 similar to the Gn- and Gp-interfaces in GPRS. The S5- and S8-interfaces comprise the user and control planes. S6a interface connects the MME and the HSS. S11 is a control-plane interface connecting the MME and SGW. SGi is the interface connecting the EPS to the external IP networks, such as the Internet. When looking at the EPS user plane in Figure 2.11, the legacy from the previous 3GPP architecture is noticeable. When comparing the EPS user plane to the 3G-GPRS user plane in Figure 2.8, the basic difference between the two can be found in the naming of the interfaces, and of the nodes. However, again the difference is in the details. The radio interface, LTE-Uu is completely new, and it is based on the Orthogonal Frequency- Division Multiple Access (OFDMA) technology instead of TDMA or WCDMA in the previous generations. In addition, we can see differences in the protocol versions when we take a closer look at the 3GPP protocols in the next section. The differences between EPS and legacy are more apparent at the control plane. Figure 2.12 depicts the EPS control plane. Many of the interfaces are quite different from the previous generations. The main difference is that the control plane goes through some different elements from the user plane. In addition, there are no SS7 based interfaces anymore. All the interfaces are on IP. The protocol architecture shown in Figures 2.12 and 2.11 is sometimes called GTP based architecture. This is to distinguish it from another architecture variant that 3GPP has defined for EPS - the Proxy Mobile IP (PMIP) based EPS architecture [30]. The difference between these two architectures, however, at this level is very small. Therefore, we will concentrate at this point on the GTP variant, and we will look at the PMIP variant later, when we look in more detail at the 3GPP protocols. Deploying IPv6 in 3GPP Networks GTP-C GTP-C GTP-C S1-AP S1-AP SCTP/IP SCTP/IP UDP/IP UDP/IP UDP/IP RLC/MAC RLC/MAC LTE-Uu eNodeB S1-MME Figure 2.12 EPS control-plane protocols. 2.2.4 Control and User P