TABLE OF CONTENTS Compared to the GSM network architecture, the radio access network of UMTS, called the UTRAN ( Universal Terrestrial Radio Access Network), constitutes the main innovation. The UTRAN is responsible for the control and the handling of radio resources, and allows data and signaling traffic exchange between user equipment (UE) and core network (CN). It handles the allocation and withdrawal of radio bearers required for the traffic support on the radio interface and controls some functions related to UE mobility and network access.
The UTRAN architecture and functioning are determined by the characteristics of the new radio access technology based on WCDMA with its two modes UTRA/FDD and UTRA/TDD. We will see for instance that with the use of macrodiversity in UTRA/FDD mode, the mobility handling is partly located in the UTRAN. All functional entities composing the UTRAN and their different roles are described in this chapter. Furthermore, the chapter will also detail the communication protocols used for information exchange on the one hand between UTRAN internal nodes and on the other hand between the UTRAN and the CN. As ATM is the transfer mode chosen for data transport through internal and external interfaces, its principle is also described in this chapter.
As illustrated by Figure 6.1, the UTRAN is the link between the UE and the CN domains through, respectively, the Uu and Iu interfaces. The UE and the CN are described respectively in Chapters 3 and 4. We therefore only focus here on...
