Troubleshooting VOIP issues can be tricky especially when dealing with an intermittent issue.
In some cases I’ve been asked to give an opinion if a WAN link or WiFi network can support voice or video calls.
One option is to get modeling software to get an idea of what it thinks. Another option would be to get a traffic simulator and test various scenarios, settings and vendors equipment.
A while ago I came across a really neat application called, “microsip”. It is a portable SIP client. You can configure it to communicate to most VOIP systems as a typical SIP client or as a ‘peer to peer’ configuration.
The peer to peer configuration is the one I am focusing on since you can use the client to replicate the performance of various audio/video codecs.
The video speaks for itself and hope you find it helpful.