Metallic sound, at times, absent

When you have problems with intermittent audio, metallic or absent voice it is likely that some terminal is blocked on an old SIP session, flooding the PBX with packets on an RTP port that should instead be free for the PBX. The PBX, knowing that the port is free, allocates it for a new call, but that terminal continues to “disturb” the same port causing the audio problems already described.

To make sure that this diagnosis is correct, it is necessary to open the current textual log contained in the log folder of the PBX installation folder and look for the messages of the RTP REMOTE IP \ PORT CHANGED. The complete message looks like this:

Warning: ProcessRtpAudioPacket -> RTP REMOTE IP \ PORT CHANGED – from 192.168.150.117:4002 to 192.168.150.227:4870

Where the IPs are those of SIP devices / terminals that are communicating: among these the offending device may be present.

Among these messages, which are typically repeated many times within a second, it is necessary to identify the IP that occurs most frequently. That is the IP of the terminal potentially guilty of the disturbance.

Try disconnecting it from the network to see if the problem goes away within a few seconds. If necessary, continue with the other IPs if the problem does not disappear.

Once the device has been identified, it is typically sufficient to turn it off and on again. In some cases, the blockage of the device is due to overheating: therefore make sure that it is not overheated and, if necessary, place it in a more suitable place.