s the radio protocols. In UMTS, the RNC is also responsible for header compression. Content compression is not supported in UMTS. The name of the MS has also changed to User Equipment (UE) in UMTS. However, the MS and the UE terminology is used somewhat interchangeably in literature and in the specifications. We will use the UE terminology in this book. Together with the new radio access network, there is a new interface. Instead of Gb-interface, 3G-GPRS has the Iu-interface. Figure 2.8 shows the 3G-GPRS user plane protocols, and Figure 2.9 describes the control plane. If compared to the 2G-GPRS interfaces in Figure 2.5, it can be seen that the Gn-interface has stayed the same. However, there is a significant difference in the Iu-interface compared to the Gb-interface. The Iu-interface is based on the same protocol as the Gn-interface - GTP. In addition, the transport in the Iu-interface has changed to IP from Frame Relay. The 3G-GPRS control plane in Figure 2.9 shows that in addition to the radio interface the Iu-interface has replaced the Gn-Interface in the 2G-GPRS described in Figure 2.6. This change has introduced some new protocols. GMM/SM is, like GMM/SM in the 2G-GPRS, the protocol that performs mobility management and session management functions. Radio Access Network Application Part (RANAP) is a UMTS protocol that carries the higher layer signaling. It runs on the Signalling System No. 7 (SS7) protocol suite [27]. Originally the Iu-interface was specified to be transported only on Asynchronous Transfer Mode (ATM) [28]. However, the standard has been updated to enable any transport network technology to be used. Signalling Connection Control Part (SCCP) is a protocol used in the SS7 protocol suite. Basics of the 3GPP Technologies GMM/SM GMM/SM GTP-C GTP-C RANAP RANAP SCCP/ SCCP/ Signaling Signaling UDP/IP UDP/IP Transport Transport UTRAN Figure 2.9 3G-GPRS control-plane protocols. 2.2.3 Evolved Packet System The newest member of the 3GPP technology family is Evolved Packet System (EPS). As with GSM and 