Re: iSCSI: 12-97 Bit Rule

[Luben Tuikov <luben@splentec.com>]

"CAVANNA,VICENTE V (A-Roseville,ex1)" wrote:
> 
> I believe Bill is correct. The receiver, unlike the transmitter, should not complement the remainder if he expects to get 0x1c2d19ed.
> I am afraid I may be reponsible for this mistake during an email exchange I and others had with Julian recently. Julian and those others must have trusted me a little too much. Sorry Julian and others.

Vince, you had it right. The text was mentioning that it was the CRC that
was the magic constant, and since the CRC is complemented in the course of
computation, one more was needed to get ``back'' to the remainder.

Yes, Bill, your empirical conclusion is correct.

The magic constant _is_ the pure remainder in polynomial
form (0x1c2d19ed).

The CRC is the complemented (and byte mirrored) remainder.

That is: you have 2 algoritms, one to compute the pure
remainder, and another to complement it (and maybe byte-mirror)
and inject it at the end of the message to be sent.

The sender does both algorithms (compute and inject),
and the receiver does just the first (compute) and compares
the result with the magic value.

This has already been mentioned in a more formal (and
maybe confusing :-)) manner in an email from me at the
beginning of this thread (take a look at it, the one
with bit-sequences).

-- 
Luben