Help with fiber SFP's

Unanswered Question
Apr 21st, 2009

My company is currently in the process of building a new multistory building and we plan to run 62.5nm fiber from each floor up to the server room. I talked to Cisco for help because I don't have a whole lot of experience dealing with fiber and they recommended using 1000Base-BX SFP's but as I read about them it seems like they are for single mode fiber, is this true? It seems like I should be using the GLC-SX-MM (1000Base-SX) SFP's for this; if anyone can help shed some light it would be greatly appreciated.

I also accidentally posted this same question in the 'WAN, switching and routing' section before noticing the 'WAN' part, this 'LAN' forum seems more appropriate.

I have this problem too.
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houstonrob Tue, 04/21/2009 - 12:01

Hi, thanks for the response. I read that document and it is what initially prompted the question. 1Gb and the distance is only about 30 meters. my understanding is the 1000Base-BX SFP's are not able to be used with this type of fiber, that i'd need single mode fiber and i was just hoping someone with a better understanding could verify that i'm correct. Its also my understanding that with single mode fiber i'd need two SFP's for each connection (one tx and one rx).

NeoGen_fev Tue, 04/21/2009 - 13:55

The hardware for single-mode and multi-mode fiber is diffrent, yes, you need another type of SFP. On the other hand, why would you be using multi-mode fibers? They're inferior in every way.

Also, instead of running the fiber to every floor, and go with copper from there out to the workstations, do some calculations on how much more it would cost you to run fiber to each workstation with a fiber converter instead, and have ONE centralized switch in the server room, running 100Base-TX SFP's instead. Better infrastructure, less switches, and it might be cheaper, unless you've got ALOT of connections.

And no, single mode doesn't always require 2 fibers (1 x TX, 1 x RX). Newer hardware (standard nowdays I think?) has built-in support for running TX and RX at diffrent wavelenghts, making one fiber per connection sufficient.

Hope this clears some things up for you.

Cheers

NickNac79 Tue, 04/21/2009 - 23:53

Hi,

Your Choice of running Single or Multi might also be affected by your potential for going 10Gig in the future...

If you are planning to run 1Gig to the desktop, and you're going to have lots of clients, then you are eventually going to need to increase your uplink speeds.

One way of future proofing yourself is to put in single-mode fibre now, as it can used to carry 10Gig and above.

Having said that, in every building I've ever worked we always put a MINIMUM of 8-Cores (Multimode) to each wiring closet, allowing 4Gb etherchannels back to your central (Distribution) Switches

In this way you get the advantage of the cheap Fibre, cheap fibre patch cables and cheap SFP modules. and you can start with 1Gig uplinks and scale up as needed.

You'll also find that most cabling contractors won't charge very much more for installing 8-core over 4-core fibre runs - The majority of what you are paying them is labour - and whether it's 4, 8, 12 or even higher bundles they are pulling - it's just one cable to them!

Plus the patch panel they will be putting in for your fibre will almost certainly be at least 24 core - so you won't even be paying extra for that.

If you want high resilience, have 2 distribution points and run 1x 8Core multimode from each distribution point to each wiring closet, then your closet won't go down if one fibre bundle gets cut/snagged.

Nick

houstonrob Wed, 04/22/2009 - 07:07

Hi, thanks for all the replies, they answer my question. Thanks for the insight too

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