  A wide array of dynamic bandwidth allocation (DBA) mechanisms have recently
been proposed for improving bandwidth utilization and reducing idle times and
packets delays in passive optical networks (PONs). The DBA evaluation studies
commonly assumed that the report message for communicating the bandwidth
demands of the distributed optical network units (ONUs) to the central optical
line terminal (OLT) is scheduled for the end of an ONU's upstream transmission,
after the ONU's payload data transmissions. In this article, we conduct a
detailed investigation of the impact of the report message scheduling (RMS),
either at the beginning (i.e., before the pay load data) or the end of an ONU
upstream transmission on PON performance. We analytically characterize the
reduction in channel idle time with reporting at the beginning of an upstream
transmission compared to reporting at the end. Our extensive simulation
experiments consider both the Ethernet Passive Optical Networking (EPON)
standard and the Gigabit PON (GPON) standard. We find that for DBAs with
offline sizing and scheduling of ONU upstream transmission grants at the end of
a polling cycle, which processes requests from all ONUs, reporting at the
beginning gives substantial reductions of mean packet delay at high loads. For
high-performing DBAs with online grant sizing and scheduling, which immediately
processes individual ONU requests, or interleaving of ONUs groups, both
reporting at the beginning or end give essentially the same average packet
delays.
