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

2.2 Evolved UMTS Concepts

This section describes the main concepts driving the structure of Evolved UMTS networks, through the following sub-sections:

• The move towards ‘packet only’ architecture.
• The evolution towards a fully shared radio interface.
• The opening towards other access types.

2.2.1 A Packet-Only Architecture

In order to understand the major trends of evolved 3G architecture, it is necessary to look at the main steps of wireless network evolution, starting with 2G networks.

(i) 2G Initial Architecture

2G GSM cellular networks were initially designed for voice and circuit-switched services. For that reason, the architecture of such networks was comparatively simple and comprises two main parts:

• The Access Network part, which includes the radio interface as well as the network nodes and interfaces supporting radio-related functions. In initial 2G GSM systems, the radio interface was specifically designed and optimized for voice or low bit rate circuit data transmission.
• The CS part – or circuit-switched core network domain providing circuit services support (this includes call setup, authentication and billing) and inter-working with classical PSTN (Public Switched Telephone Network).

(ii) 2G Packet Evolution

With the emergence of IP and Web services, 2G GSM networks eventually evolved to efficiently support packet data transmission:

• The Access Network part was partly redesigned to support packet transmission and shared resource allocation schemes – as for GPRS and ...