n the radio and user plane for each PDU session. The GTPU header has a field to depict the QFI, which is used to differentiate flows. The QFI values can be repeated within the same user equipment for different PDU sessions for the same subscriber. 5G network concepts IP UPF -> dst port= IP int > QFI 1 IP gNB DL TEID IP mobile GTP-U header NG-RAN Node gNB, ng-eNB DRB 5 Web Browser QFI 2 5QI 8 QFI = 2, 5QI 8 Internet LCID 5 LCID 5 DL TEID QFI 1 5QI 9 QFI = 1, 5QI 9 PDU Session GTP-U Tunnel Figure 2.18 - 5G PDU session In the preceding figure, we can see that the UE is accessing the internet. The UE interacts with the NG-RAN node, which is, in turn, connected to the 5G user and control planes. When the UE powers up, a PDU session is established; this is the default session used to access the internet. In this case, it has a 5Q1 of 9, indicating a class of QoS for non-guaranteed bitrate sessions with a delay budget of 300 ms, used for browsing, file downloads, and SO on. A second flow is installed within the same PDU session with a 5QI of 8, which has higher priority than the first flow with a 5QI of 9. This flow is denoted within the PDU session by QFI 2. A single GTPU tunnel will serve both flows in the PDU session, and hence a single tunnel endpoint identifier is allocated to both these flows. The diagram also shows the GTPU packet with the source and destination IP information, destination port information, tunnel endpoint identifier details, QFI, and the actual data payload. Next, considering that the UE now wishes to access voice services, a second PDU session will be set up. Firstly, a flow with 5QI of 5 is set up, which is used for IMS signaling. Then, subsequently, when the user actually places a voice call and dials a number, a second flow is installed with a 5QI of 1 and this is used to carry the voice traffic. Note that within the PDU session, we have two flows denoted by QFI 1 and QFI 2 with a 5QI of 5 and a 5QI of 1 respectively. There is a second GTPU tunnel in addition to the one established earlier f