Message Switching
Message Switching• In message switching, a message is relayed from one switch to another until
the message arrives at the destination
• A message switch operates in store and forward fashion (a message has to be
completely received by the switch before it can be forwarded to next switch)
• At the source each message has header attached to it to provide source and
destination address.
• Each switch performs an error check, and if no errors are detected, the switch
examines the header to determine the next hop in the path to the destination.
• Loss of messages may occur when a switch has insufficient buffering to store
• The message has to traverse the link to the first switch
• We assume
– the link has propagation delay in seconds,
T – the transmission time
• The message must traverse the link that connect two switches and from
second switch to the destination.
• It follows that the minimum delay is 3 + 3T
• In general, the delay incurred in message switching involving L hops is L +
LT
Disadvantages of message switching
• The probability of error increases with the length of the block. Thus long
messages are not desirable
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