re similar in spirit to MAP such as the DS-Lite variant described in [46, 47]. The basic principle is always the same, though, when it comes to address sharing: a number of end hosts that share the exactly same IPv4 address are differentiated by the port range (e.g. 1024 ports each) assigned to them. The port range does not need to be contiguous but distributed into the 65536 ports space using some method [48]. There are obvious similarities to NAT44 at the conceptual level. Address and port sharing may have additional concerns and issues beyond the normal known NATting issues. For instance, some protocols check for IP addresses and limit a number of connections seemingly originating from or terminating at the same host. When address and port sharing is used, this can obviously lead to false positives, since the same shared address can belong to multiple end hosts [49]. DS-Lite with B4 in UE Dual-stack Lite (DS-Lite) [8] is yet another IPv6 transition solution, which tunnels IPv4 packets over IPv6 tunnels. DS-Lite was aimed at deployments where the ISP core network is IPv6-only and still customer networks are dual-stack or IPv4-only. A DS-Lite solution has two functional entities: a Basic Bridging BroadBand (B4) and an Address Family Transition Router (AFTR). The B4 resides at the customer premises or in the end host, and terminates the IPv6 tunnels that carry IPv4 traffic. The AFTR is the ISP side IPv6 tunnel concentrator, which also contains a centralized Carrier Grade NAT (CGN). IPv6 traffic is delivered natively over the ISP core network between the customer sites and the Internet. Customers, or rather their CPEs, are identified and numbered using the unique IPv6 address of the tunnel endpoint used for tunneling the IPv4 traffic. This identifier is often referred to as the Softwire-ID. In a typical DS-Lite deployment the B4 function resides inside the CPE device. How- ever, RFC 6333 also allows a deployment model where the B4 is located inside the end host, which in our 3GPP architecture case would be the UE.