prioritize taffic for H.323 video

Hi

I'm wondering how to configure a PC6224 and PC5548 to prioritize traffic for H.323 video conferencing. The H.323 traffic comes and goes from the Cisco 3825 router that is handle by our ISP. It is connected to our core switch PC6224 on a islolated VLAN (no ip interface nor routing on the vlan). This vlan is then trunked to another PC6224 and also a PC5548 where the H.323 video conference equipments are.

This is Layer 2 traffic, what is the config to use here and whrere do I put it? On the vlan or on the ethernet/fiber ports?

Thanks