(Lan systems (chapter 14
اسلاید 1: William Stallings Data and Computer CommunicationsChapter 14LAN Systems
اسلاید 2: Ethernet (CSAM/CD)Carriers Sense Multiple Access with Collision DetectionXerox - EthernetIEEE 802.3
اسلاید 3: IEEE802.3 Medium Access ControlRandom Access Stations access medium randomly ContentionStations content for time on medium
اسلاید 4: ALOHAPacket RadioWhen station has frame, it sendsStation listens (for max round trip time)plus small incrementIf ACK, fine. If not, retransmitIf no ACK after repeated transmissions, give upFrame check sequence (as in HDLC)If frame OK and address matches receiver, send ACKFrame may be damaged by noise or by another station transmitting at the same time (collision)Any overlap of frames causes collisionMax utilization 18%
اسلاید 5: Slotted ALOHATime in uniform slots equal to frame transmission timeNeed central clock (or other sync mechanism)Transmission begins at slot boundaryFrames either miss or overlap totallyMax utilization 37%
اسلاید 6: CSMAPropagation time is much less than transmission timeAll stations know that a transmission has started almost immediatelyFirst listen for clear medium (carrier sense)If medium idle, transmitIf two stations start at the same instant, collisionWait reasonable time (round trip plus ACK contention)No ACK then retransmitMax utilization depends on propagation time (medium length) and frame lengthLonger frame and shorter propagation gives better utilization
اسلاید 7: If Busy?If medium is idle, transmitIf busy, listen for idle then transmit immediatelyIf two stations are waiting, collision
اسلاید 8: CSMA/CDWith CSMA, collision occupies medium for duration of transmissionStations listen whilst transmittingIf medium idle, transmitIf busy, listen for idle, then transmitIf collision detected, jam then cease transmissionAfter jam, wait random time then start againBinary exponential back off
اسلاید 9: CSMA/CD Operation
اسلاید 10: Collision DetectionOn baseband bus, collision produces much higher signal voltage than signalCollision detected if cable signal greater than single station signalSignal attenuated over distanceLimit distance to 500m (10Base5) or 200m (10Base2)For twisted pair (star-topology) activity on more than one port is collisionSpecial collision presence signal
اسلاید 11: IEEE 802.3 Frame Format
اسلاید 12: 10Mbps Specification (Ethernet)<data rate><Signaling method><Max segment length> 10Base510Base210Base-T10Base-FPMediumCoaxialCoaxialUTP850nm fiberSignalingBasebandBasebandBasebandManchester ManchesterManchesterManchesterOn/OffTopologyBusBusStarStarNodes10030-33
اسلاید 13: 100Mbps (Fast Ethernet) 100Base-TX100Base-FX100Base-T42 pair, STP2 pair, Cat 5UTP2 optical fiber4 pair, cat 3,4,5MLT-3MLT-34B5B,NRZI8B6T,NRZ
اسلاید 14: Gigabit Ethernet Configuration
اسلاید 15: Gigabit Ethernet - DifferencesCarrier extensionAt least 4096 bit-times long (512 for 10/100)Frame bursting
اسلاید 16: Gigabit Ethernet - Physical1000Base-SXShort wavelength, multimode fiber1000Base-LXLong wavelength, Multi or single mode fiber1000Base-CXCopper jumpers <25m, shielded twisted pair1000Base-T4 pairs, cat 5 UTPSignaling - 8B/10B
اسلاید 17: Token Ring (802.5)MAC protocolSmall frame (token) circulates when idleStation waits for tokenChanges one bit in token to make it SOF for data frameAppend rest of data frameFrame makes round trip and is absorbed by transmitting stationStation then inserts new token when transmission has finished and leading edge of returning frame arrivesUnder light loads, some inefficiencyUnder heavy loads, round robin
اسلاید 18: Token Ring Operation
اسلاید 19: Token Ring MAC Frame
اسلاید 20: Priority Scheme
اسلاید 21: Dedicated Token RingCentral hubActs as switchFull duplex point to point linkConcentrator acts as frame level repeaterNo token passing
اسلاید 22: 802.5 Physical LayerData Rate416100Medium UTP,STP,FiberSignaling Differential ManchesterMax Frame45501820018200Access ControlTP or DTRTP or DTRDTRNote: 1Gbit in development
اسلاید 23: FDDI100MbpsLAN and MAN applicationsToken Ring
اسلاید 24: FDDI MAC Frame Format
اسلاید 25: FDDI MAC ProtocolAs for 802.5 except:Station seizes token by aborting token transmissionOnce token captured, one or more data frames transmittedNew token released as soon as transmission finished (early token release in 802.5)
اسلاید 26: FDDI Operation
اسلاید 27: FDDI Physical LayerMediumOptical FiberTwisted PairData rate100100Signaling4B/5B/NRZIMLT-3Max repeaters100100Between repeaters2km100m
اسلاید 28: LAN GenerationsFirstCSMA/CD and token ringTerminal to host and client serverModerate data ratesSecondFDDIBackboneHigh performance workstationsThirdATMAggregate throughput and real time support for multimedia applications
اسلاید 29: Third Generation LANsSupport for multiple guaranteed classes of serviceLive video may need 2MbpsFile transfer can use background classScalable throughputBoth aggregate and per hostFacilitate LAN/WAN internetworking
اسلاید 30: ATM LANsAsynchronous Transfer ModeVirtual paths and virtual channelsPreconfigured or switchedGateway to ATM WANBackbone ATM switchSingle ATM switch or local network of ATM switchesWorkgroup ATMEnd systems connected directly to ATM switchMixed system
اسلاید 31: Example ATM LAN
اسلاید 32: ATM LAN HUB
اسلاید 33: CompatibilityInteraction between end system on ATM and end system on legacy LANInteraction between stations on legacy LANs of same typeInteraction between stations on legacy LANs of different types
اسلاید 34: Fiber Channel - BackgroundI/O channelDirect point to point or multipoint comms linkHardware basedHigh SpeedVery short distanceUser data moved from source buffer to destiation bufferNetwork connectionInterconnected access pointsSoftware based protocolFlow control, error detection &recoveryEnd systems connections
اسلاید 35: Fiber ChannelBest of both technologiesChannel orientedData type qualifiers for routing frame payloadLink level constructs associated with I/O opsProtocol interface specifications to support existing I/O architecturese.g. SCSINetwork orientedFull multiplexing between multiple destinationsPeer to peer connectivityInternetworking to other connection technologies
اسلاید 36: Fiber Channel ElementsEnd systems - NodesSwitched elements - the network or fabricCommunication across point to point links
اسلاید 37: Fiber Channel Network
اسلاید 38: Fiber Channel Protocol Architecture (1)FC-0 Physical MediaOptical fiber for long distancecoaxial cable for high speed short distanceSTP for lower speed short distanceFC-1 Transmission Protocol8B/10B signal encodingFC-2 Framing ProtocolTopologiesFraming formatsFlow and error controlSequences and exchanges (logical grouping of frames)
اسلاید 39: FC-3 Common ServicesIncluding multicastingFC-4 MappingMapping of channel and network services onto fiber channele.g. IEEE 802, ATM, IP, SCSIFiber Channel Protocol Architecture (2)
اسلاید 40: Wireless LANsIEEE 802.11Basic service set (cell)Set of stations using same MAC protocolCompeting to access shared mediumMay be isolatedMay connect to backbone via access point (bridge)Extended service setTwo or more BSS connected by distributed systemAppears as single logic LAN to LLC level
اسلاید 41: Types of stationNo transitionStationary or moves within direct communication range of single BSSBSS transitionMoves between BSS within single ESSESS transitionFrom a BSS in one ESS to a BSS in another ESSDisruption of service likely
اسلاید 42: Wireless LAN - Physical Infrared1Mbps and 2MbpsWavelength 850-950nmDirect sequence spread spectrum2.4GHz ISM bandUp to 7 channelsEach 1Mbps or 2MbpsFrequency hopping spread spectrum2.4GHz ISM band1Mbps or 2MbpsOthers under development
اسلاید 43: Media Access ControlDistributed wireless foundation MAC (DWFMAC)Distributed coordination function (DCF)CSMANo collision detectionPoint coordination function (PCF)Polling of central master
اسلاید 44: 802.11 MAC Timing
اسلاید 45: Required ReadingStallings chapter 14Web sites on Ethernet, Token ring, FDDI, ATM etc.
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