[OpenSIPS-Users] Transfer issue with Cisco unified call manager

[Chen-Che Huang]

Dear all,

For collaboration purpose and some reasons, we have set up a kind-of-weird
architecture with Cisco unified call manager (abbreviated CUCM) as follows. 

client A
client B <---->OpenSIPS SIP proxy<---->CUCM
client C                   |
                         RTP proxy
                               

The OpenSIPS SIP proxy here acts as clients to CUCM. For each client, the
OpenSIPS SIP proxy creates a unique socket to CUCM. All the requests and
responses between clients and CUCM pass through the OpenSIPS SIP proxy. All
the RTP packets between clients are relayed by RTP proxy.

Although this architecture is kind-of-weird, it works for client
registration and call setup. However, in this architecture, we cannot
support a particular call transfer case.
Client A calls client B (OK)
Client A transfers the call to client C (OK)
Client A transfers the call to make client B talk to client C (Failed in
terms of media relay).

The SIP signalling flow is basically okay. The problem is that we cannot let
client B and client C's RTP packets relayed by the RTP Proxy because the SIP
messages in this case are two separate dialogs (the CUCM acts in B2BUA
mode). I have do a preliminary study to address issue by using the B2BUA
module of the OpenSIPS but the module seems not to have the ability to
modify SDP.

Has anyone encountered similar issues or had any suggestion on this issue?
Many thanks for any comments.

Yours sincerely,
Chen-Che




 where client A transfers the call to make client B and client C with each
other. Because CUCM acts like in B2BUA mode, 



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