 then the overbooking factor is calculated as follows. factor (OB_factor>1) (8.1) The total requested bandwidth by N Node Bs is expressed as value OB _factor should be greater than or equal to 1. If OB _factor equals to 1, that means no overbooking is applied as the backbone link offers the same bandwidth to each last mile link as its requested bandwidth C. If OB _factor is larger than 1, the backbone link is overbooked as the total requested bandwidth by N Node Bs is above the given backbone link capacity. A higher value of the OB factor means a more aggressive or higher overbooking, i.e. less capacity is offered on the backbone link. In this chapter, overbooking will be investigated for both ATM and IP RAN. Their impacts and various important aspects that have influence on the overbooking will be discussed. More importantly, analytical approaches will be presented, which can estimate the optimum overbooking factor for network dimensioning. The estimation is based on the developed analytical models for dimensioning the multi-Jub RAN. And the estimated overbooking factor is validated with simulations. 8 Dimensioning for Multi-lub RAN Scenario 8.2 Dimensioning for Circuit-Switched Traffic As introduced in Chapter 1, the circuit-switched traffic is subject to a connection admission control (CAC) function. In the star topology multi-lub RAN, it is considered that the CAC function is performed through the UTRAN network. That means, a new connection needs to reserve transport bandwidth throughout the radio access network domain and it can be only accepted to transport if both the last mile link and the backbone link provide sufficient bandwidth to accommodate the requested bandwidth of the new connection. However, overbooking is allowed on the backbone link. That means, the CAC guaranteed bandwidth on the backbone link can be scaled adequately by taking into account the effect of overbooking. Nevertheless, the degree of overbooking which can be done on the backbone link depends on the QoS requirements and the achieved