[802.3_NGMMF] modal noise and commonality with 100G BiDi
I'm picking up the trail where it was left at the end of today's
ad-hoc teleconference.
I understand how adding 0.3 dB of extra transmit OMA would address the
modal noise penalty. I also understand how that same 0.3 dB aligns
the 400G-SR4.2 transmitter spec with that of 100G-BiDi. Two birds
with one stone, so to speak.
Where I'm having difficulty is resolving both the modal noise penalty
and getting to interoperable optical specs between the two with the
same power boost. The key word here is interoperable, which goes
beyond just spec alignment. My rationale is as follows. If the power
boost is needed to cover additional modal noise penalty for
400G-SR4.2, then is it also likely to be needed for the same purpose
for 100G-BiDi. That means 0.3 dB is insufficient to do both, and a
spec change to the 100G-BiDi MSA may also be needed. Further, any
such changes present a moving target for spec alignment with
400G-SR4.2.
One can argue that any inadequacy in the 100G-BiDi power budget is not
the concern of 802.3cm. But while Jonathan Ingham's Tx-power-boost
rationale has changed from interoperability to commonality (because of
blowback on the prior call), the underlying major benefit off
increased market potential comes not from optical spec alignment, but
from enabling interoperability.
So while adding 0.3 dB covers both the commonality and modal noise
issues, the flank may remain open on error performance of 100G-BiDi.
Given that the graph of market sales volume of 100G-BiDi showed
substantial numbers (i.e. hundreds of thousands) of ports shipped, it
would be a valuable data point to get feedback from the purveyors if
links are operating without significant reports of elevated BER. In
other words, is the 100G-BiDi specification, as it now stands,
supporting at least the promised BER performance in virtually all
installations?
That is a difficult question to answer, but BER trouble report
incidences are the converse and are more tractable. So here is
another way of asking. Are BER-related trouble reports running at
normally acceptable levels for 100G-BiDi?
Regards,
Paul
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