Calls transfered using SIP REFER are terminated by Plivo

[Alejandro Recarey]

Hello, I'm having an issue while transferring calls.

When one IP phone tries to transfer (both attended and unattended) to another, the original call is dropped. These are regular transfers using SIP REFER, we are not using the plivo REST endpoint.

Example

(A) ---[calls]---> (B) ---[transfers]---> (C)

In this case, caller A is hungup, and thus the call made by B is also terminated.

Freeswitch logs say that plivo terminated A's call. Looking at the plivo logs, we can see "No more elements, hangup now!". This led us to the source code, outboundsocket.py where I think plivo checks a channel variable that is set on transfers ('plivo_transfer_progress') and because it cannot find it, terminates the call because there are no more elements to execute after the dial command.

We are having the same issue when a call is placed on hold, and then is later resumed. "No more elements, hangup now!" and the call is terminated.

Any help or pointers to how to fix would be appreciated. If we need to change the source, some insight in how to do it would also be fantastic. We will of course contribute back any feature improvement.

Thanks!

Alex