store and forward switching

8/3/2019 Store and Forward Switching

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Md. Saquib Faraz



Sharing is done on demand basis.

Message is accepted from sender and forwarded to

receiver, on availability of an outgoing channel.

Frames are completely processed before being forwardedout the appropriate port.

When a link has traffic to send, it may be more fully utilized.



Includes calculating the Cyclic Redundancy Check(CRC) and checking the destination address.

This technique originates the delay-tolerantnetworks.

Example: messaging in mobile communication

Two basic type of store and forward switching are :-

1. Message switching.2. Packet switching.



Each message is treated as a separate entity.

A conversation of several messages may not betransferred over the same path.

Node stores the message, checks for errors, selects thebest available route and forwards it.

More devices can share the network bandwidth.



Continued..

y A message might occupy the buffers for minutes, due tolarge size.

y A message switch is transactional.

y An incoming message is not lost when the requiredoutgoing route is busy.

y Email is a common application for Message Switching.



Message Switching

Advantages Disadvantages

y Improves the use of bandwidth.

y Messages can be storedtemporarily at messageswitches.

y Priorities may be used to

manage network traffic.

y Broadcast addressing usesbandwidth more efficiently .

y Requires large buffers

y Due to large size, it may take

too long to tie to a link.



There are no dedicated circuits.

Ability to route data units over any route, ratherthan a fixed route.

Message larger than specified size is broken intosegments(packets).

Can be viewed as a distributed pool of productiveresources.



Characteristics of intelligentswitching nodes

y All data messages are divided into short blocksof data.

y The packets move between nodes very quickly.

y The node computers do not store data.



1Packet switching might be more economical than using private lines.

2. More economical than dialed data when the data communicationsessions are shorter than a telephone call minimum chargeable timeunit.

3. Destination information is contained in each packet, so numerousmessages can be sent very quickly to many different destinations.

4. Computers at each node allow dynamic data routing.

5. The packet network inherent intelligence also allows graceful

degradation of the network in the event of a node or path (link)failure.

6. Other features of this intelligence are error detection andcorrection, fault diagnosis, verification of message delivery, message

sequence checking, reverse billing (charging), etc.



Comparison between message andpacket switching

Message switching Packet switching

y Message are stored and relayed

from secondary storage (disk).

y A node receives a message storesit until the appropriate route isfree, then sends it along.

y Message switching sends dataunits that can be of any length.

y In Packet switching the packets

are stored and forwarded fromprimary storage (RAM)

y In Packet switched network dataare transmitted in discrete unitsof potentially variable lengthblocks called packets.

y Packet switching has amaximum packet size. Any message longer than that is split-up into multiple packets



Conclusion

y Store and forward switching is more efficient thancircuit switching .

y Packet switching succeeded message switching.

store and forward switching

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