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

[Gonzalo Camarillo <Gonzalo.Camarillo at ericsson.com>]

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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>
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