. The former document describes a series of transition scenarios providing connectivity for the UE. GPRS network internal transition scenarios were not discussed. The document describes the transition scenarios for GPRS and IMS use cases. However, we will focus here on the GPRS use cases. Figure 5.14 describes the GPRS scenarios. The idea of listing scenarios in RFC 3574 was to document the likely use cases, but not to impose any particular solutions. RFC 4215 documented an analysis of the scenarios described in RFC 3574. The analysis strongly favored the use of dual-stack in the 3GPP environment, and discouraged the use of translators between IPv4 and IPv6. This was logical at the time as adequate number of IPv4 addresses were still available. The analysis rather suggested turning on IPv6 in addition to IPv4. While work was ongoing on RFC 3574 and RFC 4215, obtaining IPv6 upstream, was still a real issue. In addition, the operators' own network equipment infrastructure, such as routers and switches, did not necessarily support IPv6 at all. This is clearly visible in the scenarios in Figure 5.14, where transporting IPv6 over IPv4 is prominently visible. Today, the scenarios are not really relevant anymore. However, the scenario for tunneling IPv4 over IPv6, which at that time did not seem important, may become relevant in the future as discussed earlier in this Chapter. IPv6 Transition Mechanisms for 3GPP Networks BSS/UTRAN Dual-Stack BSS/UTRAN IPv6 nodes communicating over IPv4 BSS/UTRAN IPv4 nodes communicating over IPv6 BSS/UTRAN IPv6 node communicating with IPv4 node BSS/UTRAN IPv4 node communicating with IPv6 node Figure 5.14 RFC 3574 and RFC 4215 transition scenarios. Although, IMS is not really within the scope of this book, the discussion about the IP version used in IMS has had implications for the transition scenarios of the packet service as well. 3GPP documented IMS transition scenarios in the technical report 23.981 'Inter- working aspects and migration scenarios for IPv4-based IP Multimedia Subsyste