5.31.4.3 Control Plane Relocation Indication procedure

For intra-NB-IoT mobility when UE and AMF are using Control Plane CIoT 5GS Optimisation, the CP Relocation Indication procedures may be used. The purpose of the CP Relocation Indication procedure is to request the AMF to authenticate the UE's re-establishment request (see TS 33.501 [29]) and initiate the establishment of the UE's N2 connection after the UE has initiated an RRC Re-Establishment procedure in a new NG-RAN node (see TS 38.300 [27]).

The RRC Re-Establishment procedure uses the Truncated 5G-S-TMSI as the UE identifier. The NG-RAN is configured with the sizes of the components of the Truncated 5G-S-TMSI and it is configured with how to recreate the AMF Set ID, the AMF Pointer and 5G-TMSI from the equivalent truncated parameters (see TS 23.003 [19]).

The AMF configures the UE with the Truncated 5G-S-TMSI Configuration that provides the sizes of the components of the Truncated 5G-S-TMSI as described in TS 24.501 [47] during the Registration. The configuration of these parameters are specific to each PLMN.

NOTE: Network sharing default configuration of the sizes of the truncated components is described in TS 23.003 [19].