RE: iSCSI: 12-97 Bit Rule

[pat_thaler@agilent.com]

All,

 

I am also done with this thread.

 

Regards,

Pat

-----Original Message-----
From: Julian Satran [mailto:Julian_Satran@il.ibm.com]
Sent: Friday, June 14, 2002 6:02 AM
To: pat_thaler@agilent.com
Cc: ips@ece.cmu.edu; luben@splentec.com; owner-ips@ece.cmu.edu
Subject: RE: iSCSI: 12-97 Bit Rule
Importance: High

Excellent - 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

pat_thaler@agilent.com Sent by: owner-ips@ece.cmu.edu 06/14/2002 02:38 AM Please respond to pat_thaler

To:        luben@splentec.com         cc:        ips@ece.cmu.edu         Subject:        RE: iSCSI: 12-97 Bit Rule

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