Abstract
We investigate optical network unit (ONU) grant scheduling techniques
for multichannel Ethernet passive optical networks (EPONs), such as wavelength
division multiplexed (WDM) EPONs. We take a scheduling theoretic approach
to solving the grant scheduling problem. We introduce a two-layer structure
of the scheduling problem and investigate techniques to be used at both layers.
We present an extensive ONU grant scheduling simulation study that provides:
1) insight into the nature of the ONU grant scheduling problem and 2) indication
of which scheduling techniques are best for certain conditions. We find that
the choice of scheduling framework has typically the largest impact on average
queueing delay and achievable channel utilization. An offline scheduling framework
is not work conserving and consequently wastes channel resources while waiting
for all ONU REPORT messages before making access decisions. An online scheduling
framework, although work conserving, does not provide the best performance
since scheduling decisions are made with the information contained in a single
ONU REPORT. We propose a novel online just-in-time (JIT) scheduling framework
that is work conserving while increasing scheduling control by allowing the
channel availability to drive the scheduling process. In online JIT, multiple
ONU REPORTs can be considered together when making scheduling decisions, resulting
in lower average queueing delay under certain conditions and a more effective
service differentiation of ONUs.
© 2008 IEEE
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