Description
When the Grandstream UCM's extension is configured with 'Call Forward Unconditional' with an external number (for eg. mobile number), the user experiences one-way or no audio at the mobile phone upon receiving an inbound call.
Try these:
a. Go to PBX Settings > SIP Settings > ToS > RTP Keep Alive : set to 1
This feature can be used to avoid abnormal call drop when the remote provider requires RTP traffic during proceeding.
**Setting it to '1' may cause the UCM sends out Comfort Noise packet in the RTP stream every seconds, which may cause the system performance.
b. Point the inbound call to an IVR with a Welcome prompt. On the IVR, change the Key Pressing event 1 to dial the external number. You may also test by configuring the extension's Unconditional Call Fwd to an IVR to ensure the 2-way audio is working in the UCM itself.
Troubleshooting
If the steps above do not work, kindly run Ethernet Packet Capture and submit a Helpdesk ticket with the Support team.
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