 In the case of 3GPP archi- tecture and DS-Lite deployment, the Software-ID would be the IPv6 address that the UE configured using the PDN Connection assigned IPv6 prefix. Figure 5.13 illustrates how a DS-Lite deployment could be overlaid on 3GPP architecture. The AFTR most probably Dual-stack UE ((g)) GGSN/PGW (S)Gi Tunnel NAT44 Private Intenet IPv6 only PDP/PDN Operator core / PDN Figure 5.13 DS-Lite with a B4 in the UE deployed in 3GPP network. IPv6 Transition Mechanisms for 3GPP Networks is a standalone node but could also be integrated into a PGW. Since DS-Lite relies on the NAT44 in the network, and the customer networks are identified using the IPv6 address of the tunnel endpoint, the private IPv4 addressing has no real function than to make the UE side IP stack work. In that sense DS-Lite resembles GTP whose user plane addressing is merely to please the UE side IP stack, and Softwire-ID would be used in a similar manner to Tunnel Endpoint Identifiers (TEIDs). Since a dual-stack UE may want to use Dynamic Host Configuration Protocol version 4 (DHCPv4) for configuring itself (e.g. DNS server addresses), the B4 typically has to implement a DHCPv4-proxy functionality. The DHCPv4-proxy would essentially do an address family translation to DHCPv6 and use that over the IPv6-only access. DS-Lite has been criticized for a number of reasons (and not only in 3GPP network architectures). First, it would use tunneling over the wireless leg, which is highly undesirable in 3GPP networks. Second, DS-Lite relies on a powerful NAT44 function (i.e. CGN) in the core network side. Third, DS-Lite with B4 inside the UE requires end host modifications. For any larger deployment the bootstrapping of the DS-Lite service has to be automated. RFC 6334 [50] defines the required DHCPv6 options that the B4 can use for bootstrap- ping the AFTR address. From the 3GPP networks and deployments point of view the dependency on DHCPv6 could be an issue. As we know, DHCPv6 is not a mandatory part of the 3GPP system architecture. Furthermore, s