Using SM Optics over MM Fibre

[wij]

Simple question (I hope).

We have loads of Cisco GLC-LH-SM SFP's and normally we run in our own fibres (we do networking for big events so things are temporary) however in a couple of weeks we have a job in a venue where we will be using their internal structured fibre links between floors.

I've been told by their network folks that this is spangly new OM3 MM fibre.

Our SFP's are supposed to be able to work over SM and MM fibre, and I know that when they are being used on OM1/2 you are meant to use a mode conditioning cable (though the costs I've seen these cables sold for I would be inclined to just buy new MM modules).

Cisco's documentation is quite clear on this, what its a bit confusing on though is that it states with regards to OM3 fibre:

"MCP is required for 1000BASE-LX/LH applications over FDDI-grade, OM1, and OM2 fiber types. MCP should never be used for applications over OM3, also known as "laser-optimized fiber."

Now I understand why on OM1/2 you need it because of the way the LED light is spread across the fibre core, but I'm not sure of the way OM3 works.

Simply put will our SFP modules with MM OM3 fibre running between them magically *just work* or will it not work at all ?

 

[bigredshark]

It's a minefield but I'm going for not working at all, then again I've never tried it.

 

[wij]

It's a minefield but I'm going for not working at all, then again I've never tried it.

Thanks Mr BRS

Indeed it is a minefield, I've been told by a couple of folk on the phone this morning that it *should* work but they weren't sure as they have never tried.

I'm going to see if I can get my hands on a MM OM3 patch cable and plug that between a couple of switches and see if it works at all, though thats no guarantee that it will do so over distance.

Another company that we sub-hire in kit from on occasion has lots of MM SFP modules so I think in the end I will just borrow those and take them to site with me to avoid any embarrassment - especially as this job is in another country and getting the bits to fix the issue out there will likely be impossible

 

[Trifid]

Indeed it is a minefield, I've been told by a couple of folk on the phone this morning that it *should* work but they weren't sure as they have never tried.

So that means that it won't work.

I'd also play this safe and take the correct SFPs.