Subject: [rohc] Examples for Uni-Directional Compression

From: [email-masked]
Date: Thu, 15 Apr 2004 20:06:08 +0530

Hi all,
     RFC 3320 mentions that unidirectional compression is possible using
SIGCOMP.
According to my understanding

      A
B
      |        SiGComp Compressed Message       |
      |---------------------->----------------------------------- |
      |                             |
      |                             |
      |  Un Compressed Message (normal)   |
      |-----------------------<---------------------------------- |
      |                             |
      |                             |

That means that Endpoint B is also SIGCOMP aware .
My basic doubts is in which pratical scenario Endpoint B will choose to
send
normal message in place of the compressed messages.This is will drastically
effect the compression ratio.

Thanks & Regards
Saurabh

Saurabh Gupta - HSS Bangalore Ext 7067

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From: Carsten Bormann <[email-masked]>
Date: Thu, 15 Apr 2004 17:40:07 +0200

>      RFC 3320 mentions that unidirectional compression is possible 

I think you are referring to the last paragraph of section 3:

    When compressing a bidirectional application protocol the choice to
    use SigComp can be made independently in both directions, and
    compression in one direction does not necessarily imply compression
    in the reverse direction.  Moreover, even when two communicating
    endpoints send SigComp messages in both directions, there is no need
    to use the same compression algorithm in each direction.

> effect the compression ratio.

This paragraph is more about describing how SigComp works than about 
making the right choices.
It is very important that, in a bidirectional application, both SigComp 
directions are independent -- this allows the compressor to choose a 
compression algorithm without regard to what the other compressor can 
do.
The fact that you can use SigComp in a unidirectional way may be useful 
if you cannot establish SigComp capability in the reverse direction.
There may be other reasons (e.g., highly asymmetric data rates), but 
this is not of concern to RFC3320 -- it just provides the capability, 
and the implementation gets to decide whether to use it.

Gruesse, Carsten