Versions: U1911 V2R3C50SPC300; eSpace 7910 IP Phone V2R3.
Networking: The U1911 connects to the PSTN through the SIP trunk.
Fault symptom: Intra-office calls are normal. However, after an outer-office user calls an intra-office user and the call is connected, the intra-office phone does not hear any voice, but the outer-office phone can hear voice.
1. Check that the outgoing trunk of the U1911 is normal.
2. Check that the network configuration of the phone is normal. The ping test of the PSTN device is normal.
3. Use the Wireshark to capture packets. Packet analysis finds that the media address of the PSTN device is changed to the address of the U1911.
4. Set software parameter 393 of the U1911 to 0. Perform the test again. The one-way audio problem is rectified. The service test is normal.