Data Communications

Data Communication

OutlineSwitched NetworkCircuit-Switched NetworkDatagram NetworksVirtual-Circuit Network

Data Communication*

Data Communication

IntroductionIn large networks we need some means to allow one-to-one communication between any two nodes. This is achieved using one of three methods:Direct point-to-point connection (mesh)Via central controller (star)Connection to common bus in a multipoint configuration (bus/hup)Data Communication*

Data Communication

IntroductionNone of the previous works in larger networks with large physical separation or consisting of a large number of computersThe solution is a switching networkData Communication*

Data Communication

Switched NetworkConsists of a series of interlinked nodes called switched.Switches are capable to create temporary connections between two or more devicesData Communication*

Data Communication

Data Communication*

Data Communication

Circuit-Switched NetworkA circuit-switched network consists of a set of switches connected by physical links.A connection between two stations is a dedicated path made of one or more linkseach connection uses only one dedicated channel on each linkEach link is normally divided into n channels by using FDM or TDM.The link can be permanent (leased line) or temporary (telephone)Data Communication*

Data Communication

Circuit-Switched NetworkData Communication*

Data Communication

Circuit-Switched NetworkSwitching take place at physical layerResourcesSuch as bandwidth in FDM and time slot in TDMSwitch bufferSwitch processing timeSwitch I/O portsData transferred are not packetized, continuous flowNo addressing involved during data transfer. Switches route the data based on occupied band(FDM or TDM)Data Communication*

Data Communication

ExampleData Communication*

Data Communication

Transmission phasesSetup phaseA dedicated circuit needs to be establishedSo create dedicated channel by sending a requestData Communication*

Data Communication

Transmission phasesData transfer phaseTeardown phaseSignal is sent to each switch to release resourcesData Communication*

Data Communication

Delay & EfficiencyData Communication*

Data Communication

Datagram NetworksData are transmitted in discrete units called packetsSize of the packet depends on the protocol and networkResources are allocated based on demandPackets switched networks are connectionless, hence no resource allocationConnectionless means the switch does not keep information about the connection state.Datagram switching is done at network layerData Communication*

Data Communication

Datagram NetworksData Communication*

Data Communication

Routing table & Destination Add.A switch in a datagram network uses a routing table that is based on the destination address.The destination address in the header of a packet in a datagram network remains the same during the entire journey of the packet.Data Communication*

Data Communication

Delay & EfficiencyTotal Delay = 3T + 3t+ w1+ w2Data Communication*

Data Communication

Virtual-Circuit NetworkIt uses some characteristic of circuit switch and datagram network.CharacteristicsIt has teardown and setup phase like circuit switch networkResources can be allocated during setup phase & demand during data transfer phaseData are packetized and each packet carries an address in the headerAll packets follow the same pathImplemented in data link layerData Communication*

Data Communication

Virtual-Circuit NetworkData Communication*

Data Communication

AddressingGlobal addressingSource and destination needs unique addressesVirtual-circuit identifierData Communication*

Data Communication

Transmission phasesSetup phaseA switch creates an entry for a virtual circuit.RequestacknowledgmentData Communication*

Data Communication

SetupData Communication*

Data Communication

acknowledgmentData Communication*

Data Communication

Data transfer and teardown phasesData Communication*After sending all frames, a special frame is send to end the connection

Data Communication

EfficiencyResources allocation is done during setup phase or demand during data transfer phase1st case delay is same for each packet and in 2nd case encounter different delay.The source can check the availabity of resources before reserving it.Data Communication*

Data Communication

DelayTotal delay = 3T + 3+ setup delay + teardown delayData Communication*

Data Communication

Data Communication*ReferencesAyman, Maliha, Data Communication Lectures, IUG.BehrouzA. Forouzan , Data Communications and Networking, 4rdEdition, Chapter8, 2007

Data Communication

Data Communication*Thanks

Data Communication