[pjsip] 3PCC transfer implementation

Anshuman S. Rawat arawat at 3clogic.com
Tue Nov 13 08:43:24 EST 2007

Hi All,

We want to add 3PCC call transfer support in PJSIP as a part of our 
requirement. We wanted to get pointers as to where would be the best place 
to do this. We thought of 2 ways to do this. In bout cases, we (obviously) 
act as the controller (a B2BUA).

- One way would be to do so from our application wherein we disable sending 
'ACK' from the stack and pass that job to the application. Our application 
receives all the requests and responses and sends out requests and responses 
(after necessary SDP modifications). This looks simpler to implement but 
doesn't look very extendible. As in, for our requirement, the transferee may 
want to transfer the call and send a REFER for that purpose. This REFER 
should reach our B2BUA who then sends the new INVITE instead of stack doing 
it. This will require more change to stack (besides the change for sending 

- Another way is to add the 3PCC "application" as a module with a higher 
priority than pjsip_module so that incoming requests/responses first are 
sent to 3PCC module first. From what I understand, if the request/response 
is not handled by this module, it will then be passed to the pjsip_module. 
(Is my understanding correct?)

Suggestions are very welcome. Hopefully I was clear enough.


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