Enhanced P-CSCF restoration procedure

A policy server for Proxy-Call Session Control Function (P-CSCF) restoration, the policy server comprising processing circuitry configured to cause the policy server to:

• receive a P-CSCF restoration message, the P-CSCF restoration message including an indication of a failed P-CSCF server, wherein the indication of the failure of the P-CSCF server is based on one of a failure alarm message from the failed P-CSCF server or a periodic polling of a plurality of P-CSCF servers, and wherein the plurality of P-CSCF servers includes the P-CSCF server, wherein every P-CSCF of a plurality of P-CSCF is registered with Network Function Repository Function (NRF), and every serving-CSCF (S-CSCF) of a plurality of S-CSCF subscribes with the NRF to the status of each of P-CSCF handled by the corresponding S-CSCF;
• as a result of the received P-CSCF restoration message, identify at least one corresponding Session Management Function (SMF) server or a corresponding Access and Mobility Function (AMF) server associated with each of IMPI/IMPU pair corresponding to the failed P-CSCF server;
• based on a message from a Home Subscriber Server (HSS), the S-CSCF communicates with the HSS for each of the IMPI/IMPU pair of the list of IMPU/IMPU pairs corresponding to the failed P-CSCF server, and wherein each of the plurality of S-CSCF stores:
• a list of IMPU/IMPU pairs per P-CSCF with which the corresponding S-CSCF is associated, and contacts of the list of IMPU/IMPU pairs that are registered with the P-CSCF server;
• and
• communicate, to each of the identified at least one SMF server or to each of the AMF server, a restoration message for tearing down at least one session for at least one user equipment (UE) associated with the failed P-CSCF server, wherein based on the restoration message, the SMF or the AMF clears a current session and force the at least one UE to re-register in a new IMS with another P-CSCF server different from the failed P-CSCF server.

A Session Management Function (SMF) server for Proxy-Call Session Control Function (P-CSCF) restoration, the SMF server comprising processing circuitry configured to cause the SMF server to:

• receive a restoration message from a Home Subscriber Server (HSS), the restoration message including an indication of a failed P-CSCF server, wherein the indication of the failure of the P-CSCF is based on one of a failure alarm message from the failed P-CSCF server or a periodic polling of a plurality of P-CSCF servers, wherein the plurality of P-CSCF servers includes the P-CSCF server, wherein every P-CSCF of the plurality of P-CSCF is registered with the NRF, and every serving-CSCF (S-CSCF) of a plurality of S-CSCF subscribes with the NRF to the status of each of P-CSCF handled by the corresponding S-CSCF, wherein each of the plurality of S-CSCF stores:
• a list of IMPU/IMPU pairs per P-CSCF with which the corresponding S-CSCF is associated, and contacts of the list of IMPU/IMPU pairs that are registered with the P-CSCF server, and wherein the S-CSCF communicates with the HSS for each of the IMPI/IMPU pair of the list of IMPU/IMPU pairs corresponding to the failed P-CSCF server;
• and
• as a result of the received restoration message, at least one of:
• tear down at least one session for at least one user equipment (UE) associated with the failed P-CSCF server;
• notify the at least one UE of the failed P-CSCF server;
• based on a message from the HSS, the S-CSCF communicating with the HSS for each of the IMPI/IMPU pair of the list of IMPU/IMPU pairs corresponding to the failed P-CSCF server;
• and
• clear a current session and force the at least one UE to re-register in a new IMS with another P-CSCF server different from the failed P-CSCF server.