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Download  Circuit Switching  Packet Switching  Message Switching WCB/McGraw-Hill  The McGraw-Hill Companies, Inc., 1998

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  • Circuit SwitchingPacket SwitchingMessage SwitchingWCB/McGraw-Hill The McGraw-Hill Companies, Inc., 1998

  • SwitchingCircuit SwitchingMessage switchPacket Switching Packet Switching TechniquesDatagram ApproachVirtual Circuit Approach Virtual Circuits Vs Datagram

  • The process of transfering data blocks from one node to another is called switching.

    In a switched communications network, data entering the network from a station are routed to the destination by being switched from node to node.

    Data entering the network from a station are routed to the destination by being switched from node to node.

  • uses a dedicated path between two stations

    has three phasesestablishtransferdisconnectInefficientchannel capacity dedicated for duration of connectionif no data, capacity wasted

    set up (connection) takes time

    once connected, transfer is transparent

    back

  • Circuit switching:

    There is a dedicated communication path between two stations (end-to-end)The path is a connected sequence of links between network nodes. On each physical link, a logical channel is dedicated to the connection.

    Communication via circuit switching has three phases:Circuit establishment (link by link)Routing & resource allocation (FDM or TDM)Data transferCircuit disconnectDeallocate the dedicated resources

  • Simple

    Once the circuit is established, data is transmitted with no delay.

  • Uneconomical method.

    Time required to established a physical link between two station is very large.

    Network resources are not properly utilised.

  • back

  • Sending device appends the destination address to the message

    Passes it to the network from one node to another node till it reaches to the intended destination.

    Switching node receive the message ,store it and then transmit it to the next node.

  • No physical connection is required between source and destination node.

    This method uses the communication channel very effectively because channels are used when messages are transmitted.

  • This method is slow for interactive real time application.

    As message length is unlimited (not fixed),each node must have sufficient storage to store message.

    A message is delayed at each node.

    back

  • packet switching was designed for data

    transmitted in small packets

    packets contains user data and control infouser data may be part of a larger messagecontrol info includes routing (addressing) info

    packets are received, stored briefly (buffered) and past on to the next node

  • line efficiencysingle link shared by many packets over timepackets queued and transmitted as fast as possible

    data rate conversionstations connects to local node at own speednodes buffer data if required to equalize rates

    packets accepted even when network is busy

    priorities can be used

    back

  • station breaks long message into packets

    packets sent one at a time to the network

    packets can be handled in two waysdatagramvirtual circuit

    back

  • Each packet treated independently

    Packets can take any practical route

    Packets may arrive out of order

    Packets may go missing

    Up to receiver to re-order packets and recover from missing packets

  • back

  • Preplanned route established before any packets sent

    Call request and call accept packets establish connection (handshake)

    Each packet contains a virtual circuit identifier instead of destination address

    No routing decisions required for each packet

    Clear request to drop circuit

    Not a dedicated path

  • back

  • virtual circuitsnetwork can provide sequencing and error controlpackets are forwarded more quicklyless reliable

    datagramno call setup phasemore flexiblemore reliable

    back

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