Section: 5.3.3.2.2 CM-IDLE state
Content: A UE in CM-IDLE state has no NAS signalling connection established with the AMF over N1. The UE performs cell selection/cell reselection according to TS 38.304[ NR; User Equipment (UE) procedures in Idle mode and in RRC Inactive state ]  [50] and PLMN selection according to TS 23.122[ Non-Access-Stratum (NAS) functions related to Mobile Station (MS) in idle mode ]  [17]. There are no AN signalling connection, N2 connection and N3 connections for the UE in the CM-IDLE state. If the UE is both in CM-IDLE state and in RM-REGISTERED state, the UE shall, unless otherwise specified in clause 5.3.4.1: - Respond to paging by performing a Service Request procedure (see clause 4.2.3.2 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3]), unless the UE is in MICO mode (see clause 5.4.1.3); - perform a Service Request procedure when the UE has uplink signalling or user data to be sent (see clause 4.2.3.2 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3]). Specific conditions apply for LADN, see clause 5.6.5. When the UE state in the AMF is RM-REGISTERED, UE information required for initiating communication with the UE shall be stored. The AMF shall be able to retrieve stored information required for initiating communication with the UE using the 5G-GUTI. NOTE: In 5GS there is no need for paging using the SUPI/SUCI of the UE. The UE provides 5G-S-TMSI as part of AN parameters during AN signalling connection establishment as specified in TS 38.331[ NR; Radio Resource Control (RRC); Protocol specification ]  [28] and TS 36.331[ Evolved Universal Terrestrial Radio Access (E-UTRA); Radio Resource Control (RRC); Protocol specification ]  [51]. The UE shall enter CM-CONNECTED state whenever an AN signalling connection is established between the UE and the AN (entering RRC_CONNECTED state over 3GPP access, or at the establishment of the UE-N3IWF connectivity over untrusted non-3GPP access or the UE-TNGF connectivity over trusted non-3GPP access). The transmission of an Initial NAS message (Registration Request, Service Request or Deregistration Request) initiates the transition from CM-IDLE to CM-CONNECTED state. When the UE states in the AMF are CM-IDLE and RM-REGISTERED, the AMF shall: - perform a network triggered Service Request procedure when it has signalling or mobile-terminated data to be sent to this UE, by sending a Paging Request to this UE (see clause 4.2.3.3 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3]), if a UE is not prevented from responding e.g. due to MICO mode or Mobility Restrictions. The AMF shall enter CM-CONNECTED state for the UE whenever an N2 connection is established for this UE between the AN and the AMF. The reception of initial N2 message (e.g. N2 INITIAL UE MESSAGE) initiates the transition of AMF from CM-IDLE to CM-CONNECTED state. The UE and the AMF may optimize the power efficiency and signalling efficiency of the UE when in CM-IDLE state e.g. by activating MICO mode (see clause 5.4.1.3).