Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.3 4.3bsd-beta 6/6/85; site ucbvax.BERKELEY.EDU
Path: utzoo!decvax!decwrl!ucbvax!tcp-ip
From: DCP@SCRC-QUABBIN.ARPA (David C. Plummer)
Newsgroups: mod.protocols.tcp-ip
Subject: Zero window probes
Message-ID: <851209131105.0.DCP@NEPONSET.SCRC.Symbolics.COM>
Date: Mon, 9-Dec-85 13:11:00 EST
Article-I.D.: NEPONSET.851209131105.0.DCP
Posted: Mon Dec  9 13:11:00 1985
Date-Received: Fri, 13-Dec-85 01:41:54 EST
References: <851108205728.000456@CISL-SERVICE-MU
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The ARPA Internet
Lines: 9
Approved: tcp-ip@sri-nic.arpa

(Sorry for the slow comment, I've been off the net for a month.)  I
agree with the philosophical basis as stated by CERF.  TCP allows the
sending of one byte beyond the window for the purposes of probing.
Since the byte is outside the window, the receiver MUST send an ACK.
This shows that both TCP's are alive, and it is up to the higher level
protocols to decide that the connection is worthless, even though the
connection still validly exists.  Therefore, I believe TOPS-20 and Unix
(whichever version somebody mentioned) are in error by having TCP do the
timeout.