What is the best way to monitor call quality on a working Asterisk box?

Hello!

I have a working Asterisk environment, and sometimes we have issues with users reporting call quality issues, usually from offsite via remote phones. Remote phones connect via a provisioning server through port udp/5060. Most of time everything works fine, leading me to believe that the issue is (most likely) network congestion on the internet circuits between the user and the server.

What is the best way to troubleshoot this kind of issue? Is there a way to install a server or service between the Asterisk server and the firewall to monitor calls? Perhaps a session border controller between the Asterisk and the firewall that records calls? I'm open to suggestions, thanks!