r prefixes are not for the use on the UE to PGW link but for the networks and devices on the UE's downstream interfaces. Since the 3GPP link-model is a point-to-point link without native multicast capability, there is no real broadcast or multicast capabilities for IPv4 or IPv6 that would affect anything beyond the directly connected link. When a UE decides to use DHCPv4 for its IPv4 address allocation, the UE has to transmit that decision to the network using NAS signaling (see Section 4.4.7). A PGW may have a role of a DHCPv4 server or a relay [25]. The use of DHCPv4 makes it possible for the UE to defer its address allocation to the point where the address is really needed. This so-called deferred address allocation procedure, in combination with PDN Type IPv4v6 bearers, could be used to conserve scarce IPv4 numbering resources. The DHCPv4 functionality also allows renewing and releasing the acquired IPv4 address at any time, which could be useful when using PDN Type IPv4v6 bearers. In the event that the UE decides to release its IPv4 address and the PDN Type is IPv4, the PGW starts a gateway initiated bearer deactivation procedure, which eventually leads to closing of the PDN Connection. The deferred IPv4 (home) address allocation is available for 3GPP accesses using DHCPv4, for trusted non-3GPP access (the S2a-interface) also using DHCPv4, and for Dual-Stack Mobile IPv6 (DSMIPv6) [19] (the S2a-interface) using Home Address (HoA) re-registration procedure. Section 4.4.2 discusses the IPv6 and its lifetime, in more detail. However, generally speaking the lifetime of the IPv6 prefix fate-shares the PDN Connection lifetime. The 3GPP architecture handles overlapping user plane address spaces rather well. Since the user plane traffic is always tunneled within the core network and identified with Tunnel Endpoint IDentifiers (TEIDs) or other tunneling identifiers (e.g., GRE keys), the IP numbering gets 'meaningful' only when the IP packet reaches the UE or its first- hop router, that is, a PGW in the case of GTP-bas