LX sfp minimum range

Pierre-Yves Maunier nanog at maunier.org
Thu Jan 26 08:24:01 CST 2012


2012/1/26 David Storandt <dstorandt at teljet.com>

> You can put a 3dB or 5dB optical pad on the link if the receiver can't
> handle zero-distance optical power.
>

We're using SFP LX for a couple of years even in back to back configuration
for equipments within the same rack with a 1 meter patch cord without any
problem.

Max TX is -3dBm, Max RX sensivity is -3dBm so there is no problem.

1. I don't think I've ever had a LX SFP that TX at -3 dBm, they're usually
around -5 to -7 dBm.

and example in a live router :

pymaunier at re1.tcr1.rb.par> show interfaces diagnostics optics ge-7/3/* |
match "Laser output power  "
    Laser output power                        :  0.3160 mW / -5.00 dBm
    Laser output power                        :  0.1800 mW / -7.45 dBm
    Laser output power                        :  0.2600 mW / -5.85 dBm
    Laser output power                        :  0.3210 mW / -4.93 dBm
    Laser output power                        :  0.3070 mW / -5.13 dBm
    Laser output power                        :  0.3200 mW / -4.95 dBm
    Laser output power                        :  0.3180 mW / -4.98 dBm
    Laser output power                        :  0.3140 mW / -5.03 dBm

2. You can assume a patch cord add between 0.2 to 0.5 dB of attenuation so
even with a SFP TX at -3dBm, you won't receive at the Max RX sensitivity.

-- 
Pierre-Yves Maunier


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