I have home network and 5 satelite stores with a L2TP VPN link between RB450 boards to each store over a 3rd party wireless network.
We use VoIP telephones between all sites with the SIP server on the home network.

I test each link for speed using a 30 count ping with a 64 and a 1500 packet size every 2 hours.

The one link which appears to be the best link from the above test is actually the worst for VoIP comms. The line drops all the time and it is often not usable. All other network functionality works well.
Are there any QOS or other settings which will give the VoIP priority and perhaps improve the comms and/or is there a better way of testing the links to identify a VoIP problem?