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The Transport Layer Revisited: UDP
The User Datagram Protocol provides a connectionless alternative
transport service to TCP for applications where reliable stream
service is not needed. UDP datagrams can be droppped, duplicated or
delivered out of order, exactly as for IP.
The UDP transport service add to IP the ability to deliver a
datagram to a specified destination process using a
port abstraction, in an analogous way to that used
by TCP.
Examples of applications where UDP is used include:
- Any application where loss of a datagram is not critical
because later datagrams will imply the missing information. Some
situations include:
- A "timekeeper" host sends the current "wallclock" time to a
slave host.
- Routers broadcast copies of their routing tables every 30
seconds.
- An application process which performs its own error correction
is used.
- The reduced overhead of connectionless operation suits some
time-critical applications where (occasional) loss of data may be
unimportant. An example is voice communications over the
Internet.
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