ing of an IP packet to the QFI is performed by the NAS layer, based on its configuration. 3.4 NR Protocol Stack Applications Applications Applications Applications PDU session PDU session PDU session PDU session Filters Filters Filters Filters Core network QoS flows: [QFI marking] RAN DRB RAN DRB RAN DRB RAN DRB RAN DRB muxing/ RAN DRB muxing/ muxing/ muxing/ muxing/ muxing/ demuxing demuxing demuxing demuxing demuxing demuxing DRBs: [QFI, RQI] Figure 3.4.7 QoS flow mapping in the CN, RAN, and UE. The QFI is carried in the GTP header (3GPP TS 29.281) and provided to the gNB with each packet. Similar to LTE, Radio Bearers are used for transferring data over the radio interface, that is, RRC messages are carried by SRBs and user data is transferred over DRB. Each radio bearer provides a certain QoS for the data exchanged over it and multiple RBs can be set up per UE as needed to provide different QoS requirements for different services. RAN is responsible for setting up DRBs supporting different QoS and also for data to be sent on the DRB that meets its QoS requirement. RAN node has the flexibility to decide when and how many DRBs are to be set up for the UE. For example, data with different QFIs can be mapped into one DRB, provided that the QoS of the DRB meets the QoS requirements of all the QFIs mapped to it. The mapping of QoS flows to DRBs is shown in Figure 3.4.7. In the downlink, this mapping can be decided by the gNB without any preconfiguration to the UE by simply sending data for the QFI on a DRB. For the uplink, the mapping infor- mation from QFI to DRB has to be provided to the UE by gNB. This could be by explicit signaling using RRC Reconfiguration message or using the new concept of AS reflective mapping. With AS reflective mapping, the mapping table for a QFI can be updated to use the DRB on which the UE received a downlink packet for the QFI with a RQI bit set in the SDAP header. This allows RAN to change the uplink mapping dynamically using user-plane signaling without using RRC. The signaling for 