Cisco Systems, Inc., Exhibit 1115
`Page 1
`
`

`
`Published by CMP Books
`An imprint of CMP Media LLC
`Main office: CMP Books, 600 Harrison St., San Francisco, CA 94107 USA
`Phone:415-947-6615;Fax:415-947-6015
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`Copyright© 2003 CMP Media LLC. All rights reserved. No part of this publication may
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`
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`Cisco Systems, Inc., Exhibit 1115
`Page 2
`
`

`
`xii
`
`N E T W 0 R K T U T 0 R I A L
`
`Hinners. Melanie McMullen and Steve Steinke expanded and upgraded the glossary to provide
`an even more comprehensive quick reference for unfamiliar terms.
`The third edition was edited by Steve Steinke, building on the editorial framework created
`by Patricia Schnaidt from the first and second editions.
`The tutorials new to the 4th edition ran between January 1996 and March 2000. The
`authors who wrote tutorials in that time span were Lee Chae, Alan Frank, David Greenfield,
`Anita Karve, Steve Steinke, and Alan Zeichick.
`I have one request to make of the reader: Please grant the authors a fair degree of slack
`with respect to the URLs cited here. Internet links get changed all the time, for reasons trivial
`and profound. We tend to print URLs with as much specificity as possible in order to unam(cid:173)
`biguously identify sources. However, these detailed locators are consequently fragile things.
`Aside from these considerations, URLs printed in a book will lack a certain degree of fresh(cid:173)
`ness from the mere facts of printing technology delays and shelf lives. A bit of ingenuity with
`a general search engine, or with the search features at one of the domains we cite, will go a
`long ways toward tracking down documents that are no longer in the place they were when we
`found them. The good news is that as far as I can tell, hardly anything that has been posted to
`the Web ever goes away completely.
`
`Steve Steinke
`January 2000
`
`Cisco Systems, Inc., Exhibit 1115
`Page 3
`
`

`
`Networks Protocols
`Part One
`A network protocol is a set of rules for com:unicating between computers. Protocols
`
`govern format, timing, sequencing, and error control. Without these rules, the computer can(cid:173)
`not make sense of the stream of incoming bits.
`But there is more than just basic communication. Suppose you plan to send a file from one
`computer to another. You could simply send it all in one single string of data. Unfortunately,
`that would stop others from using the network for the entire time it takes to send the message.
`This would not be appreciated by the other users. Additionally, if an error occurred during the
`transmission, the entire file would have to be sent again. To resolve both of these problems, the
`file is broken into small pieces called packets and the packets are grouped in a certain fashion.
`This means that information must be added to tell the receiver where each group belongs in
`relation to others, but this is a minor issue. To further improve transmission reliability, timing
`information and error correcting information are added.
`Because of this complexity, computer communication is broken down into steps. Each
`step has its own rules of operation and, consequently, its own protocol. These steps must be
`executed in a certain order, from the top down on transmission and from the bottom up on
`reception. Because of this hierarchical arrangement, the term protocol stack is often used to
`describe these steps. A protocol stack, therefore, is a set of rules for communication, and each
`step in the sequence has its own subset of rules.
`What is a protocol, really? It is software that resides either in a computer's memory or in
`the memory of a transmission device, like a network interface card. When data is ready for
`transmission, this software is executed. The software prepares data for transmission and sets
`the transmission in motion. At the receiving end, the software takes the data off the wire and
`prepares it for the computer by taking off all the information added by the transmitting end.
`There are a lot of protocols, and this often leads to confusion. A Novell network can com(cid:173)
`municate through its own set of rules (its own protocol called IPX/SPX), Microsoft does it
`another way (NetBEUI), DEC once did it a third way (DECnet), and IBM does it yet a fourth
`(NetBIOS). Since the transmitter and the receiver have to "speak" the same protocol, these
`
`3
`
`Cisco Systems, Inc., Exhibit 1115
`Page 4
`
`

`
`4
`
`UNDERSTANDING NETWORKS-LAYERS AND PROTOCOLS
`
`four systems cannot talk directly to each other. And even if they could directly communicate,
`there is no guarantee the data would be usable once it was communicated.
`Anyone who's ever wanted to transfer data from an IBM-compatible personal computer
`to an Apple Macintosh computer realizes that what should be a simple procedure is some(cid:173)
`times anything but. These two popular computers use widely differing-and incompati(cid:173)
`ble-file systems. That makes exchanging information between them impossible, unless
`you have translation software or a LAN. Even with a network, file transfer between these two
`types of computers isn't always transparent. [Editor's note: Even in the Internet age,
`Mac/Windows/Unix file exchange is often less than perfectly transparent.]
`If two types of personal computers can't communicate easily, imagine the problems
`occurring between PCs and mainframe computers, which operate in vastly different envi(cid:173)
`ronments and usually under their own proprietary operating software and protocols. For
`example, the original IBM PC's peripheral interface-known as a bus-transmitted data
`eight bits at a time. The newer 386,486, and Pentium PCs have 32-bit buses, and mainframes
`have even wider buses. This means that peripherals designed to operate with one bus are
`incompatible with another bus, and this includes network interface cards (NICs). Similar
`incompatibilities also exist with software. For instance, Unix-based applications (and often
`the data generated with them) cannot be used directly on PCs operating under Windows or
`MS-DOS. Resolving some of these incompatibilities is where protocol standards fit in.
`A protocol standard is a set of rules for computer communication that has been widely
`agreed upon and implemented by many vendors, users, and standards bodies. Ideally, a proto(cid:173)
`col standard should allow computers to talk to each other, even if they are from different ven(cid:173)
`dors. Computers don't have to use an industry-standard protocol to communicate, but if they
`use a proprietary protocol then they can only communicate with equipment of their own kind.
`There are many standard protocols, none of which could be called universal, but the suc(cid:173)
`cessful ones can be characterized with something called the OSI model. The standards and
`protocols associated with the OSI reference model are a cornerstone of the open systems
`concept for linking the literally dozens gf dissimilar computers found in offices throughout
`the world.
`
`THE OSI MODEL
`The Open System Interconnection ( OSI) model includes a set of protocols that attempt to
`define and standardize the data communications process. The OSI protocols were defined by
`the International Organization for Standardization {ISO). The OSI protocols have received
`the support of most major computer and network vendors, many large customers, and most
`governments, including the United States.
`
`Cisco Systems, Inc., Exhibit 1115
`Page 5
`
`

`
`NETWORK PROTOCOLS PART ONE
`
`5
`
`..
`
`The OSI model is a concept that describes how data communications should take place.
`It divides the process into seven groups, called layers. Into these layers are fitted the protocol
`standards developed by the ISO and other standards bodies, including the Institute of Elec(cid:173)
`trical and Electronic Engineers (IEEE), American National Standards Institute (ANSI), and
`the International Telecommunications Union (ITU), formerly known as the CCITT (Comite
`Consultatif International Telephonique et Telegraphique).
`The OSI model is not a single definition of how data communications actually takes place
`in the real world. Numerous protocols may exist at each layer. The OSI model states how the
`process should be divided and what protocols should be used at each layer. If a network ven-
`dor implements one of the protocols at each layer, its network components should work with
`other vendors' offerings.
`The OSI model is modular. Each successive layer of the OSI model works with the one
`above and below it. At least in theory, you may substitute one protocol for another at the same
`layer without affecting the operation of layers above or below. For example, Token Ring or
`Ethernet hardware should operate with multiple upper-layer services, including the trans(cid:173)
`port protocols, network operating system, internetwork protocols, and applications inter(cid:173)
`faces. However, for this interoperability to work, vendors must create products that meet the
`OSI model's specifications.
`Although each layer of the OSI model provides its own set of functions, it is possible to
`group the layers into two distinct categories. The first four layers- physical, data link, net(cid:173)
`work, and transport-provide the end-to-end services necessary for the transfer of data
`between two systems. These layers provide the protocols associated with the communica(cid:173)
`tions network used to link two computers together.
`The top three layers-the application, presentation, and session layers-provide the
`application services required for the exchange of information. That is, they allow two appli(cid:173)
`cations, each running on a different node of the network, to interact with each other through
`the services provided by their respective operating systems.
`A graphical illustration of the OSI model is shown above. The following is a description
`of just what each layer does.
`
`1. The Physical layer provides the electrical and mechanical interface to the network
`medium (the cable). This layer gives the data-link layer (layer 2) its ability to transport a
`stream of serial data bits between two communicating systems; it conveys the bits that
`move along the cable. It is responsible for making sure that the raw bits get from one place
`to another, no matter what shape they are in, and deals with the mechanical and electri(cid:173)
`cal characteristics of the cable.
`
`Cisco Systems, Inc., Exhibit 1115
`Page 6
`
`

`
`6
`
`UNDERSTANDING NETWORKS-LAYERS AND PROTOCOLS
`
`• The OS! model is not a sin(cid:173)
`gle definition of how data
`communications takes place.
`It states how the processes
`should be divided and offers
`several options. In addition to
`the OS! protocols, as defined
`by ISO, networks can use the
`TCP/IP protocol suite, the
`IBM Systems Network Archi(cid:173)
`tecture (SNA) suite, and oth(cid:173)
`ers. TCP/IP and SNA roughly
`follow the OS! structure.
`
`TCP/IP
`
`SMTP
`FI'P
`NFS
`Telnet
`SNMP
`
`UDP
`TCP
`
`IP
`
`LLC
`Ethernet
`
`IBM
`
`NetBIOS
`APPC
`
`NetBEUI
`APPC
`
`APPC
`
`LLC
`HDLC
`SDLC
`MAC
`
`MYRIAD PROTOCOL STACKS
`
`layer
`
`ISO
`
`7. Application
`
`FI'AMX.400
`JTAMX.500
`vr
`CASE
`
`6. Presentation
`
`5. Session
`
`8923
`
`8327
`
`8073 (TPO)
`8602 (CONS)
`
`8208 (X.25)
`8473 (CLNS)
`9542 (ES-IS)
`8348 (CONS)
`
`8802.2 LLC
`8802.3/4/5
`
`4. Transport
`
`3. Network
`
`2. Data-Link
`
`1. Physical
`
`8802.3 Ethernet
`8802.4 Token Bus
`8802.5 Token Ring
`
`Ethernet
`FDDI
`Token Ring
`
`Token Ring
`Ethernet
`FDDI
`
`2. The Data-Link layer handles the physical transfer, framing (the assembly of data into a
`single unit or block), flow control and error-control functions over a single transmission
`link; it is responsible for getting the data packaged for the Physical layer. The data link
`layer provides the network layer (layer 3) reliable information-transfer capabilities. The
`data-link layer is often subdivided into two parts-Logical Link Control (LLC) and
`Medium Access Control (MAC)-depending on the implementation.
`
`3. The Network layer establishes, maintains, and terminates logical and physical connec(cid:173)
`tions among multiple interconnected networks. The network layer is responsible for
`translating logical addresses, or names, into physical (or data-link) addresses.lt provides
`network routing and flow-control functions across the computer-network interface.
`
`4. The Transport layer ensures data is successfully sent and received between two end
`nodes. If data is sent incorrectly, this layer has the responsibility to ask for retransmission
`of the data. Specifically, it provides a reliable, network-independent message-interchange
`service to the top three application-oriented layers. This layer acts as an interface
`
`Cisco Systems, Inc., Exhibit 1115
`Page 7
`
`

`
`NETWORK PROTOCOLS PART ONE
`
`7
`
`between the bottom and top three layers. By providing the session layer (layer 5) with a
`reliable message transfer service, it hides the detailed operation of the underlying net(cid:173)
`work from the session layer.
`
`5. The Session layer decides when to turn communication on and off between two com put(cid:173)
`ers-it provides the mechanisms that control the data-exchange process and coordinates
`the interaction between them. It sets up and clears communication channels between two
`communicating components. Unlike the network layer (layer 3), it deals with the programs
`running in each machine to establish conversations between them. Some of the most com(cid:173)
`monly encountered protocol stacks, including TCP/IP, don't implement a session layer.
`
`6. The Presentation layer performs code conversion and data reformatting (syntax transla(cid:173)
`tion).It is the translator of the network, making sure the data is in the correct form for the
`receiving application. Of course, both the sending and receiving applications must be
`able to use data subscribing to one of the available abstract data syntax forms. Most com(cid:173)
`monly, applications handle these sorts of data translations themselves rather than hand(cid:173)
`ing them off to a Presentation layer.
`
`7. The Application layer provides the interface between the software running in a computer
`and the network. It provides functions to the user's software, including file transfer access
`and management (FTAM) and electronic mail service.
`
`Unfortunately, protocols in the real world do not conform precisely to these neat defini(cid:173)
`tions. Some network products and architectures combine layers. Others leave layers out. Still
`others break the layers apart. But no matter how they do it, all working network products
`achieve the same result-getting data from here to there. The question is, do they do it in a
`way that is compatible with networks in the rest of the world?
`
`WHAT 051 IS AND IS NOT
`While discussing the OSI reference model it is important to understand what the model
`does not specify as well as what it actually spells out. The ISO created the OSI reference model
`solely to describe the external behavior of electronics systems, not their internal functions.
`The reference model does not determine programming or operating system functions,
`nor does it specify an application programming interface (API). Neither does it dictate the
`end-user interface-that is, the command-line and/or icon-based prompts a user uses to
`interact with a computer system.
`The OSI standards merely describe what is placed on a network cable and when and how
`it will be placed there. It does not state how vendors must build their computers, only the
`
`Cisco Systems, Inc., Exhibit 1115
`Page 8
`
`

`
`8
`
`UNDERSTANDING NETWORKS-LAYERS AND PROTOCOLS
`
`• ISO has specified
`many different protocols
`at each layer of the OS!
`model. Some of the
`options are shown here.
`
`7
`
`6
`
`5
`
`4
`
`3
`
`2
`
`THE OSI PROTOCOLS
`
`X.400
`
`~
`
`s:
`
`fJ.l
`rJ)
`~
`
`C5
`0
`
`0
`0
`lJ")
`><
`
`0..
`::E
`u
`ACSE
`
`Presentation
`
`Session
`
`Transport Class 0-4
`
`Connection-Oriented, Connectionless
`
`~
`a
`
`l.l<
`
`~
`
`<:
`~
`
`CSMA/CD Token
`(Ethernet) Bus
`
`Token
`Ring
`
`FDDI
`
`X.25
`
`ISDN
`
`8802/3
`
`8802/4
`
`8802/5
`
`XT3.9 HDLC I.APB
`
`ISDN
`
`114A IEIA232
`
`kinds of behavior these systems may exhibit while performing certain communications
`operations.
`The OSI standards are distinct from the OSI suite of protocols. This concept permits a
`vendor to develop network elements that are more or less ignorant of the other components
`on the network. They are said to be ignorant in that they may need to know that other net(cid:173)
`work components exist, but not the specific details about their operating systems or interface
`buses. One of the primary benefits of this concept is that vendors can change the internal
`design of their network components without affecting their network functionality, as long as
`they maintain the OSI-prescribed external attributes. The figure below shows the protocols
`in the OSI suite.
`
`CONNECTION TYPES
`The OSI protocol suite is inherently connection-oriented, but the services each OSI layer
`provides can either be connection-oriented, or connectionless. In the three-step connection(cid:173)
`oriented mode operation (the steps are connection establishment, data transfer, and connec(cid:173)
`tion release), an explicit binding between two systems takes place.
`In connectionless operation, no such explicit link occurs; data transfer takes place with no
`specified connection and disconnection function occurring between the two communicating
`systems. Connectionless communication is also known as datagram communication.
`
`Cisco Systems, Inc., Exhibit 1115
`Page 9
`
`

`
`NETWORK PROTOCOLS PART ONE
`
`9
`
`AT THE PHYSICAL LAYER
`Let's compare some real protocols to the OSI model. The best known physical layer stan(cid:173)
`dards of the OSI model are those from the IEEE. That is, the ISO adopted some of the IEEE's
`physical network standards as part of its OSI model, including IEEE 802.3 or Ethernet, IEEE
`802.4 or token-passing bus, and IEEE 802.5 or Token Ring. ISO has changed the numbering
`scheme, however, so 802.3 networks are referred to as ISO 8802-3, 802.4 networks are ISO
`8802-4, and 802.5 networks are ISO 8802-5.
`Each physical layer standard defines the network's physical characteristics and how to get
`raw data from one place to another. They also define now multiple computers can simulta(cid:173)
`neously use the network without interfering with each other. (Technically, this last part is a
`job for the data-link layer, but we'll deal with that later.)
`IEEE 802.3 defines a network that can transmit data at lOMbps and uses a logical bus (or
`a straight line) layout. (Physically, the network can be configured as a bus or a star.) Data is
`simultaneously visible to all machines on the network and is nondirectional on the cable. All
`machines receive every frame, but only those meant to receive the data will process the frame
`and pass it to the next layer of the stack. Network access is determined by a protocol called
`Carrier Sense Multiple Access/Collision Detection (CSMA/CD). CSMA/CD lets any computer
`send data whenever the cable is free of traffic. If the data collides with another data packet,
`both computers "back off,' or wait a random time, then try again to send the data until access
`is permitted. Thus, once there is a high level of traffic, the more users there are, the more
`crowded and slower the network will become. Ethernet has found wide acceptance in office
`automation networks.
`IEEE 802.4 defines a physical network that has a bus layout. Like 802.3, Token Bus is a
`shared medium network. All machines receive all data but do not respond unless data is
`addressed to them. But unlike 802.3, network access is determined by a token that moves
`around the network. The token is visible to every device but only the device that is next in
`line for the token gets it. Once a device has the token it may transmit data. The Manufactur(cid:173)
`ing Automation Protocol (MAP) and Technical Office Protocol {TOP) standards use an 802.4
`physical layer. Token Bus has had little success outside of factory automation networks.
`IEEE 802.5 defines a network that transmits data at 4Mbps or 16Mbps and uses a logical
`ring layout, but is physically configured as a star. Data moves around the ring from station to
`station, and each station regenerates the signal. It does not support simultaneous multiple
`access as Ethernet does. The network access protocol is token-passing. The token and data
`move about in a ring, rather than over a bus as they do in Token Bus. Token Ring has found
`moderate acceptance in office automation networks and a greater degree of support in IBM(cid:173)
`centric environments.
`
`Cisco Systems, Inc., Exhibit 1115
`Page 10
`
`

`
`10
`
`UNDERSTANDING NETWORKS-LAYERS AND PROTOCOLS
`
`There are other physical and data-link layer standards, some that conform to the OSI
`model and others that don't. ARCnet is a well known one that only became standardized in
`1998, long after the time when it had any commercial significance. It uses a token-passing
`bus access method, but not the same as does IEEE 802.4. LocalTalk is Apple's proprietary
`network that transmits data at 230.4Kbps and uses CSMA/CA (Collision Avoidance). Fiber
`Distributed Data Interface (FDDI) is an ANSI and OSI standard for a fiber-optic LAN that
`uses a token-passing protocol to transmit data at 100Mbps on a ring.
`
`WHEN IT BEGAN
`The International Standards Organization, based in Geneva, Switzerland, is a multina(cid:173)
`tional body of representatives from the standards-setting agencies of about 90 countries.
`These agencies include the American National Standards Institute (ANSI) and British Stan(cid:173)
`dards Institute (BSI).
`Because of the multinational nature of Europe, and its critical need for intersystem com(cid:173)
`munication, the market for OSI-based products is particularly strong there. As a result, the
`European Computer Manufacturers' Association (ECMA) has played a major role in devel(cid:173)
`oping the OSI standards. In fact, before the Internet's Transmission Control Protocol/Internet
`Protocol (TCP/IP) began to dominate international networks, European networking vendors
`and users were generally further advanced in network standards, based on OSI implementa(cid:173)
`tions, than were their American counterparts, who relied principally on proprietary solu(cid:173)
`tions such as IBM's Systems Network Architecture (SNA) or TCP/IP.
`Creating the OSI standards was a long, drawn-out process: The ISO began work on OSI
`protocols in the late 1970s, finally releasing its seven-layer architecture in 1984. It wasn't
`until1988 that the five-step standards-setting process finally resulted in stabilized protocols
`for the upper layers of the OSI reference model. [Editor's note: From the perspective of 2000,
`the primary worldwide significance of the OSI protocols was in the use of the seven layer
`stack model as a way oflearning about networks. While there remain many implementations
`of OSI protocols, particularly in E~rope where they were in some cases legally imposed, it's
`clear that worldwide, the lion's share of new development and investment is devoted to
`TCP/IP and will be for the foreseeable future.]
`
`This tutorial, number 2, was originally published in the September 1988 issue of LAN
`Magazine/Network Magazine.
`
`Cisco Systems, Inc., Exhibit 1115
`Page 11
`
`

`
`NETWORK PROTOCOLS PART TWO
`
`11
`
`Network Protocols
`Part Two
`The Data-Link layer (the second OSI layer) is often divided into two sublayers; the Logi(cid:173)
`cal Link Control (LLC) and the Medium Access Control (MAC). The IEEE also defines stan(cid:173)
`dards at the data-link layer. The ISO standards for the MAC layer, or lower half of the data(cid:173)
`link layer, were taken directly from the IEEE 802.x standards.
`Medium Access Control, as its name suggests, is tlte protocol that determines which com(cid:173)
`puter gets to use the cable (the transmission medium) when several computers are trying.
`For example, 802.3 allows packets to collide with each other, forcing the computers to retry a
`transmission until it is sent successfully. 802.4 and 802.5limit conversation to the computer
`with the token. Remember, this is done in fractions of a second, so even when the network is
`busy, users don't wait very long for access on any of these three network types.
`The upper half of the data-link layer, the LLC, provides reliable data transfer over the
`physical link. In essence, it manages the physical link.
`The IEEE splits the data-link layer in half because the layer has two jobs to do. The first is
`to coordinate the physical transfer of data. The second is to manage access to the physical
`medium. Dividing the layer allows for more modularity and therefore more flexibility. The
`type of medium access control has more to do with the physical requirements of the network
`than the actual management of data transfer. In other words, the MAC layer is closer to the
`physical layer than the LLC layer. By dividing the layer, a number of MAC layers can be cre(cid:173)
`ated, each corresponding to a different physical layer, but just one LLC layer can handle them
`all. This increases flexibility and gives the LLC an important role in providing an interface
`between the various MAC layers and the higher-layer protocols. The role of the data-link's
`upper layer is so crucial, the IEEE gave it a standard of its own: 802.2 LLC.
`Besides 802.2,other protocols can perform the LLC functions. High-level Data-Link Con(cid:173)
`trol (HDLC) is a protocol from ISO, which also conforms to the OSI model. IBM's Synchro(cid:173)
`nous Data-Link Control (SDLC) does not conform to the OSI model but performs functions
`similar to the data-link layer. Digital Equipment's DDCMP or Digital Data Communications
`Protocol provides similar functions.
`
`THREE TRANSPORT PROTOCOLS
`The ISO has established protocol standards for the middle layers of the OSI model. The
`transport layer, at layer four, ensures that data is reliably transferred among transport serv(cid:173)
`ices and users. Layer five, the session layer, is responsible for process-to-process communi(cid:173)
`cation. The line between the session and transport layers is often blurred.
`
`Cisco Systems, Inc., Exhibit 1115
`Page 12
`
`

`
`12
`
`UNDERSTANDING NETWORKS-LAYERS AND PROTOCOLS
`
`As of yet, no ISO transport or session layer has been implemented on a widespread
`basis, nor has the complete OSI protocol stack been established. To make matters more con(cid:173)
`fusing, most middle-layer protocols on the market today do not fit neatly into the OSI
`model's transport and session layers, since many were created before the ISO began work on
`the OSI model.
`The good news is many existing protocols are being incorporated into the OSI model.
`Where existing protocols are not incorporated, interfaces to the OSI model are being imple(cid:173)
`mented. This is the case for TCP/IP, and IPX, which are the major middle-layer protocols
`available today.
`In the PC LAN environment, NetBIOS has been an important protocol. IBM developed
`NetBIOS (or Network Basic Input/Output System) as an input/output system for networks.
`NetBIOS can be considered a session-layer protocol that acts as an application interface to
`the network. It provides the tools for a program to establish a session with another program
`over the network. Many programs have been written to this interface.
`NetBIOS does not obey the rules of the OSI model in that it does not talk only to the layers
`above and below it. Programs can talk directly to NetBIOS, skipping the application and presen(cid:173)
`tation layers. This doesn't keep NetBIOS from doing its job; it just makes it incompatible with the
`OSI model. The main drawback of NetBIOS is that it is limited to working on a single network.
`TCP/IP or Transmission Control Protocol/Internet Protocol is actually several protocols.
`TCP is a transport protocol. IP operates on the network layer. TCP/IP traditionally enjoyed
`enormous support in government, scientific, and academic internetworks and in recent years
`has dominated the commercial networking environment, too. Part of the explanation is that
`corporate networks began to approach the size of networks found in the government and in
`universities, which drove corporations to look for internetworking protocol standards. They
`found TCP/IP to be progressively more useful as it became more widespread. Many people
`once viewed TCP/IP as an interim solution until OSI could be deployed, but no one seriously
`believes that the OSI protocols will ever have more than a niche role in the future.
`Often when TCP/IP is discussed, the subjects of SMTP, FTP, Telnet, and SNMP are also
`raised. These are application protocofs developed specifically for TCP/IP. SMTP or the Sim(cid:173)
`ple Mail Transfer Protocol is the electronic mail relay standard. FTP stands for File Transfer
`Protocol and is used to exchange files among computers running TCP/IP. Telnet is remote
`log-in and terminal emulation software. SNMP or the Simple Network Management Protocol
`is the most widely implemented network management protocol. The figure shows the proto(cid:173)
`cols of TCP /IP.
`Novell traditionally used IPX/SPX as its native transport protocols, though the company
`introduced a "native" implementation of TCP/IP in place of IPX/SPX. Internetwork Packet
`Exchange (IPX) and Sequenced Packet Exchange (SPX) are both variants of Xerox's XNS
`
`Cisco Systems, Inc., Exhibit 1115
`Page 13
`
`

`
`NETWORK PROTOCOLS PART TWO
`
`13
`
`• The TCP/IP stack includes pro(cid:173)
`tocols that provide services equiv(cid:173)
`alent to the OS! stack.
`
`5-7
`
`4
`
`3
`
`2
`
`THE TCP/IP PROTOCOL STACK
`
`File
`Transfer
`Protocol
`(FTP)
`
`Trivial
`File
`Transfer
`Protocol
`(TFTP)
`
`Simple
`Mail
`Transfer
`Protocol
`(SMTP)
`
`Telnet
`
`Simple
`Network
`Management
`Protocol
`(SNMP)
`
`Transmission Control
`Protocol (TCP)
`
`User Datagram
`Protocol (UDP)
`
`Internet Protocol (IP)
`
`Logical Unk Control (LLC)
`
`···································-···-················--·······--·-············-·······-~---·····················-·············
`
`Medium Access Control (MAC)
`
`Ethernet
`
`Token
`Ring
`
`FDDI
`
`X.25
`
`protocol. IPX provides network layer services, while SPX is somewhat rarely employed by
`applications that need transport layer services. Because IPX implementations prior to the
`introduction of Net Ware Link Services Protocol (NLSP) in Net Ware 4 caused a great deal of
`broadcast traffic and required frequent transmission acknowledgements, which can cause
`problems in a WAN, Novell also supported TCP/IP with gateways prior to its native TCP/IP
`implementation.
`Other transport layer protocols include XNS and NetBEUI. XNS or Xerox Network System
`was one of the first local area network protocols used on a wide basis, mainly for Ethernet
`networks. 3Com's 3+ used a version of it. NetBEUI is IBM's transport protocol for its PC net(cid:173)
`working products. (The legacy of IBM's long-deceased partnership with Microsoft lives on in
`Microsoft's default implementations of NetBEUI in Windows for Workgroups, Windows
`95/98, and Windows NT.)
`
`PROTOCOL BABEL
`If the number of available protocols seems like senseless confusion, it is and it isn't. Cer(cid:173)
`tain protocols have different advantages in specific environments. No single protocol stack
`will work better than every other in every setting. NetBIOS works well in small PC networks
`but is practically useless for communicating with WANs; APPC works well in peer-to-peer
`mainframe environments; TCP/IP excels in internetworks and heterogeneous environments.
`On the other hand, much more is made about the differences in protocols than is war(cid:173)
`ranted. Proprietary protocols can be perfect solutions in many cases. Besides, if proprietary
`protocols are sufficiently widespread, they become de facto standards, and gateways to other
`
`Cisco Systems, Inc., Exhibit 1