Patent ID: 8170005

Claim:
A call session control server assignment method for assigning a particular call session control server (S-CSCF server) that registers a user equipment and administrates call session control on the user equipment from a plurality of S-CSCF servers in an IP network for achieving IMS (IP Multimedia Subsystem) architecture, the method comprising: providing a S-CSCF server selection table that stores in correspondence with each S-CSCF server priority information indicating an order of priority when assigning user equipment in accordance with a current operation condition of each S-CSCF server in a home subscriber server (HSS server) that stores user information for each user equipment; referring to the S-CSCF server selection table by the HSS server when it receives an interrogation from an interrogating session control server (I-CSCF server) for determining the particular S-CSCF server that registers the user equipment at a time of registration thereof; sending back, by the HSS server, information including the priority information of the plurality of S-CSCF servers registered in the S-CSCF server selection table to the I-CSCF server from which the interrogation is sent; determining, by the I-CSCF server, the particular S-CSCF server to be assigned based upon the sent back priority information of each S-CSCF server, wherein at the time of sending back the information including the priority information of the plurality of S-CSCF servers to the I-CSCF server from which the interrogation is sent, the HSS server rearranges the plurality of S-CSCF servers in the sequence corresponding to the priority information before sending back to the I-CSCF server from which the interrogation is sent.