fix used by the UE. Furthermore, the branching point merges and forwards downlink traffic from the PDU session anchors to the UE. As the UE changes location and the forwarding path to a previous PDU session anchor becomes inefficient, the SMF may add another UPF acting as a PDU session anchor and providing access to a closer local data network. The new PDU session anchor will then assign another IPv6 address to the UE. Previously used PDU session anchors for local data network instances that have become inefficient will be removed by the SMF. In a multi-homed PDU session the IPv6 prefix that the UE uses when sending uplink traffic also determines the PDU session anchor that the uplink traffic is forwarded to by the branching point. Therefore, it is important for the network to be able to influence the UE's decision as to which source IPv6 prefix to use for which traffic. The latter is achieved by enhancements to IPv6 Router Advertisements (Draves and Thaler 2005), which enable operators to provide routing information and preferences for source IPv6 selection to the UE. Another approach to enable the UE to access both local and central services is to establish multiple PDU sessions: one PDU session terminating at a PDU session anchor located close to the RAN and one located deeper in the network for access to central services. The challenge of this approach is how to ensure that the PDU session for local services is updated SO that it always terminates at a PDU session anchor that is close to the UE's location. At the same time, the system needs to ensure that the PDU session for central services is not modified. To address this challenge, three different Session and Service Continuity (SSC) modes have been defined, which determine whether a PDU session is to be relocated upon UE (R)AN Central (Branching Session data network point) Anchor 1) Local Session data network Anchor 2) Figure 3.2.8 A multi-homed IPv6 PDU session provides access to both a local and central data network in the same PDU session. 3.2 5G Core 