[22971] in North American Network Operators' Group
Re: Why the temptation for dial users to crank back rwin/mtu?
daemon@ATHENA.MIT.EDU (Forrest W. Christian)
Sat Feb 6 13:57:20 1999
Date: Sat, 6 Feb 1999 11:11:31 -0700 (MST)
From: "Forrest W. Christian" <forrestc@iMach.com>
To: mcmanus@appliedtheory.com
cc: nanog@merit.edu
In-Reply-To: <199902061802.NAA00623@justice.atc-bos.com>
On Sat, 6 Feb 1999 mcmanus@appliedtheory.com wrote:
> apparently there's some performance value in this (at least to the
> immediate user) because they keep doing it in droves. It's not obvious
> to me why the heck this would be. (warning: I am a protocol guy, but
> I'm not a dialup guy at all.. and even less of a windows guy)
This has been generally beat to death on nanog in the past. If you
weren't around back then, dig around in the archive. I remember one of
the subjects being "PC Bozoworld strikes again" or something like that.
The short recap is that for some unknown reason the Microsoft TCP/IP stack
is broken in some bizzare way that setting down the MTU on a good chunk of
the machines out there will result in a dramatic speed increase. Why
this occurs, I'm not sure anyone really knows. It would be really
interesting to see a study of what the MS stack is doing and why it's
faster.
> MTU - at least this makes a little bit of sense.. If they're doing
> HTTP/1.0 stuff with parallel connections then a smaller MTU is going
> to make that parallelization latency much more effective and perceived
> performance will go up some.. it doesn't impact full document
Just for my information, does the MTU setting affect <received> packets
in some way? My understanding was that a machine wouldn't send packets
over the MTU size, but could recieve anything up to whatever the TCP/IP
stack writer included in the stack. Guess I'll have to go dig out the
RFC's.
- Forrest W. Christian (forrestc@imach.com)
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