RE: LX sfp minimum range

["Holmes,David A" <dholmes () mwdh2o com>]

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 () 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>wrote:

> 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

This communication, together with any attachments or embedded links, is for the sole use of the intended recipient(s) 
and may contain information that is confidential or legally protected. If you are not the intended recipient, you are 
hereby notified that any review, disclosure, copying, dissemination, distribution or use of this communication is 
strictly prohibited. If you have received this communication in error, please notify the sender immediately by return 
e-mail message and delete the original and all copies of the communication, along with any attachments or embedded 
links, from your system.