Call forking allows you to send one particular call to different Signaling Groups (up to 8 endpoints) at the same time.
Maybe you face an issue where you have no-audio when it comes to call forking. This could be the case if you are forking to any PBX and S4B/Lync as alternative target.
If so, it could be that S4B is cutting through the media and then returning a 404 because the number doesn’t exist in S4B, only in the other systems that this forking goes to.
When the call is answered on such other PBX there is no audio.
Solution in my case was easy:
Go into the SIP profile defined for the S4B/Lync trunk and set the 100rel parameter to Not Present.
This will stop S4B to send early media and fixes the issue with the no-audio for the second involved PBX.
