Section: 5.4.6.2 Core Network assisted RAN parameters tuning
Content: Core Network assisted RAN parameters tuning aids the RAN to minimize the UE state transitions and achieve optimum network behaviour. How the RAN uses the CN assistance information is not defined in this specification. Core Network assisted RAN parameters tuning may be derived by the AMF per UE in the AMF based on collection of UE behaviour statistics, Expected UE Behaviour and/or other available information about the UE (such as subscribed DNN, SUPI ranges, or other information). If the AMF maintains Expected UE Behaviour parameters, Network Configuration parameters (as described in clause 4.15.6.3 or 4.15.6.3a, TS 23.502[ Procedures for the 5G System (5GS) ]  [3]) or SMF derived CN assisted RAN parameters tuning, the AMF may use this information for selecting the CN assisted RAN parameter values. If the AMF is able to derive the Mobility Pattern of the UE (as described in clause 5.3.4.2), the AMF may take the Mobility Pattern information into account when selecting the CN assisted RAN parameter values. The SMF uses the SMF-Associated parameters (e.g. Expected UE Behaviour parameters or Network Configuration parameters of the UE) to derive the SMF derived CN assisted RAN parameters tuning. The SMF sends the SMF derived CN assisted RAN parameters tuning to the AMF during the PDU Session establishment procedure and if the SMF-Associated parameters change the PDU Session modification procedure is applied. The AMF stores the SMF derived CN assisted RAN parameters tuning in the PDU Session level context. The AMF uses the SMF derived CN assisted RAN parameters tuning to determine a PDU Session level "Expected UE activity behaviour" parameters set, which may be associated with a PDU Session ID, as described below in this clause. The Expected UE Behaviour parameters or the Network Configuration parameters can be provisioned by external party via the NEF to the AMF or SMF, as described in clause 5.20. The CN assisted RAN parameters tuning provides the RAN with a way to understand the UE behaviour for these aspects: - "Expected UE activity behaviour", i.e. the expected pattern of the UE's changes between CM-CONNECTED and CM-IDLE states or the duration of CM-CONNECTED state. This may be derived e.g. from the statistical information, or Expected UE Behaviour or from subscription information. The AMF derives one or more sets of the "Expected UE activity behaviour" parameters for the UE as follows: - AMF may derive and provide to the RAN a UE level of "Expected UE activity behaviour" parameters set considering the Expected UE Behaviour parameters or Network Configuration parameters received from the UDM (see clauses 4.15.6.3 or 4.15.6.3a of TS 23.502[ Procedures for the 5G System (5GS) ]  [3]) and the SMF derived CN assisted RAN parameters tuning associated with a PDU Session using Control Plane CIoT 5GS Optimisation. This set of "Expected UE activity behaviour" parameters is valid for the UE; and - AMF may provide to the RAN a PDU Session level "Expected UE activity behaviour" parameters set, e.g. considering the SMF derived CN assisted RAN parameters tuning, per established PDU Session. The PDU Session level "Expected UE activity behaviour" set of parameters is associated with and valid for a PDU Session ID. The RAN may consider the PDU Session level "Expected UE activity behaviour" parameters when the User Plane resources for the PDU Session are activated; - "Expected HO behaviour", i.e. the expected interval between inter-RAN handovers. This may be derived by the AMF e.g. from the Mobility Pattern information; - "Expected UE mobility", i.e. whether the UE is expected to be stationary or mobile. This may be derived e.g. from the statistical information or Expected UE Behaviour parameters or from subscription information; - "Expected UE moving trajectory" which may be derived e.g. from the statistical information or Expected UE Behaviour parameters or from subscription information; or - "UE Differentiation Information" including the Expected UE Behaviour parameters excluding the Expected UE moving trajectory (see clause 4.15.6.3 of TS 23.502[ Procedures for the 5G System (5GS) ]  [3]) to support Uu operation optimisation for NB-IoT UE differentiation if the RAT type is NB-IoT. The AMF decides when to send this information to the RAN as "Expected UE activity behaviour" carried in N2 request over the N2 interface (see TS 38.413[ NG-RAN; NG Application Protocol (NGAP) ]  [34]). NOTE: The calculation of the CN assistance information, i.e. the algorithms used and related criteria, and the decision when it is considered suitable and stable to send to the RAN are vendor specific.