 forwarded by the source gNB over the data from the CN. To minimize the New Radio Access Layer 2/3 Aspects and System Operation 265 losses when a QoS flow is mapped to a different DRB at handover, the old DRB needs to be configured in the target cell. For in-order delivery in the downlink, the target gNB should first transmit the forwarded PDCP SDUs on the old DRB before transmitting new data from 5G CN on the new DRB. In the uplink, the target gNB should not deliver data of the QoS flow from the new DRB to 5G CN before receiving the end-marker on the old DRB from the UE. The UE does not retransmit any PDCP SDU in the target cell for which transmis- sion had been completed in the source cell. The source NG-RAN node may request downlink data forwarding per QoS flow to be estab- lished for a PDU session and may provide information on how it maps QoS flows to DRBs. The target NG-RAN node decides whether data forwarding per QoS flow should be estab- lished for a PDU session. If lossless handover is desired and the QoS flow to DRB mapping, applied at the target NG-RAN node, allows employing data forwarding with the same QoS flow to DRB mapping that was used in the source NG-RAN node for a DRB and if all QoS flows mapped to that DRB are accepted for data forwarding, the target NG-RAN node establishes a downlink forwarding tunnel for that DRB. For a DRB for which SN status preservation is important, the target NG-RAN node may decide to establish an uplink data forwarding tunnel. The target NG-RAN node may also decide to establish a downlink forwarding tunnel for each PDU session. In this case, the target NG-RAN node provides information related to the QoS flows for which data forwarding has been accepted and the corresponding uplink TNL information for data forwarding tunnels to be established between the source and the target NG-RAN nodes [8]. 2.5.2 UE-Based Mobility The PLMN selection in NR is based on 3GPP PLMN selection rules. Cell selection is required upon transition from RM-DEREGISTERED to RM-REGISTERED, from CM-