Re: Tim Berners-Lee worries?

Robert S. Thau (
Fri, 30 Aug 1996 11:38:38 -0400

Excuse me? UDP bullying TCP? If a network gets too congested, the
routers drop packets. It doesn't matter if they are TCP or UDP. If
the program using UDP wants to make sure it gets its packet there it
implements flow control and reliability at a higher protocol level.
TCP makes sure your packets get where they should.

What was being alluded to here is that TCP implementations are
required to detect congestion, and back off on a slow link. Since UDP
leaves transmission rates up to the application layer, and since the
UDP layer in the stack doesn't have enough information itself to do
its own congestion control, there can be no such protocol-level
requirement for UDP. Hence, if you've got a crowded link with active
TCP and UDP-based traffic, and the UDP applications don't implement
any congestion-detection and back-off of their own, the TCPs will back
off, the UDPs won't, and the net effect --- exactly as stated --- is
that UDP hogs the links.