LX sfp minimum range

Holmes,David A dholmes at mwdh2o.com
Thu Jan 26 12:46:44 CST 2012


I have found that -5dB or -10dB attenuators must be used on the send or receive strands between Cisco LX connected switches at relatively short distances 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 at smugmug.com]
Sent: Thursday, January 26, 2012 9:41 AM
To: Pierre-Yves Maunier
Cc: nanog at 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 at maunier.org>wrote:

> 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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