Subject: [rddp] re: draft-elzur - Partial CRC

From: Caitlin Bestler <[email-masked]>
Date: Thu, 20 Feb 2003 10:53:35 -0600

draft-elzue in section 4 makes the assumption that CRC32c
must be calculatd serially. Section 4.a.ii.1 states:

> When a complete FPDU is available, a similar procedure to
> the in-order algorithm above is used. There is additional
> complexity, though, because when the missing segment
> arrives, this TCP segment must be run through the CRC
> engine after the CRC is calculated for the missing
> segment.

While this is a vaid implementation, it is not required.
Each bit in the CRC32c for the FPDU is an XOR of a set
of the covered bits within the FPDU. XOR is a commutative
operation, hence the FPDU's CRC32c does not need to be
calculated in order.

However, the buffering benefits cited for aligned FPDUs
remain valid. Additionally, a serial CRC32c calculation is
simpler to implemenet than a random one.

Caitlin Bestler
http://asomi.com/CaitlinBestler/
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