RE: [rohc] Query about draft-ietf-rohc-sigcomp-sip-07

["Asher Shiratzky" <Ashers at radvision.com>]

Simplicity is very important, but what will happened in cases where
there is INVITE without registration like emergency calls?
 

-----Original Message-----
From: Gonzalo Camarillo [mailto:Gonzalo.Camarillo at ericsson.com] 
Sent: Wednesday, August 22, 2007 2:22 PM
To: Dikla Dror
Cc: rohc at ietf.org
Subject: Re: [rohc] Query about draft-ietf-rohc-sigcomp-sip-07

Hi,

previous versions of the draft addressed this type of on-the-fly
compartment creation. However, the agreement was to go for a simpler
solution that requires registrations. Therefore, the compartments would
have been created at registration time, not when A and B start
exchanging INVITEs.

Cheers,

Gonzalo

Dikla Dror wrote:
> Hi,
> 
> I've sent a question concerning chapter 9 in
> draft-ietf-rohc-sigcomp-sip-07 few weeks ago, but got no answer yet.
> 
> I would appreciate any feedback to the following issue (I've turned my

> question into a simpler scenario):
> 
>  
> 
> According to chapter 9, I might encounter imbalanced compartments at 2

> different communicating endpoints in the following scenario:
> 
>  
> 
> This scenario includes 2 endpoints (A, B), communicating over TCP.
> 
>  
> 
>                                                 
> A                                                          B
> 
>                                                 |              (1)

> INVITE                          |
> 
>           Create Compartment (A1)
> |--------------------------------------------------------->| Create
> Compartment (B1)
> 
>                                                 
> |                                                           |
> 
>                                                 |               (2)
200 
> OK                             |
> 
>                                                 
> |<---------------------------------------------------------| Use
> Compartment (B1)
> 
>                                                 
> |                                                           |
> 
>                                                 |              (3)

> INVITE                          |
> 
>           Create Compartment (A2)
> |<---------------------------------------------------------| Use
> Compartment (B1)
> 
>                                                 
> |                                                           |
> 
>                                                 
> |                                                           |
> 
>                                                             And so
on...
> 
>            
> 
> As you can see endpoint A is sending an INVITE (1) toward B, 
> specifying its local urn (A's urn). However A doesn't know yet B's 
> urn, thus it creates a local compartment (A1), related to the INVITE 
> outgoing connection.
> 
> Now B:
> 
> -          Responds the first INVITE with 200 OK (2), related to 
> compartment (B1)
> 
> -          Sends an outgoing INVITE (3) to A, related to compartment 
> (B1). This (3) INVITE includes B's urn.
> 
>  
> 
> However, upon receiving (3) INVITE, endpoint A is not aware of the 
> relation between B's urn and the first INVITE (1). Thus, A will 
> maintain
> 2 different compartments - (A1) and (A2) for these 2 sessions while B 
> will maintain only one compartment (B1). This will lead to 
> inconsistency within the SigComp mechanism.
> 
>  
> 
>  How can I solve this asymmetry according to the draft?
> 
>  
> 
> Thanks,
> 
> Dikla.
> 
> 
> ----------------------------------------------------------------------
> --
> 
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