WorldCom WorldCom dynamicsoft TransNexus This draft specifies the AAA functions and message exchanges for interdomain SIP telephony call setup with QoS. Usage accounting is provided with clearing house support using the Open Settlement Protocol. Interdomain message exchanges use existing IETF protocols. The use of existing protocols is however modeled in the proposed AAA Architecture of the IETF AAAArch RG [1]. Though the approach has been developed specifically for IP telephony, using the AAA Architecture may allow a future AAA protocol to go beyond IP telephony to serve alike for other applications.