Feature Description
Connection Management (CM) includes the functions to establish and release a NAS signaling connection between a UE and the Access and Mobility Management Function (AMF) over the N1 interface. This signaling connection enables the NAS signaling exchange between the UE and the core network.
The 5GS CM states determine the NAS signaling connection of the UE with the AMF. The following are the CM states:
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CM-Idle—When a UE is in the CM-Idle state, the UE has no NAS signaling connection established with the AMF over the N1 interface. The AN signaling connection, N2 connection, and N3 connection do not exist in this state.
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CM-Connected—When a UE is in the CM-Connected state, the UE has a NAS signaling connection with the AMF over the N1 interface. A NAS signaling connection uses an RRC Connection between the UE and the NG-RAN and an NGAP UE association between the AN and the AMF for the 3GPP access.
The CM states for the 3GPP access and the non-3GPP access are independent of each other. It implies that both the access can be in the CM-Idle state and the CM-Connected state simultaneously.
SMF supports network-initiated messages when a UE is either in the CM-Idle state or in the CM-Connected state.