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

2.  Switching Switching  Circuit Switching Circuit Switching  Message switch Message switch  Packet Switching Packet Switching  Packet Switching Techniques Packet Switching Techniques  Datagram Approach Datagram Approach  Virtual Circuit Approach Virtual Circuit Approach  Virtual Circuits Vs Datagram Virtual Circuits Vs Datagram

3.  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.

4.  uses a dedicated path between two stations  has three phases ◦ establish ◦ transfer ◦ disconnect  Inefficient o channel capacity dedicated for duration of connection o if no data, capacity wasted  set up (connection) takes time  once connected, transfer is transparent back

6.  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 transfer ◦ Circuit disconnect  Deallocate the dedicated resources

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

8.  Uneconomical method.  Time required to established a physical link between two station is very large.  Network resources are not properly utilised.

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10.  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.

11.  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.

12.  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

13.  packet switching was designed for data  transmitted in small packets  packets contains user data and control info  user data may be part of a larger message  control info includes routing (addressing) info  packets are received, stored briefly (buffered) and past on to the next node

15.  line efficiency  single link shared by many packets over time  packets queued and transmitted as fast as possible  data rate conversion  stations connects to local node at own speed  nodes buffer data if required to equalize rates  packets accepted even when network is busy  priorities can be used back

16.  station breaks long message into packets  packets sent one at a time to the network  packets can be handled in two ways  datagram  virtual circuit back

17.  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

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19.  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

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21.  virtual circuits ◦ network can provide sequencing and error control ◦ packets are forwarded more quickly ◦ less reliable  datagram ◦ no call setup phase ◦ more flexible ◦ more reliable back