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From: tcp-ip@ucbvax.ARPA
Newsgroups: fa.tcp-ip
Subject: Re:  A Noop Strategy for TCP
Message-ID: <9339@ucbvax.ARPA>
Date: Thu, 25-Jul-85 22:48:45 EDT
Article-I.D.: ucbvax.9339
Posted: Thu Jul 25 22:48:45 1985
Date-Received: Sat, 27-Jul-85 03:01:09 EDT
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Organization: University of California at Berkeley
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From: Bob Walsh <walsh@BBN-LABS-B.ARPA>


TCP is designed to provide a reliable transport layer.  It is NOT designed
to ensure application <-> application reliability.  Robustness of application
communication is the responsibility of the application.  Mechanisms have
been tried to solve this problem.

For example, the Berkeley 4.2BSD TCP periodically
sends a byte just beyond the window in an attempt to force an ack when the
connection is otherwise idle.   But not every system is a 4.2BSD host, and
what happens when it communicates with a generous implementation that
recognizes the high per packet overhead (interrupt processing, header checking,
and network resources) and buffers the incoming packet?  A garbage byte
may make its way in to the stream.  And yet, the receiving TCP has made no
mistake.

Don't try to change the protocol, or you may run into problems.
Interoperability is one of the benefits of standards.  The RDP protocol
specifiers recognized this problem and addressed it through the use of
NULL messages to which all implementations must respond.  They also
recognized that the application layer must be responsible for end to end
reliability and forced the developer to keep this in mind through RDP's
abrupt closing method.

bob walsh