Ims network system and data restore method

When an S-CSCF detects that subscriber data is lost due to node resumption or the like, the S-CSCF transmits an SIP Reset signal to report to an adjacent P-CSCF that the subscriber data has been lost. The P-CSCF which has received the SIP Reset signal searches for a subscriber who has been registered in the S-CSCF which has transmitted the SIP Reset signal. If any subscriber is found, the P-CSCF performs a flag control indicating that the S-CSCF subscriber data has been lost, on the P-CSCF registration information and transmits an SIP Register signal to the S-CSCF. Upon reception of the SIP Register signal, the S-CSCF performs the registration process based on the existing procedure and rebuilds the subscriber data which has been lost from a subscriber database HSS.