Range using single-mode SFPs across multi-mode fiber

Keegan Holley keegan.holley at sungard.com
Wed Dec 14 21:08:26 UTC 2011

2011/12/14 Jeff Kell <jeff-kell at utc.edu>

> 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
> They specify that line conditioning cables were used.  I would say if
you're going to bother purchasing why not purchase SM?

> 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.

What distances?

>  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 don't think changing core sizes in the middle would work even with SM

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