 page that UE, what we don't want to have to do is page every single gNB in the NG-RAN. So, consequently, the NG-RAN is broken down into tracking areas. What's crucial in the system is that the UE might be autonomously making cell reselection when it is in the IDLE mode. The UE will keep the network updated as to which tracking area it is currently in. A tracking area is simply an administrative collection of gNBs and their associated radio coverage, as depicted in the figure. The 5G Core Access and Mobility Management Function (AMF) in the 5GC keeps track of the tracking area that the subscriber is currently in. So, the subscriber's UE will be required to update the network any time it moves into a new tracking area. The User Plane Function (UPF) in the 5GC is responsible for the user plane data. If user data comes into the UPF, it will inform the AMF and the AMF will page a specific tracking area instead of paging every gNB in the network, since it already knows which tracking area the UE is in. Mobility Management Idle Mobiles - TAI Connected Mobiles - Cell ID TAI 1 5G Core Network TAI 2 TAI 3 Figure 1.6 - Tracking areas The tracking areas effectively make paging much more efficient. As soon as the UE connects to the network, the AMF will know its cell ID. But when it is IDLE, it just knows the location of the UE to the granularity of the tracking area. Tracking area planning is all about making the paging more efficient. 5G RAN deployment options Service providers will be in a transition phase as they move from 4G toward 5G networks. They can't just switch on the 5G network suddenly. There are some strategy options for service providers in terms of migration. Now notice that in the diagram, there are 4G EPC and 5GCs. The first question Introduction to 5G is, will the service provider be deploying the 5GC or 5G Radio Access Network first or will they both be deployed in parallel? Either way, there are various connectivity and deployment options available for the service providers to choose from. It is not nece