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From: wunder@HP-SES.SDE.HP.COM (Walter Underwood)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Beginner's info TCP & UDP
Message-ID: <9007171707.AA01515@hp-ses.sde.hp.com>
Date: 17 Jul 90 17:07:31 GMT
References: <Jul.16.21.14.16.1990.26321@athos.rutgers.edu>
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Organization: The Internet
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Hedrick's and Warnock's explanations are interesting, but I sent Pete
a rather different explanation for UDP's existance.  UDP is for
protocols that don't want or need byte streams.  It is for protocols
that need pure datagrams, often for request/response, and it is for
building custom protocols, like NTP.  TIME and DAYTIME are the classic
request/response examples -- if the reply is lost, TCP would
retransmit the old timestamp after a timeout, but with UDP, the
requestor times out, asks again, and gets a new timestamp.

A transaction protocol that supports idempotent requests would satisfy
a lot of the current users of UDP, but it would not obsolete UDP.

wunder