Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!att!pacbell.com!ucsd!ucbvax!md.interlink.com!fab
From: fab@md.interlink.com (Fred Bohle)
Newsgroups: comp.protocols.tcp-ip
Subject: Re:  TCP window size restriction
Message-ID: <9101022244.AA02309@leo.md.interlink.com>
Date: 2 Jan 91 22:44:37 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
Lines: 25

Window size expansion has already been covered by RFC 1072.  An option
code of 3 gives a shift amount for the 16-bit window field.  Note that
other parts of RFC 1072 have not been generally agreed to, but *this*
part of it is.  It is a simple matter to generate this option in the
open logic and look for it from the other end.  Then simply shift the
window the specified amount to use expanded windows.  Note also that
both ends must specify the option in order for either side to use it.
One side may specify a shift amount of zero, in order to indicate
support, but no expanded window.

Some brain-dead TCP implementations may hiccup at an unrecognized
option code, but they are non-compliant if they do.  RFC 1122 says
in 4.2.2.5 "A TCP MUST ignore without error any TCP option it does
not implement..."

So please explore using RFC 1072 for your needs.  I put it into our
product, SNSTCP/access, and it works fine.

Fred
------------------------------------------------------------------------
Fred Bohle			EMAIL: fab@leo.md.interlink.com
Interlink Computer Sciences	AT&T : 301-317-6600 
9145 Guilford Road, Suite 175
Columbia, MD 21046
------------------------------------------------------------------------