On Location Management Technology In IMS Network

The notable features of 3G (Third Generation) are providing voice, video, messaging, data and web-based multimedia mobile services for the wireless users. It enables the convergence of mobile telecommunications networks and Internet which are the most successful network at present with the largest development potential in the future. For this purpose, IMS (IP Multimedia subsystem) is introduced in UMTS (Universal Mobile Telecommunications System) R5. It is the development trends and directions of NGN (next generation networks) and doubtlessly becoming the focus of technical research. SIP (Session Initiation Protocol) is one of the main protocols which support service mobility management, and it is also the key protocol used in location management in IMS. The location management in IMS involves location registration and location query. The users' location information is recorded through location registration; while in session setup procedure, the user is located by location query. And it is not the same as the location management in cellular mobile communication systems and Mobile IP network that the text-based SIP messages in IMS need more resource in processing, which impacts on the signaling process efficiency during location management.This dissertation concentrates on the research of location query in IMS session establishment, registration of location management and the efficiency of SIP message parsing, involving: 1. Session setup handling, focusing on the improvement of location query procedure for terminating network during the session establishment; 2. Location management, focusing on how to improve on location management policy and user location update procedure in IMS to reduce the cost of network; and 3. SIP message parsing, focusing on how to optimize the SIP message parsing during the session setup and registration.This dissertation is organized as follows. Firstly the status and problems of the location management in IMS network are analyzed in chapter 1. Also IMS is introduced, as the base of the following researches. Then in chapter 2, the session setup procedure is investigated, and the serial and parallel session mechanisms are proposed according to the locality of call traffic along with the caching algorithm to improve IMS session setup mechanism. Moreover, in chapter 3 location management scheme is improved further and a new distributed location management scheme with VSS (Visitor Subscriber Server) is presented to advance the efficiency of session setup procedure and decrease the network cost. Following the research, based on the concept of tiered location management a two-tier location management mechanism in chapter 4 and a dynamic location update mechanism in chapter 5 are proposed. In these researches, analytical models are used to analyze the cost of new mechanisms, and the results are proven by simulation experiments. At last, in chapter 6 a SIP selective parsing method is introduced to offer efficient session establishment and registration.The principal contributions of the dissertation are:(1) Based on the IMS specification of UMTS R7, and due to the locality of call traffic (the quantity of session requests within one area including roamers and non-roamers is a large proportion of the total quantity), a novel serial session setup mechanism through the caching in the original S-CSCF (Serving-Call Session Control Function) is proposed. Moreover, the performance of this mechanism is evaluated over the basic session setup mechanism and the outcomes show that the novel mechanism gets the benefit in cost and time delay.(2) Base on the research of serial session setup mechanism, in order to further decrease the session setup delay, a novel parallel is proposed: when data has been the cached, originating S-CSCF sends two parallelling session requests. The cost and delay functions are deduced by analysis model, and the performance of this mechanism is compared with the basic mechanism and the former serial mechanism. The result shows that parallel session mechanism can effectively reduce the session setup delay with some additional cost. Furthermore, according to the locality of call traffic and cache policy, the cost and delay critical points of serial and parallel session setup mechanism is analyzed.(3) The IMS home service control model and location management policy are improved for the flexible service control scheme. The users' location information stored in visited network can fasten the user location information request and session setup procedure, as well as effectively prevent the register signaling long-distance transfer. Then, simulations and analysis verify that the performance of this new mechanism gets the benefit in cost and time.(4) The home networks (including HSS (Home Subscriber Server)/S-CSCF) and visited networks (including P-CSCF(Proxy-Call Session Control Function)) are divided functionally into two-tier mobile database; then the two-tier location management is proposed: the visited network registration and the home network registration, in which the visited network registration is responsible for its registered user location update. When subscriber roams, the location information of home network will be updated by the visited network based on the change of UE (user equipment's IP address. Importantly, the cost analytical model is investigated, and the two-tier location management mechanism outperforms the current mechanism is proven by both theoretically analysis and simulation experiments.(5) In IMS network, PRR (Periodic Re-Registration) and CCRR (Change Capabilities Re-Registration) are utilized to update the registration timer as well as to detect the presence and location of UE. Taking session activities of users into consideration, the DLU (dynamic location update mechanism) is proposed. And then the performance modeling of DLU and PCR (PRR+CCRR) is presented, as well as the cost functions of them are deduced. With theoretical analysis and simulation results, we find that, DLU efficiently reduces the signaling cost of IMS network and increases the service traffic of the system.(6) It is different from the location management in cellular mobile communication systems and Moblie IP network that the text-based SIP messages in IMS need more resource for both processing and transport. So an efficient SIP message processing is important and critical to the performance of the whole network and the delay during location management. The performance of SIP message processing in SIP servers is investigated, mainly focusing on improving message parsing by introducing a method named SP4SIP (selective parsing for SIP message). To validate the approach, it has been implemented in a high performance SIP server in our labs. Measurements show that selective parsing for SIP message can indeed decrease processing time.