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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.
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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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