Chapter 5
LTE and SAE Architecture
5.1 Introduction
The evolved 3G system consists of radio and core networks. The core side of the new network is called System Architecture Evolution (SAE) and the radio part is called LTE (Long Term Evolution). It should be noted that SAE was used at the beginning of the standardization, but nowadays the core part is called EPC (Evolved Packed Core). As the term SAE has been established in common terminology, it can be used in parallel with EPC. This book uses both the official standard term, EPC, and the nonstandard SAE.
This chapter presents the functional blocks and interfaces of LTE/EPC. The new architecture is illustrated using comparisons of the solutions with the earlier mobile communications systems.
A protocol layer structure and the functioning of the LTE/EPC protocols are described, and examples are given in order to clarify the principles of each protocol.
The LTE architecture is defined in 3GPP specification 36.401 (E-UTRAN architecture description).
5.2 Elements
LTE is based on flat architecture, meaning that there is only one element type for the radio network, and one element type for the core network [1]. Figure 5.1 shows the high-level architecture of LTE and compares it with the packet-switched domain of the earlier systems.
Figure 5.1 The evolution of network architectures. LTE simplifies the general layout of the network via the flat architecture by providing only packet switched connections.
The overall ...
