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In message switching, the switches wait for the entire message to arrive (store) and then forward it to other switches.

Does packet switching also use store and forward technique ? I know that in packet switching, the message is divided into packets and sent across the links. But are the packets sent as soon as they arrive at the switch or are they stored in a similar way as message switching?

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    You can use store-and-forward or cut-through switching with either packet or message switching. – Ron Maupin Aug 25 '17 at 6:03
  • I have a slight doubt in the definition of store and forward technique. Is store and forward technique associated with the entire message or a single packet ? I mean if we store a single packet and then send, is it also store and forward technique? – Zephyr Aug 25 '17 at 6:09
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Nowadays, message switching is implemented at application level and it is actually transported by packet switching at the network level.

The most common example of this is email: an email is the message, the emails servers are the switches. The email is transferred using store and forward technique between each email servers, through SMTP protocol.

Between two email server, this message is divided into packets that are transported using TCP and IP protocols and pass through several IP networks. Each of this network can contain several switches and routers.

On a single path, the packets may traverse switches that use store and forward as well as other switches that use cut-through switching.

Since different packets may take different paths, you can have for a single message (email) some packets that will traverse some cut-through switches and other packets that will not encounter a single one.

Edit following comments:

Store and Forward vs Cut-Through is the way a specific switch behave. It is not a characteristic of a message / packet.

As stated by @Ron Maupin in comment you can use both technique with either message or packets.

The difference between message switching vs packet switching (in today's network) is that they don't happen at the same level.

They are not of the same nature and doesn't require the same treatment.

In the case of email messages, a small delay is not important, but the integrity of the message is critical. So a store and forward technique is much more appropriate, so each intermediate switch can check the integrity of the message before passing it to the next.

If you care more about speed than about integrity, then you can use cut-through switching. I don't have a good example in mind right now except for audio/video message that doesn't fit well here.

Note that if the message is sent to a network you don't control, or traverse such network, you cannot know how the intermediate switches are configured to behave. Once again in the case of email, it is likelt that all email servers will use S&F but it may traverse an anti-spam / anti-virus gateway that use some kind of cut-through.

The same logic apply for packet switching, but it happen at a different level.

A difference in packet switching is that the packet may be treated differently depending on its content.

  • I have a slight doubt in the definition of store and forward technique. Is store and forward technique associated with the entire message or a single packet ? I mean if we store a single packet and then send, is it also store and forward technique? – Zephyr Aug 25 '17 at 7:20
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    It is not related to the packet or the message itself, but rather to how a given switch will treat a packet/message. The same message/packet can be stored and forwareded on a given switch then transferred "cut-through" on the following switch, etc... – JFL Aug 25 '17 at 7:27
  • So the only difference between message and packet switching is that in message switching, the switch waits for the entire message so that it could transfer it(maybe store it or transfer it right away) and in packet switching it waits for the entire packet so that it could transmit it. Am I right? – Zephyr Aug 25 '17 at 7:51
  • see my edit in the answer. – JFL Aug 25 '17 at 8:32
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➨ Message switching overhead is lower compare to packet switching. Fig-3 depicts that single datagram is transmitted in message switching. As mentioned, message is appended with header before transmission. In packet switching message is divided into smaller packets amd each packet is appended with header before transmission. Overhead in message switching = header/(header+message) Overhead in packet switching = [nheader/(nheader+message)], Where, n = [message/packet_size]

➨ Message switching has higher reliability and lower complexity. As in message switching, one single datagram is either received or lost. One single network path is used for the same.

In packet switching, many packets generated by same node and belonging to the same destination may take different paths. The packets received out of order will need to be sequenced using sequence number embedded in the header part. May lose or corrupt a subset of the message but do not discard the entire message as in message switching. Hence based on overall corrupt message received, what could be correct message can be interpreted. Due to this reason, sometimes in the real time scenarios such as voice, message switching is not possible.

➨As explained above message switching takes more time compare to packet switching as entire message will be stored at each of the hop points till it is completely received.

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