Efficient P-CSCF discovery through NASS-IMS

P-CSCF discovery is made prior to communication to the IMS core network and only performed before an initial registration. The approach introduced in this paper is to provide an efficiency mechanism to retrieve the proper P-CSCF for the SIP terminal through Network Attachment Subsystem of IMS. The proposed discovery procedure advanced a `nearest contact retrieval´ method based on improved quad-tree to obtain the P-CSCF in Connectivity Session Location and Repository Function of IMS and transmit the selected P-CSCF to SIP terminal by enhancing the communication interface in Network Attachment Subsystem of IMS and DHCP message. The presented discovery mechanism focused primarily on terminal moves between visited networks in IMS architecture, since it needs to communicate via its first outbound SIP proxy, fast proxy query processing is necessary. The method requires limited changes in function and almost no changes in interfaces. With this method, P-CSCF could be provided to terminal more intelligent, also the registration could be smoother.