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Re: Range using single-mode SFPs across multi-mode fiber
From: Jeff Kell <jeff-kell () utc edu>
Date: Wed, 14 Dec 2011 15:50:47 -0500

On 12/14/2011 3:37 PM, Keegan Holley wrote:

Single mode just has a smaller core size for the smaller "beam" emitted by
laser vs. LED.  it works although I've never done it outside of a lab (MM
is cheaper). As for the distance it theory that should come down to the
optics and your transmit power.  Hopefully this is just a cable connecting
the router to a long line.  I've never heard of a 10K MM fiber run since SX
optics can't shoot that far.  You should be able to get through the 500m or
so that MM optics are rated for, but YMMV (errors, light levels, bounces,
etc etc)

Cisco gives specs for SFP LX over MM (they aren't that great at gig, and really suck at
10G; if you have 50u OM3/OM4 you can do much better at 10G).

See SFP/fiber/distance table at
http://www.cisco.com/en/US/prod/collateral/modules/ps5455/ps6577/product_data_sheet0900aecd8033f885.html

We have run LX-over-MM (62.5) on short building runs as a band-aid until SM is
available, and trying to do all new building MM with 50u OM3/OM4.  We do have some
dependence on 62.5u MM - used by our aging Simplex alarm system - which does
point-to-point looped token ring <*cough*> on the alarm side.  I'm trying to get them to
confirm 50u will work point-to-point, but at some non-alarm-points there would be a
necessary 50-to-62.5 exchange taking place and I'm not certain how to accomplish that
(50->62.5 would likely have tolerable loss, but not 62.5->50).

(I would suspect similar results cross-vendor but YMMV)

Jeff


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