【Issue description】
After a SIP trunk call is connected for five minutes, one-way audio occurs, and the internal network user cannot hear the voice of the external network user. The fault is automatically rectified three minutes later.
【Analysis Procedure】
If one-way audio occurs during a SIP call, the possible causes are as follows:
1、 During the call, the SIP signaling negotiation is abnormal. As a result, the voice is connected.
2、 An exception occurs during the transmission of RTP packets. As a result, one-way audio occurs. If the problem occurs, obtain the Wireshark network package to locate the fault. You are advised to obtain the IP phone network package and IP PBX logs.
【Issue Cause】
One-way audio occurs because the transmission device between the internal switch and the SBC is abnormal.
【Handling Method】
1. You are advised to use the LMT to obtain IP PBX logs and obtain the network package of the calling IP phone.
2. According to the signaling obtained from the IP PBX, the IP PBX does not perform SIP signaling negotiation during abnormal voice services. As a result, the possibility of one-way audio caused by SIP signaling negotiation is excluded.
3. Check the network package of the IP phone. It is found that the IP phone does not receive the voice stream from the switch at the abnormal time. (The voice stream in the pure SIP scenario does not pass through the IP PBX.) Check the NEs on the live network one by one. Contact onsite engineers to capture the network packages of the IP phones, firewall ingress and egress, and contact firewall engineers for analysis.
4. According to the onsite network packets sent from the firewall, the length of all UDP message headers sent from the SBC is inconsistent with the actual data length. As a result, the firewall fails to parse data.
5. Check the other NEs on site. It is found that a voice packet sent by a transmission device between the firewall and the SBC is abnormal. Contact the device vendor to rectify the fault.
【Suggestion and conclusion】
NA
