# Fiber topography



## HARRY304E (Sep 15, 2010)

McCracken said:


> I don't do any network designing, I have seen fiber run to IDF's in a ring, I have also seen home runs from the IT room to each IDF. What is most common and why? Reason I am asking, a customer has a fiber run in a ring to 4 IDF's and are looking for a second ring in a different path for redundancy.
> 
> It seems to me that a star would make more sense, but like I said I just install what they want. I'm just looking to understand the reasoning a little better is all.
> 
> Thanks


..........Bump!


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## sarness (Sep 14, 2010)

Typically it would be less cable to run a ring, also uses less ports. You would need one port in and one out in each IDF and the MDF. 

If you did home runs you would need a four port switch in the MDF. Unless you did a pseudo ring with patch cords.

The ring already gives redundancy, if a line gets cut it just travels the other way. Only way for a complete failure would be for it to be cut on both sides.


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## McCracken (Jul 10, 2010)

Thanks, that makes sense. Buy why, if a ring already gives redundancy, might somebody run a second ring? Is it that they just like spending money or hae you seen that done before?


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## sarness (Sep 14, 2010)

For redundancy? No, I haven't, did have one job where they did both star and ring runs, but never saw how they used it. Having it just adds more hardware, but still a single point of failure, the switch itself. 

Might do it to physically separate traffic or some other reason, but with today's managed switches its usually unnecessary. Our maybe for speed.

Honestly, it's been very rare to see cabling fail for no reason. If it does, its because someone physically damaged it.


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## sarness (Sep 14, 2010)

I should add that it does need to be properly installed, it does little to have a ring or redundant cabling and have them travel through the same path. And I mean this anywhere such as in the rack, penetrations, etc etc, true redundancy takes some planning and thought and can take many forms.

I can't tell you how many times I've come across people who have redundant power supplies and have both cords plugged into the same UPS or branch circuit.

It doesn't do any good if it's not installed properly.


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