Taking Turns With Adaptive Cycle Time a Decentralized Media Access Scheme for LR-PON

The extended network span of next-generation long-reach passive optical networks (LR-PONs) results in extremely long propagation delays that severely degrade the performance of centralized bandwidth allocation algorithms. This is because these algorithms are based on bandwidth negotiation messages frequently exchanged between the optical line terminal (OLT) in the central office and optical network units (ONUs) near the users, which become seriously delayed when the network is extended. To address this problem, we propose a decentralized media access scheme for emerging LR-PONs to make the performance independent of the physical length between the OLT and ONUs. We also maintain centralized control over the network, usually missed in conventional decentralized schemes, to support and manage quality of service according to user service level agreements. The scheme thus combines decentralized media access with centralized control to meet the special requirements of emerging LR-PONs. We investigate the performance of the proposed scheme in contrast with centralized schemes under worst case conditions. We also explore various approaches to further enhance the performance of our scheme. Simulation results show that the average upstream packet delay can be decreased by 60% while also maintaining a high throughput.