[148943] in North American Network Operators' Group
RE: LX sfp minimum range
daemon@ATHENA.MIT.EDU (Holmes,David A)
Thu Jan 26 13:47:12 2012
From: "Holmes,David A" <dholmes@mwdh2o.com>
To: Jon Heise <jon@smugmug.com>, Pierre-Yves Maunier <nanog@maunier.org>
Date: Thu, 26 Jan 2012 10:46:44 -0800
In-Reply-To: <CAGaZ0PyZJ8tJrocHmva13eSAMOhs6=g=5AbVMWg6Sw8J92UUew@mail.gmail.com>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
I have found that -5dB or -10dB attenuators must be used on the send or rec=
eive strands between Cisco LX connected switches at relatively short distan=
ces of < 1 km over standard singlemode fiber.
Other Vendors' SFPs rated up to 25 km do not need attenuators at distances =
<1 km.
-----Original Message-----
From: Jon Heise [mailto:jon@smugmug.com]
Sent: Thursday, January 26, 2012 9:41 AM
To: Pierre-Yves Maunier
Cc: nanog@nanog.org
Subject: Re: LX sfp minimum range
Awesome, i got some single mode LC LC fiber off monoprice, sounds like i
should be all set for this. Thanks for everyones info
- Jon
On Thu, Jan 26, 2012 at 6:24 AM, Pierre-Yves Maunier <nanog@maunier.org>wro=
te:
> 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 configurati=
on
> 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 usuall=
y
> 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 s=
o
> even with a SFP TX at -3dBm, you won't receive at the Max RX sensitivity.
>
> --
> Pierre-Yves Maunier
>
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