 registration request and updates the user agent's information into a location server or other database. iii) SIP location databases support the location information of users, such as URLs or IP addresses, scripts, features and other preferences. SIP invitations are used to create sessions and carry session descriptions that allow participants to agree on a set of compatible media types. SDP [6] has been designed to convey session description information, such as session name and purpose, the type of media (e.g., video, audio, etc.), the transport protocol (e.g., RTP/UDP/IP or H.320), and the media encoding scheme (e.g., H.261 video, MPEG video, etc.). SDP also includes information associated with QoS (e.g., bandwidth, delay and jitter) and security (e.g., encryption key). For a multicast session, multicast IP address and transport layer port for media are delivered; for a unicast session, the remote contact addresses (e.g., IP address and port number) are delivered. When a multimedia communication session is accepted by the SIP/SDP signaling, the related traffic and QoS parameters should be determined. The traffic parameters for real-time multimedia services are committed informa- tion rate (CIR), committed burst size (CBS), excess burst size (EBS), and peak information rate (PIR). The QoS parameters include end-to-end transfer delay, delay variation (jitter) tolerance, packet error rate (PER), and packet loss rate (PLR). Based on the determined QoS and connection parameters, a network-layer connection establishment is requested using User-Network Interface (UNI) and Network-Node Interface (NNI) signaling [10]. When the subnetwork access mechanism is based on connectionless or con- tention mode, however, the network layer should allocate the required resources with the appropriate CAC mechanism. Some examples of contention-based subnetworks are IEEE 802.3 Fast/Gigabit Ethernet and IEEE 802.11 wireless LAN. In following section, we propose a detailed procedure of the network resource allocation scheme for QoS-gua