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

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

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

6. All Communications are bursty
Time
D A T A
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. Message Switching A B D E
Store & Forward M2 M1

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. Packet Switching: Statistical MultiplexingB B D 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. Packet Switching F: A flag to delimit the data transmitted by one host
Direction of transmission
F: A flag to delimit the data transmitted by one host F
FFFFFF
FFFFFF101010CF BF AF
A, B, C: Identifier for the transmitting host
(Address or Virtual channel no.) C B A

14. Packet Switching C is denied the opportunity to transmitB C A C D
Direction of transmission
FFFFFF101010CF AF
C is denied the opportunity to transmit

15. Packet Switching The whole data for A is retransmittedB C D
Direction of transmission
FFFFFF101010CF AF 1 1 1 1 1
The whole data for A is retransmitted

16. PACKETS Packet Switching Solution is break data into small blocks
Direction of transmission
FFFFFF101010CF AF
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. Connection Oriented Data Communications.
I/C
O/G P
CHL 1 5 3 7 2 20 49 35 2 3 4 2 1 3 2 4 1 5 1 3 2 1

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

21. Permanent Virtual Circuit-PVC4 3 2 1 2 1 4 3 2 1 2 1 1 2 3 4 2 1

22. Switched Virtual Circuit-SVC4 3 2 1 2 1 4 3 2 1 2 1 1 2 3 4 2 1 2 1

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

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

26. Thank you
Questions?