Evolved Packet System (EPS): The LTE and SAE Evolution of 3G UMTS

2.3 Overall Evolved UMTS Architecture

Figure 2.6 describes the overall network architecture, not only including the Evolved Packet Core and Access Network, but also other blocks, in order to show the relationship between them. For simplification, the picture only shows the signalling interfaces. In some cases, both user data and signalling are supported by the interface (like the S1, S2 or 3G PS Gi interfaces) but, in some other cases, the interfaces are dedicated to the Control plane, and only support signalling (like the S6 and S7 interfaces).

The new blocks specific to Evolved UMTS evolution, also known as the Evolved Packet System (EPS), are the Evolved Packet Core (or EPC) and the Evolved UTRAN (or E-UTRAN).

Other blocks from the classical UMTS architecture are also displayed, such as the UTRAN (the UMTS Access Network), the PS and the CS Core Networks, respectively, connected to the public (or any private) IP and Telephone Networks. The IMS (IP Multimedia Subsystem) is located on top of the Packet Core blocks and provide access to both public or private IP networks, and the public telephone network via Media Gateway network entities. The HSS, managing user subscription information is shown as a central node, providing services to all Core Network blocks of 3G and evolved 3G architecture. The picture does not represent the nodes involved in the support of charging function. The architecture and interfaces related to charging are described in a specific section, further in ...