Towards More Dynamic Energy-Efficient Bandwidth Allocation in EPONs

Power conservation in passive optical networks (PONs) has been an active area of research since the cyclic sleep-mode was first proposed for optical network units (ONUs). Many studies have then settled upon locking downstream and upstream transmissions for each ONU in a cyclic fixed slot, thus allowing the ONU to switch to sleep-mode for the rest of the transmission cycle. However, such fixed allocation limits the flexibility and dynamicity of the bandwidth allocation and leads to upstream underutilization. Moreover, to maximize power conservation, the cycle duration used must be long enough to make up for mode-switching overheads, which significantly degrades the network performance in terms of packet delays. In this paper, we develop a novel energy-efficient framework for Ethernet PONs (EPONs). To that end, we propose different upstream allocation schemes to improve the fixed-slot performance while maintaining energy-efficiency at acceptable levels. We also propose a more accurate arrangement for downstream-upstream locking. Moreover, we use a long-reach PON setting, where the long propagation delays impact the network performance posing further challenges to the bandwidth allocation. Numerical results show that, under heavily loaded network conditions, packet delays can be reduced by around 60% at an additional power cost of less than 5%.