[rohc] draft-ietf-rohc-sigcomp-sip-07, Chapter 9

Hi,

I have a question/comment, concerning draft-ietf-rohc-sigcomp-sip-07, chapter 9.

According to this chapter, 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)

| |

| (2) 200 OK (Finally received) |

|<-------------------- |

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 (before the (2) 200 OK) endpoint A is not aware of the relation between B’s urn and the first INVITE compartment (A1). 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.