IMS NETWORK SYSTEM AND DATA RESTORE METHOD

When detecting that subscriber data has been lost due to a reason such as node restart, the S-CSCF transmits a SIP RESET signal to notify a neighboring P-CSCF of the loss of the subscriber data. Receiving the SIP RESET signal, the P-CSCF searches for subscribers who are registered to the S-CSCF having transmitted the SIP RESET signal. If any, the P-CSCF performs flag control on registration information of the P-CSCF to identify that the subscriber data has been lost in the S-CSCF, and transmits a SIP REGISTER signal to the S-CSCF. Receiving the SIP REGISTER signal, the S-CSCF rebuilds the lost subscriber data from the subscriber database HSS by performing registration processing according to existing procedures.