The adaptive cross validation (AVC) method is a very general method for system performance optimization. It can be used in the design phase to determine how a system should be designed, or it could be used during the operational phase to dynamically determine the control of the system. A novel formalism, suitable for presentation of mathematical models in technical publications, is used to formally describe the studied system, which is a circuit switched network. The generality of the method implies that it, is valid for general distributions describing inter-arrival and holding times, as well as for complex routing methods which make an analytical approach infeasible. The method is used for real-time control of two routing algorithm parameters. The results are very satisfactory.