RE: [Tsvwg] [SCTP checksum problems]

["CAVANNA,VICENTE V (A-Roseville,ex1)" <vince_cavanna@agilent.com>]

Hi Jim,
I don't think iSCSI can be completely relieved of performing some data
integrity checking as long as there exists the possibility of "middle boxes"
opening up the transport protocol's packet and thus potentially invalidating
any reliability guarantees the transport protocol makes.
Vince

|-----Original Message-----
|From: WENDT,JIM (HP-Roseville,ex1) [mailto:jim_wendt@hp.com]
|Sent: Tuesday, April 17, 2001 11:44 AM
|To: 'julian_satran@il.ibm.com'
|Cc: ips@ece.cmu.edu; tsvwg@ietf.org; 'Craig Partridge'; Jonathan Wood;
|xieqb@cig.mot.com; Jonathan Stone; Randall Stewart; WENDT,JIM
|(HP-Roseville,ex1)
|Subject: Re: [Tsvwg] [SCTP checksum problems]
|
|
|Julian,
|The SCTP folks are right now discussing changing the SCTP 
|checksum to be a
|CRC-32 (or other). This is a very good thing and really what 
|needs to happen
|with SCTP for it to support iSCSI and other data-critical applications
|effectively (and also relieve iSCSI from having to implement 
|data integrity
|checking and transport-like functionality over SCTP).
|
|They are looking for inputs as to which CRC-32 or checksum to 
|use. The iSCSI
|WG's CRC investigation work and conclusion would be a valuable 
|input into
|their decision. The sooner that you can provide the iSCSI 
|recommended CRC
|and reasoning behind it to them, the better, even before the 
|forthcoming I-D
|is distributed.
|
|Jim Wendt
|Networked Storage Architecture
|Hewlett-Packard Company
|jim_wendt@hp.com 916-785-5198
|
|---------------------------------------------------------------
|-------------
|-
|
|> -----Original Message-----
|> From: julian_satran@il.ibm.com [mailto:julian_satran@il.ibm.com]
|> Sent: Sunday, April 15, 2001 7:58 AM
|> To: ips@ece.cmu.edu
|> Subject: CRCs
|> 
|> 
|> 
|> 
|> Dear colleagues,
|> 
|> We will probably not be able to finish the CRC/checksum 
|> document in time
|> for Nashua but we hope it will be out very soon after that.   
|> However I
|> would like to inform you that while in Orlando and 
|> Minneapolis we where
|> still talking about different CRCs we (Dafna Sheinwald, Pat 
|> Thaler, Matt
|> Wakeley, Vince Cavanna and myself) have agreed on a CRC and 
|> the forthcoming
|> ID will give all the reasons and why we recomend it.
|> 
|> Regards,
|> Julo
|> 
|
|---------------------------------------------------------------
|-------------
|-
|
|-----Original Message-----
|From: Randall Stewart [mailto:rrs@cisco.com]
|Sent: Tuesday, April 17, 2001 4:31 AM
|To: Jonathan Wood
|Cc: xieqb@cig.mot.com; tsvwg@ietf.org; Jim Wendt; Jonathan Stone; Craig
|Partridge
|Subject: Re: [Tsvwg] [SCTP checksum problems]
|
|
|Jonathan:
|
|I will make sure everyone at the bakeoff is aware of the upcoming
|"checksum" change... Now one of the big questions yet is
|what checksum should we use?
|
|I kinda lean towards crc-32 myself (but of course I have no technical
|basis for this and need to keep silent on which one to use anyway :->),
|but do we have other candidates besides fletcher-32 and possibly
|modified 
|Adler-32 (i.e. 16 bit adds instead of 8)??
|
|I will take the above 3 and do a bit of performance work this
|week and post some numbers... thats about all I can do i.e.  tell
|how much time the options I know of take... 
|
|If you have some other candidates let me know and I can possibly get
|some performance numbers on these as well...
|
|As far as which is the best... I encourage all of you check-sum
|experts out there to please join the thread :)
|
|Oh, I know Jonathan Stone's paper will NOT be ready until sometime
|in May.. so we may want to proceed slowly so that Craig Partridge and
|he can have some cycles to add to this dicussion :)
|
|R
|
|Jonathan Wood wrote:
|> 
|> As an SCTP implementor and someone who will want to get the 
|hardware folks
|to
|> help with checksumming, I wholeheartedly agree with Randy. 
|Remember that
|SCTP is
|> just a proposed standard, and is as such not all that far along the
|> standardization process. We should still be able to make 
|changes like this
|if
|> necessary.
|> 
|> Jon
|> 
|> >
|> >Q:
|> >
|> >The only problem with an additional "CRC chunk" is that
|> >it makes hardware assistance to error correction much
|> >more difficult. It is better (I think) to just realize
|> >we made a mistake. Get the opinions of the experts as to
|> >what checksum to use... i.e.:
|> >
|> >- CRC-32
|> >- Modified Adler-32 (16 bit word sums)
|> >- Fletcher-32
|> >- ???
|> >
|> >And then go with this as a replacement... Admit we were wrong
|> >and fix the problem..
|> >
|> >This way you have ONE and only ONE checksum algorithm making
|> >hardware designers life much easier...
|> >
|> >R
|> >
|> >Qiaobing Xie wrote:
|> >>
|> >> Another solution could be (I think I mentioned this to 
|Randy and a few
|> >> others at last IETF):
|> >>
|> >> - Define a CRC-32 (or other strong checksum) control 
|chunk and when the
|> >> sender wishes to use a stronger checksum protection, in 
|addition to the
|> >> Adler-32 in the common SCTP header it includes this 
|CRC-32 chuck in the
|> >> outbound packet. When the packet arrives, the receiver will do the
|> >> Adler-32 first, and then if the receiver supports the 
|CRC-32 and sees
|> >> the presence of the CRC-32 chunk in the packet it will 
|further verify
|> >> the CRC-32.
|> >>
|> >> We could also use a bit pattern in the chunk type of the 
|CRC-32 chunk
|so
|> >> that if the receiver doesn't understand the CRC-32 chunk 
|it would drop
|> >> it with a report back to the sender.
|> >>
|> >> -Qiaobing
|> >>
|> >> _______________________________________________
|> >> tsvwg mailing list
|> >> tsvwg@ietf.org
|> >> http://www1.ietf.org/mailman/listinfo/tsvwg
|> >
|> >--
|> >Randall R. Stewart
|> >Systems & Solutions Engineering
|> >Cisco Systems Inc.
|> >rrs@cisco.com 815-342-5222 or 815-477-2127
|> >
|> >_______________________________________________
|> >tsvwg mailing list
|> >tsvwg@ietf.org
|> >http://www1.ietf.org/mailman/listinfo/tsvwg
|
|-- 
|Randall R. Stewart
|Systems & Solutions Engineering
|Cisco Systems Inc.
|rrs@cisco.com 815-342-5222 or 815-477-2127
|
|> 
|