Research On The Mobility Management Of IMS

With the evolution of communication networks, the requirement of theservices provided becomes much higher than before. As IMS (IPMultimedia Subsystem) enables 3G (Three Generation) network to be afull-service converging network, it is doubtlessly becoming the focus oftechnical research. The success of an IMS network depends on the varietyand QoS (Quality of service) of its services and applications. A networksupporting mobile terminals with QoS guarantee must provide highmobility support. IMS mobility includes personal mobility, sessionmobility and service mobility. The terminal mobility is the responsibilityof the access network. This thesis concentrates on the research of IMSmobility management, involving: 1．Personal mobility, focusing on userlocation management; 2．Session mobility, focusing on fastening sessionhandover and keeping media transfer continuity; and 3．Service mobility,focusing on the service control model, how to provide services to mobileusers.This thesis is organized as follows. Firstly the status and problems ofthe mobility in IMS network are analyzed in chapter 1．Then in chaper 2,the IMS network is introduced, as the base of the following researches.Following the research of the session mobility of IMS, a new handoverprocedure of GPRS (General Packet Radio Service) and MESOCK(Mobile Extension SOCKET), a mobility extension of TCP/UDP(Transmission Control Protocol User Datagram Protocol) are proposed tooffer smooth session handover in chapter 3．In chapter 4 the personalmobility is studied and a new location management scheme with anauto-adaptive location caching algorithm is presented. At last, chapter 5concentrates on differenceless mobility and a brand new service controlnetwork is introduced to offer service mobility.This work is supported by: (1) National Science Fund for Distinguished Young Scholars (No. 60525110) ; (2) Program for NewCentury Excellent Talents in University (No.NCET-04-0111) ; (3) Specialized Research Fund for the Doctoral Program of Higher Education(No. 20030013006) .The principal contributions of the thesis are:(1) Based on the GPRS specification of UMTS R6, an inter-GGSN(Gateway GPRS Support Node) handoff procedure is proposedwhich uses a PDP (Packet Data protocol) context soft handoff.With the new procedure, data path can be shortened for roamingusers, which reduces the handover delay of upper layer andenhances the session mobility.(2) MESOCK is proposed which adapts TCP/UDP to mobileenvironment. In case of IP address change during the session, thetwo parties can use the new address for data transfer after sessionrefreshing without connection re-establishment. The sessionrefresh processing has no influence on the data transfer. Thisscheme matches the low layer well which assigns new IPaddresses for terminals in order to reduce the indirection of userdata. The data transfer continuity is guaranteed during the changeof IP address, which enhances the support for session mobility.(3) A new location management is introduced for flexible servicecontrol model. It stores the location information at the networkedge to fasten the user localization and the session creation. Thetraffic of registration signaling is also decreased. For supportingthis method, a location information caching algorithm is proposedwhich makes the change of cached location information close tothe change of user location locations and increases the hitting rate.(4) Differenceless mobility management concept is presented,corresponding to the architecture of home and visited network. Inthis concept, there is differenceless wherever the user accessesnetwork.(5) A brand new service control model, service control network, isproposed to implement the differenceless mobility management. With this model user can subscribe any service in spite of thelocation of the service support node. It is the service controlnetwork to decide which node serves the user, which is transparentto users. The result of analysis shows that this provides betterpersonal mobility and service mobility than current scheme inIMS.