traffic into IPv6 just by providing IPv6 connectivity for the hosts they serve, and therefore, operators can reduce Network Address Translation (NAT) costs by deploying IPv6. This is significant, as it concretely allows the first cost savings of IPv6. The operating systems used by hosts, especially those of personal computers (desktops, laptops), are generally IPv6 enabled already. Hence if provided with IPv6 connectivity, these hosts actually start using IPv6. Unfortunately, the situation with 3GPP User Equip- ments (UEs) is not as good. The UEs at the time of writing this book are generally (but with exceptions) unable to use IPv6 on cellular access. Not all of the components on the UEs that need updating (as shown in Figure 4.28) are done, yet. Thus, we can see that even the equipment implementation part of the transition is still ongoing. Due to the end equipment being increasingly IPv6 enabled (hosts, content), the burden of progressing the transition is now mostly on the access network providers but partly also on the UE vendors, whose devices are not yet IPv6 enabled, and obviously on the remaining content providers. We have written this book to help people advocate and add IPv6 support to the components they are responsible for. We expect to see an increase in access network IPv6 support during the coming few years, in addition to increased support by hosts and content providers. Especially in 3GPP, the IPv6 deployments are expected to become more widespread through deployment of Long Term Evolution (LTE). The vast majority of the deployments will look like dual-stack to the hosts, hence the dual-stack transition continues to be dominant - even if tunneling or double translation would be internally used by access networks. IPv6 Transition Mechanisms for 3GPP Networks The need to provide connectivity for IPv4-only hosts will remain for a long time. It is not justifiable to disconnect the huge number of IPv4-only computers and entertainment systems that people have in their homes. Perhaps a decade after the