[j-nsp] acceptable/good laser receive power in case of different interfaces

[Jonathan Lassoff]

On Tue, Aug 2, 2011 at 2:26 PM, Martin T <m4rtntns at gmail.com> wrote:
> What is the acceptable Rx power in case of SFP/XFP? For example, here
> are XFP Tx and Rx signals from six FXP's:
>
> 1:
> Laser output power                        :  1.2920 mW / 1.11 dBm
> Laser rx power                            :  0.0285 mW / -15.45 dBm
>
> 2:
> Laser output power                        :  0.6420 mW / -1.92 dBm
> Laser rx power                            :  0.3054 mW / -5.15 dBm
>
> 3:
> Laser output power                        :  0.4230 mW / -3.74 dBm
> Laser rx power                            :  0.5092 mW / -2.93 dBm
>
> 4:
> Laser output power                        :  0.4180 mW / -3.79 dBm
> Laser rx power                            :  0.4208 mW / -3.76 dBm
>
> 5:
> Laser output power                        :  1.0920 mW / 0.38 dBm
> Laser rx power                            :  0.1801 mW / -7.44 dBm
>
> 6:
> Laser output power                        :  0.7680 mW / -1.15 dBm
> Laser rx power                            :  0.3337 mW / -4.77 dBm
>
>
> Is there some sort of pattern? It looks like if the Rx signal is
> lower, the Tx is higher?

Yes, usually. Unless you have a perfect conductor or transmission
medium between the transmitter and receiver, there is bound to be some
loss.
TX is the optical power going out of the device, RX is coming into it.

> And what can one consider a decent Rx laser
> power level?

Personally, I would start to get concerned around -13bdm to -15dbm.
The actual thresholds will depend heavily on the sensitivity of the receiver.

Depending on your platform, there's probably some good information
when you run "show interfaces diagnostics optics"

Cheers,
jof