We have 3CX phone system installed our head office and PSTN lines are connected to the system.Our branches are connected to head office through site to site VPN and head office running Internet with speed of 75 Mbps and branch is 12 Mbps. We are facing audio clarity issues at times and seems that happens in branches more frequently. Hope setting up Qos will help to rectify the problem. What network zone I suppose to choose if I set Qos for Head office voip service and Branches. Is it LAN to WAN or LAN to VPN?