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Packet Switching


packet switching systems use statistical multiplexing to make better use of a
channel:
1. Data is sent in individual messages (packets).
2. Each message is forwarded from switch to switch, eventually reaching its destination.
3. Each switch has a small amount of bu er space to temporarily hold messages. If an
outgoing line is busy, the packet is queued until the line becomes available.
Packet switching vs circuit switching:
1. (Current) packet switching system do not provide known delay or capacity
characteristics. Some applications, like those making use of real-time voice and video,
cannot tolerate high variation in delays.
2. If many sites send data at the same time, end-to-end delay increases. That is,
per-user response and throughput drops as more users share a channel.
3. Packet switching utilizes resources more eciently (similar to multiprocessing in
operating systems). In particular, with circuit switching, bandwidth can be allocated
but unused, as when no one talks.
4. Packet switching systems doesn’t usually require opening a connection before sending
data. This important for applications that send only a single packet of data; the cost
of opening and closing a connection may exceed the cost of sending the data.
5. Billing algorithm more complex in packet switching systems. It’s easy to bill for a
connection, because one can gure out who to charge during the connection set up.
With packet-switching, each packet must be accounted for individually.





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