Troubleshooting Fiber Issues – CompTIA Network+ N10-006 – 4.5

| May 11, 2015 | 0 Comments


Fiber optics require very specialized installation and handling. In this video, you’ll learn how to troubleshoot attenuation, fiber modules, fiber mismatches, connector mismatches, bend radius, and fiber distance limitations.
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One of the challenges you have with fiber is you want to keep as much signal across that fiber as possible. Any way of attenuating that signal or causing signal loss is going to be a problem when you get to the other side.

You want to be careful with splices and terminations of the cable. Every time you terminate that connection and plug into a patch panel, for instance, or add a connector on to the end, you’re going to lose a bit of signal on that fiber. If you’re terminating these things in the field, you have additional concerns, because the equipment you use in the field may not be as accurate as the equipment you might use at the factory.

The connector itself needs to be perfectly clear. It can’t have any scratches on it. It doesn’t need to have any dirt on it. If it does, we need to clean that off. And if we aren’t able to resolve that, we need to cut that off and put a new connector onto the end of it.

If you have breaks in the fiber or cracks in the fiber, you’re going to have attenuation. You’re going to lose signal somewhere along the fiber, and it may make sense to get an OTDR and have it determine where the cracks or problems are along that very long fiber run.

The equipment you use might have modular types of fiber connectors on them where you can put in your own SFP, SFP+, or GBIC into that connection for the type of fiber that you happen to be using. But not all modules work exactly the same. And if your manufacturer is recommending a certain type or brand of module, then you want to be sure to use those with that equipment.

Also check your fiber types. Examine what fiber is expected by the equipment, and check the fiber that you’re using on your network. You do not want to mix and match fiber types between these pieces of equipment.

One nice thing about these fiber modules is that you can pull them out and replace them with a new one in a matter of seconds. So if you need to test or try to see if a replacement might fix the problem, you might want to have some spares on hand so you can easily swap those out.

And of course, monitor the statistics. You’ll be able to see CRC errors on the connection or be able to understand if there’s any type of signal problem for this particular link.

There are some very standardized fiber sizes that you might see. We’re talking specifically about the core of the fiber itself and the cladding that goes around it. Of course, you need to make sure that everything matches between your fiber and the equipment that you’re using. This is what’s commonly seen with multi-mode fiber that’s described as 50/125 microns or micrometers. You can see that 50 microns is the size of the core inside, and the total size is 125 microns.

On multi-mode, you might also see 62.5, which is a little bit larger core, but you can see the overall size is still going to be 125 microns. And then single mode you can see is much smaller. Only nine microns for the core, but of course, we’re keeping this same standard, 125 microns, for the cladding around it.

If you are connecting fiber to each other, you want to be sure that you have the right kind of connection between. Every time you’re connecting these fibers together, and there’s any type of difference, you’re going to lose signals. So you want to be sure that these are very precisely engineered and that you’re getting a very good signal every time you’re connecting these together.

The bend radius for fiber is very important. The fiber is effectively glass. It is very fragile, and you do not want to bend it farther than its standard bend radius. The bend radius is going to be different depending on the fiber itself, so check the manufacturer’s specifications, and you want to have equipment that’s able to handle these bend radiuses.

There are two different kinds of bendings that you might see described. One is a microbending, and the other is a macrobending. Microbending is a bit difficult to see. This might be something that might be indenting the fiber itself or sitting on the fiber and putting pressure. A macrobending is a bending of the fiber itself, perhaps as it goes through conduit and turns a corner. If you turn that corner too sharply, the fiber will not be able to make the turn, and it will leak out of the cladding itself.

You will ultimately have a maximum distance that you can go with this fiber. The total distance is really going to be dependent on a number of variables. You’re going to be sending a signal out through the fiber, and of course, the fiber is going to lose signal as it goes a longer and longer distance. The key is that you have to have enough light when it gets to the other side. The total amount of light that you need is going to be dependent on the equipment that’s on the end, so check the manufacturer’s specifications to find out what that might be and see if you can use some testing equipment to see just how much light is getting to the other side.

We commonly use multi-mode fiber for shorter distances. This might be 600 meters, or 2,000 feet or so, plus or minus, depending on the fiber you’re using and depending on the equipment that you have on both ends. A single mode fiber is used over much longer distances. We usually will see all kinds of different technologies to be able to send this traffic over such a long distance, and it’s not unusual to see single mode fiber runs that might go up to 100 kilometers, or 60 miles, as the distance.

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Category: CompTIA Network+ N10-006

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