H.3 High Level Procedures for IMS emergency calls

23.1673GPPIP Multimedia Subsystem (IMS) emergency sessionsRelease 17TS

For the high level procedures (as described in clause 7.1.1) the following statements apply for UE detected emergency calls when PS domain with UTRAN, E-UTRAN or NG-RAN access is used:

– the bearer registration to the IP-CAN is the PS attach or PS Registration procedure;

– the IP-CAN bearer resource is the PDP context for GPRS, EPS Bearer for EPS and QoS Flow for 5GS, and TS 23.060 [2], TS 23.401 [28] and TS 23.501 [48] respectively describe how to indicate that the request is for emergency;

– the release of reserved bearer resources is the release of a PDP context, an EPS Bearer or a QoS Flow.

For the high level procedures (as described in clause 7.1.2) the following statements apply for Non UE detectable emergency calls when PS domain with UTRAN, E-UTRAN or NG-RAN access is used:

– The P-CSCF rejects the session initiation request with an indication that this is an emergency session; or

– the P-CSCF allows the session initiation request to continue and the E-CSCF informs the UE that it is an emergency session. Such a session will not use an emergency PDN connection or emergency PDU session and will not have SRVCC or SRVCC for IMS emergency session support.

For the IMS Emergency Session Establishment without Registration (as described in clause 7.4), P-CSCF retrieves the additional subscriber related identifier(s) from IP-CAN via PCC in TS 23.203 [20] when PS domain with UTRAN and E-UTRAN access is used.