Hello, we’re having some issues with a phone system on our network. We have two offices that connect via an IPsec VPN, both using Sophos UTM routers. The main site has an Esi phone system, and the remote site has a few remote Esi phones that connect through the VPN to the phone system.
Each phone connects to the phone system via a nonstandard UDP port across the VPN. No public IP addresses are used.
The main issue we’re having is a phone call starts out okay. Everything is fine until about 2 or 3 minutes into the call, then the audio will start to echo or repeat and isn’t understandable. Sounds kind of like Max Headroom. This seems to only occur for outside callers. The user of the remote phone generally doesn’t have issues, but the person who placed the call to that phone will hear the audio problem.
I thought this may some kind of UDP flooding prevention kicking in, but I can’t find anything in the logs related to that port being blocked. I actually can’t find anything at all listed in the logs related to the UDP ports, so maybe I’m just not looking in the right area.
I also created a QoS rule on both sides that didn't seem to help. Added the main phone system IP to advanced threat protection exceptions, as well as intrusion prevention exceptions.
Any insight would be great. Thanks.
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