Research On Key Technologies For Session Control Of IP Multimedia Subsystem

With the development of communications technology and the evolution of networks, the existing and future wireless access technologies co-exist, both competing and complementary, and merging to a heterogeneous network environment. Nowadays, researchers focus on how to enable the users to attach services at any time, any place, by any means seamlessly and pervasively.3GPP (3rd Generation Partnership Project) proposes the IMS (IP Multimedia Subsystem) that is accepted as the best control plane for the evolution of networks. Session control is the basic and core functionality of IMS, however, there are still many problems in support of multi-service invocation, session continuity in heterogeneous network and Quality of Service (QoS) control. To solve these problems, the author deeply researches the mutli-service invocation mechanism, the session handoff technology, the NEMO QoS control scheme and the session control protocol for home network. The work provides better QoS experience for the users, and optimizs the network performance, based on the session setup procedure.This dissertation summarizes the author's major research work.1) The key technology issues of IMS session control are addressed.2) A novel multiple service invocation mechanism based on distributed SCIM (Service Capability Interaction Manager) is proposed, to improve the session setup procedure.3) A application based cross-layer session handoff mechanism is presented, which provides the functionalities as user mobility prediction, access network selection, parallel soft handoff and media rate control.4) The QoS control scheme for the Network Mobility (NEMO) in IMS is proposed and optimized.5) The performance of Session Initiation Protocol (SIP) for home network in IMS is investigated and a demand-driven SIP parsing method is introduced. Simulation and performance analysis are carried out to evaluate these new mechanisms and algorithms.The principal contributions of the work presented in this dissertation are:(1) A novel Distributed SCIM (DSCIM) multiple service invocation mechanism is introduced. It makes use of the SCIM server and the SCIM node that is deployed in the AS to invoke each AS consecutively without signaling being forwarded back to the Serving-Call Session Control Function (S-CSCF). The service invocation mechanisms are modeled through Jackson network and the result of simulation and analysis verify that new mechanism can effectively reduce session setup delay and decrease the load level of the S-CSCF.(2) An Enhanced cross-layer Handoff Mechanism (EHM) is proposed, which is based on application layer control and improves the current IMS session handoff mechanism through the information sharing and collaboration of all the network layers. On the signaling control plane, EHM makes use of the user mobility prediction algorithm to avoid multiple useless advance resource reservations and evolves a network-driven access network selection scheme to support the heterogeneous networks. On the bearing control plane, EHM provides parallel soft handoff algorithm and media rate adjustment policy. It exploits two networks efficiently by parallel transmission. Analytical and simulation results show that EHM can minimize resource reservation cost, decrease session handoff delay, reduce session incompletion probability, lower packet loss rate and obtain a more efficient use of the wireless bandwidth.(3) The NEMO is proposed by The Internet Engineering Task Force (IETF) to support the mobility management when users moving as a whole. A novel heterogeneous bandwidth sharing (HBS) scheme for IMS-NEMO is presented by considering the heterogeneous networks and IMS QoS control features. HBS provides an aggregate IP bearing for all sessions inside the mobile network, in order to avoid the excessive signaling cost of independently QoS control. At the same time, HBS scheme solves some problems of current NEMO QoS scheme by selecting the suitable access network for each session and enabling the new coming non-real-time sessions to share bandwidth with the Variable Bit Rate (VBR) coded media flows. The modeling and simulation results demonstrate that the HBS can satisfy users'QoS better and obtain a more efficient use of the scarce wireless bandwidth.(4) SIP is used as the session control signaling for home network in IMS. However, the ability to process SIP messages quickly and efficiently is critical for the performance of consumer electronic devices in the house. A thorough analysis of the SIP message processing reveals that parsing messages entirely is the bottleneck of a SIP server performance. To solve this problem, a demand-driven parsing method (DPM) for home devices is introduced, which only parses part of the entire SIP message. The test is carried out and the measurements show that the DPM for SIP message can indeed decrease SIP processing time.