The Protocol Interworking Between IMS And R4 Network In Control Plane

IMS——IP multimedia subsystems,which was drawn in 3GPP R5, is an IP-based network,and it has been extended in 3GPP R6,R7 .It can provide multimedia services on the common network construction. IMS at first is aims at the motion network, but on the current development of the communication network, the IMS network possibly becomes a hot spot in the future's communication network development.3GPP is an organization of 3G mobile communications standards, and 3GPP R4 is based on softswich.And it's a kind of electric circuit exchange network .3GPP R4 has its huge user group. It is now have some realistic problems if load bearing the circuit switch network's users to the IP network completely in a short time. So, a connection process is necessary. So perhaps, the IMS network will have a long coexistent time with the electric circuit switch network.This topic analyzed the architecture and the system protocol of the IMS system, and has carried on the comparison to the IMS network with the other networks. It proposed the problems when the IMS network intercommunicates with the 3GPP R4 circuit switch network. The control layer protocol of the IMS system is the SIP session initiation protocol. It's transmit format is text format while BICC take the octet form as the message transmission format.When the IMS network has a intercommunication with the current 3GPP R4 electric circuit switch network, the problem that the two sides'control protocol can't matches each other will come out. It is necessary for the protocol conversion to make the signal transmit correctly.The article researched the structure as well as each layer's function of the SIP protocol as a emphasis. Through the analysis of the differences of the SIP and BICC message to find the key-point for the intercommunication. The mapping method for the SIP and BICC message has been given out, include the address and signal message parse method.The oSIP and eXoSIP protocol stack have been used for the proper function expand, and implement the SIP client and the SIP server function. Based on the former research, a deeper research on the intercommunication for the BICC and SIP protocol has been made, and the interworking uint (IWU) has been designed and implemented. A test has been made for the whole system's run status and capabilities. But the test just focus on the least requirements when a call happens. The test mainly on the register function of the SIP client, the checking function of the SIP server as well as the interworking function for the SIP and BICC end point's intercommunication.