The Ims Sip Signaling Qos Assurance Mechanism

It is one of the obvious trends for the 3rd generation mobile system to provide abundant mobile multimedia service, including data, voice, image and video etc. The IP multimedia subsystem (IMS) which is introduced in 3GPP UMTS specifications is designed to support the mobile multimedia service. Session Initiate Protocol (SIP) is accepted in IMS as the session control signaling protocol. The signaling message controls the whole processes of the session, including the session establishment, session management, session end. It's a key factor of a successful session for which the quality of service (QoS) must be guaranteed. However, in fact, compared with the media message, the question of signaling message transmission quality is paid less attention to. This paper emphasizes on the QoS question of SIP signaling message in IMS. The main task is to study the related specification of SIP standard and the application environment of the IMS architecture, propose the improved QoS mechanism of the SIP signaling which is suitable to 3G according to the known research results and the lack in current mechanism.Firstly, this paper introduces the background knowledge related to the research field in detail, including the characteristic, the network architecture, the function element, the service process of the IMS and the basic concept of the SIP, especially explain the extension of the SIP in IMS and the QoS signaling interaction by SIP. Then, we discuss the virtual SIP link (VSL) concept based on the QoS requirement of SIP signaling transmission and propose the variable rate leaky bucket algorithm as the traffic control and access control algorithm choice. Thereafter, We analyze and compare the performance of the algorithm by calculating several important QoS parameters, such as the packet loss probability and the packet delay time etc. It is proved that, in comparison with the ordinary leaky bucket algorithm, the variable rate leaky bucket algorithm make progress in the effect of QoS guarantee. Furthermore, we give a calculating model of the QoS parameters based on the characteristic of the SIP signaling transmission process.