Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!A.ISI.EDU!CERF
From: CERF@A.ISI.EDU
Newsgroups: comp.protocols.tcp-ip
Subject: Re: SO_KEEPALIVE considered harmful?
Message-ID: <[A.ISI.EDU]28-May-89.14:23:38.CERF>
Date: 28 May 89 18:23:00 GMT
References: <2681@elxsi.UUCP>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
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When TCP was first designed, and for all subsequent versions, it was
thought inappropriate to impose any kind of semantics on the logical
connections extablished by TCP. In particular, no sense of absolute
timeout for the severing of a connection was desired. We thought that
such notions of "impatience" or "time to give up" ought to be the
choice of the upper level protocol using TCP as the basis merely for
reliable delivery.

A part of this view stemmed from the fact that the networks over which
TCP had to function, for the DoD applications we had in mind, were
potentially very unpredictable as to loss and delay. Mobile packet
radio systems had to function under jamming and radio shadow effects,
for instance. TCP never unilaterally severed connections but only
reported failure to achieve positive acknowledgement after a time
which could be controlled by the application or upper-level protocol.
It was up to the application to decide whether to sever the connection
and, even then, the choice to do so gracefully or abruptly was also
left to the application.

The use of a feature (X-level NOP) to test the liveness of a TCP
connection is consonant with the model against which the TCP was
designed. 

Vint Cerf