Packet / Message Switching Concepts

1. Packet / Message Switching Concepts

2. Contents • Circuit Switching v/s Packet switching • Logical Channel v/s Physical channel • Statistical Time Division Multiplexing • Connectionless and Connection Oriented Data Communications

3. Switching Message Switching Circuit Switching Packet Switching Datagram Approach Virtual Circuit Approach SVC PVC Switching Methods

4. A B D C B A D C B A S C D Direction of transmission Circuit Switching A S D C B A D C B Physical Channels (Time Slots)

5. A B - - - A - - - A S C D Direction of transmission Circuit Switching A S - - - A - - - Inefficient Utilization of media

6. DATA Time All Communications are bursty Request for some website home page Data transfer from the web site

7. Message Switching • Store and Forward technique • Send the message to next node • Next node stores it in memory • It takes a decision about the next hop closer to destination • Forwards it to next hop when link to the next hop is available and next node is ready to receive it • Next hop repeats the same process • Message finally reaches its destination node

8. M1 M1 M1 M1 D A Store & Forward Store & Forward Store & Forward Store & Forward E B M2 M2 M2 Message Switching

9. Message Switching • Messages are bigger in size • Storage and processing requires more resources • Sometimes nodes may not have sufficient resources • Messages remain stored in memory of a node for longer period • Entire process becomes slow • Error will require full message to be retransmitted • Suitable for services like Telegraphs etc • Not suitable for fast modern networks

10. Evolution of Packet switching • Break the message into smaller packets • Transmit the packets hop by hop to destination • Destination reassembles packets into original message • Requires less resources at nodes • Process becomes faster compared to message switching • Error requires only retransmission of errored packet not the full message

11. D B A Packet Switching: Statistical Multiplexing A B D B A C D Direction of transmission Virtual Channels No Physical channel like a Time Slot

12. Packet Switching • Allot Bandwidth on Demand • Buffer Data and allow bandwidth to only those hosts which have data to transmit. • To the data, add some delimiters to indicate end of data transmitted by a particular host. • Add some tags (addresses or channel identifiers) to indicate the sender.

13. FFFFFF C F B F A F F: A flag to delimit the data transmitted by one host A, B, C: Identifier for the transmitting host (Address or Virtual channel no.) Packet Switching A B D B A C D Direction of transmission FFFFFF101010CF001010101110BF101111011AF

14. Packet Switching A B C A C D Direction of transmission FFFFFF101010CF00101010111010101111011AF C is denied the opportunity to transmit

15. Packet Switching A B C A C D Direction of transmission FFFFFF101010CF00101010111010101111011AF 1 1 1 1 1 The whole data for A is retransmitted

16. Packet Switching A B C A C D Direction of transmission FFFFFF101010CF00101010111010101111011AF Solution is break data into small blocks PACKETS

17. Packet Switching Techniques • Connection Oriented • End to end path is setup before any data communication happens • Every packet need not carry the destination address • Destination address is send to the network only once during the call setup process • Connectionless • Path setup is not required. Drop the packet in network and network takes it to destination • Every packet should must carry the source and destination address • Every packet is examined independently by the nodes for its routing

18. Connection Oriented Data Communications • A path is established before actual data transfer. • All packets take the same path. • Routing decision is taken before actual data transfer. • Actual data packets contains the routing labels. • All packets follow the same path • Packets reach its destination in sequence • Disruption in communication if link fails during data transfer. • Quality of service can be guaranteed. • Example X.25, Frame Relay, Asynchronous Transfer Mode(ATM).

19. 1 49 3 35 . . . . I/C I/C I/C I/C O/G O/G O/G O/G P P P P CHL CHL CHL CHL P P P P CHL CHL CHL CHL 1 5 3 7 2 7 5 20 1 20 2 49 Connection Oriented Data Communications 2 3 4 2 1 3 2 4 1 5 1 3 2 1

20. B B A A C C Routing Table I/c O/g P Chl P Chl Connect B Chl No.1 Connect C Chl No.2 A 1 B x A 2 C y F F Virtual Channel 1001010110F010101001F 10 01

21. 4 4 3 3 2 2 1 1 4 3 2 1 2 2 2 2 1 1 1 1 Permanent Virtual Circuit-PVC

22. 4 4 3 3 2 2 1 1 4 3 2 1 2 2 2 2 1 1 1 1 Switched Virtual Circuit-SVC

23. Connectionless Data Communications • A path is not established before actual data transfer. • All packets do not take the same path • Routing decision is taken on the arrival of every packet at every node. • Every packet contains the full destination address. • No disruption in communication if link fails during data transfer and an alternate path exists. • Quality of service is not guaranteed. • Packet can follow different path • Packet can arrive out of sequence at destination • Example Internet

24. Routing Table Dest. Next Hop Connectionless Data Communications Packet 1 Packet 2

25. 2 1 1 1 1 4 3 2 1 3 1 4 3 3 3 1 1 4 4 2 2 2 3 4 1 4 1 2 1 2 4 2 2 Datagram Approach

26. Thank you Questions?