Editing My 3GPP 23.501 Notes (section)

== 5.3 Registration and Connection Management ==

=== 5.3.1 General ===

The Registration Management is used to register or deregister a UE/user with the network (via AMF), and establish the user context in the network. The Connection Management is used to establish and release the signalling connection between the UE and the AMF.

=== 5.3.2 Registration Management ===

==== 5.3.2.1 General ====

A UE/user needs to register with the network to receive services that requires registration. Once registered and if applicable the UE updates its registration with the network (see TS 23.502):
* periodically, in order to remain reachable (Periodic Registration Update); or
* upon mobility (Mobility Registration Update); or
* to update its capabilities or re-negotiate protocol parameters (Mobility Registration Update).

The Initial Registration procedure involves execution of Network Access Control functions as defined in clause 5.2 (i.e. user authentication and access authorization based on subscription profiles in UDM). As result of the Registration procedure, the identifier of the serving AMF serving the UE in the access through which the UE has registered will be registered in UDM.

The registration management procedures are applicable over both 3GPP access and Non-3GPP access. The 3GPP and Non-3GPP RM states are independent of each other, see clause 5.3.2.4.

==== 5.3.2.2 5GS Registration Management states ====

===== 5.3.2.2.1 General =====

Two RM states are used in the UE and the AMF that reflect the registration status of the UE in the selected PLMN:
* RM-DEREGISTERED.
* RM-REGISTERED.

===== 5.3.2.2.2 RM-DEREGISTERED state =====

In the RM DEREGISTERED state, the UE is not registered with the network. The UE context in AMF holds no valid location or routing information for the UE so the UE is not reachable by the AMF. However, some parts of UE context may still be stored in the UE and the AMF e.g. to avoid running an authentication procedure during every Registration procedure.

In the RM-DEREGISTERED state, the UE shall:
* attempt to register with the selected PLMN using the Initial Registration procedure if it needs to receive service that requires registration (see clause 4.2.2.2 of TS 23.502).
* remain in RM-DEREGISTERED state if receiving a Registration Reject upon Initial Registration (see clause 4.2.2.2 of TS 23.502).
* enter RM-REGISTERED state upon receiving a Registration Accept (see clause 4.2.2.2 of TS 23.502).

When the UE RM state in the AMF is RM-DEREGISTERED, the AMF shall:
* when applicable, accept the Initial Registration of a UE by sending a Registration Accept to this UE and enter RM-REGISTERED state for the UE (see clause 4.2.2.2 of TS 23.502); or
* when applicable, reject the Initial Registration of a UE by sending a Registration Reject to this UE (see clause 4.2.2.2 of TS 23.502).

===== 5.3.2.2.3 RM-REGISTERED state =====

In the RM REGISTERED state, the UE is registered with the network. In the RM-REGISTERED state, the UE can receive services that require registration with the network.

In the RM-REGISTERED state, the UE shall:
* perform Mobility Registration Update procedure if the current TAI of the serving cell (see TS 37.340 [31]) is not in the list of TAIs that the UE has received from the network in order to maintain the registration and enable the AMF to page the UE;
:NOTE: Additional considerations for Mobility Registration Update in case of NR satellite access are provided in clause 5.4.11.6.
* perform Periodic Registration Update procedure triggered by expiration of the periodic update timer to notify the network that the UE is still active.
* perform a Mobility Registration Update procedure to update its capability information or to re-negotiate protocol parameters with the network;
* perform Deregistration procedure (see clause 4.2.2.3.1 of TS 23.502), and enter RM-DEREGISTERED state, when the UE needs to be no longer registered with the PLMN. The UE may decide to deregister from the network at any time.
* enter RM-DEREGISTERED state when receiving a Registration Reject message or a Deregistration message. The actions of the UE depend upon the cause value' in the Registration Reject or Deregistration message. See clause 4.2.2 of TS 23.502.

When the UE RM state in the AMF is RM-REGISTERED, the AMF shall:
* perform Deregistration procedure (see clauses 4.2.2.3.2, 4.2.2.3.3 of TS 23.502), and enter RM-DEREGISTERED state for the UE, when the UE needs to be no longer registered with the PLMN. The network may decide to deregister the UE at any time;
* perform Implicit Deregistration at any time after the Implicit Deregistration timer expires. The AMF shall enter RM-DEREGISTERED state for the UE after Implicit Deregistration;
* when applicable, accept or reject Registration Requests or Service Requests from the UE.

=== 5.3.3 Connection Management ===

==== 5.3.3.1 General ====

Connection management comprises the functions of establishing and releasing a NAS signalling connection between a UE and the AMF over N1. This NAS signalling connection is used to enable NAS signalling exchange between the UE and the core network. It comprises both the AN signalling connection between the UE and the AN (RRC Connection over 3GPP access or UE-N3IWF connection over untrusted N3GPP access or UE-TNGF connection over trusted N3GPP access) and the N2 connection for this UE between the AN and the AMF.

==== 5.3.3.2 5GS Connection Management states ====

===== 5.3.3.2.1 General =====
Two CM states are used to reflect the NAS signalling Connection of the UE with the AMF:
* CM-IDLE
* CM-CONNECTED
The CM state for 3GPP access and Non-3GPP access are independent of each other, i.e. one can be in CM-IDLE state at the same time when the other is in CM-CONNECTED state.