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Posted by Winston on September 9, 2006, 11:12 am
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I originally posted:
>> I've always thought 55 dBmV was the maximum upstream power level cable
>> modems are capable of. Tonight while speaking to a Time Warner / Road
>> Runner tech. support guy, he said he'd seen numbers up to 65 and that
>> his DOCSIS monitoring software showed anything up to 58 as green, up to
>> 62 as yellow, and above 62 as red (I may be off by 1 in those cutoffs,
>> but roughly that, and all the numbers were >55).
>> Anyone know what the story is? ...
> Well, the DOCSIS 1.0 spec stated that a modem must transmit from +8dB
> to +58dB.
And indeed, I've now seen +58dB from a Motorola 4200, indicating that at
least some cable modems do go higher than +55.
> Manufacturers were allowed to have their modems transmit higher levels
> if they wanted, but the spec says 8-58dB.
Thanks for confirming that.
> [...] depending on the modem, it may or may not show a change, and the
> CMTS may take the power level change into account and not need to make
> the modems transmit higher (Cisco uBRs know that the levels are
> different, Arris Pizza boxes did not, IIRC).
...
> At any rate, your cable tech needs to go through the class again.
> Any modem transmitting higher than about 55dB should be investigated.
In my conversation with him, it's RR's DOCSIS monitoring software that
shows green for anything up to 58, yellow up to 62, or red if higher, so
I'm not going to fault him for using the tool he's given. However, if
those cutoffs are unadjusted copies of the upstream power level, it does
sound like the monitoring software's cutoffs are too high.
Thanks,
-WBE
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