ful, a PDU session is finally established. Figure 7.2 describes the procedure through which this end-to-end connectivity is established. It can be noticed here that the participating nodes are as follows: gNB (gNodeB/RAN) AMF (Access and Mobility Function) SMF (Session Management Function) SCP (Service Communications Proxy) UDM (Unified Data Management) PCF (Policy Control Function) CHF (Charging Function) UPF (User Plane Function) Note that, optionally, a Network Registration Function (NRF) can also be used for service registration and discovery, but we have left it out of our example here for the sake of simplicity. PDU session establishment in 5G PDUSessionEstablishmentRed PDUSessionEstablishment Req (Uplink NAS) SMF Selection PDUSession Create SM Context Req UDM Registration Request UDM Registration Response UDM Subscription Fetch Req UDM Subscription Fetch Res Subscription Notification Req Subscription Notification Res PDUSession Create SM Context Res Figure 7.2 - PDU session establishment in 5G - part 1 Let us elaborate on each of the steps mentioned. In Steps 1 and 2, the UE initiated a PDU session establishment message, which is directed from the UE to the AMF via the gNB. This comprises a NAS container that has various information, such as the following: S-NSSAI(s) UE-generated PDU session ID DNN information Packet Core Procedures Request type, which could be one of the following: i. Initial Request - corresponding to the request for a new PDU session Existing PDU Session - if the request refers to an existing PDU session switching between 3GPP and non-3GPP access, or in the case of being handed over from a 4G Evolved Packet Core (EPC) iii. Emergency Request - for establishing a PDU session for emergency calls PDU session type (IPv4, IPv6, IPv4v6, Ethernet, unstructured, etc.) Requested SSC mode type 5GSM capability, which contains information on whether the Ethernet PDU session type is supported, whether Reflective QoS is supported, whether it is a Multi-Homed IPv6 PDU Session, ATSSS capability, and the