Each AWG
output port is connected further on with a PSC performing the power-splitting operation
for a single wavelength channel selected previously by the AWG component. This way,
all ONUs connected to a given PSC module receive the same downstream channel, ?»3,
thus making this scenario a simple CWDM overlay over the standard EPON structure,
where ONUs are unaware of any existing multiple wavelength structure in the
network. Such an approach has one huge advantage??”namely a high degree of backward
compatibility with existing PON equipment (no dynamic wavelength tuneability
is required for ONUs operating at predefined downstream and upstream channels).
Unfortunately, there are more drawbacks to such a system because static wavelength
assignment through AWG routing operations causes stock problems for the network
operator; ONUs cannot be switched between different domains without retuning the
receiver filters and replacing the laser transmitter module. Additionally, the network
operator must keep track of the wavelength domain ONU assignment by hand, since
the system is unaware of this fact. There are also concerns with the dynamic allocation
of resources because in this case, it is virtually impossible to effect this particular function.
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