Session initiated protocol (sip) session establishment with a home subscriber server (hss) outage

A system comprising:

• one or more processors;
• and
• one or more computer-readable media storing instructions that, when executed by the one or more processors, cause the system to:
• receive a terminating message from a UE;
• determine an occurrence of a Home Subscriber Server (HSS) outage;
• send a query for a Serving (S)-Call Session Control Function (CSCF) identifier;
• receive a particular S-CSCF identifier at least partly in response to the query;
• generate a modified terminating message from the terminating message;
• and
• send the modified terminating message to a particular S-CSCF associated with the particular S-CSCF identifier.

A method comprising:

• receiving a terminating message from an Interrogating (I)-Call Session Control Function (CSCF) including an indication of an occurrence of a Home Subscriber Server (HSS) outage;
• sending, based at least partly on receiving the indication of the occurrence of the HSS outage, a query for a Serving (S)-CSCF identifier;
• receiving the S-CSCF identifier based at least partly on the query;
• generating a modified terminating message from the terminating message;
• sending the modified terminating message to a particular S-CSCF associated with the S-CSCF identifier;
• and
• sending the modified terminating message to a Telephony Application Server (TAS).