16.5 Emergency Services
38.3003GPPNRNR and NG-RAN Overall descriptionRelease 17Stage 2TS
16.5.1 Overview
NG-RAN provides support for Emergency Services either directly or through fallback mechanisms towards E-UTRA. The support of Emergency Services is broadcast in system information (see TS 38.331 [12]).
16.5.2 IMS Emergency call
An IMS Emergency call support indication is provided to inform the UE that emergency bearer services are supported. In normal service state the UE is informed if the PLMN supports emergency services through an Emergency Service Support indicator in the Attach and TAU procedures (see TS 23.501 [3]). In limited service state and for emergency services other than eCall over IMS, a UE is informed about if a cell supports emergency services over NG-RAN from a broadcast indication (ims-EmergencySupport). The broadcast indicator is set to "support" if any AMF in a non-shared environment or at least one of the PLMN’s in a shared environment supports IMS emergency bearer services.
16.5.3 eCall over IMS
NG-RAN broadcast an indication to indicate support of eCall over IMS (eCallOverIMS-Support). UEs that are in limited service state need to consider both eCallOverIMS-Support and ims-EmergencySupport to determine if eCall over IMS is possible. UEs that are not in limited service state need to only consider eCallOverIMS-Support to determine if eCall over IMS is possible. The broadcast indicator is set to "support" if the PLMN in a non-shared environment, or all PLMNs in a shared environment, supports eCall over IMS.
16.5.4 Fallback
RAT fallback towards E-UTRA connected to 5GC is performed when NR does not support Emergency Services and System fallback towards E-UTRA connected to EPS is performed when 5GC does not support Emergency Services. Depending on factors such as CN interface availability, network configuration and radio conditions, the fallback procedure results in either CONNECTED state mobility (handover procedure) or IDLE state mobility (redirection) – see TS 23.501 [3] and TS 38.331 [12].