ferences in interfaces mean that messages have to be carried by quite different protocols - depending on the characteristics of an interface. The radio interfaces, 2G, 3G, and LTE, are just a single hop long, and therefore they do not have to be routed over network. However, errors or complete loss of a message can easily occur over the radio interface. Therefore, the protocols have to make sure that the messages actually get over the hop with a relatively high probability. In addition, the radio interface is out there in very public space. Anybody could try to listen or even attempt to inject traffic. Therefore, the protocols have to make sure that the integrity and confidentiality of the messages are protected. On the other hand, the protocols within the network itself may have to be transported over the operator's underlying transport network. Sometimes these may be over long distances and over different kinds of transport technologies. Some of these links can be point-to-point (or made to look like point-to-point links by the underlying transport technology). However, they can also be networks of different links. Therefore, many of the protocols within the network are on top of IP. Non-IP-based networking protocols were also used in the networks, especially within the RAN. However, the 3GPP architectures have mostly either replaced these interfaces with IP-based transport, or at least provided an IP-based alternative. Deploying IPv6 in 3GPP Networks In the following, we will be taking a closer look at the most relevant control- and user-plane protocols. 2.3.1 Control-Plane Protocols As described earlier, the control-plane protocols are, as the name suggests, controlling the network. They are used to attach the subscriber to the network, authenticate and authorize the subscriber, and for session and mobility management. Excluding the actual moving of user packets, the whole functionality of the network is performed by the control- plane protocols. All this is extremely fascinating technology, and especially th