Decentralized media access vs. credit-based centralized bandwidth allocation for LR-PONs

Several centralized dynamic bandwidth allocation algorithms have been proposed for Ethernet Passive Optical Networks (EPONs), making the optical line terminal (OLT), located in the central office, the intelligent device that arbitrates time-division access to the shared upstream channel. When the network span is extended to 100 km and beyond, as suggested by next generation long-reach PONs (LR-PONs), the increased propagation delays severely degrade the performance of these algorithms since they are based on bandwidth negotiation messages frequently exchanged between the optical network units (ONUs) and the OLT. In this paper, we propose a decentralized media access scheme for the emerging LR-PON that would enable sooner transmission of upstream packets. We accompany this scheme with centralized control over the network. Through simulation, we compare the performance of the proposed scheme with centralized credit-based schemes that are thought to be able to mitigate the degradation of centralized schemes in LR-PONs. Results show that the proposed scheme is less affected by the network extension and can reduce average packet delays beyond those of credit-based schemes.