w 2 N3 GTP-U Tunnel QoS Flow 3 PDU Session 2 QoS Flow 4 N3 GTP U Tunnel QoS Flow 5 PDU Session 3 QoS Flow 6 N3 GTP U Tunnel Figure 2.16 - QoS in 5G This connection determines the QoS experienced by the user. Consider a case in which the UE initiates an attach request to the network SO that it can access the internet; what happens in the background is that a logical connection (or pipe) is created between the UE and the 5G network that carries the data flows associated with browsing the internet. This logical connection is defined by attributes such as a QoS parameter. Certain PDU sessions require a guaranteed QoS, which must be provided by the network if the PDU session is accepted. Hence, the network must reserve resources for this kind of PDU session. A classic example of this is an emergency call. When a user places an emergency call, the network must admit the call and provide the necessary resources. We will learn more about 5G QoS in the upcoming sections. 5G network concepts In the preceding diagram, three PDU sessions are depicted between the same UE and the network. Each PDU session can have one or more QoS flows, differentiated by the QoS flow indicator. In the example, one PDU session is an IMS session, the second can be a data session, and the third can be IoT or enterprise access. Hence, the same device is able to cater to multiple types of applications that require different types of resources from the network simultaneously. Every PDU session in UE is associated with an identification number, which is known as the PDU session ID. In the 5GS, this can range between 1 and 15. For a PDN connection established via MME, the PDU session ID value is set to 64, plus the EPS bearer ID for the default EPS bearer of the PDN connection; for a PDN connection established via an ePDG, the PDU session ID value is set to 80, plus the EPS bearer ID for the default EPS bearer of the PDN connection: PDU session identity value (octet 1, bit 1 to bit 8 No PDU session Identity assigned PDU session Identity value 1 000001