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Re: [RPRWG] CRC check in each node?



Also the source address and destination address must be available befoe a forward decission can be made. I think that we should not be that picky about what cut-through is. Everyone need to store some parts of the packet (at least the header) to process the packet. The question really comes to wether the delay depends on the packet size or not and wether it does so regardless of of contention or not. Even cut through  may store a complete packet due to contention.

If a CRC is used to validate the header, it should only cover the header. There may be a seperate CRC to cover the payload. In my view a payload error should not lead to having the packet discardet, whereas a header error should defenitely discard the packet. We want to monitor payload CRCs as a part of performance monitoring and performance degradation location. The destination node should be able to monitor the same payload CRC error in order to collect _flow_ performance statistics.

Robin

Martin Brewer wrote:

Be aware also that Store and Forward has the opportunity to strip the frame whereas a cut through archecture does not.  Since the TTL is a way of determining the validity of the frame, if used in a cut through architecture, the frame should start transmission out until the TTL field has been read.Martin
-----Original Message-----
From: Ajay Sahai [mailto:Ajay.Sahai@xxxxxxxxxxxxxxx]
Sent: Thursday, June 21, 2001 1:36 PM
To: Angela T. Faber
Cc: ieee 802.17 list
Subject: Re: [RPRWG] CRC check in each node?
 
Hi All

Obviously, if TTL is part of the header and protected by CRC then CRC check/update has to be done at every node.  There can be a CRC for the header alone. That might mitigate Angela's concerns.

Regards

Ajay Sahai

"Angela T. Faber" wrote:

Folks One question regarding CRC check: are we assuming CRC will be checked at every node (as the frame is forwarded) or it will be checked only at the destination/source node?My initial thought on this is that, if we don't do it at every node, than how do we remove the frame from ring if the source and destination addresses are corrupted? On the other hand I assume that if every node checks it, more time is spent with forwarding it.... Any insights are welcomed.Thanks! Angela

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Robin Olsson
Vitesse Semiconductors, Denmark
Phone: +45 4596 9659
fax: +45 4596 9699
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