Wavelength contention resolution in WSS based ROADMs

WSS (wavelength selective switch) based ROADM (reconfigurable optical add/drop multiplexer) node is vital for telecom networks by rapidly re-routing wavelength channels in a multi-directional, degree-upgradeable way. In the conventional WSS based ROADM, which is not equipped with any wavelength converters, wavelength conversion is frequently resolved by a pair of back-to-back transponders in the add/drop part. However, this conventional contention resolution scheme transfers the conflicted demands to the client side and will interfere with the demands that already exist in the add/drop part and therefore severely affect the blocking performance for its special constraints. In this paper, we first reveal through simulation that the conventional contention resolution scheme has inherent shortcomings by blocking performance analysis. Then, we propose a new contention resolution scheme, which converts wavelengths with tunable wavelength converters and add/drop demands as usual. We compare inside the WSS based ROADM the proposed contention resolution scheme with the conventional contention resolution scheme in relative costs, conversion efficiency and blocking performance. Results show that the proposed contention resolution scheme has improved the blocking performance than the conventional one without expanding the dimension of the add/drop part at a lower relative cost.