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For 25GBASE-ER, my feeling is that we’ve already put the sensitivity as low as it ought to be for APD receivers. The transmitter OMA is also on the high side. So, to budget for MPI, I’d prefer to trade off a small amount of channel loss, leaving the powers as they are. One would expect use cases requiring the full loss budget to be rare, so it doesn’t seem necessary to burden the transmitter or receiver specifications further, unless justification is provided from channel data.
That’s my initial proposal. However if enough people object to the 0.7 dB reduction in sensitivity & SRS, we’ll need to introduce a loss table similar to the one in 100GBASE-DR.
During the ad hoc call there was opposition to the idea of giving users a tradeoff table for insertion loss for the 10km application. The point was that some users would want to operate over existing cable plant currently operating at 10 Gb/s. If we were to accept what I proposed, then those users would still need to check on how many connectors and the RL of each one, before knowing they could use it for 25 Gb/s. At least they would not need to measure channel loss before knowing they could re-use a 10 Gb/s cable.
Is your proposal to not make any allowed trade offs between number of connectors and link loss? If so I think the numbers in the table on slide 6 would be replaced by ticks. I do wonder with such a large difference between TDP and the allowance for penalties whether we should give people a clue what that is for. Maybe split the row into two. One that says “Allocation for TDP” (value of 2.7dB) and the other says “Allocation for other penalties including Multi Path Interference” (value of 0.7dB).
At the ad hoc on Wednesday I took an action to provide the changes that would be needed in the optical link parameter tables for an MPI penalty of 0.7 dB. See the attached presentation for what I think is needed.
The approach is to tighten Rx sensitivity and SRS by 0.7 dB for both the -LR and -ER variants. In addition this proposal tightens the Transmitter reflectance from a maximum of -12 dB to a maximum of -26 dB.
Please use the reflector for discussion of this topic. Our next ad hoc is on Wed June 28th and will be the only one between now and when the sponsor recirculation ballot ends.
P802.3cc Task Force Chair