usage of the 3GPP networks has changed significantly during that time. Especially drastic changes in the environment have been the recent exhaustion of the IPv4 address space on the other side, and the exponentially increased data use in mobile broadband networks on the other. Hence, the original transition scenarios, which relied on IPv4 addresses to be relatively easily available, or that took shortcuts in performance due to assuming transition mechanisms to be relatively short lived workarounds, did not serve the changed environment at all. In addition, the availability of IPv6 has increased significantly in infrastructure equipment, and in the infrastructure on which the operators build their mobile networks. Whereas, at the beginning of the transition specification work a real concern for the mobile operators was obtaining IPv6 access, this is hardly a concern anymore. Therefore, the 3GPP community has had to go through multiple transition scenario iterations for different environmental situations. In addition to the transition scenarios, the 3GPP community has had multiple opportunities to change its mind on the role of IPv6 in general. For instance, the IP Multimedia Subsystem (IMS) [51] IP version has swung between being exclusively IPv6, dual-stack, and mostly IPv4 over the years. The first transition scenarios were made only for 2nd Generation (2G) and 3G-GPRS because the specification for Evolved Packet System (EPS) has not even started yet. In addition, the support for dual-stack PDP Context was not originally in the 3GPP specifications. Later on, scenario work did take these changes and enhancements into account. In this section, we will first look at the evolution of the transition scenarios in 3GPP networks, and then look at the scenarios that have survived over time. 5.4.1 Transition Scenario Evolution The first attempt to agree on the 3GPP transition scenarios was done at the IETF in the early 2000s. The result was two documents discussing IPv6 transition in GPRS, RFC 3574 [52], and RFC 4215 [53]