[Freeswitch-users] Late SDP causing switch to sendonly mode - one way calls (3PCC?)

Callum Guy callum.guy at x-on.co.uk
Fri May 24 12:54:09 UTC 2019

Hi All,

In short I have an established bridged call out to a 3rd party SIP IVR -
this IVR appears to be performing 3pcc meaning I am receiving RE-INVITEs
w/o SDP as the call plays prompts, goes to queue and when it is answered.
For each INVITE FreeSWITCH responds with 200 with SDP and we get an ACK
back with SDP. During the queue phase the ACK SDP contains a=sendonly - all
previous SDP have implied sendrecv on both sides. All is OK at this stage.
When the call is finally answered we get an INVITE w/o SDP and FreeSWITCH
responds with SDP including a=sendonly, to which the remote replies
a=sendrecv. Hence we get one way audio at the time when the conversation
should be starting.

Can anyone help explain why FreeSWITCH would be switching to sendonly mode?
I have enable_3pcc=true configured but otherwise this is a fairly
standard/vanilla configuration. The behaviour I would expect is for
FreeSWITCH to continue to omit the attribute and imply sendrecv.

Are there specific variables which might allow me to manage the SDP

Please find a trace log attached.

FreeSWITCH Version 1.8.5-6-31281a0bf1~64bit (-6-31281a0bf1 64bit)
Linux my.network 4.9.0-8-amd64 #1 SMP Debian 4.9.144-3.1 (2019-02-19)
x86_64 GNU/Linux

Let me know if I can offer any more details regarding the implementation,



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