Manipulating VIA header in Sailfin

Question

This might be a basic problem I'm facing during integration of application over sailfin with a PSTN gateway. The initial INVITE is received from the gateway and processed internally then the 100 trying and 200 OK response is sent back to the gateway. But the gateway never responds back with ACK.

Initial investigation shows that the INVITE has been received from remote port xxxxx (any random UDP port) while inside INVITE Header, the via header contains port as 5060 and the contact header also contains 5060. As the via header has port information 5060, Sailfin always sends responses back to the port 5060 instead of port xxxxx on which the request has been received.

Is there any way in Sailfin to ignore the via header information and send back the response to the port on which it has received the request? Or do I need to manipulate the via header?

Answer 1

I would say that Sailfin is acting correctly. Section 18.2.2 of the SIP specification defines the behavior. The PSTN gateway has declared that responses should be sent to port 5060, and if it cannot receive traffic on that port, then it is a problem of the PSTN gateway.

And no, since Via is a system header, you cannot manipulate it.