TABLE OF CONTENTS When a UMTS subscriber originates (or terminates) a call to access circuit- or packet-switched services, the connection is controlled by the core network. If the desired service is provided by an external network, the core network further provides interworking functionality. The core network also manages the mobility of the UE within its home network (i.e. the network where the subscription data is stored) and within a visited network in the case where the UE is roaming. Finally, the core network performs high-level security functions such as location updating and authentication, and controls charging and accounting aspects.
This chapter will give an overview of the UMTS core network as specified by Release 99, i.e. the 3GPP set of specifications used as a reference for the first UMTS network deployments. This chapter also outlines certain procedures handled by the core network which are studied in more detail in Chapter 8.
As shown in Figure 4.1, the basic core network architecture for UMTS can be seen as a combination of GSM network subsystem (NSS) and GPRS backbone. The overall UMTS architecture can be seen as the combination of a completely new radio network (UTRAN) in the "front end" of an "evolved" GSM Phase 2+ core network (see also Chapter 2).
The pragmatic choice taken for this architecture resides in the concern of 2G operators to make cost-effective the investments made on GSM and...
