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

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Contents
Contents

  • Circuit Switching v/s Packet switching

  • Logical Channel v/s Physical channel

  • Statistical Time Division Multiplexing

  • Connectionless and Connection Oriented Data Communications


Switching methods

Switching

Message Switching

Circuit Switching

Packet Switching

Datagram Approach

Virtual Circuit Approach

SVC

PVC

Switching Methods


Circuit switching

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)


Circuit switching1

A

B

-

-

-

A

-

-

-

A

S

C

D

Direction of transmission

Circuit Switching

A

S

-

-

-

A

-

-

-

Inefficient Utilization of media


All communications are bursty

DATA

Time

All Communications are bursty

Request for some

website home page

Data transfer

from the web site


Message switching
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


Message switching1

M1

M1

M1

M1

D

A

Store & Forward

Store & Forward

Store & Forward

Store & Forward

E

B

M2

M2

M2

Message Switching


Message switching2
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


Evolution of packet switching
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


Packet message switching concepts

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


Packet switching
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.


Packet message switching concepts

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


Packet message switching concepts

Packet Switching

A

B

C

A

C

D

Direction of transmission

FFFFFF101010CF00101010111010101111011AF

C is denied the opportunity to transmit


Packet message switching concepts

Packet Switching

A

B

C

A

C

D

Direction of transmission

FFFFFF101010CF00101010111010101111011AF

1

1

1

1

1

The whole data for A is retransmitted


Packet message switching concepts

Packet Switching

A

B

C

A

C

D

Direction of transmission

FFFFFF101010CF00101010111010101111011AF

Solution is break data into small blocks

PACKETS


Packet switching techniques
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


Connection oriented data communications
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).


Connection oriented data communications1

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


Virtual channel

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


Permanent virtual circuit pvc

4

4

3

3

2

2

1

1

4

3

2

1

2

2

2

2

1

1

1

1

Permanent Virtual Circuit-PVC


Switched virtual circuit svc

4

4

3

3

2

2

1

1

4

3

2

1

2

2

2

2

1

1

1

1

Switched Virtual Circuit-SVC


Connectionless data communications
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


Connectionless data communications1

Routing Table

Dest. Next Hop

Connectionless Data Communications

Packet 1

Packet 2


Datagram approach

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


Packet message switching concepts

Thank you

Questions?