RE: iSCSI: CRC description

["Julian Satran" <Julian_Satran@il.ibm.com>]

The thing about this text that is going on and on is very frustrating.
First Vince insisted on emphasis.
Now you find it confusing.

I gave it as a quiz to a undergraduate class and no one made a mistake.

How much effort do you think I will spend on it? And who are the people that are confused?

Julo

pat_thaler@agilent.com 06/12/2002 09:24 PM Please respond to pat_thaler

To:        Julian Satran/Haifa/IBM@IBMIL         cc:        ips@ece.cmu.edu, owner-ips@ece.cmu.edu         Subject:        RE: iSCSI: CRC description

Julian,
 
The changes to the text on CRC are a step down rather than up in clarity.
 
In particular:

 " - In the bit stream mentioned above the CRC bits are appended   to the message bits with x^31 first followed by x^30 etc. In   the examples provided in Appendix B.4 - CRC Examples, the   value is outlined as a word sent or received and therefore   the CRC bits are mapped into the CRC word according to Section   1.3.4 Bit Rule - i.e., the x^31 coefficient in bit 7 of   the first byte of the digest continuing to through the byte the x^24 coefficient in bit 0 of the first ! byte, continuing with the x^23 coefficient in bit 7 of second byte through x^0 in bit 7 of the last byte.  

This statement will be very confusing to readers. The there is no abstract bit stream in which the CRC bits follow each other. Trying to specify the CRC with respect a bit stream will just lead to confusion. The old text with the changes I had suggested would provide more clarity.

Also, there is no MUST on the CRC computation method. Using a compatible computation method is necessary to produce interoperability so there should be a MUST. I suggest the following  which should allow for compatible variations in implementation:

Replace, "The CRC should be calculated as follows:" with "The CRC MUST be calculated using a method that produces the same result as the following process:"

Regards,
Pat