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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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Presentation Transcript
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
slide11

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.
slide13

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

slide14

Packet Switching

A

B

C

A

C

D

Direction of transmission

FFFFFF101010CF00101010111010101111011AF

C is denied the opportunity to transmit

slide15

Packet Switching

A

B

C

A

C

D

Direction of transmission

FFFFFF101010CF00101010111010101111011AF

1

1

1

1

1

The whole data for A is retransmitted

slide16

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

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
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
slide26

Thank you

Questions?

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