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ALTTC/DX/SKG/Packet & Message Switching Concepts 1.

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Presentation on theme: "ALTTC/DX/SKG/Packet & Message Switching Concepts 1."— Presentation transcript:

1 ALTTC/DX/SKG/Packet & Message Switching Concepts 1

2 ALTTC/DX/SKG/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 ALTTC/DX/SKG/Packet & Message Switching Concepts 3 Switching Methods Switching Circuit Switching Message Switching Packet Switching Datagram Approach Virtual Circuit Approach SVCPVC

4 ALTTC/DX/SKG/Packet & Message Switching Concepts 4 Circuit Switching A B C D S A S Direction of transmission Physical Channels (Time Slots) BCD A BCD A BCDCABD

5 ALTTC/DX/SKG/Packet & Message Switching Concepts Circuit Switching A B C D S A S Direction of transmission Inefficient Utilization of media --- A --- A A-

6 ALTTC/DX/SKG/Packet & Message Switching Concepts 6 All Communications are bursty Time DATADATA Request for some website home page Data transfer from the web site

7 ALTTC/DX/SKG/Packet & Message Switching Concepts 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 ALTTC/DX/SKG/Packet & Message Switching Concepts 8 Message Switching A B D E Store & Forward M1 M2

9 ALTTC/DX/SKG/Packet & Message Switching Concepts 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 ALTTC/DX/SKG/Packet & Message Switching Concepts 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 ALTTC/DX/SKG/Packet & Message Switching Concepts 11 Packet Switching: Statistical Multiplexing A B C D A Direction of transmission Virtual Channels No Physical channel like a Time Slot BD ABD

12 ALTTC/DX/SKG/Packet & Message Switching Concepts 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 ALTTC/DX/SKG/Packet & Message Switching Concepts 13 Packet Switching A B C D ABD Direction of transmission FFFFFF101010CF BF AF F: A flag to delimit the data transmitted by one host FFFFFFFFF A, B, C: Identifier for the transmitting host (Address or Virtual channel no.) CBA

14 ALTTC/DX/SKG/Packet & Message Switching Concepts 14 Packet Switching A B C D AC Direction of transmission FFFFFF101010CF AF C is denied the opportunity to transmit

15 ALTTC/DX/SKG/Packet & Message Switching Concepts 15 FFFFFF101010CF AF Packet Switching A B C D AC Direction of transmission The whole data for A is retransmitted

16 ALTTC/DX/SKG/Packet & Message Switching Concepts 16 FFFFFF101010CF AF Packet Switching A B C D AC Direction of transmission Solution is break data into small blocks PACKETS

17 ALTTC/DX/SKG/Packet & Message Switching Concepts 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 ALTTC/DX/SKG/Packet & Message Switching Concepts 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 ALTTC/DX/SKG/Packet & Message Switching Concepts 19 Connection Oriented Data Communications. I/C O/G PCHL P I/C O/G PCHL P I/C O/G PCHL P I/C O/G PCHL P

20 ALTTC/DX/SKG/Packet & Message Switching Concepts F F Virtual Channel Connect B Chl No.1Connect C Chl No.2 Routing Table I/c O/g P Chl A C B A B C A1Bx yC2A F F 0110

21 ALTTC/DX/SKG/Packet & Message Switching Concepts 21 Permanent Virtual Circuit-PVC

22 ALTTC/DX/SKG/Packet & Message Switching Concepts 22 Switched Virtual Circuit-SVC

23 ALTTC/DX/SKG/Packet & Message Switching Concepts 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 ALTTC/DX/SKG/Packet & Message Switching Concepts 24 Connectionless Data Communications Packet 1 Packet 2 Routing Table Dest. Next Hop

25 ALTTC/DX/SKG/Packet & Message Switching Concepts 25 Datagram Approach

26 ALTTC/DX/SKG/Packet & Message Switching Concepts 26


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