m (IMS) implementations' [54]. Although most of the document concentrates on IMS scenarios, it considers the applicable GPRS network scenarios as well. In early 2000, when IMS was considered, the support for PDP Type IPv6 was not considered to be widespread in the networks deployed at the time. Hence, considerable effort had to go into discussing what Deploying IPv6 in 3GPP Networks PDN type IPv4 Dual-stack PDN type IPv6 PDN type IPv4v6 Dual-stack Figure 5.15 Dual-stack with two PDN Connections (upper) or single PDN Connection (lower). should happen in situations where some of the elements in a GPRS network did support IPv6 and others did not. 3GPP decided that it would not support any translation of PDP Type during the network transit, for example between Serving Gateway Support Node (SGSN) and GGSN. Practically, if one of the elements did not support PDP Type IPv6, the UE would need to use IPv4. This simplified the transition scenarios significantly. The conclusion here was also that supporting dual-stack in the UE is key to transition, and the networks would also need to be upgraded to support PDP Type IPv6 over time. More recently, 3GPP has agreed on a new set of IPv6 transition scenarios. These scenarios are listed in the 3GPP 23.975 'IPv6 migration guidelines' document [55] and include dual-stack, IPv6-only, and Gateway-Initiated Dual-Stack Lite. The last of which does not seem to have traction in the industry, and hence we do not consider it in any in depth this section. Appendix B of 23.975 also includes an set of other technologies that were topical when the core of 23.975 was written. These are Dual-Stack Lite, Address+Port. Protocol Translation, Per-interface NAT44 [56], and BIH/NAT64. From this set of additional tech- nologies, the Protocol Translation is the one currently seeing market adoption, and hence we have included it in this section. 5.4.2 Dual-stack As described above, the recommended transition model is the dual-stack deployment model. This is true for the more generic case recommended by t