work and device vendors reluctant to implement its required components as part of their default feature sets. 5.5 Transition Impacts on 3GPP Architecture We have now discussed the different transition technologies, and the 3GPP specific scenarios where they apply. Now it is time to look at how the transition affects the 3GPP architecture itself, and its support functions. The 3GPP networks include quite a lot of elements and functionality that is not visible in the 3GPP architecture, but is still vital for the system. These include DHCP, AAA, and DNS servers. Sometimes the operators also have additional infrastructure that is transparent to the user, but very much part of the operator's infrastructure. In this section, we will look at the impacts that the transition technologies have on the 3GPP architecture - including new elements, and what the impact transition to IPv6 has on all the functionality that 3GPP networks rely on. 5.5.1 Transition Impact on the Supporting Infrastructure The 3GPP network architecture pictures we saw in Chapter 2 show the 3GPP network elements, and present almost a sterile picture of the network architectures. However, in reality the network is much bigger than what is visible from those pictures. The little lines between the little boxes are actually more than just point-to-point connections (except for the radio interface) - they are complete networks with cables, wireless microwave links, IPv6 Transition Mechanisms for 3GPP Networks switches, and routers. In addition to these networks, there are also other networks that are not visible. These networks include the operations and management network, which is used to configure, monitor, and maintain the network elements themselves. And it is not only packet network infrastructure that is needed. A complete infrastruc- ture of support functions is needed to drive a mobile network. The infrastructure includes DNS servers, AAA servers as described in Chapter 4, network management infrastruc- ture, and the complete billing and charging in