th packet-switched web and circuit-switched voice services when the OB _factor is above 2. This investigation demonstrates the importance of selecting optimum OB factor to provide a good balance between the costs, i.e. to utilize the bandwidth resource as much as possible, and satisfy the predefined QoS objectives. If A.19 Investigating Overbooking in the ATM-Based UTRAN several QoS requirements need to be fulfilled, then the minimum OB factor should be chosen which satisfies all QoS constrains. Overbooking under different last mile utilizations This part evaluates the impact of different last mile utilizations on the setting of the optimum OB _factor. In the investigated scenarios, there are 4 Node Bs and the last mile link is set to 1 E1 (1.6 Mbps for user plane). Here investigates four different traffic profiles: pure packet-switched web traffic, pure circuit-switched voice, traffic mix with packet-switched traffic dominant (85% web) and voice dominant (60% voice) individually. The last mile utilization varies between 10% and 60%. In Figure A.33, the left diagram shows the selected optimum overbooking factors over different last mile utilizations and the right one shows the resultant backbone link utilizations. It shows that with the increased last mile utilization in terms of higher offered load per Node B, the selected optimum OB factor declines for all traffic profiles. This is because when the offered traffic on the last mile is larger, the room for statistical multiplexing in the aggregated traffic on the backbone link is less and therefore the potential overbooking capability is lower. Moreover, by comparing different traffic profiles we can observe that the selected optimum OB _factor for packet-switched traffic only and packet-switched traffic dominant scenario are similar, and when there is more voice traffic the selected optimum OB factor gets increased and for voice only scenario it becomes the highest. The is because that for the defined 1% packet loss ratio, the voice traffic requires less bandwid