he routing of traffic to local services or not. 3.2.5.2 Single PDU Session-Based Access to Local Services 5GC supports two mechanisms operating within a single PDU session: Uplink Classifier (ULCL) and multi-homed PDU sessions. As illustrated in Figure 3.2.7, the ULCL is a UPF functionality that can be activated by the SMF to divert some of the uplink traffic of a PDU session toward a local data network that hosts a local copy (or instance) of the service that the UE is trying to access. Similarly, in the downlink direction, ULCL injects traffic from the service instance hosted in the local data network into the PDU session and forwards the traffic to the UE. Traffic classification is done based on filtering rules (e.g. matching certain destination IP ranges, etc.) provided by the SMF based on operator configuration. As the UE changes location, the SMF ensures an efficient routing path between the UE and the closest service instance by selecting a different UPF to terminate the N3 interface from NG-RAN and to act as a ULCL. The new UPF diverts the traffic to a local data network that is closer to the UE's new location and that also hosts an instance of the same service. The UE is generally not aware of the ULCL. In other words, the UE is not aware that some of its traffic is routed to a local data network. Central (R)AN (ULCL) data network Local data network Figure 3.2.7 Uplink classifier (ULCL) functionality in a UPF is used to divert some uplink traffic to a local data network and inject downlink traffic from the local data network to the UE. 3 5G System Overview 3.2.5.3 Multiple PDU Session-Based Access to Local Services As depicted in Figure 3.2.8, a multi-homed PDU session refers to a configuration where the UE has been assigned different IPv6 prefixes by multiple PDU session anchors in the same PDU session. The SMF configures one UPF to act as a branching point, which for- wards uplink traffic to the appropriate PDU session anchor (connected to the central or local data network) based on the source IPv6 pre