Re: [rohc] sigcomp - meaning of the F bit in the input_bit_order register

[r.parthasarathi at flextronicssoftware.com]

Hi,

Please read in-line

Cristian CONSTANTIN <constantin at fokus.fraunhofer.de>
Sent by: rohc-bounces at ietf.org

04/13/2005 04:18 PM

To	rohc at ietf.org
cc
Subject	[rohc] sigcomp - meaning of the F bit in the input_bit_order        register

hi!

please help me to grasp the meaning of the F/H bits :-) 
in the SigComp rfc, at 8.2.  Requesting Additional Compressed Data
there
is this statement:

  "When an INPUT instruction requests n bits of compressed data,
it
   interprets the received bits as an integer between 0 and 2^n -
1.
   The F-bit and the H-bit specify whether the bits in these integers
   are considered to arrive in MSB to LSB order (bit set to 0) or
in LSB
   to MSB order (bit set to 1)."

how should this be interpreted?

1. same as for the P bit; that is the bytes themselves are always in 
network byte order but the bits in the bytes are in LSB to MSB order when
F=1 and the other way around for F=0.

<Partha> Yes, F-Bit is same as P-Bit
for the INPUT-BITS instruction </Partha>

2. the bits in the _(short) integer_ are:
   
a. LSB to MSB for F=1. that would mean that the component bytes are
   also swapped which would more or less contradict another statement
in
   8.2:
   "Note that the input_bit_order register cannot change the
order in
   which the bytes themselves are passed to the INPUT instructions
   (bytes are always passed in the same order as they occur in the
   SigComp message)."
 
<Partha>  The input_bit_order
register talks only about the order of flow of bits within a byte.
          It has
nothing to do with the order of flow of bytes </Partha>
   
b. MSB to LSB for F=0. 

now, if 1 is the right interpretation, then wouldn't P=1 && F=1
cancel 
each other's effect?

<Partha>  Yes, your understanding
of the above point is correct. </Partha>

thank you for your attention.
bye now!
cristian
-- 
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(_'_        | who IMHO do not understand UNIX.
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