THIRD EDITION
`0MPUTER NETWORKS
`
`ANDREW S.TANENBAUM
`
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`Unified Patents Ex. 1002, pg. 1
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`Unified Patents Ex. 1002, pg. 1
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`

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`Computer Networks
`
`Third Edition
`
`Andrew S. Tanenbaum
`
`Vrije Universiteit
`Amsterdam, The Netherlands
`
`For book and bookstore information
`
`
`
`Prentice Hall PTR
`
`Upper Saddle River, New Jersey 07458
`
`
`
`Unified Patents Ex. 1002, pg. 2
`
`Unified Patents Ex. 1002, pg. 2
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`

`

`Library of Congress Cataloging in Publication Data
`Tanenbaum, Andrew S. 1944—.
`Computer networks / Andrew S. Tanenbaum. -— 3rd ed.
`p.
`cm.
`Includes bibliographical references and index.
`ISBN 0-13—349945-6
`I.Computer networks.
`TK5105.5.T36 1996
`004.6»dc20
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`I. Title.
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`Interior design and composition: Andrew S. Tanenbaum
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`Unified Patents Ex. 1002, pg. 3
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`Unified Patents Ex. 1002, pg. 3
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`

`

`
`
`4
`
`INTRODUCTION
`
`CHAP.
`
`1
`
`Client
`process
`
`Client machine
`
`Sewer machine
`
`
`
`Server
`process
`
`Network
`
`Fig. 1-1. The client—server model.
`
`The server then does the work and sends back the reply. Usually, there are many
`clients using a small number of servers.
`Another networking goal is scalability, the ability to increase system perfor—
`mance gradually as the workload grows just by adding more processors. With
`centralized mainframes. when the system is full, it must be replaced by a larger
`one. usually at great expense and even greater disruption to the users. With the
`client—server model. new clients and new servers can be added as needed.
`Yet another goal of setting up a computer network has little to do with tech-
`nology at all. A computer network can provide a powerful communication
`medium among widely separated employees. Using a network, it is easy for two
`or more people who live far apart to write a report together. When one worker
`makes a change to an on—line document, the others can see the change immedi—
`ately, instead of waiting several days for a letter. Such a speedup makes coopera-
`tion among far-flung groups of people easy where it previously had been impossi-
`ble.
`In the long run, the use of networks to enhance human-touhuman communi—
`cation will probably prove more important than technical goals such as improved
`reliability.
`
`1.1.2. Networks for People
`
`The motivations given above for building computer networks are all essen—
`tially economic and technological in nature.
`If sufficiently large and powerful
`mainframes were available at acceptable prices, most companies would simply
`choose to keep all their data on them and give employees terminals connected to
`them.
`In the 1970s and early 19803, most companies operated this way. Com-
`puter networks only became popular when networks of personal computers
`offered a huge price/performance advantage over mainframes.
`Starting in the 19905, computer networks began to start delivering services to
`private individuals at home. These services and the motivations for using them
`
`Unified Patents Ex. 1002, pg. 4
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`Unified Patents Ex. 1002, pg. 4
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`

`

`SEC.
`
`[.1
`
`USES OF COMPUTER NETWORKS
`
`5
`
`are quite different than the “corporate efficiency” model described in the previ-
`ous section. Below we will sketch three of the more exciting ones that are starting
`to happen:
`
`1. Access to remote information.
`
`2. Person-to-person communication.
`
`3.
`
`Interactive entertainment.
`
`Access to remote information will come in many forms. One area in which it
`is already happening is access to financial
`institutions. Many people pay their
`bills, manage their bank accounts, and handle their investments electronically.
`Home shopping is also becoming popular, with the ability to inspect the on-line
`catalogs of thousands of companies. Some of these catalogs will soon provide the
`ability to get an instant video on any product by just clicking on the product’s
`name.
`
`It will be possible to tell the
`Newspapers will go on-line and be personalized.
`newspaper that you want everything about corrupt politicians, big fires, scandals
`involving celebrities, and epidemics, but no football, thank you. At night while
`you sleep, the newspaper will be downloaded to your computer’s disk or printed
`on your laser printer. On a small scale, this service already exists. The next step
`beyond newspapers (plus magazines and scientific journals) is the on-line digital
`library. Depending on the cost, size, and weight of book—sized notebook comput—
`ers. printed books may become obsolete. Skeptics should take note of the effect
`the printing press had on the medieval illuminated manuscript.
`Another application that falls in this category is access to information systems
`like the current World Wide Web, which contains information about the arts, busi-
`ness, cooking, government, health, history, hobbies, recreation, science, sports,
`travel, and too many other topics to even mention.
`All of the above applications involve interactions between a person and a
`remote database. The second broad category of network use will be person-to-
`person interactions, basically the let Century’s answer to the 19th Century’s tele-
`phone. Electronic mail or email is already widely used by millions of people and
`will soon routinely contain audio and video as well as text. Smell in messages
`will take a bit longer to perfect.
`Real—time email will allow remote users to communicate with no delay, possi—
`bly seeing and hearing each other as well. This technology makes it possible to
`have virtual meetings, called videoconference, among far—flung people.
`It
`is
`sometimes said that transportation and communication are having a race, and
`whichever wins will make the other obsolete. Virtual meetings could be used for
`remote school, getting medical opinions from distant specialists, and numerous
`other applications.
`Worldwide newsgroups, with discussions on every conceivable topic are
`already commonplace among a select group of people, and this will grow to
`
`
`
`
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`Unified Patents Ex. 1002, pg. 5
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`Unified Patents Ex. 1002, pg. 5
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`

`

`6
`
`INTRODUCTION
`
`CHAP.
`
`1
`
`include the population at large. These discussions, in which one person posts a
`message and all the other subscribers to the newsgroup can read it, run the gamut
`from humorous to impassioned.
`Our third category is entertainment, which is a huge and growing industry.
`The killer application here (the one that may drive all
`the rest) is video on
`demand. A decade or so hence, it may be possible to select any movie or televi-
`sion 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.
`On the other hand, maybe the killer application will not be video on demand.
`Maybe it will be game playing. Already we have multiperson real-time simula-
`tion games, like hide—and—seek in a virtual dungeon, and flight simulators with the
`players on one team trying to shoot down the players on the opposing team.
`If
`done with goggles and 3—dimensional real-time, photographic-quality moving
`images. we have a kind of worldwide shared virtual reality.
`In short, the ability to merge information, communication, and entertainment
`will surely give rise to a massive new industry based on computer networking.
`
`1.1.3. Social Issues
`
`The widespread introduction of networking will introduce new social, ethical,
`political problems (Laudon, 1995). Let us just briefly mention a few of them; a
`thorough study would require a full book, at least. A popular feature of many net-
`works are newsgroups or bulletin boards where people can exchange messages
`with like—minded individuals. As long as the subjects are restricted to technical
`topics or hobbies like gardening, not too many problems will arise.
`The trouble comes when newsgroups are set up on topics that people actually
`care about, like politics, religion, or sex. Views posted to such groups may be
`deeply offensive to some people. Furthermore, messages need not be limited to
`text. High-resolution color photographs and even short video clips can now easily
`be transmitted over computer networks. Some people take a live-and—let-live
`view, but others feel that posting certain material (e.g., child pornography) is sim—
`ply unacceptable. Thus the debate rages.
`People have sued network operators, claiming that they are responsible for the
`contents of what they carry, just as newspapers and magazines are. The inevitable
`response is that a network is like a telephone company or the post office and can-
`not be expected to police what its users say. Stronger yet, having network opera-
`tors censor messages would probably cause them to delete everything with even
`the slightest possibility of their being sued, and thus violate their users’ rights to
`free speech.
`It is probably safe to say that this debate will go on for a while.
`
`Unified Patents Ex. 1002, pg. 6
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`Unified Patents Ex. 1002, pg. 6
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`

`

`SEC. 1.!
`
`USES OF COMPUTER NETWORKS
`
`7
`
`Another fun area is employee rights versus employer rights. Many people
`read and write email at work. Some employers have claimed the right to read and
`possibly censor employee messages, including messages sent from a home termi-
`nal after work. Not all employees agree with this (Sipior and Ward, 1995).
`Even if employers have poWer over employees, does this relationship also
`govern universities and students? How about high schools and students? In 1994,
`Carnegie-Mellon University decided to turn off the incoming message stream for
`several newsgroups dealing with sex because the university felt the material was
`inappropriate for minors (i.e., those few students under 18). The fallout from this
`event will take years to settle.
`In
`Computer networks offer the potential for sending anonymous messages.
`some situations, this capability may be desirable. For example, it provides a way
`for students, soldiers, employees, and citizens to blow the whistle on illegal
`behavior on the part of professors, officers, superiors, and politicians without fear
`of reprisals. 0n the other hand, in the United States and most other democracies,
`the law specifically permits an accused person the right to confront and challenge
`his accuser in court. Anonymous accusations cannot be used as evidence.
`In short, computer networks, like the printing press 500 years ago, allow ordi-
`nary citizens to distribute their views in different ways and to different audiences
`than were previously possible. This new-found freedom brings with it many
`unsolved social, political, and moral issues. The solution to these problems is left
`as an exercise for the reader.
`
`1.2. NETWORK HARDWARE
`
`It is now time to turn our attention from the applications and social aspects of
`networking to the technical issues involved in network design. There is no gen-
`erally accepted taxonomy into which all computer networks fit, but two dimen-
`sions stand out as important: transmission technology and scale. We will now
`examine each of these in turn.
`
`Broadly speaking, there are two types of transmission technology:
`
`1. Broadcast networks.
`
`2. Point-to-point networks.
`
`Broadcast networks have a single communication channel that is shared by all
`the machines on the network. Short messages, called packets in certain contexts,
`sent by any machine are received by all the others. An address field within the
`packet specifies for whom it is intended. Upon receiving a packet, a machine
`checks the address field.
`If the packet
`is intended for itself,
`it processes the
`packet; if the packet is intended for some other machine, it is just ignored.
`As an analogy, consider someone standing at the end of a corridor with many
`rooms off it and shouting “Watson, come here.
`I want you.” Although the packet
`
`Unified Patents Ex. 1002, pg. 7
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`Unified Patents Ex. 1002, pg. 7
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`

`

`8
`
`INTRODUCTION
`
`CHAP.
`
`l
`
`Watson responds. The
`be received (heard) by many people, only cement asking all flight
`may actually
`t. Another example is an airport announ
`others just ignore i
`644 passengers to report to gate 12.
`Broadcast systems generally also allow the possibility of addressing a packet
`e address field. When a packet
`to all destinations by using a special code in th
`with this code is transmitted, it is received and processed by every machine on the
`network. This mode of operation is called broadcasting. Some broadcast sys-
`tems also support transmission to a subset of the machines, something known as
`multicasting. One possible scheme is to reserve one bit to indicate multicasting.
`The remaining :1 F 1 address bits can hold a group number. Each machine can
`“subscribe" to any or all of the groups. When a packet is sent to a certain group,
`it is delivered to all machines subscribing to that group.
`I networks consist of many connections between
`In contrast, point-to-poin
`individual pairs of machines. To go from the source to the destination, a packet
`on this type of network may have to first visit one or more intermediate machines.
`Often multiple routes, of different lengths are possible. so routing algorithms play
`an important role in point—to-point networks. As a general rule (although there are
`many exceptions), smaller, geographically localized networks tend to use broad—
`casting, whereas larger networks usually are point-to-point.
`Processors
`Example
`Interprooessor
`located in same
`distance
`
`Circuit board
`
`
`
`Data flow machine
`Multicomputer
`
`Local area network
`
`Metropolitan area network
`
`Wide area network
`
`The internet
`
`Fig. 1-2. Classification of interconnected processors by scale.
`networks is their scale.
`In Fig. 1—2 we
`An alternative criterion for classifying ystems arranged by their physical size.
`give a classification of multiple processor s
`At the top are data flow machines, highly parallel computers with many func-
`tional units all working on the same program. Next come the multicomputers,
`systems that communicate by sending messages over very short, very fast buses.
`Beyond the multicomputers are the true networks, computers that communicate
`
`Unified Patents Ex. 1002, pg. 8
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`Unified Patents Ex. 1002, pg. 8
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`

`

`
`
`INTRODUCTION
`
`1
`CHAP.
`and
`
`50
`interface to the network (sockets) and wrote many application, utility,
`management programs to make networking easier.
`The timing was perfect.
`VAX computer and a LAN to connec
`sockets, and many network utilities, the
`When 4.2BSD came along, with TCP/IP, tely. Furthermore, with TCP/IP,
`it was
`complete package was adopted immedia
`easy for the LANs to connect to the ARPANET, and many did.
`By 1983, the ARPANET was stable and successful, with over 200 IMPs and
`hundreds of hosts. At this point, ARPA turned the management of the network
`over to the Defense Communications Agency (DCA), to run it as an operational
`network. The first thing DCA did was to separate the military portion (about 160
`IMPs, of which 110 in the United States and 50 abroad) into a separate subnet,
`MILNET, with stringent gateways between MILNET and the remaining research
`subnet.
`y LANs, were connected to
`During the 19803, additional networks, especial]
`the ARPANET. As the scale increased, finding hosts became increasingly expen-
`sive, so DNS (Domain Naming System) was created to organize machines into
`domains and map host names onto IP addresses. Since then, DNS has become a
`generalized, distributed database system for storing a variety of information
`related to naming. We will study it in detail in Chap. 7.
`NET had been overtaken by newer networks that it itself
`By 1990, the ARPA
`hut down and dismantled, but it lives on in the hearts and
`had spawned, so it was s
`minds of network researchers everywhere. MILNET continues to operate, how-
`
`ever.
`
`1.5.3. NSFNET
`
`Science Foundation) saw the enor—
`By the late 19705, NSF (the US. National
`ARPANET was having on university research, allowing scien—
`mous impact the
`ry to share data and collaborate on research projects. How-
`tists across the count
`ever, to get on the ARPANET. a university had to have a research contract with
`the DOD, which many did not have. This lack of universal access prompted NSF
`to set up a virtual network. CSNET, centered around a single machine at BBN
`that supported dial-up lines and had connections to the ARPANET and other net-
`works. Using CSNET, academic researchers could call up and leave email for
`other people to pick up later. It was simple, but it worked.
`By 1984 NSF began designing a high-speed successor to the ARPANET that
`would be open to all university
`h groups. To have something concrete to
`start with, NSF decided to build a bac
`‘
`'
`nters, in San Diego, Boulder, Champaign, Pittsburgh, Ithaca, and Prince—
`little brother, consisting of an LSl-ll
`puter ce
`ton. Each supercomputer was given a
`ed with 56 kbps
`microcomputer called a fuzzball. The fuzzballs were connect
`hnology as the
`leased lines and formed the subnet.
`the same hardware tec
`
`Unified Patents Ex. 1002, pg. 9
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`Unified Patents Ex. 1002, pg. 9
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`

`

`SEC. 1.5
`
`EXAMPLE NETWORKS
`
`51
`
`ARPANET used. The software technology was different however: the fuzzballs
`spoke TCP/IP right from the start, making it the first TCP/IP WAN.
`NSF also funded some (eventually about 20) regional networks that connected
`to the backbone to allow users at thousands of universities, research labs, libraries,
`and museums to access any of the supercomputers and to communicate with one
`another. The complete network,
`including the backbone and the regional net-
`works, was called NSFNET.
`It connected to the ARPANET through a link
`between an [MP and a fuzzball in the Carnegie-Mellon machine room. The first
`NSFNET backbone is illustrated in Fig. 1-26.
`
` 0 NSF Supercomputer center
`
`at NSF Mid-level network
`0 Both
`
`Fig. 1-26. The NSFNET backbone in 1988.
`
`NSFNET was an instantaneous success and was overloaded from the word go.
`NSF immediately began planning its successor and awarded a contract
`to the
`Michigan-based MERIT consortium to run it. Fiber optic channels at 448 kbps
`were leased from MCI to provide the version 2 backbone.
`IBM RSéOOOs were
`used as routers. This, too, was soon overwhelmed, and by 1990, the second back-
`bone was upgraded to 1.5 Mbps.
`As growth continued, NSF realized that the government could not continue
`financing networking forever. Furthermore, commercial organizations wanted to
`join but Were forbidden by NSF’s charter from using networks NSF paid for.
`Consequently, NSF encouraged MERIT, MCI, and IBM to form a nonprofit cor—
`poration, ANS (Advanced Networks and Services) as a step along the road to
`commercialization.
`In 1990, ANS took over NSFNET and upgraded the 1.5—
`Mbps links to 45 Mbps to form ANSNET.
`In December 1991, the U.S. Congress passed a bill authorizing NREN, the
`National Research and Educational Network,
`the research successor
`to
`NSFNET, only running at gigabits speeds. The goal was a national network
`
`Unified Patents Ex. 1002, pg. 10
`
`Unified Patents Ex. 1002, pg. 10
`
`

`

`W
`
`1
`CHAP.
`INTRODUCTION
`52
`running at 3 Gbps before the millenium. This network is to act as a prototype for
`the much-discussed information superhighway.
`By 1995, the NSFNET backbone was no longer needed to interconnect the
`NSF regional networks because numerous companies were running commercial
`IP networks. When ANSNET was sold to America Online in 1995,
`the NSF
`regional networks had to go out and buy commercial IP service to interconnect.
`To ease the transition and make sure every regional network could communi-
`cate with every other regional network, NSF awarded contracts to four different
`network operators to establish a NAP (Network Access Point). These operators
`were PacBell (San Francisco), Ameritech (Chicago), MFS (Washington, DC),
`and Sprint (New York City, where for NAP purposes, Pennsauken, NJ. counts as
`New York City). Every network operator that wanted to provide backbone ser—
`vice to the NSF regional networks had to connect to all the NAPS. This arrange-
`ment meant that a packet originating on any regional network had a choice of
`backbone carriers to get from its NAP to the destination’s NAP. Consequently,
`the backbone carriers were forced to compete for the regional networks' business
`on the basis of service and price, which was the idea, of course.
`In addition to the
`NSF NAPS, various government NAPS (e.g., FIX-E, FIX—W, MAE-East and
`MAE-West) and commercial NAPS (e.g., ClX') have also been created, so the con—
`cept of a single default backbone was replaced by a commercially—driven com-
`petitive infrastructure.
`Other countries and regions are also building networks comparable to
`NSFNET.
`In Europe, for example, EBONE is an IP backbone for research organ-
`izations and EuropaNET is a more commercially oriented network. Both connect
`numerous cities in Europe with Z-Mbps lines. Upgrades to 34 Mbps are in prog—
`ress. Each country in Europe has one or more national networks, which are
`roughly comparable to the NSF regional networks.
`
`1.5.4. The Internet
`The number of networks, machines, and users connected to the ARPANET
`grew rapidly after TCP/IP became the only official protocol on Jan. 1, 1983.
`When NSFNET and the ARPANET were interconnected,
`the growth became
`exponential. Many regional networks joined up, and connections were made to
`networks in Canada, Europe, and the Pacific.
`Sometime in the mid-19805, people began viewing the collection of networks
`as an internet, and later as the Internet, although there was no official dedication
`with some politician breaking a bottle of champagne over a fuzzball.
`Growth continued exponentially, and by 1990 the Internet had grown to 3000
`networks and 200,000 computers.
`In 1992, the one millionth host was attached.
`By 1995, there were multiple backbones, hundreds of mid-level (i.e., regional)
`networks, tens of thousands of LANS, millions of hosts, and tens of millions of
`users. The size doubles approximately every year (Paxson, 1994).
`
`Unified Patents Ex. 1002, pg. 11
`
`J
`
`Unified Patents Ex. 1002, pg. 11
`
`

`

`EXAMPLE NETWORKS
`
`53
`
`Much of the growth comes from connecting existing networks to the Internet.
`In the past these have included SPAN, NASA’s space physics network, HEPNET,
`a high energy physics network, BITNET, IBM’s mainframe network, EARN, a
`European academic network now widely used in Eastern Europe, and many oth-
`ers. Numerous transatlantic links are in use, running from 64 kbps to 2 Mbps.
`The glue that holds the Internet together is the TCP/IP reference model and
`TCP/IP protocol stack. TCP/IP makes universal service possible and can be com—
`pared to the telephone system or the adoption of standard gauge by the railroads in
`the 19th Century.
`What does it actually mean to be on the Internet? Our definition is that a
`machine is on the Internet if it runs the TCP/IP protocol stack, has an IP address,
`and has the ability to send IP packets to all the other machines on the Internet.
`The mere ability to send and receive electronic mail is not enough, since email is
`gatewayed to many networks outside the Internet. However, the issue is clouded
`somewhat by the fact that many personal computers have the ability to call up an
`Internet service provider using a modem, be assigned a temporary IP address, and
`send IP packets to other Internet hosts.
`It make sense to regard such machines as
`being on the Internet for as long as they are connected to the service provider’s
`router.
`
`the old informal way of running the Internet no
`With exponential growth,
`longer works.
`In January 1992, the Internet Society was set up, to promote the
`use ofthe Internet and perhaps eventually take over managing it.
`Traditionally, the Internet had four main applications, as follows:
`
` SEC. 1.5
`
`1. Email. The ability to compose, send, and receive electronic mail has
`been around since the early days of the ARPANET and is enor—
`mously popular. Many people get dozens of messages a day and
`consider it their primary way of interacting with the outside world,
`far outdistancing the telephone and snail mail. Email programs are
`available on virtually every kind of computer these days.
`
`2. News. Newsgroups are specialized forums in which users with a
`common interest can exchange messages. Thousands of newsgroups
`exist, on technical and nontechnical tOpics, including computers, sci—
`ence, recreation, and politics. Each newsgroup has its own etiquette,
`style, and customs, and woe be to anyone violating them.
`
`3. Remote login. Using the Telnet, Rlogin, or other programs, users
`anywhere on the Internet can log into any other machine on which
`they have an account.
`
`is possible to copy files
`it
`4. File transfer. Using the FTP program.
`from one machine on the Internet to another. Vast numbers of arti—
`cles, databases, and other information are available this way.
`
`Unified Patents Ex. 1002, pg. 12
`
`Unified Patents Ex. 1002, pg. 12
`
`

`

`54
`
`1
`CHAP.
`INTRODUCTION
`Up until the early 19905, the Internet was largely populated by academic,
`government, and industrial researchers. One new application, the WWW (World
`Wide Web) changed all that and brought millions of new, nonacademic users to
`the net. This application, invented by CERN physicist Tim Berners-Lee, did not
`change any of the underlying facilities but made them easier to use. Together
`with the Mosaic viewer. written at the National Center for Supercomputer Appli-
`cations, the WWW made it possible for a site to set up a number of pages of infor-
`mation containing text, pictures, sound, and even video, with embedded links to
`other pages. By clicking on a link, the user is suddenly transported to the page
`pointed to by that link. For example, many companies have a home page with
`entries pointing to other pages for product information, price lists, sales, technical
`support, communication with employees, stockholder information, and much
`more.
`Numerous other kinds of pages have come into existence in a very short time,
`including maps, stock market tables, library card catalogs, recorded radio pro-
`grams, and even a page pointing to the complete text of many books whose copy-
`rights have expired (Mark Twain, Charles Dickens, etc.). Many people also have
`personal pages (home pages).
`In the first year after Mosaic was released, the number of WWW servers grew
`from 100 to 7000. Enormous growth will undoubtedly continue for years to come,
`and will probably be the force driving the technology and use of the Internet into
`the next millenium.
`Many books have been written about the Internet and its protocols. For more
`information, see (Black, 1995; Carl-Mitchell and Quarterman, 1993; Comer,
`1995; and Santifaller, 1994).
`
`1.5.5. Gigabit Testbeds
`
`The Internet backbones operate at megabit speeds, so for people who want to
`push the technological envelope, the next step is gigabit networking. With each
`increase in network bandwidth, new applications become possible, and gigabit
`networks are no exception.
`In this section we will first say a few words about
`gigahit applications, mention two of them, and then list some example gigabit
`testbeds that have been built.
`Gigabit networks provide better bandwidth than megabit networks, but not
`always much better delay. For example, sending a 1—KB packet from New York
`to San Francisco at 1 Mbps takes 1 msec to pump the bits out and 20 msec for the
`transcontinental delay, for a total of 21 msec. A l-Gbps network can reduce this
`to 20.001 msec. While the bits go out faster, the transcontinental delay remains
`the same, since the speed of light in optical fiber (or copper wire) is about 200,000
`ka'sec, independent of the data rate. Thus for wide area applications in which
`low delay is critical, going to higher speeds may not help much. Fortunately, for
`
`Unified Patents Ex. 1002, pg. 13
`
`#—
`
`Unified Patents Ex. 1002, pg. 13
`
`

`

`SEC.
`
`1 .5
`
`EXAMPLE NETWORKS
`
`55
`
`some applications, bandwidth is what counts, and these are the applications for
`which gigabit networks will make a big difference.
`One application is telemedicine. Many people think that a way to reduce
`medical costs is to reintroduce family doctors and family clinics on a large scale,
`so everyone has convenient access to first line medical care. When a serious
`medical problem occurs, the family doctor can order lab tests and medical imag-
`ing, such as X—rays, CAT scans, and MRI scans. The test results and images can
`then be sent electronically to a specialist who then makes the diagnosis.
`Doctors are generally unwilling to make diagnoses from computer images
`unless the quality of the transmitted image is as good as the original image. This
`requirement means images will probably need 4K X 4K pixels, with 8 bits per
`pixel (black and white images) or 24 bits per pixel (color images). Since many
`tests require up to 100 images (e.g., different cross sections of the organ in ques-
`tion), a single seiies for one patient can generate 40 gigabits. Moving images
`(e.g., a beating heart) generate even more data. Compression can help some but
`doctors are leary of it because the most efficient algorithms reduce image quality.
`Furthermore, all the images must be stored for years but may need to be retrieved
`at a moment’s notice in the event of a medical emergency. Hospitals do not want
`to become computer centers, so off-site storage combined with high—bandwidth
`electronic retrieval is essential.
`Another gigabit application is the virtual meeting. Each meeting room con—
`tains a spherical camera and one or more people. The bit streams from each of
`the cameras are combined electronically to give the illusion that everyone is in the
`same room. Each person sees this image using virtual reality goggles. In this way
`meetings can happen without travel, but again, the data rates required are stupen—
`dous.
`
`Starting in 1989, ARPA and NSF jointly agreed to finance a number of
`university—industry gigabit testbeds, later as part of the NREN project.
`In some of
`these, the data rate in each direction was 622 Mbps, so only by counting the data
`going in both directions do you get a gigabit. This kind of gigabit is sometimes
`called a “government gigabit.” (Some cynics call it a gigabit after taxes.) Below
`we will briefly mention the first five projects. They have done their job and been
`shut down, but deserve some credit as pioneers, in the same way the ARPANET
`does.
`
`1. Aurora was a testbed linking four sites in the Northeast: M.I.T., the
`University of Pennsylvania, IBM’s TJ. Watson Lab, and Bellcore
`(Morristown. NJ.) at 622 Mbps using fiber optics provided by MCI,
`Bell Atlantic, and NYNEX. Aurora was largely designed to help
`debug Bellcore’s Sunshine switch and IBM’s (proprietary) plaNET
`switch using parallel networks. Research issues included switching
`technology, gigabit protocols, routing, network control, distributed
`virtual memory, and collaboration using videoconferencing. For
`more information, see (Clark et al., 1993).
`
`Unified Patents Ex. 1002, pg. 14
`
`Unified Patents Ex. 1002, pg. 14
`
`

`

`
`
`56
`
`INTRODUCTION
`
`CHAP.
`
`l
`
`2. Blanca was originally a research project called XUNET involving
`AT&T Bell Labs, Berkeley. and the University of Wisconsin.
`In
`I990 it added some new sites (LBL, Cray Research. and the Univer-
`sity of Illinois) and acquired NSF/ARPA funding. Some of it ran at
`622 Mbps. but other parts ran at lower speeds. Blanca was the only
`nationwide testbed; the rest were regional. Consequently, much of
`th