A nesting ranging algorithm for a Hybrid WDM/TDM PON with colorless Reflective-ONUs under different distances OLT-ONUs

To reduce costs and cumbersome laser provisioning at the Optical Network Unit (ONU) user level in an access Passive Optical Network (PON), the use of a Reflective-ONU (R-ONU) is a good choice for up-data transmission. An optical carrier is sent by the Optical Line Terminal (OLT) at the Central Office, and a device at the ONU modulates the carrier with the upstream data. This allows all ONUs to be equal and colorless, without a light source in a Hybrid WDM/TDM architecture. A Dynamic Bandwidth Allocation is placed at the OLT, managing the lasers and photodetectors shared by all R-ONUs. The OLT laser and photodetector employed in an up-data transmission must be tuned for each ONU and a particular Round Trip Time (RTT), which is twice the propagation time from OLT to ONU. When an R-ONU is served by a laser, the photodetector must also be available after the RTT to demodulate the up-data. We propose a novel nesting ranging algorithm to deal with large different distances OLT–ONUs avoiding collisions and minimizing the delay under Priority Queuing with Quality of Service (QoS).