The introduction of broadband ATM networks and services will raise new operational issues. An area of significant challenge to the network operators will be network dimensioning. ATM networks differ from today's STM networks in that they will have to provide acceptable performance with respect to not only call blocking, but also cell loss and cell delay. Consequently, it is important to understand the interaction of call blocking and cell loss/delay in ATM networks. The paper presents a method of exploiting the interaction of call blocking and cell loss performance in order to efficiently operate the ATM networks. Specifically, the paper demonstrates that when the network is dimensioned or engineered to meet an appropriate call blocking objective, the cell loss performance perceived by the accepted calls can be significantly better than the cell loss objective set for the connection admission control (CAC) to admit or deny a call. >