Reducing both power consumption and the ecological impact of networks has become a priority. Solutions which allow us to reduce these factors are based on all-optical technologies. All-optical rings are beginning to be deployed as metropolitan networks and new more energy efficient equipments are being proposed. We present one of these equipments and explain how to reduce the CAPEX of such networks by properly dimensioning them. Receivers located in nodes read information from wavelengths. We study a dimensioning problem which consists in minimizing the number of wavelengths and the total number of receivers in a ring for a given traffic matrix. We prove that this problem is NP-complete and propose a heuristic algorithm. The solution has been validated under realistic traffic conditions and achieved near-optimal results. The solution could be extended to wider networks if we consider working with multi-ring networks.