Section: 4.3.5.3 Tracking Area list management
Content: Tracking Area list management comprises the functions to allocate and reallocate a Tracking Area Identity list to the UE. All the tracking areas in a Tracking Area List to which a UE is registered are served by the same serving MME. The "tracking area list concept" is used with E-UTRAN. With this concept, when the UE registers with the network, the MME allocates a set (a "list") of tracking areas to the UE. By making the centre of this set of tracking areas close to the UE's current location, the chance of a UE rapidly making another tracking area update can be reduced. If SIPTO at local network with stand-alone GW, Serving GW relocation without mobility and ISR are supported in the core network the Tracking Area list should only contain either Tracking Areas inside one local network or inside the macro network. If the tracking area list covers both local network and macro network, the ISR shall not be activated if the UE is allowed to use SIPTO at local network. The MME determines the RAT type the UE is camping on, i.e. NB-IoT or WB-E-UTRAN for terrestrial access and WB-E-UTRAN or NB-IoT RAT types for satellite access, based on the Tracking Area indicated in the INITIAL UE MESSAGE by the eNodeB. To ensure a UE initiates tracking area updating procedure when performing inter-RAT mobility between NB-IoT and WB-E-UTRAN, the E-UTRAN shall be configured such that a Tracking Area does not contain both WB-E-UTRAN and NB-IoT cells, and, the MME shall not allocate a Tracking Area Identity list that contains both NB-IoT and WB-E-UTRAN Tracking Areas. To ensure the UE initiates tracking area update procedure when it moves to and from an MME that supports 15 EPS bearers per UE as defined in clause 4.12 to an MME that does not support 15 EPS bearers per MME and vice versa, the MME shall allocate a Tracking Area Identity list that provides homogenous support for 15 EPS bearers per UE. Other features (e.g. User Plane CIoT EPS Optimisation, Supporting up to 15 EPS bearers per UE, satellite access) may require the MME to adapt how it creates the "list" of TAIs. NOTE: This TAI list functionality is different to the SGSN behaviour in GERAN and UTRAN systems. In GERAN/UTRAN the UE is only registered in one Routeing Area at a time.