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

From: "Dikla Dror" <[email-masked]>
Date: Mon, 6 Aug 2007 15:47:20 +0300

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.  

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