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From: CERF@A.ISI.EDU
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Error Control and ATM (was: TCP Fletcher Checksum Option)
Message-ID: <[A.ISI.EDU]12-Dec-89.08:01:34.CERF>
Date: 12 Dec 89 13:01:00 GMT
References: <6528@cbnewsh.ATT.COM>
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
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Tony,

Let's see. One might take the view that there is a
tradeoff between sequence numbering of cells and strong
checksumming to detect misordering (followed by
frame retransmission).  When cell sizes get very small
(e.g. your one byte T1 example) then sequence numbers
are silly and checksums are necessary. The current 48 byte cell
size is pretty small - perhaps small enough that sequence
numbering is too expensive. This motivates the interest in
checksumming of a stronger variety than TCP currently supports.

Vint

What I meant about link checksumming not catching the problem
is based on the idea that if cell reassembly happens in the
ATM and THEN a link level checksum is computed to "secure"
the transmission of the frame to the host, the checksum would
not detect the reassembly of misordered cells. If the checksum
is computer end to end, then it covers more of the intervening
transmission and switching plant and thus allows potential
detection of misordering (if the checksum is strong enough).