User ID provisioning for SIP registration in IMS

SIP registration is needed prior to communicating with SIP terminal in IMS core network. The approach introduced in this paper provides the capability to provision the user identifier assigned to a specific terminal which depends on the user location by NACF (Network Attachment Control Function of IMS). It serves two purposes: avoiding any need for user interaction; avoiding fraud. The proposed procedure that implementation provision SIP user identifier from NACF is described in three parts: enable the function, get the user ID from relay agent and send back user ID to terminal. With user ID information, the SIP registration will be invoked by SIP terminal automatically. The presented provision mechanism focused primarily on interaction between NACF, ARF (Access Relay Function of IMS) and SIP terminal. The method requires limited changes in function and almost no changes in interfaces. With this method, user identifier could be provided to terminal more intelligent, also the registration could be smoother.