LAN andI/O Convergence:
`A Surveyof the Issues
`
`Martin W. Sachs, Avraham Leff, and Denise Sevigny
`International Business Machines
`
`ocal area networks (LANs) and computer[/O are both interconnects that
`move information from one location to another. Despite this shared purpose,
`LANshavetraditionally connected independent and widely separated com-
`puters.In contrast, computerI/O hastraditionally connected a host to peripheral de-
`vices such asterminals, disks, and tape drives. Because these connection tasks were
`different, the architectures developed for one task were notsuitable for the other.
`Consequently, the technologies used to implement one architecture could not ad-
`dress the issues faced by the other, and the technologies were seen as fundamentally
`different.
`However, an examination of the architectural requirements of modern I/O and
`LANsshowsthat the differences between the two technologies are now disappear-
`ing. We believe that LANandI/O architecturesare in fact converging, andthat this
`convergence reflects significant changes in how — and where — computing resources
`are used. Toillustrate this convergence andits implications, this article examinessey-
`eral modern LANsandchannels.
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`Reyironment and architecture convergence
`Once two distinctly
`Today’s I/O channels and LANsare characterized by a configuration size of less
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`than SO kilometers. Within this area, the environments under consideration include
`separate technologies,
`@ back-end networks (machine room environment),
`LANs and Vo are
`e front-end networks(office environment),
`‘
`<
`client-server networks, and
`becoming more alike
`© campus backbonenetworks.
`through similar
`distances, media, and—=—Modern 1/0 channels do notobviate the need for wide-area networks (WANs) or
`even large metropolitan-area networks (MANs). The general-purpose I/O channels
`purposes. Whatfew that wediscusslater in this article also do not lessen the need for optimized chan-
`<
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`nels for real-time applications such as embedded systems.
`differences exist may
`Figure 1 (on page 26) depicts the evolution of the relationship between intercon-
`disappear in the next
`nect type and distance. Historically, I/O and communication network interconnects
`ij
`partitioned the space at the machine room boundary.In the 1980s, the communica-
`ecade.
`tions space wasfurther subdivided into LANs and WANs,followedby the introduc-
`0018-9162/94/$4.00.0 1994 IEEE
`COMPUTER
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`24
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`Petitioner Valve - Ex. 1019, Page 24
`Petitioner Riot Games,Inc. - Ex. 1019, p. 24
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`Petitioner Valve - Ex. 1019, Page 24
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` fore theerroroccured.”
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`— The network layer ofthe internet com-
`terriet Protocol)
`tions. protocol:‘tdefines theInternet. datagram as the ba-
`- SigInformationunit passed acrossthe Internet and provides a
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`~goninectionless delivery service.
`IPH
`Higent Peripheral interface) — An ANSi-standard 1/O
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`primarily:used for attachmefit of data storage devices to
`a intet
`2 processors.
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`LAN (local ‘rea network). — A communications system typically
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`designed for use within a single organization, having a diameter
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`greater than 10 m:butiess than several km.
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`LLC (logical link control) — One of two sublayers of the OSI
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`model's data link layer. It includes functions unique to the partic-
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`ular link control procedures associated with the attached node
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`and ate independent of the underlying communication medium.
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`The LLC subiayer uses services provided by the MAC sublayer
`and provides services to the networklayer.
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`MAC (medium access control) — A sublayer of the OS!
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`mode's datalink layer. It uses the services of the physical layer
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`and supports topology-dependentfunctions, whichit providesto
`the LLC subiayer.
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`MAN(metropolitan area network) — A communications
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`system designed to covercity-wide areas (tens of km), using
`LAN technology.
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`Native /O — The I/O system designed as anintrinsic
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`componentof a given computerarchitecture.
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`Node — A communications entity.
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`OSI (Open SystemsInterconnection) architecture — A
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`framework for coordinating the developmentof standardsfor the
`interconnection of computer systems. Network functions are di-
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`vided into a hierarchy of seven layers: each layer represents a
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`collection of related communication functions.
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`Quality of service — Parameters characterizing communication
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`service that a serviceusereither desires or requires as minimum
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`satisfactory service. Exampiesinclude specifications for through-
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`put, delay, and error rates.
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`SCSI (Small Computer Systems Interface) —- An ANSI-stan-
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`dard {/O interface primarily used for attachment of data starage
`devices to processors.
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`Shared-medium topology — A communication network in
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`which a single communication channel is shared amongall the
`stations on the network. Examples are bus and ring topologies.
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`Station — A communication device attached to a network. The
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`station is the component of a node that provides at least the
`MACandphysical-layer function.
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`Switch-based topology — A communications network thatis
`based on one or more discrete switches, which maybecithercir-
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`cuil or packet switches,
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`TCP (Transmission Control! Protocol) — The transport layerof
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`the Internet communications protocol. It provides reliable, full du-
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`plex service, and allows arbitrarily iong streams of data to be
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`transmitted. It provides a connection-oriented service and
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`typically uses the IP protocolto transmit data.
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`WAN(wide area network) — A communications system
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`typically designed to provide services to a geographical area that
`is larger than the area served bya single LAN.
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`von:
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`si
`BroadcastnetworkApeheenkinwhich dataare
`ously transmitted to all. destinations.
`coe
`Class-1 service — A ’Fibre.Charinel service thatestablishes a
`circuit-switched connection between two communicatingentities
`(N_Ports).
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`GClass-2 service — A Fibre Channel Service that multiplexes
`frames to and from N_Ports with acknowledgment provided.
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`Class-3 service — A Fibre Channel service that multiplexes
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`frames to and from N_Ports without acknowledgment.
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`Connection-oriented — A service in which a connection
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`between source and destination mustfirst be established before
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`communication can take place. Once the connectionis
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`established, messagesarrive at the destination in the orderthat
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`they are transmitted.
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`Connectioniess — A communication service in which every
`messageis transmitted independently of any other.
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`CSMA/CD(carrier sense muitipie access with collision
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`detection) — A bus network in which the MACprotocolrequires
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`a station to detect whether anotherstation is already transmitting
`before transmitting its own frame and in which error conditions
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`resulting from simultaneous transmission by more than one sta-
`tion are resolved through retransmission.
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`Cut-through — A technique used in frame buffering that permits
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`the beginning of a frame to be movedoutof the buffer before the
`whole framehasarrivedin the buffer.
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`Data tink layer — The OS!layer that controls data transfer over
`a link between two nodes and performserror controlfor the link.
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`ESCON(Enterprise Systems Connection) — A fiber-optic 1/O
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`channel developed by IBM that transmits data at 17 Mbytes/sec.
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`It provides point-to-point connections of up to 40 km and uses a
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`nonblocking circuit switch.
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`Fabric —- The part of a network that transmits data from one
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`node to another, usually including routing function.
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`FDDI (Fiber Distributed Data Interface) —- A high-
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`performance, ANSI-standardfiber-optic token ring LAN running
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`at 10 Mbytes/sec overdistances of up to 200 km with up to 1,000
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`conneciedstations.
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`Fibre Channel — A proposed ANSI serial I/O channel standard
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`capable of transmitting at gigabit rates. It provides both circuit
`and frame switching using spacedivision switchesorloops.
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`HiPPt (High-Performance Parallel Interface) — A high-speed
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`ANSEstandard parallel interface that transmits either 32 or 64
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`bits in parallel and transmits data at up to 860 Mbits/sec.
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`Hop count — A unit of distance in a communications network. A
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`hop count of 4 meansthat 3 nodes or gateways separate the
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`source from the destination.
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`/O channel — An I/O mechanism that managesthe flow of data
`between a processor memory andthelinkto attached VO
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`devices.
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`December 1994
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`bo
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`are
`
`Petitioner Valve - Ex. 1019, Page 25
`Petitioner Riot Games,Inc.
`- Ex. 1019, p. 25
`
`Petitioner Riot Games, Inc. - Ex. 1019, p. 25
`
`Petitioner Valve - Ex. 1019, Page 25
`
`

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`Communications
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`1
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`10
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`Distance (meters)
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`Figure 1. Interconnect type and interconnect distance for various epochs.
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`link control
`layer. The same logical
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`Wide
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`Metropolitan
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`(LLC) sublayerof the data link layeris ,
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`area
`area network
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`used by more than one type of LAN. 1/0
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`network
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`Local area network
`channelarchitectures can be viewed as
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`vO vO
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`consisting of three layers. The lowest two
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` 1990s|(backplane) (cable) are functionally equivalent to the OSI
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`physical anddata link layers. The highest
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`layer specifies device commandsets (for
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`vO
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`example, disk and tape commands) to-
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`gether with their associated protocols.
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`c 4980s|(backplane) (cable) | network network
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`awi
`§
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`The layer structures of LANs and
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`channelsare illustrated in Figure 2. Typ-
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`ically, the software that supports a LAN
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`implements a layered architecture, which
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`1970s|(backplane) (cable)
`mayconform either to the higher layers
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`of the OSI model or to some other com-
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`munications architecture. In general,
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`these higher layers are not specific to
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`LANsand the same software may con-
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`currently support LAN, MAN, and
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`WAN communications. For a channel,
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`the supporting software consists of an I/O
`supervisorand the device-specific and ap-
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`plication-specific software.
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`Interconnect media and bandwidthsare
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`dealt with in the physical layer. The same
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`physical layer specifications can be used
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`for both LANs and I/O channels, inde-
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`pendentof functional convergence issucs.
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`Abovethedatalink layer, protocols re-
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`flect specific application types. Examples
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`are communications, such as the Internet
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`Protocol, and device architectures, such
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`as the American National Standards In-
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`stitute Intelligent Peripheral Interface
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`(IPI-3). These applications andtheir pro-
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`tocols are not converging. The data link
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`layer, however,is the focus of our dis-
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`cussion on architecture convergence.
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`At this point, it is worth briefly men-
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`tioning architecture openness. Tradition-
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`ally, a given 1/O architecture was opti-
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`mizedfor a given system architecture for
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`the purposeofattaching I/O devices to a
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`particular processor. In contrast to LAN
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`architectures, I/O architectures were never
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`open in the sense of being ableto incor-
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`porate the identical I/O architecture with
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`different system architectures. Early ex-
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`ceptions to this were the ANSI Small
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`Computer System Interface (SCSJ) and
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`IPI architectures.
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`The SCSI and IPI standards both in-
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`clude a device model, which detines the
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`characteristics of the device (for example,
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`a disk drive) and its commandset, and a
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`channel model, which describes the ar-
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`chitecture of the channel that connects
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`the device to the host. However, most im-
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`plementations of these standards were
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`made on processorsthat already had na-
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`tive I/O systems to which SCSI and IPI
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` Device command set
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`li
`Logical
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`_. Logical linkcontrol
`Data link
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` Medium accesscontrol
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`Physical
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`Physical
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`(b)
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`Figure 2. Layer
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`structures of
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`(a} LANs and
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`Table 1. Interconnect requirements.
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`Definition
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`Requirement
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`Interconnect distance
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`Information model
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`Maximum distance between any two points ofthe
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`configuration
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`Characteristics of the application information
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`carried by the interconnect
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`Relationship between the interconnected computers
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`or devices (for example, master-slave, peer-to-
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`peer)
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`generally optimized for long distances
`tion of MANsin the 1990s. In today’s sys-
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`tems, distances served by 1/O channels
`and multiple hops, and they have too
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`and networks now overlap in local and
`much overhcad for high-performance
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`metropolitan areas.
`I/O. However, in intermediate configu-
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`rations for distances of 1 to 50 km,theis-
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`Althoughthe traditional dichotomyis
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`sues faced by LANsand I/Oareincreas-
`still valid at opposite ends ofthe scale,it
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`blurs toward the middle. Some aspectsof
`ingly similar.
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`computerI/O, such as flow control, can
`In the terminology of the OSI (Open
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`be optimizedfor short distances through
`Systems Interconnection) reference mod-
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`simple hardware protocols, but they do
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`el, LANsare characterized by the phys-
`not perform well at very long distances.
`ical layer and by the medium-access-
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`Similarly, communications systemsare
`control (MAC)sublayerof the data link
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`26
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`COMPUTER
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`Petitioner Valve - Ex. 1019, Page 26
`Petitioner Riot Games,Inc. - Ex. 1019, p. 26
`
`Petitioner Riot Games, Inc. - Ex. 1019, p. 26
`
`Petitioner Valve - Ex. 1019, Page 26
`
`

`

`adapters were attached. The emerging
`ANSIFibre Channel’ standardgoesfur-
`ther: It is a true open I/O architecture
`that is both processor and device inde-
`pendent. Moreover, some implementa-
`tions in which Fibre Channelis the native
`I/O system arelikely.
`
`Interconnect
`requirements
`
`Amongthe requirements that must be
`addressed by anyinterconnect architec-
`ture are the expected interconnect dis-
`tance, the information model, and the
`computation model (see Table 1). As
`shownin Table 2, both the interconnect
`distance and the computation model
`have traditionally differed for I/O and
`LANs. Forshortdistances, I/O channels
`efficiently connected a smart host to a
`few dumbperipherals in a centralized,
`master-slave manner (Figure 3). Where
`longer distances were a factor, LANar-
`chitectures were needed to connect many
`autonomous,smart processorsin a dis-
`tributed, peer-to-peer manner(Figure 4).
`With respect to the information model,
`both I/O channels and LANswerepri-
`marily used for transferring data.
`Interconnect requirementsare chang-
`ing. Both LANs and channels have
`benefited from advancesin fiber-optic
`technologythat greatly extend the com-
`bination of bandwidth and interconnect
`distance. At the sametime,the informa-
`tion model — driven by multimedia ap-
`plications using voice and video — is
`evolvingto include informationwith very
`different characteristics,
`In the evolving /O computation model,
`dataare increasingly off-loaded from the
`hostto intelligentfile servers that formthe
`basis ofclient/serverarchitectures, The re-
`sult is that a traditional LAN peer-to-peer
`interconnect quite naturally supports the
`currentI/O computation model. There are
`few differences between LAN and I/O
`architectures developedto serve the de-
`mands of multimedia and client/server ap-
`plications, and eventhese differences may
`disappearin the next decade.
`
`Technology
`Someof the classic differences be-
`tween channels and LANsare indepen-
`dent ofthe interconnect’s intrinsic archi-
`tecture. Instead, they’re technological —
`
`December 1994
`
`Table 2. Traditional requirements for communication and I/O.
`
`Master-slave
`
`Requirement
`
`Interconnect distance
`Information model
`Computation model
`
`> 10? meters
`Data
`Peer-to-peer
`
`< 10 meters
`Data
`
`
`
`Channel
`
`Channel!
`
`
`
`
`Channel!
`
`
`
`
`file server.
`
`Host
`
`Channel
`
`Figure 3. Typical /O interconnect configuration.
`
`Figure 4.
`| Typical LANinter-
`|
`connects—bus and
`|
`ring. Several work-
`|
`stations are shown
`interconnected to
`each other and to a
`
`27
`
`Petitioner Valve - Ex. 1019, Page 27
`Petitioner Riot Games,Inc. - Ex. 1019, p. 27
`
`Petitioner Valve - Ex. 1019, Page 27
`
`

`

`10 Mbytes/sec
`
`Attribute
`
`Interconnect distance
`
`Bandwidth
`
`> 10? meters
`
`
`1 Mbyte/sec
`
`Channels
`
`< 10? meters
`
`
`
`
`
`
`
`
`
`
`
`such ascarrier sense multiple access with
`
`
`
`
`collision detection (CSMA/CD) and
`
`
`
`
`
`token-passing. Moreover, in a shared-
`
`
`
`
`
`
`medium topology, the bandwidth of a sin-
`
`
`
`
`
`
`
`
`gle link is divided amongall the stations.
`
`
`
`
`
`Future applications will require LANs
`
`
`
`
`
`
`
`with more bandwidth perstation thanis
`
`
`
`
`now feasible through shared-medium
`
`
`
`topologies. Switch-based LANs — such
`
`
`
`
`
`
`
`
`as asynchronous-transfer-mode (ATM)>
`LANsand switched Ethernet — areat-
`
`
`
`
`
`tractive because they provide aggregate
`
`
`
`
`
`
`
`bandwidth, which is a multiple of the
`
`
`
`
`
`
`
`bandwidth ofa single link. ATM tech-
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`nology is even being applied as an I/O in-
`terconnect.® In the extreme, a nonblock-
`
`
`
`
`
`
`
`ing circuit switch, similar to the IBM
`
`
`
`
`
`
`ESCONDirector? or a Fibre Channelcir-
`
`
`
`
`
`
`cuit switch, provides the full bandwidth
`
`
`
`
`
`
`
`
`of a single link concurrently to every sta-
`
`
`
`
`
`tion engaged in a connection. Channels
`
`
`
`
`
`
`
`and LANsareclearly evolving from their
`
`
`
`
`original shared-medium topologies to
`
`
`switch-based topologies.
`
`
`
`
`
`Transmission latency. The intrinsic la-
`
`
`
`
`
`
`
`
`tencyof all channels and LANsis similar
`
`
`
`
`
`for a given transmission medium,being
`
`
`
`
`
`
`
`determined by the signal speed in the
`
`
`
`
`
`
`transmission medium.Foroptical fiber,
`
`
`
`
`this is approximately 2 x 108 meters/sec,
`
`
`
`
`
`
`corresponding to a propagation delay of
`
`
`
`
`
`5 nanoseconds/meter, that is, 50 micro-
`
`
`
`
`
`seconds at 10 kilometers. However,
`
`
`
`
`
`
`whereas channellatency is measured in
`
`
`
`
`
`microseconds, LANlatency is measured
`
`
`
`
`
`
`in milliseconds. This difference relates to
`
`
`
`
`
`aspects of architecture and implementa-
`
`
`
`
`
`
`tion above the OSIphysical layer.
`
`
`
`
`Interconnect architecture affects latency
`
`
`
`
`
`
`
`because of the access protocols needed to
`
`
`
`
`mediate simultaneous transmission re-
`
`
`
`
`
`quests. For example, the medium-access-
`
`
`
`
`
`
`contro] protocol used in CSMA/CD and
`
`
`
`
`
`token-ring LANs causes considerable
`
`
`
`
`
`transmission latency, comparedto the sim-
`
`
`
`
`
`
`
`
`
`
`
`
`
`pler switch-based access protocols of chan-
`nels. In addition, the end-to-end latency of
`
`
`
`
`
`
`
`
`both channels and LANs may,in fact, be
`
`
`
`
`
`dominated by software that implements
`
`
`
`
`
`
`
`the applications and higher layers of the
`
`
`
`
`
`
`communications protocolstack. In the fu-
`
`
`
`
`
`
`
`ture, as both channels and LANs adopt
`
`
`
`
`
`similar switch-based topologies,the laten-
`
`
`
`
`
`
`
`cies in the MAC-layer function will be-
`
`
`
`
`
`
`comesimilar. Further, improvementsin ar-
`
`
`
`
`
`
`chitecture will reduce theeffect of software
`
`
`on latency.
`
`
`
`
`
`Single-hop versus multihop. An inter-
`
`
`
`
`
`
`connect must ensure that data are trans-
`
`
`
`
`
`
`mitted from the source to the destination.
`
`
`
`
`
`COMPUTER
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Table 3. Two major technological differences between traditional LANs and chan-
`
`
`nels (late 1980s).
`
`
`
`
`
`
`
`
`
`
`
`for example, the use ofparallel versus se-
`
`
`
`
`
`
`
`rial links or copper cable versus optical
`
`
`
`
`
`
`fiber. These design decisions depend on
`
`
`
`
`product-specific cost, performance, and
`
`
`
`
`
`
`distance trade-offs, In theory, both inter-
`
`
`
`
`
`
`connects could use the same technology.
`
`
`
`
`Table 3 compares two technologically
`
`
`
`determined attributes — interconnect
`
`
`
`
`distance and bandwidth — that distin-
`
`
`
`
`
`
`
`guished channels from LANsinthe late
`
`
`
`
`
`1980s. Compared to channels, LANs
`
`
`
`
`
`
`have had lower bandwidth and a longer
`
`
`interconnection distance.
`
`
`
`
`
`Table 4 compares channel and LAN
`
`
`
`
`
`bandwidth over three generations of
`
`
`
`
`
`technology. Through the mid-1980s, both
`
`
`
`
`
`
`used the same basic copper-wire trans-
`
`
`
`
`
`mission medium. Channels were de-
`
`
`
`
`
`
`
`signed to move large volumes of data
`
`
`
`
`
`
`rapidly between a host andits attached
`
`
`
`high-performancedata-storage devices,
`
`
`
`
`
`
`while LANswere designed as low-cost,
`
`
`
`
`
`
`higher bandwidth alternatives to the ex-
`
`
`
`
`isting communication networks over
`
`
`
`
`shorter distances. Therefore, channels
`
`
`
`
`
`
`
`were optimized for high speed and very
`
`
`
`
`
`
`low errorrates, using parallel transmis-
`
`
`
`
`
`
`sion forrelatively short distances. LANs
`
`
`
`
`
`
`were optimized for economyandrela-
`
`
`
`
`
`tively long interconnect distances, and
`
`
`
`
`
`
`they featured serial transmission andtol-
`
`
`
`
`
`
`erated higher error rates. LAN specifi-
`
`
`
`
`
`
`cations also permitted repeaters to ex-
`
`
`
`
`
`
`tend distance; indeed, repeating is an
`
`
`
`
`
`
`
`
`
`essential part of a ring, one of the com-
`
`
`
`mon LANtopologies.
`
`
`
`
`
`Recent developmentsin serial fiber
`
`
`
`
`optics permit multikilometer attachment
`
`
`
`
`
`
`
`of peripheral devices to channels. For ex-
`
`
`
`
`
`
`ample, the IBM Enterprise Systems Con-
`
`
`
`
`
`
`
`
`
`
`nection (ESCON)* channel has 3-km
`point-to-point connections and a laser
`
`
`
`
`
`
`
`option that enables up to 20-km point-to-
`
`
`
`
`
`point connections, Fibre Channel speci-
`
`
`
`
`
`
`
`fies a gigabit/sec option with a 10-km
`
`
`
`
`point-to-point connection. Moreover,the
`
`
`
`
`
`
`actual maximum distance for both the
`
`
`
`
`
`
`ESCONchanneland Fibre Channel can
`
`
`
`
`
`be greatly extended through repeaters
`
`
`
`
`
`
`and complex switching fabrics. At the
`
`
`28
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`same time, emerging LANssuch as the
`
`
`
`
`
`ANSIFiber Distributed Data Interface
`
`
`
`
`
`(FDDI) have applied fiber-optic tech-
`
`
`
`
`
`
`nology to greatly extend the combination
`
`
`
`
`
`of bandwidth and interconnect distance
`
`
`
`
`
`
`
`available with earlier LANs, such as Eth-
`
`
`
`
`
`
`ermet and token-ring topologies. Thus,in-
`
`
`
`
`
`terconnect distance and bandwidth no
`
`
`
`
`
`longer distinguish channels from LANs.
`
`
`Architectural aspects
`
`
`
`
`
`To compare I/O and LANarchitec-
`
`
`
`
`
`
`tures, we identify and discuss nine key
`
`
`
`features: topology, transmission latency,
`
`
`
`single-hop versus multihop configura-
`
`
`
`tions, connection-oriented versus con-
`
`
`
`nectionless service, real-time constraints,
`
`
`
`
`fair access, priorities, multiplexing, and
`
`
`bandwidth management.
`
`
`
`
`Topology. Channel topology originally
`
`
`
`
`reflected the host/peripheralrelationship
`
`
`
`
`
`
`very strongly. A host communicated in
`
`
`
`
`
`
`master-slave fashion to its attached de-
`
`
`
`
`
`
`vices. Devices could share the medium
`
`
`
`
`
`because the master-slave relationship al-
`
`
`
`
`
`
`
`
`lowed them to use a very simple access-
`
`
`
`
`
`control protocol to mediate contention.
`
`
`
`
`
`
`Device sharing among multiple hosts was
`
`
`
`
`
`
`provided by the device’s controller. Each
`
`
`
`
`
`
`controller had multiple ports for channel
`
`
`
`
`
`
`connections and a switch that resolved
`
`
`
`
`
`contention amonghosts. Newer channels,
`
`
`
`
`
`
`
`such as the ESCONchannel, Fibre Chan-
`
`
`
`
`
`nel, and ANSI High-PerformanceParal-
`
`
`
`
`
`
`
`
`
`
`
`lel Interface (HiPPI),* have movedto a
`switch-based topology thatis intrinsically
`
`
`
`
`
`
`
`peer to peer. Hosts set up connections
`
`
`
`
`
`
`through the switch to share devices.
`
`
`
`
`
`
`In contrast to the master-slave topol-
`
`
`
`
`
`
`
`ogy of early channels, LANsevolved ina
`
`
`
`distributed, peer-to-peer environment.
`
`
`
`
`Shared-medium topologies (for example,
`
`
`
`
`
`
`rings and buses) were attractive because
`
`
`
`
`
`
`
`
`
`
`
`
`they provided sufficient bandwidth at low
`cost. However, the combination of peer-
`
`
`
`
`
`to-peer relationship and shared medium
`
`
`
`
`
`required more complexaccess protocols,
`
`
`| a
`
`
`
`r
`
`
`
`
`
`Petitioner Valve - Ex. 1019, Page 28
`Petitioner Riot Games,Inc. - Ex. 1019, p. 28
`
`Petitioner Riot Games, Inc. - Ex. 1019, p. 28
`
`Petitioner Valve - Ex. 1019, Page 28
`
`

`

`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Table 4. A comparison of LAN and channel bandwidth over several generations of technology.
`
`
`
`
`
`Local area networks
`Time period
`
`
`
`
`
`
`
`
`1970s—mid 1980s
`1-2 Mbytes/sec (CSMA/CD)
`
`
`
`
`
`Early 1990s
`10 Mbytes/sec (FDDI)
`Mid 1990s-late 1990s
`100 Mbytes/sec (ATM)
`
`
`
`
`
`
`
`100 Mbytes/sec (Fibre Channel)
`
`
`
`
`
`Channels
`
`
`
`
`
`
`>4 Mbytes/sec (IBM 370)
`
`
`
`17 Mbytes/sec (ESCON I/O)
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`This task is complicated when interme-
`
`
`
`
`
`diate nodes separate the destination from
`
`
`
`
`
`the source. Such sutihop configurations
`
`
`
`
`
`usually require the interconnect
`to
`
`
`
`
`
`
`choose among several potential trans-
`
`
`
`
`
`mission routes. It’s important to avoid
`
`
`
`
`
`
`overwhelmingthe interconnectwith traf-
`
`
`
`
`
`
`fic interaction from multiple nodes. This
`
`
`
`
`
`
`task, termed congestion control, is inde-
`
`
`
`
`
`
`
`pendentfrom flow control; the latter re-
`
`
`
`
`
`lates only to the point-to-pointtraffic be-
`
`
`
`
`
`
`
`tween source and destination. Routing
`
`
`
`
`
`
`
`and congestion control are dealt with in
`
`
`
`
`
`the network layer of the OSI model.
`
`
`
`
`
`
`
`Channels have traditionally been sin-
`
`
`
`
`
`
`
`gle-hop: A single path connected the host
`
`
`
`
`
`
`ta the device, with no intervening node.
`
`
`
`
`
`
`Evenin the switch-based ESCONarchi-
`
`
`
`
`
`
`tecture, the ESCONDirectoris a switch,
`
`
`
`
`not an intermediate node. Fibre Channel
`
`
`
`
`
`
`also providesa circuit-switched (known
`
`
`
`
`
`as class-1) service. Consequently, few tra-
`
`
`
`
`
`
`ditional network-layer issues and algo-
`
`
`
`rithms are present in channel architec-
`
`
`
`
`
`
`ture and implementations.
`
`
`
`
`
`
`Today, both channels and LANsare
`
`
`
`
`
`
`beginning to provide some multihop ser-
`
`
`
`
`
`vices. In Fibre Channel, for example,
`
`
`
`
`
`
`frame-switched service is multihop since
`
`
`
`
`the interconnect medium is a fabric of
`
`
`
`
`
`
`
`
`store-and-forward nodes. Each station
`
`
`
`
`
`has a directlink to the fabric; the fabric is
`
`
`
`
`
`
`responsible for buffering and delivering
`
`
`
`
`
`
`
`frames to their destinations. For effi-
`
`
`
`
`
`
`
`ciency, taking advantageof the low error
`
`
`
`
`
`
`
`rates on the opticalfiberlink, addressing
`
`
`
`
`
`
`
`and error checking are doneonly end-to-
`
`
`
`
`
`
`end: No checking is doneat intermediate
`
`
`
`
`
`
`nodes, Fibre Channel performs the end-
`
`
`
`
`
`
`to-end addressing and error checking in
`
`
`
`
`
`
`
`its FC-2 level (this includes functions
`
`
`
`
`
`
`equivalentto the data link layer), which
`
`
`
`
`is usually implemented in adapter mi-
`
`
`
`
`
`
`crocode and hardware. Communications
`
`
`
`
`
`
`architectures, on the other hand, perform
`
`
`
`
`
`
`these functions in higher level software
`
`
`(OSI network and transport layers or
`
`
`
`
`
`their equivalent).
`
`
`
`
`
`
`Asbroadcast networks, the main con-
`cern for traditional LANs has been de-
`
`
`December 1994
`
`
`
`
`
`
`
`
`
`
`
`
`
`termining interconnect usage among
`
`
`
`
`
`
`competing stations. Once contention is
`
`
`
`
`
`resolved, LANs behave essentially as sin-
`
`
`
`
`
`
`gle-hop configurations. When LANsare
`
`
`
`
`
`
`
`
`bridged, however, the resulting set of
`
`
`
`
`
`bridged LANstakes on someofthe char-
`acteristics of a multihop network.
`
`
`
`
`
`
`
`
`Connection-oriented yersus connec-
`
`
`
`
`tionless service. From an end-to-end
`
`
`
`
`interconnects can provide
`viewpoint,
`either connection-oriented or connec-
`
`
`
`
`
`
`
`Longer distances for
`
`
`
`channels mean
`
`
`increasedbit rates
`
`
`and switch
`
`fabrics with
`multihop properties.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`tionless service (see Tanenbaum’for an
`
`
`
`
`
`extended discussion). In connection-
`
`
`
`oriented service, data cannot be trans-
`
`
`
`
`
`mitted before establishing a connection
`
`
`
`
`
`between the source and destination. Con-
`
`
`
`
`
`
`nections deliver data in sequence; error
`
`
`
`
`
`
`control and flow controlare provided as
`
`
`
`
`
`
`part ofthe service. In connectionless ser-
`
`
`
`
`
`vice, as the phrase implies, no connection
`
`
`
`
`
`is established between the source and
`
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`destination. Instead, each unit of data
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`contains the destination address and is
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`transmitted independently. The inter-
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`connect makes a “besteffort” attempt to
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`deliver the data. Connectionless service
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`does not guarantee sequentialdelivery of
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`data, nor doesit provide error and flow
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`control. A common example of a con-
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`nectionless service is Internet Protocol
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`(IP), in which each message (IP data-
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`gram) is sent separately to the destina-
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`tion, An exampleof a connection service
`is Transmission Control Protocol (TCP),
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`which provides the connection services
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`on top of IP.
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`LANstypically support both connec-
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`tionless and connection-oriented service
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`at the logical link control sublayer. Al-
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`though LANsare basically single-hop
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`topologies, and hence provide ordered
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`delivery, the use of bridges to intercon-
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`nect multiple LANs introduces the pos-
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`sibility of multiple routes between two
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`endpoints. The distinction between con-
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`nectionless and connection-oriented ser-
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`vice is thus meaningful for LANs. Emerg-
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`ing switch-based LANs(for example,
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`ATM)illustrate a trend toward connec-
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`tion-oriented services.
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`In the past, the issue of connectionless
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`versus connection-oriented service never
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`arose for channels. The reasonis that
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`channels have alwayshad single-hop bus
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`or circuit-switched topologies, which are
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`inherently connection oriented. Further,
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`the timeto establish a circuit-switched
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`connection in a channelinterconnectis
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`primarily a round-trip propagation delay
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`between the endpoints and has been
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`fairly short comparedto the duration of
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`a connection. As the distances encom-
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`passed by modern channels increase, the
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`bit rates increase, and switchf