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ctagleFlag for United States of America

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Can You Connect a Single Mode Fiber Run to a Multi-Mode Fiber Run

Hello Experts,

We have about 3/4 of a mile of fiber between two buildings.  In one building the fiber terminates in the MDF but in the other for some reason when it was put in the fiber was terminated in one of the IDF's.  So what we would like to do is put in a run through the building the extra 300 feet to bring that run into the MDF.  What I am wondering is for that 300 foot run can I use MM fiber, or does it have to be SM?  I was thinking that I can plug the SM run into a patch panel in the IDF, use a mode conditioning patch cable to connect it to the MM run on the same patch panel heading to the MDF and then plug that run into a patch panel and into a MM SFP on one of the switches in the stack in the MDF.  Would that work, or am I totally off base?

On another note would I have to use an attenuator if I put in SM for that short of a distance (300 ft)?
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Predrag Jovic
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Limitations:
Max length for MM fiber typically 550m < 3/4 of mile.
So, you can't use MM fiber to extend SM fiber.

For mixing SM and MM in this case you need active device between cables.
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ASKER

Ok thanks, thats basically what is in place already, a switch that the SM run is connected to in the IDF and then there is a run going to the MDF, but they don't want to do that anymore, than want to take the run directly to the MDF.

But either way it sounds like what you're saying is that we would have use SM fiber for the extra 300 foot run to the switch stack in the MDF, correct?  

If that is the case we would have to use two of the strands in that SM run to connect the IDF to the MDF, since that is only a 300 foot distance between the two switches, would we need to use an attenuator?
Yes. You will need 300 feet SM cable (the same diameter as previously placed cable). Since you are patching one cable to the other you will not need attenuator. It is the total length of cable that counts in this case.
You can have problem if cables have different diameter or bad contact surface, so you could end up with weak signal in that case.
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Well I know I won't need an attenuator for the pair that I will be hooking up to the run between the buildings.  What I was saying was that I am going to need to use one of the pairs on the 300 foot SM run to connect the IDF stack in that building to the main stack in the MDF, so one of the pairs in the 300 foot SM run would be for the building to building connection, but another pair would be for connecting two switches that are only 300 feet apart its for that short run that I am asking if I'll need an attenuator.  Hopefully thats a bit clearer, I'm finding it rather difficult to describe this using text.
If you plan to run 300 feet long fiber between any two switches - use MM fiber. No attenuator is needed and it is way much cheaper (price difference GLC-SX-MMD vs GLC-LH-SMD is almost a 2x). You can't extended SM with MM fiber, but when you terminate SM on some device you can use MM from that device to connect all other devices if length between 2 devices is less than 550m (1800 feet).
User generated imageBut anyway, if you need link back to building that SM fiber is currently terminated why not use MM cable that you are using now. (I guess that is plan).  Since it is hard to say it in words - draw it, :)
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That was my original idea but the problem with doing it like that is that we would leave the SM run in the IDF, plug it into a switch, and then use a MM run to connect the IDF where the fiber comes into the building back to the MDF.  I don't think there is any issue with doing it like that but they want it to physically come directly into the MDF with no devices in between.  I've used your drawing to show a current setup and new proposed setup.

User generated image
 

User generated image
Can you please explain (or better draw it) with more details what is going on in green ellipse?

User generated image
I do not understand what is your plan how to connect this.
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I threw together something in Visio real quick.  I hope this makes it clearer and not muddier.

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Predrag Jovic
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Awesome, that's exactly what I needed to know.  Thanks for being so patient!