[c-nsp] Interpreting DOM outputs

John Gill johgill at cisco.com
Sat Dec 31 13:18:50 EST 2011

Hi Rob,
-4.9 dBm is indeed stronger than -6.9dBm.
For example:
-4.9 dBm is  .32mW
-6.9 dBm is  .20mW

These are negative values since 0dBm is the reference point of 1mW and 
you are looking at values below this.

A greater value indicates higher power.  So, you can say this is usually 
better, except in the extreme cases where you are flooding the receive 
path with too much light, maybe connecting different transceivers over 
short distances for example (LX and SX over 1m).

Anton made a good point - there can be some variance in these 
measurements from component to component so don't use them as absolute 
fact, but rather look at the data over time which can indicate a fiber 
or even a transceiver problem.

John Gill

On 12/31/11 12:10 PM, Robert Hass wrote:
> On Sat, Dec 31, 2011 at 6:02 PM, Anton Kapela<tkapela at gmail.com>  wrote:
>> That is, these measurements are best-used as a referential figure, not
>> absolute -- meaning you ought to start polling&  storing them now for
>> the most utility to be found in troubleshooting later. ;)
> Thanks for explanation.
> But I'm still unsure regarding my questions of understanding:
> Tx Power '-4.9' better/stronger than '-6.9'
> Rx Power '-9.6' is better/stronger than '-11.2'
> My above understanding is correct or incorrect ?
> Thanks,
> Rob
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