Section: A.4 New QoS Flow with Explicit NAS Signalling
Content: The following figure shows an example message flow when the gNB receives a new QoS flow establishment request from CN that involves NAS explicit signalling. The QoS flow establishment request provides the gNB and UE with the QoS parameters for the QFI. In this example, the gNB decides to establish a new DRB (rather than re-use an existing one) for this QoS flow and provides the mapping rule over RRC signalling. NAS procedures details between gNB and 5GC can be found in TS 23.501[ System architecture for the 5G System (5GS) ]  [3], TS 23.502[ Procedures for the 5G System (5GS) ]  [22] and TS 38.413[ NG-RAN; NG Application Protocol (NGAP) ]  [26]. Figure A.4-1: DL data with new QoS Flow ID sent over new DRB with explicit signalling 0. PDU session DRB(s) have been already established. 1. gNB receives a PDU SESSION RESOURCE MODIFY REQUEST message from AMF for a new QoS flow. 2. If gNB cannot find an existing DRB to map this new QoS flow, it decides to establish a new DRB. 3. gNB sends an RRCReconfiguration message to UE including the DRB configuration with the new QFI to DRB mapping rule and the NAS message received at step 1. 4. UE establishes the DRB for the new QoS flow associated with this PDU session and updates the mapping rules. 5. UE sends an RRCReconfigurationComplete message to gNB. 6. gNB sends a PDU SESSION RESOURCE MODIFY RESPONSE message to AMF. 7. User Plane Data can then be exchanged between UE and gNB over DRB(s) according to the mapping rules and between UPF and gNB over the tunnel for the PDU session.