Section: 4.3.21.1 CN Assistance Information
Content: Core Network assisted eNodeB parameters tuning aids the eNodeB to minimize the UE state transitions and achieve optimum network behaviour. How the eNodeB uses the Core Network assistance information is not in scope of this specification and is implementation specific. Core Network assistance information may be derived by the MME per UE in the MME based on collection of UE behaviour statistics or other available information about the expected UE behaviour (such as subscribed APN, IMSI ranges or other subscription information). If the HSS provides the Communication Pattern (CP) parameters (see TS 23.682[ Architecture enhancements to facilitate communications with packet data networks and applications ]  [74]) within the subscription profile information, then the MME may use the CP parameters for selecting the CN assisted eNodeB parameters. The CP parameters received from the HSS are used by the MME as input to derive the CN assisted eNodeB parameter values. For the case of statistics-based Core Network assistance information collection, this may be enabled based on local configuration (e.g. subscribed APN, IMSI ranges or other subscription information). This information provides the eNodeB 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 ECM-CONNECTED and ECM-IDLE states. This may be derived e.g. from statistical information or from subscription information. - "Expected HO interval", i.e. the expected time interval between inter-eNodeB handovers. This may be derived e.g. from statistical information or from subscription information. The "Expected HO interval" parameter is not based on subscription information. Highly mobile UEs may have the ECM-CONNECTED state reduced to reduce handover signalling, unless the activity data do not justify that, as reduced handover signalling would be outweighed by more Service Request signalling). - "UE Differentiation Information" including the Communication Pattern parameters (see TS 23.682[ Architecture enhancements to facilitate communications with packet data networks and applications ]  [74]) to support Uu operation optimisation for NB-IoT UE differentiation. The respective signalling to support this feature is specified in TS 36.413[ Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Application Protocol (S1AP) ]  [36]. The cases where the Traffic Profile (see see TS 23.682[ Architecture enhancements to facilitate communications with packet data networks and applications ]  [74]) is not used are described in clauses 5.3.4B.2 and 5.3.4B.3. The MME decides when to send this information to the eNodeB as "Expected UE behaviour" carried in S1-AP signalling over the S1-MME interface as per procedure documented in clause 4.3.21.3. NOTE 1: The calculation of the Core Network assistance information, i.e. the algorithms used and related criteria, and the decision when it is considered suitable and stable to send to the eNodeB are vendor specific. Unreliable information should not be provided to the eNodeB as it may drive undesirable system effects. NOTE 2: It is recommended the MME or, depending on where this assessment is performed, the eNodeB, can consider the average times in the ECM-CONNECTED and ECM-IDLE states an accurate representation of the traffic patterns if the average time in ECM-CONNECTED mode is short enough to assume the UE is generally actively transmitting and/or receiving data while in ECM-CONNECTED state. NOTE 3: When there are multiple overlapping CP parameter sets received from the HSS for one UE, then the MME considers a merge per CP parameter when deriving the CN assisted eNodeB parameters, e.g. based on the Scheduled communication time and/or Communication duration time parameters. A conflict on the Stationary Indication parameter can be resolved by considering the UE as "mobile".