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I need to say a bit more about my last comment
about -L budgeting.
The top of the budget adds to -3.0
dBm. -6.2 dBm min Tx OMA 3.2 dB TDP max
The low end is -12.6 dBm. Therefore, the total
budget span is 9.6 dB. D4.3 says 9.4 dB, and this discrepancy indicates an
error.
Option 1
Reduce TDP to 3.0 dB
Keep budget at 9.4 dB
Allocation for penalties stays at 3.2
dB
Option 2
Keep TDP at 3.2 dB Change
budget to 9.6 dB Change allocation for penalties to 3.4
dB
Option 1 is my preference because it lines up with
the 3 dB footnote, helps keep actual deterministic eye closure penalties a
little closer to the VECP value, and changes one less value. In both cases,
cable plant loss stays at 6.2 dB.
Note that the -6.2 dBm term for Tx OMA is 0.2 dB
more than the 6.2 dB cable plant loss above the Rx's -12.6 dBm. This is because
there is ~0.2 dB in the budget for penalties for real Rx's that should not exist
in the ref Rx used for TDP measurements. It is in the spreadsheet, we have used this ~0.2 dB in each of -S and -E budgets, and it
should apply here. If we don't, then we have ~0.2 dB of negative margin in the
model.
I am sensitive to margin because I am also aware of
the additional Fibre Channel market hoping to use the Ethernet hardware but at a
2% speed increase. The speed increase will drive their margins even more
negative.
Comments?
Tom
Stratos NW (425) 672-8035 x105
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