Section: 2.12 Structure of the Truncated 5G-S-Temporary Mobile Subscriber Identity (Truncated 5G-S-TMSI)
Content: The Truncated 5G-S-TMSI is a 40 bit UE identifier constructed from the 5G-S-TMSI. It is used in RRC Connection Re-Establishment for the control plane for NB-IoT as described in 3GPP TS 36.300[ Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 ]  [91]. The Truncated 5G-S-TMSI shall be constructed from the Truncated AMF set ID, the Truncated AMF Pointer and the Truncated 5G-TMSI: <Truncated 5G-S-TMSI> = <Truncated AMF set ID><Truncated AMF Pointer><Truncated 5G-TMSI> Truncated AMF set ID is n least significant bits of AMF Set ID, where n is no greater than 10 bits. Truncated AMF Pointer is m least significant bits of AMF Pointer, where m is no greater than 6 bits. Truncated 5G-TMSI is (40-n-m) least significant bits of 5G-TMSI. The values n and m are configurable based on network deployment. The value n+m shall be larger or equal to 8 bits. NOTE: Depending on network deployment it is up to operator configuration to ensure that Truncated AMF Set ID and Truncated AMF Pointer identify the AMF uniquely, and that Truncated 5G-TMSI identifies the UE uniquely within the serving AMF. The NG-RAN and AMF are configured with the values n and m respectively, and NG-RAN is configured with how to recreate AMF Set ID from Truncated AMF Set ID, AMF Pointer from Truncated AMF Pointer, and 5G-TMSI from Truncated 5G-TMSI. The configuration of these parameters are specific to each PLMN. 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 3GPP TS 24.501[ Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3 ]  [125] during the Registration and UE Configuration Update procedures. For Network Sharing, the sharing NG-RAN is configured with the respective values n and m that are specific to each PLMN, and AMF is configured with the same values n and m as ones configured on NG-RAN per PLMN. The AMF configures the UE with the corresponding values n and m according to the PLMN which the UE accesses to during the Registration procedure.