Path: utzoo!utgpu!watserv1!watmath!att!linac!uwm.edu!bionet!agate!ucbvax!MATHOM.CISCO.COM!BILLW
From: BILLW@MATHOM.CISCO.COM (William "Chops" Westfield)
Newsgroups: comp.protocols.tcp-ip
Subject: Re:  When is a link saturated?
Message-ID: <12654545997.12.BILLW@mathom.cisco.com>
Date: 17 Jan 91 06:17:18 GMT
References: <9101160029.AA09554@inria.inria.fr>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 27


	    Tsui noted that priority queuing is especially useful in
	    international networks, where bandwidth is often most expensive.

    Wow!  That is a new one on me.  Can someone explain how ordering
    packets (but not discarding) can save bandwidth?

Well, reordering the packets will also affect which packets get dropped
when a queue becomes full.  If you give interactive (small) packets
priority, big packets are more likely to be discarded.  Bandwidth doesn't
increas, but packets per second does.  So does number of happy users.  This
is essentially the same argument as "the bandwidth is the same but the users
are happier" that someone else made.


    Assuming that the number of retransmissions aren't influenced, but
    merely that interactive applications observe smaller round-trip times,
    the total throughput should be the same...

Unfortunately, this is a bad assumption.  TCP is perhaps the best protocol
in this regard, since round trip timers and retransmission backoff have
been in the protocol since its inception.  Still, many TCP implementations
retransmit excessively in the presence of network congestion.  Almost every
other protocol is considerably worse, especially those that need bridged.

BillW
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