Network Cabling – CompTIA A+ 220-801: 2.2

| November 14, 2012

Our cabling is the fundamental part of any network. In this video, you’ll learn about the different modes of fiber communication, the unique characteristics of twisted pair copper cabling, the importance of plenum-rated cable, and the use of coax cables in our high-speed networks.

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Review Quiz: Network Cabling

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The cabling we use in our networks is so important. It is the foundation of the communication that we’re using. And you usually get only one chance at making sure that the foundation is absolutely solid. When you’re architecting, planning out, building out new parts of your network, you want to be sure the cabling’s done right from the very, very beginning.

If you look at everything that we’re doing with wired communication, we’re obviously using cables. But even wireless communication relies on the types of fibers in cables that we’ll talk about in this video. That’s because ultimately you have to get that wireless signal down to some type of infrastructure. And we have to rely on our physical cables to be able to transfer that communication.

A cabling type that’s common to see behind the scenes is one that is fiber based. This fiber uses light to be able to communicate between devices. This is very different than the wires that we use in our copper cables that are sending electrical signals. With light, we’re able to simply send photons from one device to the other to be able to transfer information.

Because of this, there’s no electrical signal. There’s no RF. There’s no radio frequency that’s going between those two connections. So in very secure environments, this is a perfect medium to use because it’s difficult to tap into that connection. You can’t use some type of inductive listening device to hear what’s going on because it’s simply light that’s being transferred between those two devices.

Another good reason for using fiber is that the light inside of the fiber degrades much slower than an electrical signal on a copper connection. So we can really plug in devices that are kilometers apart and we’re still able to send that data because we’re using fiber to be able to connect across those long geographic distances. And since we’re not using any type of radio frequency or electrical signal on the cable– we’re simply using light to extend it across– we don’t get any type of common electrical interference.

So in an environment where you might have a lot of radio signals, if it’s a very large city where there is always some type of electrical interference, you can simply use fiber and you can avoid all of those problems.

You’ll generally use two types of communications when using fiber. One is a multi-mode communication. And the multi-mode fiber I have represented here, because this is usually used inside of a building or across very small distances, usually two kilometers and shorter.

This is also, relatively speaking, an inexpensive way to use fiber. Because the light source that we might use on a multi-mode connection is often in LED. And that’s compared to something like a laser connection that we’ll talk about in a moment. This is called multi-mode because when the light goes into the fiber, it may take different paths to get from Point A to Point B. It uses different modes. So it might bounce around one connection or it might use a different type of connection to get to the other side. So all of this bouncing inside of the fiber ultimately does end up at the other end. But every single photon going through may take a different path.

The other type of fiber you might see is single mode fiber. This is very common to see across very, very long distances. If you need to go an extended distance, you’re probably going to use single mode fiber. Because you can, in some cases, go up to 100 kilometers depending on the type of networking that you’re doing between those. And then at the end of that fiber if you need to go further, you can of course regenerate that signal. But by going such a long distance, you can really minimize the number of times you have to do that.

The light source that’s used for single mode fiber is usually much more expensive than the multi-mode fiber because with single mode fiber, we’re often using a laser. We want to have a very, very powerful light source to be able to go across such a long distance. And that’s another reason why you want to be very careful when you’re working with fiber.

You should always assume that you’re using a laser, even if you’re not. Because you want to be very careful that you don’t point that fiber anywhere into your eyes or that you look into the fiber very carefully. And that’s because that laser can damage your eyes. So the best practice is always to assume that it’s something that might damage your eyes, and never look directly in. If you need to test the fiber or you need to see if there is light coming out on the other end, you should always have specialized equipment to be able to do that.

The path that the light takes through single mode fiber looks a lot different than the multi-mode. As the name implies, there is a single path or a single mode that the light travels from one end of the fiber to the other. Perhaps the most popular cabling type you’ll run into is twisted pair cabling.

Twisted pair cabling uses something called a balanced mode. That’s why we have all of these different wires that we’re using. Because we’ll often have something called a transmit plus and a transparent minus. We’ll also have a receive plus and a receive minus at a very minimum across these connections. And that’s because we want to be able to cancel out those signals on the other side.

That’s why we twist them together. It’s the twist that really ensures that we minimize the amount of interference that’s going from one side to the other. When the signal gets to the other side, the signal is compared across both of those wires and you’re able to remove a lot of the interference that was there to begin with, ensuring that the signal’s going to be as strong as possible when you receive it.

Another important characteristic of twisted pair cable is that the cables are twisted– the pairs are twisted at different rates. So you can see in this picture that the blue has a very slow twist associated with it. And the orange cable has a completely different twist rate associated with it. That way, you’re able to differentiate between that interference regardless of what pair it may have come across.

When you’re working with copper cabling, you have a choice of whether you would like to use shielded cabling or un-shielded cabling. The shielded cabling is STP, Shielded Twisted Pair. And if you work in a very industrial environment or your cables are near a lot of electrical interference, you might want to consider using a shielded twisted pair cable because you’re able to remove or prevent a lot of that interference from ever getting inside of those wires as they’re going across that link. You don’t get any additional distance out of this. It’s following exactly the same ethernet standard. But you are able to minimize the amount of interference that you might receive on that cable.

Shielded twisted pair has a very specific use, and there is an extra cost associated with it. So most people use Un-shielded Twisted Pair or UTP. There’s no shielding inside of it. You see, there’s no foil or shielding around any of the pairs inside of this. It is probably the most common type of cable you’re going to find.

It’s relatively unusual to see someone using shielded twisted pair unless there’s really a very specific need for that. There’s of course no difference in ethernet standard between these two. They both go exactly the same distance and use exactly the same characteristics. The only difference is the shielded twisted pair is going to have the shield associated with it and a ground wire to help minimize the interference you might receive as it goes through a very electrically noisy environment.

If you’re planning to put your network cable in the ceiling or in the floor of your organization, you may be asked on whether you would like to use a cable that is rated for the plenum. The plenum is an area that’s usually above the ceiling where you might have all of the air that is going either to or from your cooling system all passing through an open area.

If you have some place in your ceiling where all of the air return is going through duct work and all of your air supply is going through duct work, then there really is not a plenum. Because you are separating the air supply from the open dead space area that’s in your ceiling. If you have a plenum, usually you aren’t using that duct work. Sometimes you have all of your return air going into a common area and that air return is finally being fed out. And in those particular cases, you want to be sure to use a cable that is rated to go in that type of plenum.

The most important part of a plenum-rated cable is the cable jacket that goes around the twisted pairs themselves. This cable jacket may be PVC, that’s a polyvinyl chloride, or it may be FEP, which is a fluoridated ethylene polymer. This is something that also causes the cable not to be quite as flexible. It’s a different kind of cabling jacket. So you don’t have the same bend radius. You don’t have the same flexibility. And then commonly, you don’t use this for the everyday cable that you might be using.

The reason we might want to use plenum cable is to limit what would happen if a fire ever occurred. A normal cable is much more flammable than a cable that’s designed to be in the plenum. And because the plenum has so much fresh air, it’s certainly an environment where the cable might be used to have the fire move from one place to the other on the floor of a building. So by using a cable that is plenum rated, we can minimize the impact and limit the movement of the fire if that should ever occur in your organization.

If you have cable that’s going between floors, you might be using a different type of cable that’s specifically designed to work in the riser. And the riser is that connection between those floors. Usually in a riser situation, you have a fire block or a physical fire wall in place that would limit any of the fire moving between those floors. So your riser cable doesn’t quite have the same strict requirements that you have in the plenum. But there is still a consideration there to limit the impact that you would have if there was ever a fire.

It’s very common to see coaxial cable being used with our cable modem networks. We also use it for wide area networking and other purposes as well. The word coaxial comes from having two or more forms that are sharing a common access– its coaxial. You’ll see this in older ethernet networks, 10BASE5, the “thicknet” which is a very, very wide, thick cable that was used.

And much more commonly probably is the 10BASE2 that you might run into, which is “thinnet” using RG-58. But these days, of course, we commonly use a coaxial cable for our television communication and of course for cable modem that is running over that television connection to give us high-speed networking both at our home and at our businesses. In our home the type of cable the we might see used for that is RG-56.

There are some cases where you might have something called an RG-59 cable that’s used for short-distance video, but most commonly you’ll probably find RG-56 being used on your broadband internet connections.

Category: CompTIA A+ 220-801

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