Subject: [rddp] Number of CRCs

From: [email-masked]
Date: Fri, 11 Apr 2003 13:31:08 -0400

The last paragraph of Paul Culley's recent post touches
on an old issue that we need to return to:

> Also, I firmly believe that we cannot completely drop CRCs, that
> essentially all customers will be quite nervous about allowing memory
> access by DDP headers that have not been checked by something better
> than a checksum.  So there will be that overhead anyway.  I think that
> checking the remaining user data will be important enough to the
> majority of customers that putting the option in for the minority that
> don't care that much is just not worth it.

This is our old friend the "one vs. two CRCs" issue.  My recollection
of prior discussion on it is that this issue was not settled because
it depended on the open "TCP alignment" issue that has now been settled
(as of the San Francisco meeting, and I believe that rough consensus
is holding).

I read Paul's email as favoring a single mandatory CRC covering
both header and data, combined with an insistence that if separate
header and data CRCs are decided upon, the header CRC needs to be
mandatory in order to increase the assurance of proper placement.

I'd invite further discussion, but this group generally doesn't
need that sort of invitation ;-).  In any case, this issue does
need to be discussed and resolved, and some of Caitlin's recent
post is also on this topic.

Thanks,
--David

----------------------------------------------------
David L. Black, Senior Technologist
EMC Corporation, 176 South St., Hopkinton, MA  01748
+1 (508) 293-7953             FAX: +1 (508) 293-7786
[email-masked]        Mobile: +1 (978) 394-7754
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