I. Introduction
As the landscape of mobile network is changing from homogenous networks to heterogeneous networks where several radio access technologies co-exist operators are being faced with the challenges of how to provide quality of service across different access technologies. In such a heterogeneous environment when mobile terminals roam across multiple wireless and mobile networks it is required that networks should support calls with different traffic characteristics and different Quality of Service (QoS) guarantees. During dedicated mode, a mobile terminal (MT) should be able to switch automatically between different radio accesses technologies seamlessly. This process must be carried out without degradation of the quality of user experience (QoE). Unfortunately current mobile networks don't meet this requirement. Therefore as mobile terminals (MTs) move from one access technology to the other the service is interrupted.