onse is sent by the eNodeB to the MME to indicate that the radio bearers have been set up. 7. PDN Connectivity Complete message is sent from the UE over the eNodeB to the MME to indicate the UE has finished the PDN Connectivity procedure. 8. Bearer Modification procedure between the MME and the SGW sets up the location of the eNodeB to the SGW. 9. The upper layer traffic can start to be transferred between the UE and the PGW. 2.3.2 User-Plane Protocols We showed in the previous section how the connections between the UE and the network are managed. Now that we have successfully created a connection it is time to transmit some user-plane IP packets. The user-plane protocols make sure the user packets make it from one side of the network to the other. Conceptually, this is relatively simple: the user packet is either sent from the UE in the upstream direction, or the packet enters the network at the GGSN in 2G and 3G, or at the PGW in EPS. In order to make sure that a packet makes it safely through to the other side, the packet has to be wrapped in the right protocols, which carry the packet over the different interfaces. As in all IP networks, the IP packets can get lost in the process. However, the user-plane protocols make sure the user packets have the best possibility of getting through. All three systems, 2G-GPRS, 3G-GPRS, and EPS are a slightly different. Therefore, we shall examine these separately: Deploying IPv6 in 3GPP Networks 2G-GPRS In Figure 2.5 we learned the user plane protocol architecture for 2G-GPRS. We can see that there are three interfaces that the packet has to travel over - the GSM radio interface (Um), the radio network interface between the BSS and the SGSN (Gb), and the core network interface between the SGSN and the GGSN (Gn). However, the IP packet comes in contact only with two protocols - the SNDCP and GTP. The lower layer protocols provide services to the upper layer protocols including transport, over the radio interface retransmission, and ciphering. In the following, we shall onl