. Unlike
`traditional e-commerce, which follows the client-server model, online auctions
`are peer-to-peer in the sense that consumers can act as both buyers and sellers.
`Some of these forms of e-commerce have acquired cute little tags based on
`the fact that ‘‘to’’ and ‘‘2’’ are pronounced the same. The most popular ones are
`listed in Fig. 1-4.
`
`Full name
`Tag
`Business-to-consumer
`B2C
`Business-to-business
`B2B
`G2C Government-to-consumer
`C2C
`Consumer-to-consumer
`P2P
`Peer-to-peer
`
`Example
`Ordering books online
`Car manufacturer ordering tires from supplier
`Government distributing tax forms electronically
`Auctioning second-hand products online
`Music sharing
`
`Figure 1-4. Some forms of e-commerce.
`
`Our fourth category is entertainment. This has made huge strides in the home
`in recent years, with the distribution of music, radio and television programs, and
`movies over the Internet beginning to rival that of traditional mechanisms. Users
`can find, buy, and download MP3 songs and DVD-quality movies and add them
`to their personal collection. TV shows now reach many homes via IPTV (IP
`TeleVision) systems that are based on IP technology instead of cable TV or radio
`transmissions. Media streaming applications let users tune into Internet radio sta-
`tions or watch recent episodes of their favorite TV shows. Naturally, all of this
`content can be moved around your house between different devices, displays and
`speakers, usually with a wireless network.
`Soon, it may be possible to search for any movie or television program ever
`made, in any country, and have it displayed on your screen instantly. New films
`may become interactive, where the user is occasionally prompted for the story
`direction (should Macbeth murder Duncan or just bide his time?) with alternative
`scenarios provided for all cases. Live television may also become interactive,
`with the audience participating in quiz shows, choosing among contestants, and so
`on.
`
`Another form of entertainment is game playing. Already we have multiperson
`real-time simulation games, like hide-and-seek in a virtual dungeon, and flight
`
`

`

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`
`10
`
`INTRODUCTION
`
`CHAP. 1
`
`simulators with the players on one team trying to shoot down the players on the
`opposing team. Virtual worlds provide a persistent setting in which thousands of
`users can experience a shared reality with three-dimensional graphics.
`Our last category is ubiquitous computing, in which computing is embedded
`into everyday life, as in the vision of Mark Weiser (1991). Many homes are al-
`ready wired with security systems that include door and window sensors, and
`there are many more sensors that can be folded in to a smart home monitor, such
`as energy consumption. Your electricity, gas and water meters could also report
`usage over the network. This would save money as there would be no need to
`send out meter readers. And your smoke detectors could call the fire department
`instead of making a big noise (which has little value if no one is home). As the
`cost of sensing and communication drops, more and more measurement and re-
`porting will be done with networks.
`Increasingly, consumer electronic devices are networked. For example, some
`high-end cameras already have a wireless network capability and use it to send
`photos to a nearby display for viewing. Professional sports photographers can
`also send their photos to their editors in real-time, first wirelessly to an access
`point then over the Internet. Devices such as televisions that plug into the wall
`can use power-line networks to send information throughout the house over the
`wires that carry electricity. It may not be very surprising to have these objects on
`the network, but objects that we do not think of as computers may sense and com-
`municate information too. For example, your shower may record water usage,
`give you visual feedback while you lather up, and report to a home environmental
`monitoring application when you are done to help save on your water bill.
`A technology called RFID (Radio Frequency IDentification) will push this
`idea even further in the future. RFID tags are passive (i.e., have no battery) chips
`the size of stamps and they can already be affixed to books, passports, pets, credit
`cards, and other items in the home and out. This lets RFID readers locate and
`communicate with the items over a distance of up to several meters, depending on
`the kind of RFID. Originally, RFID was commercialized to replace barcodes. It
`has not succeeded yet because barcodes are free and RFID tags cost a few cents.
`Of course, RFID tags offer much more and their price is rapidly declining. They
`may turn the real world into the Internet of things (ITU, 2005).
`
`1.1.3 Mobile Users
`
`Mobile computers, such as laptop and handheld computers, are one of the
`fastest-growing segments of the computer industry. Their sales have already
`overtaken those of desktop computers. Why would anyone want one? People on
`the go often want to use their mobile devices to read and send email, tweet, watch
`movies, download music, play games, or simply to surf the Web for information.
`They want to do all of the things they do at home and in the office. Naturally, they
`want to do them from anywhere on land, sea or in the air.
`
`

`

`Case 4:18-cv-07229-YGR Document 59-6 Filed 04/06/20 Page 14 of 74
`
`SEC. 1.1
`
`USES OF COMPUTER NETWORKS
`
`11
`
`Connectivity to the Internet enables many of these mobile uses. Since having
`a wired connection is impossible in cars, boats, and airplanes, there is a lot of
`interest in wireless networks. Cellular networks operated by the telephone com-
`panies are one familiar kind of wireless network that blankets us with coverage
`for mobile phones. Wireless hotspots based on the 802.11 standard are another
`kind of wireless network for mobile computers. They have sprung up everywhere
`that people go, resulting in a patchwork of coverage at cafes, hotels, airports,
`schools, trains and planes. Anyone with a laptop computer and a wireless modem
`can just turn on their computer on and be connected to the Internet through the
`hotspot, as though the computer were plugged into a wired network.
`Wireless networks are of great value to fleets of trucks, taxis, delivery vehi-
`cles, and repairpersons for keeping in contact with their home base. For example,
`in many cities, taxi drivers are independent businessmen, rather than being em-
`ployees of a taxi company. In some of these cities, the taxis have a display the
`driver can see. When a customer calls up, a central dispatcher types in the pickup
`and destination points. This information is displayed on the drivers’ displays and
`a beep sounds. The first driver to hit a button on the display gets the call.
`Wireless networks are also important to the military. If you have to be able to
`fight a war anywhere on Earth at short notice, counting on using the local net-
`working infrastructure is probably not a good idea. It is better to bring your own.
`Although wireless networking and mobile computing are often related, they
`are not identical, as Fig. 1-5 shows. Here we see a distinction between fixed
`wireless and mobile wireless networks. Even notebook computers are sometimes
`wired. For example, if a traveler plugs a notebook computer into the wired net-
`work jack in a hotel room, he has mobility without a wireless network.
`
`Wireless Mobile
`No
`No
`No
`Yes
`Yes
`No
`Yes
`Yes
`
`Typical applications
`Desktop comput