 done by the UE. Over the NG-U connection, the 6-bit QFI field is carried inside the GTP-U extension header where the GTP tunnel carries the overall PDU session. Fig. 2-9 explains the functional split between gNB and UPF elements where (in the downlink direction) the UPF components classify ingress IP flows to PDU session and QoS flow (QFI). The gNB SDAP layer maps these QoS flows to DRBs that are subject to wireless air interface scheduling and transmission over the air. Each PDU session is carried in a GRPS tunnel and identified by the Tunnel Endpoint Identifier (TEID). The TEID unambiguously identifies a tunnel endpoint in the receiving GTP-U (GPRS Tunneling Protocol-User) or GTP-C (GPRS Tunneling Protocol-Control) protocol entity. The receiving side of a GTP tunnel locally assigns the TEID value for the transmitting side to use. The TEID values are exchanged between tunnel endpoints using GTP-C messages [or RANAP (Radio Access Network Application Part) in the UTRAN (UMTS Terrestrial Radio Access Network)]. See in Fig. 2-10 for how these pieces fit together in the overall protocol stack. The QoS flow context that is pointed to by the QFI contains a set of QoS-related para- meters that includes: 5G QoS Identifier (5QI). Defines a set of preconfigured QoS characteristics. Allocation and Retention Priority (ARP). Defines traffic priority level (PL-lower number indicates higher priority) and indicates whether this flow can be preempted or preempt other flows. For GBR QoS flows: Guaranteed Flow Bit Rate for both uplink and downlink Maximum Flow Bit Rate for both uplink and downlink QoS Flow 1, QFI DRB 1 IP Flows, DSCP a IP Flows QoS Flow 2, QF12 DRB 2 IP Flows, DSCP QoS Flow 1, QFI 1 DRB 3 QoS Flow 2, QFI 2 IP Flows, DSCP y QoS Flow 3, QFI FIGURE 2-9 Mapping between IP flows, QoS flows, and DRBs (downlink). DRBs, data radio bearers; IP, Ingress Protection; QoS, Quality of Service. Open Radio Access Network (O-RAN) Systems Architecture and Design QoS behavior per DRB Packet AN/NB Packet classification classification