Taking Turns with Adaptive Cycle Time and Immediate Tagging: A Decentralized Upstream Media Access Scheme for Long-Reach PON

Several centralized algorithms have been proposed for bandwidth-allocation in passive optical networks (PONs); making the optical line terminal (OLT) in the central office the intelligent device that arbitrates time-division access to the shared upstream channel. When the distance between the OLT and optical network units (ONUs) is extended from 20 km to 100 km and beyond, as suggested by next generation long-reach PONs, it becomes difficult for centralized algorithms to maintain their performance and to support service differentiation for real-time applications. This is because these algorithms are based on bandwidth negotiation messages frequently exchanged between the OLT and ONUs, which become seriously delayed, thereby delaying packet transmissions and causing the performance to degrade. Decentralized schemes, on the other hand, are independent of the OLT distance and can perform better with such extended reach. In this paper, we introduce and enhance the performance of a decentralized scheme for the emerging LR-PON. Simulation results show that the proposed scheme can significantly reduce upstream packet delays below those of centralized algorithms by 80% while keeping a high throughput.