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From: root@asylum.sf.ca.us (Super user)
Newsgroups: comp.protocols.tcp-ip
Subject: Beginner's info TCP & UDP
Message-ID: <9007190124.AA11998@asylum.sf.ca.us>
Date: 19 Jul 90 08:24:12 GMT
References: <81247@srcsip.UUCP>
Sender: daemon@ucbvax.BERKELEY.EDU
Reply-To: romkey@asylum.sf.ca.us
Organization: The Internet
Lines: 33

UDP has a lot less overhead than TCP. For simple transaction-based
protocols (request-response) that don't carry much data, UDP is much
simpler to use. TCP would have the additional overhead of setting up
and tearing down its connection, whereas UDP sends the request and
response and doesn't care about the ret.

In request-response protocols based on UDP, you have to worry about
three main things: what happens if a packet gets lost (solution: set a
timer and retransmit), what happens if you resend the request and
its action gets duplicated (solution: be careful about your protocol
design, or put sequence numbers in the packets), and what happens if
your data doesn't all fit in one packet (solution: IP fragmentation,
or split it across packets, or you lose). Splitting data across UDP
packets is often a good reason to start using TCP, since it already
has a lot of mechanism in it for dealing with this issue.

Not many applications use UDP for transferring lots of data. Those
applications are normally TCP-based. However, UDP is very convenient
for applications wishing to use a bulk data transport protocol with
different behaviour from TCP. This kind of work would be mostly
experimental, though.

SNMP, the main network management protocol for the Internet, is
layered on top of UDP. One advantage to this is that it allows those
vendors that might provide SNMP in their products that would otherwise
have no (IP) protocol stack (like an ethernet hub) to include SNMP
without having to implement a full TCP. While getting a TCP
implementation running today is easier than it was several years ago,
UDP is orders of magnitude simpler.
			- john romkey
USENET/UUCP: romkey@asylum.sf.ca.us	Internet: romkey@ftp.com
"There is no loyalty except loyalty to the party. There is no love except love
of Big Brother. All competing pleasures we will destroy." - 1984 (film)