I am running a Samsung Office server100 Phone system in my office with 4 IP phones for staff to work at home. I have set the routers quality of service to give 25% of the bandwidth to the phones systems IP address. (10.1.1.50) The phones work fine to out side lines or any phones in the office but when they connect to each other they clash and reboot I suspect that i need to give Quality of service to each Phone but how? would I use the Wan IP of the staff's home routers or something else (Router is DrayTek Vigor 2800 with VPN to our London office)

Thanks for any help.