The downstream channel cannot
utilize dual rate transmission in a single wavelength channel due to lack of
burst mode transmission i.e., the OLT sends towards the ONUs a continuous data
stream, consisting of IDLE characters when there is no real data to send.
?– the upstream channel coexistence will most likely be resolved via TDM multiplexing,
where different data rate bursts will be received by the OLT, identified and
then processed accordingly (the so-called dual rate burst mode transmission). The
selected solution presents a number of technical hurdles which will have to be
overcome, such as burst data rate detection, adjustment of trans-amplifier gain,
and so on, and are currently under intensive study in the formed ad-hoc groups.
The dual rate burst mode transmission in the upstream channel is considered a viable
solution mainly due to the proximity of zero chromatic dispersion point for the
G.652 SMF which is the most common type of optical fibre used in PON systems.
Since the transition process from legacy 1 Gbps equipment towards fully symmetric
10 Gbps network will be gradual in most cases and will require significant modifications
of the active equipment in the deployed EPON, it is prudent to be aware of a number of
technical hurdles which lie ahead in this process.
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