1 Introduction
Currently, UMTS networks are rolled out to complement existing GSM networks. As most UMTS mobiles will also support GSM, the question of which system to select for a given service emerges. A simple solution would be to use UMTS where available and GSM only as a fall back system for areas where UMTS is not available yet. However, as radio resources and infrastructure are costly, the need for more intelligent mechanisms to balance the load between the two systems arises.