 Regarding the protocols let's continue our discussion. We are going to look at two alternatives. The dominant alternative being the GTP protocol aka the generalized packet radio service tunneling protocol. What it means is that the user equipment encapsulates signaling as well as its data using the legacy gprs encapsulation format. Since the existing 3GPP architecture as the SESN network element still there so this legacy provisioning helps in achieving interesting scenarios. So we are going to look at the situations where GTP works and then its alternative protocol implementation through the proxy mobile IP version 6. So GTP tunnels which carry either user traffic or the control traffic are established between the serving gateway and the packet gateway. GTP user is for the user traffic and control GTP C is for carrying the signaling traffic. For 3GPP radio access networks including UTRAN and G-RAN for GPRS the serving gateway actually acts more like a relay agent on behalf of the user equipment towards the packet gateway. For the dual stack mobile IP version 6 scenario the interface S2C is used over the GTP. As an alternative to the GPRS tunneling protocol we also have the proxy mobile IP version 6. It is used to carry control signaling over the S5-S8 interfaces. Now the options that we have either for GTP and the dual stack depends on the implementation at the user equipment as well as the radio access network. So let's quickly have a recap again. We look at the interfaces which use GTP. We have the S5-S8 interface which uses GTP C and GTP U over UDP over IP. Then we have X2 interface. We haven't discussed it but it is interenote B user traffic. Then we have the S4 interface. We haven't discussed it but it also implements GTP. We have S2B interface that uses GTP. The other alternative that is the proxy mobile IP version 6 also has interesting deployments and interesting application scenarios such as S2A that is the packet gateway has an interface with the trusted IP connectivity access network. It is implemented as the control plane. Likewise S2A is also implemented as the user plane. Especially in the control plane we see we have proxy mobile IP version 6 over IP version 4 and IP version 6.