 addressing on the transport plane. Again, this allows for a phased migration of the user plane to IPv6 (and to dual-stack) while still keeping the actual transport plane in IPv4. Figures 4.6a and 4.6b illustrate a typical construction of the user plane and the transport plane in the 3GPP GPRS/EPC. The separation of the transport plane from the user and control planes, and the fact that all user plane traffic is tunneled, would in theory allow deploying most packet core network elements (3GPP specific and pure IP routing/switching devices) without IPv6 support on their own networking connectivity level. For instance, if an operator has an existing IPv4-only Multi Protocol Label Switching (MPLS) [30] in their packet core network that can remain unchanged and be without IPv6 awareness or support [31, 32]. 4.2.2 Affected Networking Elements As discussed in Section 4.2.1, the division of 3GPP interfaces into a control plane, a user plane and a transport plane has made it possible to migrate different parts of the 3GPP sys- tem to IPv6 in phases. Especially, detaching the transport plane from the other two planes allows migrating the entire 3GPP system from the end user services point of view to IPv6 while still keeping the underlying operator packet core, backhaul, and radio access network IP infrastructure untouched and on IPv4. However, still at the system level most of the 3GPP networking elements are impacted when introducing IPv6 as the end user service. Figure 4.7 shows GPRS and EPS networking elements, including the UE, which are impacted by the introduction of the end user IPv6 or dual-stack service (i.e., IPv6 delivered on the user plane). Basically everything except the IP transport plane (IP transmission) and 3GPP interfaces excluding (S)Gi is affected. The affected elements are marked with a star in Figure 4.7. The figure is far more complex (and also harder to parse) than the usual conceptual architecture pictures since we need to point out all affected elements and interfaces. We will briefly go through