I've got tons of fibre in my network. However, tbh, my knowledge about correct light levels isn't great. I generally wait until my router complains about a light level before I do anything. I would like to set up SNMP monitoring for light levels, but I need some kind of baseline.

Anyone with extensive fibre experience? What light levels should I be looking at for both multimode and singlemode fibre?

Once I have thresholds I can set up alarms.

Thanks

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www.mellowd.co.uk/ccie/

Check out the specs for your optics and you should find a transmit power window and receive power window listed.

You can cause actual damage and "cook" the optics if your signal is too hot, though this shouldn't be an issue with sr/lr. For LR on short lengths of fiber, you'll likely end up near the high end of the window, and may want to attenuate if it's a permanent install.

Even if you don't know what the value should be, you do know what the value is now, and that is a very useful piece of information, since you can use it as a baseline. If there is a 5dB reduction, then you will notice, and can be proactive about locating and repairing the fault.

When you have the specs and set up your monitoring to alarm when you're getting near the threshold, you should still alarm on deviation from the baseline.

I like to keep this link handy for my Cisco stuff.
http://www.cisco.com/en/US/products/hw/ ... _home.html
It has all the specs for what is acceptable and what isn't.

If your transceivers support digital optical monitoring (DOM) then you can use that. But Im guessing that is how you are pulling your numbers anyways?

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http://blog.movingonesandzeros.net/

As said, check the specs for your optics for details, you can estimate loss in the data center based on fiber type & length & number of patches (if any). If the receive values are way off, that could indicate issues.

This thread has a link to a NANOG presentation about optical networking, some great info on the basics of it:

http://www.networking-forum.com/viewtopic.php?t=31283#p212311

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I don't have a signature.

I was always told it should be between -3dB and -15dB, and this was on various vendor platforms. All the fiber interfaces I've worked on report a loss at about -20dB.

I was going to suggest this presentation that was suggested to me when I joined this team but it looks like a previous post has already been referenced.

It's a really good one too. Download the PDF with the slides and watch the video. Highly entertaining

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- Pete