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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] RE: iSCSI: 12-97 Bit RuleExcellent - we are now spending time in the Never-Endian space :-) (coined by a good friend) - I am deleting the whole thread on my mailer. If you think I should pay attention to something please change the subject line. I know ( an changed already) the remainder word. Thanks Julo
Luben, If I ruled the world, I would number the least significant bit 0. I agree that that is a more logical numbering. My second choice would be for the whole world to use the same numbering even if it was different from that. However, neither you nor I rule the world and IETF has chosen to number the most significant bit 0 and the choices made by other organizations vary all over the map and we get to flop and flip bits to match them to the environment. A convention that is used throughout the document (like the significance of bits within a field) belongs at the front. That convention also gets reinforced when one looks at other parts of the document like chapter 9. That is why it is satisfactory for 1.3.1 through 1.3.3 to be at the front. A detail that only applies one place like the different ordering of the bits in the CRC calculation should be in the place where it is used. That is why it wasn't good to have 11.1 reference 1.3.4 for how to order the bits in the CRC calculation. This is just good editorial practice for building a usable document. On the particular text: 8) The message sent is P and appended at the end are the bit coefficients of CRC(x), with x^31 bit coefficient first, then x^30, etc. the problem is that the x^31 bit doesn't go first when it is in the frame. Also, bits can go through their entire existence without being sent in serial order so nothing is first. Say which bit of the CRC goes into which bit of the digest field and you are done. Sincerely, Pat -----Original Message----- From: Luben Tuikov [mailto:luben@splentec.com] Sent: Thursday, June 13, 2002 4:13 PM To: pat_thaler@agilent.com Cc: Julian_Satran@il.ibm.com; ips@ece.cmu.edu Subject: Re: iSCSI: 12-97 Bit Rule pat_thaler@agilent.com wrote: > > TCP/IP Illustrated numbers bits with bit 0 as the > most significant. My books on Sonet number bits > in a byte from 1 to 8. I guess you could argue > these are not books on computer architecture, but > the point is that not everyone numbers bits the > same. Uuuh, here we go again... Yes, I can argue that those are NOT books on computer architecure. Let me get home I'll send you the titles/authors/ISBN of a few books on Computer Architecture which use the NATURAL bit ordering: 2^(x+1) > 2^x, x >= 0, so it only _makes_sense_ to say that bit x+1 is more significant than bit x. Take the number 791, is the 2rd digit more significant than the 1nd? Well: 791 = 7*10^2 + 9*10^1 + 1*10^0. > If you will read 1.3.1 through 1.3.3, they do > explicitly state the significance of bits in > iSCSI words, half-words and bytes. Yep, and you were complaining that it was 200 pages away from 11.1 where the CRC digest was --- or was that in a private email? Trying to score points? > Julian's new description is accurate and clear. Are you sure? Are you really sure? > Item 8 in your description is unclear and confusing > because the bits do not "follow" each other in the > order you state (and any viewing of bits in a message > as a serial stream is entirely hypothetical). Here is 8: 8) The message sent is P and appended at the end are the bit coefficients of CRC(x), with x^31 bit coefficient first, then x^30, etc. That is after you send P, send CRC(x) as indicated. What doesn't follow what? Of course it is hypothetical... Pat, let me ask you this: Is Mathematics hypothetical? -- Luben
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