[Sip] Info regarding Preloaded Route Set

[subbac@hss.hns.com]

Hi,

I have a doubt in using Pre-Loaded Route Set at UA end.

Let us say UA1 has a Pre-Loaded Route Set of  PR1, PR2, PR3.  (all routers
are strict routers)

UA1 initiates a call to UA2.

The INVITE looks like
          INVITE: PR1
          Route:    PR2, PR3, UA2

Now PR1 doesn't Record-Route.
          UA2 sends the RPR (182) response to UA1

          with Record-Route as   PR3, PR2


On receiving the Record-Route set,  UA1 updates its local Route-Set.
Now its Route Set contains  PR2, PR3 only.  Hence successive requests
directly reaches PR2.

Now if UA1 want to terminate the call by sending CANCEL,

     As per the latest Route Set present at UA1,  CANCEL should go to PR2
directly.
     It looks like
          CANCEL:  PR2
          Route:    PR3, UA2contact

This scenario leads to two questions:

     1   Is it valid to update the local Route Set at UA1 on receiving the
Record-Route header in RPR (not final response)
          and use it for subsequent Requests related to Dialog.

     2.  If YES: where should CANCEL go.   As per RFC 3261, CANCEL should
look like its original INVITE.
          But in this case, both Request URI and Route header got modified.
Is it valid??


         If No:  Before receiving the final response, if UA1 wants send
UPDATE to modify session parameters what Route-Set
          need to be used (i.e. Initial Route-Set or Route-Set received in
RPR).


provide your valuable inputs.


regards
CSR








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