Monitor Physical Port
If there is a problem on the FXO port or FXS port, you can use the Port Monitor Tool to monitor the port, and download the packet to analyze it.
Go to System > Tool Kit > Port Monitor.
Choose the Port that has a problem.
Click Start Record. The PBX will start to monitor the port. During this time, you should duplicate the problem of the port.
Click Stop & Download to stop capturing packets.
Click Download to download the file.
Decompress the .tar.gz file and use Audition or coolpro2 software to open the .raw file and analyze it.