The Research And Design Of Call Session Control Modle Based On CSCF In IMS

At present, with the deeply research of Next Generation Network, the IP Multimedia Subsystem(IMS) has become a hotspot technology in the communication field. IMS can build up the unified core control layer of Fixed-Mobile Convergence(FMC) based on IP,providing more viv0id and open services system structure,carrying out superior services for subscribers. In all of the IMS function models, Call Session Control Function(CSCF) modle is reponsible for accomplishing originating call services, selecting route and handling call session behavior, CSCF is one of the core modle of IMS. Therefore, the main content of this paper is focus on the actual design and realization of CSCF modle.Firstly, analyzing the development and appliance of IMS in the national and international,then leads to the analysis of present actuality for IMS technique research,basic characteristic and the trend. exploring the IMS network framework,inquiring into the different and similar points between IMS and traditional Softswitch communication network,summarizing the extending functions of SIP for IMS.By leading to mCSCF concept, combining Proxy CSCF, Serving CSCF and Interrogation CSCF into one modle: mCSCF, and giving the inner interfaces of mCSCF and exterior interfaces of mCSCF in the IMS, and defining all these interfaces at the same time.On the whole design and realization of mCSCF, adopting layer framework, dividing mCSCF into three layers: Transaction and Transport layer, Leg and Dialog layer and Service Call layer, The Transaction and Transport layer is responsible for the actual transmission of requests and responses over network transports,and is used to handle SIP transaction, and ensure that message transmission is reliable and message exchange is successful; Leg and Dialog layer is designed to assist user to process dialog messages,especially INVITE, PRACK, SUBSCRIBE, NOTIFY and REFER messages and their responses; Service Call layer is responsible for the call and session control and service logic process.For the register, unregister, subscribe and session realization precedures of mCSCF, in order to describe these services call, leading to Leg(Commnication Path) and Call Segment concepts. In Leg/Dialog layer and Service Call layer, in order to describe the state change, leads to Finite State Machine(FSM), and defines FSM control and FSM Match for controlling and Match ing the mCSCF.Finally, giving parts of data design and realization of Service Call layer, the data relatives and parts of handling machnisms between Leg/Dialog layer and Service Call layer.