We propose a simple and robust automatic strat- egy for managing SDH/SONET and/or ATM virtual paths in real time to handle slow traffic variations. It consists of on-line measurements of offered traffics followed by the design and possi- ble implementation of a new virtual path network in a repeated cycle. Methods and parameters for traffic measurements and network updating are studied and optimised to achieve maximal traffic carrying capability at minimal cost. Applying our strat- egy to networks subject to partially unknown, variable traffics we discover a considerable adaptivity, large savings in transmis- sion capacity, and a performance far better than achieved by deterministic management.