ONU aggregation schemes for TWDM PONS with multiple tuning ranges

Time- and wavelength-division-multiplexed passive optical networks (TWDM PONs) have been regarded as a promising solution to meet the ever-increasing bandwidth demands of optical access networks. To reduce the investment on deploying TWDM PONs, operators can share the network infrastructures, isolated through wavelengths and timeslots. Under such circumstances, ONUs of some network operators can only work in small sets of wavelengths for the convenience of management and security. As a consequence, multiple ONU tuning ranges (fixed/ limited/full tuning ranges) may coexist, which brings challenges to ONU aggregation. With ONU aggregation, ONUs are aggregated into fewer wavelengths for benefits such as energy saving and service protection. In this work, we create mathematical models to determine minimal aggregated wavelengths under various network conditions (traffic load and tuning ranges). We also investigate ONU aggregation schemes which include both determination of minimal aggregated wavelengths and assignment of ONUs to those wavelengths. Our algorithm demonstrates a high success rate and gives explicit ONU migration schemes that assign ONUs to target aggregated wavelengths. The relationship between the number of minimal aggregated wavelengths and network conditions (traffic load and tuning ranges) is also studied. Simulation results show that the number of minimal aggregated wavelengths increases with the traffic load and number of tuning ranges. When the traffic load is relatively low, more tuning ranges result in more aggregated wavelengths. However, with high traffic load, ONU tuning ranges have limited impact on ONU aggregation performance.