How do I enable auto QOS between two 4500 series Cisco switches?

How do I enable auto QOS between two 4500 series Cisco switches connected via fiber trunk link? Each switch has an AVAYA IP gateway plugged into it. We would like the voIP traffic flowing between the gateways to have precedence over all other traffic that traverses that link. There are no IP phones plugged into either switch, just gateway to gateway traffic. Thanks!