chapter_9_circuit_switching

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(Circuit switching (chapter 9

اسلاید 1: William Stallings Data and Computer CommunicationsChapter 9Circuit Switching

اسلاید 2: Switching NetworksLong distance transmission is typically done over a network of switched nodesNodes not concerned with content of dataEnd devices are stationsComputer, terminal, phone, etc.A collection of nodes and connections is a communications networkData routed by being switched from node to node

اسلاید 3: NodesNodes may connect to other nodes only, or to stations and other nodesNode to node links usually multiplexedNetwork is usually partially connectedSome redundant connections are desirable for reliabilityTwo different switching technologiesCircuit switchingPacket switching

اسلاید 4: Simple Switched Network

اسلاید 5: Circuit SwitchingDedicated communication path between two stationsThree phasesEstablishTransferDisconnectMust have switching capacity and channel capacity to establish connectionMust have intelligence to work out routing

اسلاید 6: Circuit Switching - ApplicationsInefficientChannel capacity dedicated for duration of connectionIf no data, capacity wastedSet up (connection) takes timeOnce connected, transfer is transparentDeveloped for voice traffic (phone)

اسلاید 7: Public Circuit Switched Network

اسلاید 8: Telecomms ComponentsSubscriberDevices attached to networkLocal LoopSubscriber loopConnection to networkExchangeSwitching centersEnd office - supports subscribersTrunksBranches between exchangesMultiplexed

اسلاید 9: Circuit Switch Elements

اسلاید 10: Circuit Switching ConceptsDigital SwitchProvide transparent signal path between devicesNetwork InterfaceControl UnitEstablish connectionsGenerally on demandHandle and acknowledge requestsDetermine if destination is freeconstruct pathMaintain connectionDisconnect

اسلاید 11: Blocking or Non-blockingBlockingA network is unable to connect stations because all paths are in useA blocking network allows thisUsed on voice systemsShort duration callsNon-blockingPermits all stations to connect (in pairs) at onceUsed for some data connections

اسلاید 12: Space Division SwitchingDeveloped for analog environmentSeparate physical pathsCrossbar switchNumber of crosspoints grows as square of number of stationsLoss of crosspoint prevents connectionInefficient use of crosspointsAll stations connected, only a few crosspoints in useNon-blocking

اسلاید 13: Crossbar Matrix

اسلاید 14: Multistage SwitchReduced number of crosspointsMore than one path through networkIncreased reliabilityMore complex controlMay be blocking

اسلاید 15: Three Stage Switch

اسلاید 16: Time Division SwitchingPartition low speed bit stream into pieces that share higher speed streame.g. TDM bus switchingbased on synchronous time division multiplexingEach station connects through controlled gates to high speed busTime slot allows small amount of data onto busAnother line’s gate is enabled for output at the same time

اسلاید 17: RoutingMany connections will need paths through more than one switchNeed to find a routeEfficiencyResiliencePublic telephone switches are a tree structureStatic routing uses the same approach all the timeDynamic routing allows for changes in routing depending on trafficUses a peer structure for nodes

اسلاید 18: Alternate RoutingPossible routes between end offices predefinedOriginating switch selects appropriate routeRoutes listed in preference orderDifferent sets of routes may be used at different times

اسلاید 19: Alternate Routing Diagram

اسلاید 20: Control Signaling FunctionsAudible communication with subscriberTransmission of dialed numberCall can not be completed indicationCall ended indicationSignal to ring phoneBilling infoEquipment and trunk status infoDiagnostic infoControl of specialist equipment

اسلاید 21: Control Signal SequenceBoth phones on hookSubscriber lifts receiver (off hook)End office switch signaledSwitch responds with dial toneCaller dials numberIf target not busy, send ringer signal to target subscriberFeedback to callerRinging tone, engaged tone, unobtainableTarget accepts call by lifting receiverSwitch terminates ringing signal and ringing toneSwitch establishes connectionConnection release when Source subscriber hangs up

اسلاید 22: Switch to Switch SignalingSubscribers connected to different switchesOriginating switch seizes interswitch trunkSend off hook signal on trunk, requesting digit register at target switch (for address)Terminating switch sends off hook followed by on hook (wink) to show register readyOriginating switch sends address

اسلاید 23: Control Signals

اسلاید 24: Location of SignalingSubscriber to networkDepends on subscriber device and switchWithin networkManagement of subscriber calls and networkore complex

اسلاید 25: In Channel SignalingUse same channel for signaling and callRequires no additional transmission facilitiesInbandUses same frequencies as voice signalCan go anywhere a voice signal canImpossible to set up a call on a faulty speech pathOut of bandVoice signals do not use full 4kHz bandwidthNarrow signal band within 4kHz used for controlCan be sent whether or not voice signals are presentNeed extra electronicsSlower signal rate (narrow bandwidth)

اسلاید 26: Drawbacks of In Channel SignalingLimited transfer rateDelay between entering address (dialing) and connectionOvercome by use of common channel signaling

اسلاید 27: Common Channel SignalingControl signals carried over paths independent of voice channelOne control signal channel can carry signals for a number of subscriber channelsCommon control channel for these subscriber linesAssociated ModeCommon channel closely tracks interswitch trunks Disassociated ModeAdditional nodes (signal transfer points)Effectively two separate networks

اسلاید 28: Common v. In Channel Signaling

اسلاید 29: Signaling Modes

اسلاید 30: Signaling System Number 7SS7Common channel signaling schemeISDNOptimized for 64k digital channel networkCall control, remote control, management and maintenanceReliable means of transfer of info in sequenceWill operate over analog and below 64kPoint to point terrestrial and satellite links

اسلاید 31: SS7 Signaling Network ElementsSignaling point (SP)Any point in the network capable of handling SS7 control messageSignal transfer point (STP)A signaling point capable of routing control messagesControl planeResponsible for establishing and managing connectionsInformation planeOnce a connection is set up, info is transferred in the information plane

اسلاید 32: Transfer Points

اسلاید 33: Signaling Network StructuresSTP capacitiesNumber of signaling links that can be handledMessage transfer timeThroughput capacityNetwork performanceNumber of SPsSignaling delaysAvailability and reliabilityAbility of network to provide services in the face of STP failures

اسلاید 34: Required ReadingStallings chapter 9ITU-T web siteTelephone company web sites (not much technical info - mostly marketing)

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