Content for  TS 23.502  Word version:  18.5.0

NG-RAN initiates handover (see clause 4.9.1.3) or redirection to a 5GC-connected E-UTRAN cell, if UE is currently camped on NR.

NG-RAN initiates handover (see clause 4.11.1.2.1) or redirection to E-UTRAN connected to EPS. NG-RAN uses the security context provided by the AMF to secure the redirection procedure. If the redirection procedure is used either in 5a or 5b the target CN type (EPC or 5GC) is also conveyed to the UE in order to be able to perform the appropriate NAS procedures (S1 or N1 Mode). The UE uses the emergency indication in the RRC message as specified in clause 6.2.2 of TS 36.331 and E-UTRAN provides the emergency indication to AMF (during Registration triggered by step 5a) and MME (during Tracking Area Update triggered by step 5b). Both the Registration and the Tracking Area Update requests should contain Follow-on request and active flag respectively to indicate that the UE has "user data pending". For the handover procedure used in step 5b see clause 4.11.1.2.1, step 1. In step 5b, if the MME does not support emergency services for that UE, the MME should act such that the call for emergency service is likely to succeed promptly, e.g. if the UE successfully completed a combined TA/LA Update with the network, by using the CSFB procedures specified in TS 23.272.