associated to the destination address of the packets received, e/gNB (G) e/gNB (G) IPv6 SA=G::,DA UDP SP=0-65535. DP=2152 UDP SP=0-65535. DP=2152 UDP SP=0-65535 DP=2152 TEIDI TEID2 TEIDI IPv6 SA=U1:: DA = U2:2:TEID1 SRv6 Traditional Mode I-UPF UL CL. i-UPF A-UPF e/gNB (G) Branching point Intra/Inter-RAT anchor PSA: PDU Session Anchor UDP SP=0-65535. DP=2152 SA=U1..DA=C1:1:: IPv6 SA=U2::, DA=C2:1: TEID1 SR (U:2:TEIDI. IPv6SA=U1:.DA=U:2:TEID1 SR (U:3:TEIDI. C2:1:: SL = 1 IPv6 SA=U2:: DA= U:3:TEID1 SRv6 Enhanced Mode Figure 13.3 Uplink packet flow using Segment Routing v6 (SRv6). It shows the application of classical GTP, SRv6 in traditional mode, and SRv6 in enhanced mode. 13 5G Network Slicing for V2X Communications: Technologies and Enablers SO they are not bound to an SID, corresponding to either SRv6 source nodes that introduce the SRH in the packets or SRv6 transit nodes steering traffic. We distinguish two modes of SRv6 operation in a mobile network, depending on whether it is considered as a replacement of GTP-U or a step toward the adoption of network pro- grammability: Traditional mode: There is a direct mapping between GTP-U and SRV6 encapsulations. It does not introduce changes to the network architecture and the impact is, thus, kept minimum. This mode would be used, for instance, in the topology as per Figure 13.3, where the user packet traverses four hops to arrive at the DN. Enhanced mode: By introducing more than one SID in the SRH (i.e. a packet can traverse more nodes with respect to the traditional mode), the use of more advanced functions in the network path of the traffic user flows is allowed, enabling to steer traffic in this way by using different paths and supporting more sophisticated behaviors, e.g. service programming. Therefore, it would be possible to associate non-3GPP services, such as TE in nodes along the path, as illustrated in the bottom of Figure 13.3. In specific V2X scenarios, it might be needed to apply the SRV6 enhanced mode that may enable handover scenarios (or in some mor