In LTE systems, the MME is responsible for assigning Tracking Area (TA) to each registered UE.
In 5G, however, There’s a new concept called RAN-based Notification Area (RNA). When the UE moves out of the RNA cell list, it needs to report its location change similar to the TAU concept in LTE, which is called RAN-based Notification Area Update (RNAU) (triggered via the serving ng-eNB or gNB).
In this context, the Mobility Managed in terms of Paging and RNAU procedures for 5G have some improvement over the MM for LTE to meet the 5G use cases.
The 5GC has introduced a new mechanism for TAU, also called RNAU, for a UE in RRC-INACTIVE state to track its location more precisely with low signaling overhead. Basically, the RRC-INACTIVE state is introduced to reduce the Paging delay and enable lightweight transitions between this new state and RRC-CONNECTED.
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