Path: utzoo!attcan!uunet!husc6!rutgers!att!ulysses!smb
From: smb@ulysses.homer.nj.att.com (Steven M. Bellovin)
Newsgroups: comp.dcom.lans
Subject: Re: Token Ring (was: Re: Info on LANs)
Message-ID: <11060@ulysses.homer.nj.att.com>
Date: 4 Jan 89 02:21:57 GMT
References: <12786@cup.portal.com> <920001@hposdl.HP.COM> <10777@s.ms.uky.edu> <327@belltec.UUCP>
Organization: AT&T Bell Laboratories, Murray Hill
Lines: 23

In article <327@belltec.UUCP>, jim@belltec.UUCP (Mr. Jim's Own Logon) writes:
>     While I haven't seen anything that Mr. Jacobson has presented, he is
> clearly wrong or you are misinterpreting his results.

Van's statements were pretty unambiguous, as were his measurements.  Slower
Sun CPUs could transmit faster using Sun's LANCE-based Ethernet interface
than their faster ones could with an Intel chip.

> Both the LANCE and
> the 82586 will request data from the host at speeds sufficient to sustain
> the 10 Mbps rate of the Ethernet transmission.  Underflows do not happen 
> unless there is a system design problem.

I'm afraid you misunderstand the claim; no one is saying that the 82586
gets underflow errors.  Rather, the claim is that total protocol throughput
is far lower with the Intel chip.  Jacobson listed his guess as to what
was going on, based on his knowledge of the protocol behavior and watching
the Intel chip with a bus analyzer.  Since he asked that he not be quoted
out of context, I'm not going to be too specific, but the trouble seemed
to occur when several packets were awaiting transmission.  I'm going to
ask him if I can repost his entire article to this newsgroup.

		--Steve Bellovin