EEE 802.11 wireless LAN wireless LAN Backbone network: Backbone network: service provider A service provider B Access loop: Access loop: ADSL, PON ADSL, PON IEEE 802.3 IEEE 802.3 Ethernet LAN Ethernet LAN FIGURE 15.1 End-to-end session layer signaling and per-domain subnetwork management for QoS-guaranteed multimedia service provisioning. CAC should be provided for the Ethernet switch or WiFi access point node that may be included in the home/office gateway. 15.2.2 SIP/SDP SIP is a session-layer signaling protocol that is used for establishment, mod- ification, and release of sessions among participants [5]. The session may be VoIP, video conference, multimedia distribution, and IMS (IP Multimedia Subsystem) applications. SIP supports five facets of establishing and termi- nating multimedia communications: user location, user availability, user capa- bilities, session setup, and session management. SIP may run on top of several different transport protocols, such as UDP and TCP. SIP is composed of three major functional elements: i) SIP user agents (UAs) originate SIP requests to establish media sessions and to exchange media. A user agent can be a SIP client software running on a desktop PC, laptop, PDA, or other available devices. ii) SIP servers are intermediary devices that are positioned within the net- work and assist user agents in session establishment and other functions. There are three types of SIP servers defined in [5]: proxy, redirect, and registrar servers. A SIP proxy server is used to help the routing request to the user's current location, to authenticate and authorize users for services, to © 2009 by Taylor & Francis Group, LLC Q-SIP/SDP for Converged Heterogeneous Wired and Wireless Networks 351 implement provider's call-routing policies, and to provide features to users. A redirect server receives a request from a user agent or proxy, and returns a redirection response, indicating where the request should be redirected. A registrar server provides a registration function that receives the SIP