circuit switching packet switching message switching wcb/mcgraw-hill the mcgraw-hill...
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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
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
Once the circuit is established, data is transmitted with no delay.
Time required to established a physical link between two station is very large.
Network resources are not properly utilised.
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.
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
station breaks long message into packets
packets sent one at a time to the network
packets can be handled in two waysdatagramvirtual circuit
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
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
virtual circuitsnetwork can provide sequencing and error controlpackets are forwarded more quicklyless reliable
datagramno call setup phasemore flexiblemore reliable