IMS emergency calls for roaming UEs

A non-transitory computer readable medium having instructions stored therein that are executable by processing circuitry of a proxy call session control function (“P-CSCF”) to cause the P-CSCF to perform operations comprising:

• receiving a session initiation protocol (“SIP”) REGISTER request from the UE, the REGISTER request relating to the emergency registration;
• determining an internet protocol (“IP”) address of the UE;
• sending an identity query to a policy and charging rules function (“PCRF”) indicating the IP address of the UE and requesting other identifiers of the UE;
• receiving one or more other identifiers of the UE from the PCRF, the one or more identifiers comprising at least one of an international mobile subscriber identity (“IMSI”) and a mobile subscriber integrated services digital network number (“MSISDN”);
• obtaining a telephone (“TEL’) and/or SIP uniform resource identifier (“URI”) for the UE on the basis of at least one of the one or more other identifiers;
• and
• responsive to receiving the SIP REGISTER request, sending a 200 OK response to the UE-including the TEL and/or SIP URI,
• wherein obtaining the TEL and/or SIP URI comprises:
• responsive to the MSISDN being the only identifier received:
• constructing the TEL URI from the MSISDN;
• or
• responsive to the MSISDN and the IMSI being the identifiers received:
• extracting mobile network code (“MNC”) and mobile country code (“MCC”) codes from the IMSI;
• and
• constructing the SIP URI from the MSISDN and the MNC and MCC codes.

A system for handling an emergency registration originating from a roaming user equipment (“UE”) that is not attached to a proxy call session control function (“P-CSCF”), the system comprising:

• a non-transitory memory;
• and
• a processor configured to execute instructions from the non-transitory memory to cause the system to perform operations comprising:
• receiving a session initiation protocol (“SIP”) REGISTER request from the UE, the REGISTER request relating to the emergency registration;
• determining an internet protocol (“IP”) address of the UE;
• sending an identity query to a policy and charging rules function (“PCRF”) indicating the IP address of the UE and requesting other identifiers of the UE;
• receiving one or more other identifiers of the UE from the PCRF, the one or more identifiers comprising at least one of an international mobile subscriber identity (“IMSI”) and a mobile subscriber integrated services digital network number (“MSISDN”);
• obtaining a telephone (“TEL’) and/or SIP uniform resource identifier (“URI”) for the UE on the basis of at least one of the one or more other identifiers;
• and
• responsive to receiving the SIP REGISTER request, sending a 200 OK response to the UE-including the TEL and/or SIP URI,
• wherein obtaining the TEL and/or SIP URI comprises:
• responsive to the MSISDN being the only identifier received:
• constructing the TEL URI from the MSISDN;
• or
• responsive to the MSISDN and the IMSI being the identifiers received:
• extracting mobile network code (“MNC”) and mobile country code (“MCC”) codes from the IMSI, and
• constructing the SIP URI from the MSISDN and the MNC and MCC codes.