5
Radio Access Network Architecture
5.1 Introduction
This chapter gives a wide overview of the Universal Mobile Telephone System (UMTS) architecture, including an introduction to the logical network elements and the interfaces. The UMTS utilizes the same well-known architecture that has been used by all main second-generation systems and even by some first-generation systems. The reference list contains the related 3GPP specifications [1–24].
The UMTS consists of a number of logical network elements that each has a defined functionality. In the standards, network elements are defined at the logical level, but this quite often results in a similar physical implementation, especially since there are a number of open interfaces (for an interface to be ‘open’, the requirement is that it has been defined to such a detailed level that the equipment at the endpoints can be from two different manufacturers). The network elements can be grouped based on similar functionality, or based on which sub-network they belong to.
Functionally, the network elements are grouped into the Radio Access Network (RAN; UMTS Terrestrial RAN (UTRAN)) that handles all radio-related functionality, and the Core Network (CN), which is responsible for switching and routing calls and data connections to external networks. To complete the system, the User Equipment (UE) that interfaces with the user and the radio interface is defined. The high-level system architecture ...
