Listen in (SIP)

Turbine stations has a "Listen in" feature in SIP mode.

If the station receives “X-Zenitel-Audio: listener” in a SIP INVITE message it means that the call will not be visible in the station and that audio is only sent from the station, not played out on the speaker.
The audio sent from the station is microphone audio without echo cancellation, therefore any speaker audio caught by the microphone is included.

The station supports one "listen in call" at a time and any new "listen in calls" will be rejected.. The station can operate normally while someone is listening, for example making a new outgoing/incoming call is possible.

Asterisk configuration example. (extensions.conf):

exten => 905,1,SIPAddHeader(X-Zenitel-Audio: listener)
exten => 905,2,Dial(SIP/211)

Example Listen in SIP INVITE:

Listen-In currently supports only G.711 and G.722. G.729 is not supported