Would you mind elaborate a little more? Why you want to set QoS policy for CUPS?
On CUPS > System > Service Parameters > SIP Proxy, there's a parameter:
Differential Service Value:
This parameter specifies the TOS (Type-Of-Service) byte of the IP header of transmitted SIP packets. These values and their associated meanings are specified in RFC2474, RFC2475, RFC2597, and RFC3246.
Michael
http://htluo.blogspot.com/