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User Datagram Protocol
The User Datagram Protocol (UDP) provides an
alternative, connectionless, 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 adds 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.
UDP segments (also commonly called datagrams, see
later) have a minimal (8-byte) header. Data transfer with UDP has
no initial connection overhead, and (obviously) no waiting for ACK
segments as in TCP. Some typical UDP-based services include DNS, streaming multimedia and
"Voice over IP" applications. It's also worth noting that an
application can elect to use UDP where it's prepared to implement
its own reliability -- some proprietory streaming protocols do
this, for example.
NB: UDP communications, at the programming level, is based on
sockets, as for TCP. However instead of reading
from, and writing to, a socket in a stream-based model as for TCP,
a UDP socket supports the operations send and
receive, which are based on packet-sized chunks
of data.
The tutorial for this lecture is Tutorial
#10.
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Copyright © 2002 by
Philip Scott, La Trobe
University.
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