Taking Turns with adaptive cycle time - an upstream media access scheme for extended-reach FTTx

Several centralized algorithms have been proposed for upstream 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 beyond 100 km, as suggested by next generation long-reach PONs, it becomes difficult for centralized algorithms to support service differentiation required 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, when the network is extended, causing the performance to degrade. In this paper, we propose a distributed scheme for the emerging LR-PON while also allowing centralized control over the access network. Simulation results show that the average upstream packet delay can be significantly decreased below that of centralized algorithms while maintaining a high throughput.