Re: CRC vs CHKSUM presentation slides

["Jim Williams" <jim.williams@emulex.com>]

From: "Mark Bakke" <mbakke@cisco.com>
To: "CAVANNA,VICENTE V (A-Roseville,ex1)" <vince_cavanna@agilent.com>
Cc: <ips@ece.cmu.edu>; <ipsan@rtl.rose.agilent.com>
Sent: Thursday, March 22, 2001 4:00 PM
Subject: Re: CRC vs CHKSUM presentation slides


> Vicente-
> 
> I just took another look through your slides after seeing the
> presentation on Monday.  They were very well-done.  I have
> one question, though.  If the CCITT-CRC32 is considered "good
> enough", then would the Ethernet CRC32 also be good enough?  The
> reason I ask is that every hardware vendor involved in building
> iSCSI stuff already has implementations of the Ethernet CRC, 
> which is used for both Ethernet and Fibre Channel.
> 
> The Ethernet poly has more terms than CCITT, and perhaps is
> not as good as CRC-32C (any thoughts?), but everyone has hardware
> and software for this, with proven interoperability (bit and
> byte order, etc).  Performance-wise, it will be there for
> 10Gb Ethernet, so it should be fast enough.
> 
> So if the Ethernet poly is deemed good enough (even if it's not
> the best), and fast enough (even if it's not the fastest), why
> not use it?  I think we would stand a much better chance of
> achieving interoperability in a short time.
> 
> Please let me know what you think of this; I realize that a few
> of my questions were speculative.

Since the iSCSI messages will often be encapsulated in ethernet
packets, there is some value to using a different CRC.  Link
errors are double protected with two different CRCs.  If
ethernet and iSCSI use the same polynomial, there is little
additional coverage against link errors.  This point may not
be decisive, but all other things being equal or almost
equal, it is worth considering.