RE: I-D ACTION:draft-cavanna-iscsi-crc-vs-cksum-00.txt

["Douglas Otis" <dotis@sanlight.net>]

Matt,

Interesting article, but a comment as usual.  There is very little
difference between Fletcher-32 and Adler-32 with respect to performance.
Fletcher Checksum is divided into two (16 bit) pieces, a straight 1's
complement sum and a higher order sum of the running sums.  The modulo in
Adler-32 is simply including a subtraction with a conditional branch.  As
Dafna pointed out, this test is normally done in a predictive manner by
means of linear coding lessening this difference between Fletcher and Adler
even further.  Data access in a table lookup required for CRC represents an
impediment whereas instruction cycles are easy hidden, so either Adler-32 or
Fletcher-32 will likely see a much larger throughput for software
implementations.  As Adler-32 is already advocated for SCTP and does not
represent anything substantially different with respect to performance to
that of Fletcher-32, I would be interested to understand the differences in
real-world situations.  Perhaps there is already a history of this
discussion within the sigtran archives.

Doug


> FYI - We put this out quickly to beat the deadline - a better version will
> be submitted before the final cut-off...
>
> -Matt Wakeley
> Agilent Technologies
>
> -----Original Message-----
> From: nsyracus@cnri.reston.va.us [mailto:nsyracus@cnri.reston.va.us]On
> Behalf Of Internet-Drafts@ietf.org
> Sent: Thursday, March 01, 2001 4:21 AM
> To: IETF-Announce:
> Subject: I-D ACTION:draft-cavanna-iscsi-crc-vs-cksum-00.txt
>
>
> A New Internet-Draft is available from the on-line Internet-Drafts
> directories.
>
>
> 	Title		: iSCSI Digests û CRC or Checksum?
> 	Author(s)	: V. Cavanna, M. Wakeley
> 	Filename	: draft-cavanna-iscsi-crc-vs-cksum-00.txt
> 	Pages		: 8
> 	Date		: 28-Feb-01
>
> The iSCSI working group is currently considering the method of
> protecting iSCSI messages from errors. This I-D presents a proposal
> to use the Fletcher-32 checksum algorithm.
>
> A URL for this Internet-Draft is:
> http://www.ietf.org/internet-drafts/draft-cavanna-iscsi-crc-vs-cks
um-00.txt

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