Fiber - single vs. multi... recommendations

cfan73
cfan73 used Ask the Experts™
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I've run into this more often the past year, as customers are ready to replace their cable/fiber plants, specifically regarding the decision between deploying pervasive single vs. multi-mode fiber. I know the bandwidth/distance limitations for SMF/MMF (all flavors), and understand the additional expense for SMF optics.  

Having said all of that, I'm looking for any other reasons (to bring to the customer) regarding SMF vs. MMF.  Specifically, if cost were NO object, would there be no reason to recommend SMF for all fiber installations, no matter the distance/BW requirements?

Thanks - as always, reference docs/links are always appreciated.
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Top Expert 2014
Commented:
Sometimes, even if cost is NO object, customers like a guy who says "We can do that for half the price"!

As an example, if you only need to run 10GB/s over 50m, why bother running a SMF?  As you already know it'll cost you more for modules and plugs, and terminating a SMF is harder than MMF so therefore as a result reliability can sometimes suffer if you don't get it right.

I understand your reasoning, but I don't think it's quite as clear-cut as deciding whether to use Cat5e or Cat6, for example.
Sr. Systems Engineer
Top Expert 2008
Commented:
I would respond that there are STANDARDS as to when to use Single vs Multi mode fiber.
Building risers, for example, are almost exclusively Multi-mode. New implementations are now generally 50micron vs 62.5 micron for 10G
Almost exclusively outdoor or burried cable is single mode.
It's pretty simple argument. Inside a building = multimode, outside = single mode.
Having said that, there are places like US Army  military installations that are almost all single mode everywhere as their own "standard".
My 2 cents...
Commented:
Changing the network from multi to single might mean replacing the transceivers on both ends.  That may or may not be an option.  Aside from length limitations, multi-mode fiber works just fine and is cheaper in most cases.  Unless you need 10G or long connections, then multi works fine.

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Commented:
Thanks for the input, guys. I think these responses are confirming what I was getting at - cost is really the only factor in considering SMF over MMF, when distances/BW requirements are removed from the equation.

I understand SMF is typically for long-haul/outdoors, and MMF is typically indoors/shorter - the customer in question is building out a new facility, so they have the option to put in whatever (SMF, OM3/4, etc.).  Not knowing what technologies may come 5+ years from now (beyond 100-Gig Ethernet), and if these will still somehow function over laser-optimized MMF, I could see pulling SMF everywhere would offer protection/future-proofing.

That's really all I was getting at, if there wasn't some other factor (beyond cost) that would prevent certain deployments from functioning over SMF.  It's a physical transport, so it shouldn't matter...

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