In this paper, we propose a method to optimally partition a network's net capacity into circuit and packet switched channels. In our approach, the packet/burst switched channels are modeled as overflow channels. The overflow occurs from a group of circuit switched primary channels, which are semi-permanently allotted to a traffic source. Such a network provides balance between the statistical multiplexing gains of packet/burst switched channels and the minimum switching complexity of the circuit switching paradigm. We apply our design approach to optical core networks in which the complexity of packet/burst schemes are balanced with the cheap bulk carrying capacity of circuit switched channels. The blocking performance of various combinations of primary and overflow channels is analyzed and discussed, and optimized.