[148925] in North American Network Operators' Group
Re: LX sfp minimum range
daemon@ATHENA.MIT.EDU (Pierre-Yves Maunier)
Thu Jan 26 09:24:23 2012
In-Reply-To: <CAExLYCoyFfsDDvxVOtoVTHarLmWGeTw4pAQ9iMRFD1L9kCdxUg@mail.gmail.com>
Date: Thu, 26 Jan 2012 15:24:01 +0100
From: Pierre-Yves Maunier <nanog@maunier.org>
To: David Storandt <dstorandt@teljet.com>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
2012/1/26 David Storandt <dstorandt@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@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
