audio singal pass occured during video session between the eLTE and U1981

Issue Description：

Symptom: The LTE terminal initiates a video session with the U1981. The LTE terminal cannot hear the voice of the IP phone. The IP phone can hear the voice of the LTE terminal. The video image is normal.

abnormal terminals: EP681 ISDN 2015003 IMEI 865394021144697 B295 Q2 official version

Normal terminal: EP681 ISDN 7300001 IMEI 865394021105185 B372 Q6 test version

Handling Process：

1.One-click logs of terminals and one-click log collection and analysis of eAPP.

2. The NTP time carried in the audio and video RTCP packets sent by the peer U1981 is too much, which does not comply with the protocol. As a result, the media time calculated by the eAPP is abnormal, and the processing mechanism of the old and new versions of the eLTE terminal is different. The eLTE terminal version is as follows:

Old version Q2: The system checks the time relationship strictly and deletes the incorrect data. In this scenario, audio data is deleted and one-way audio occurs.

New version Q6: The compatibility processing of this scenario is optimized. The data is not deleted or the playback continues. However, the time relationship is incorrect, and the audio and video synchronization basis has been damaged. Therefore, the audio and video may be asynchronous.

3. In conclusion: Both the old and new versions are abnormal in this scenario. The only difference is that the new version improves the friendliness of the new version. To solve the problem, you need to analyze the source of the error.

4. 8950 Phone: According to the analysis, the NTP time of the audio is set to 1970 and the NTP time of the video is the current time of the system. The time difference between the two media is large. The eLTE terminal synchronization algorithm discards the audio packet directly. This problem occurs. According to RFC specifications, it is recommended that the two time be consistent. The customer has 600 multiple 8950 phones.

Root Cause：

The time difference between the time when the U1981 sends an audio message and the time when the video carries the NTP is too large. As a result, the message processing of the eLTE terminal is abnormal.

Solution:

Upgrade the 8950 phone to the new version to solve the problem of time difference.

Suggestions:

For similar problems, compare the differences between normal terminals and abnormal terminals in terms of configuration and version.