Subject: [rohc] draft-ietf-rohc-sigcomp-sip-08.txt and stateless compression

From: "Ofer Goren" <[email-masked]>
Date: Tue, 27 Nov 2007 17:40:16 +0200

Hi.
 
Section 9.4 in the draft suggests that stateless compression is not
recommended.
 
What if I have a session going between endpoint A supporting this draft
(sigcomp ver = 0x02) and an endpoint B with old sigcomp version (0x01).
B is sending a message using stateless compression. How can endpoint A
know that no states were created on B? In other words, what is the
backward compatibility procedures when dealing with stateless
compression?
 
Thank you,
 
Ofer Goren
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From: Adam Roach <[email-masked]>
Date: Fri, 30 Nov 2007 09:39:12 -0600

On 11/27/07 9:40 AM, Ofer Goren wrote:
> What if I have a session going between endpoint A supporting this 
> draft (sigcomp ver = 0x02) and an endpoint B with old sigcomp version 
> (0x01). B is sending a message using stateless compression. How can 
> endpoint A know that no states were created on B? In other words, what 
> is the backward compatibility procedures when dealing with stateless 
> compression?

SigComp version 1 supports the storage of states -- in other words, B 
_would_ store the states that A expected B to store (and vice-versa). 
The only difference between the versions is whether a decompression 
failure causes a NACK message to be sent.

It seems to me that you may be confusing "stateful compression" with the 
"shared compression" technique described in RFC 3321. "Shared 
compression" is also unaffected by the difference in UDVM versions.

/a