 exchange + HARQ retransmissions: Security information may already be available in the intermediate state introduced by 5G NR. Nevertheless, it is important to consider whether the security context has been discarded during the transition between the UE states. Registration with the anchor gNB + HARQ retransmissions: In the case of user-plane/ control-plane split, the UE often registers with the cell that provides the control plane. In that case, when user-plane and control-plane belong to different radio access net- works, the UE may also register with both cells. In the case of control-plane establish- ment in multi-connectivity, the UE may register with multiple cells which provide control-plane functionalities. If the radio access network does not require registration, this component can be omitted, assuming that the context can be retrieved from the pre- vious session. Mobility: Mobility is the maximum UE speed at which certain QoS can be achieved or sus- tained. There are four mobility classes defined in IMT-2020 as follows: Stationary: 0 km/h Pedestrian: 0-10 km/h Vehicular: 10-120 km/h High-speed vehicular: 120-500 km/h The upper range of high-speed vehicular mobility class is mainly considered for high-speed trains. A mobility class is supported, if the minimum required data channel link-level spec- tral efficiency on the uplink can be achieved. This assumes the user is moving at the maxi- mum speed in that mobility class in each of the test environments. The mobility class compliance is evaluated under Indoor Hotspot-eMBB, Dense Urban-eMBB, and Rural- eMBB test environments. In order to verify satisfaction of the mobility requirement, one should run system-level simulations, identical to those for calculating the average spectral Introduction and Background lvii efficiency, at the maximum speed of each mobility class, starting with link-level simulations and an appropriate link-to-system mapping (also known as physical layer abstraction), in order to collect overall statistics for uplink SINR values (i.