Optical Fiber and Copper Cabling

Many of us are accustomed to using twisted pair copper, especially if we have networks that we use at home or even at our office. But you may occasionally have a need for fiber optic connectivity, and that fiber optic connectivity allows you to send traffic across the network using light. These are often used on very secure networks because it is very difficult to tap into a fiber optic connection without having some type of notification. This is very different than a copper based network which uses RF and is relatively easy to tap and gain information from.

Fiber optics are also used over very long distances because the signal doesn’t degrade as fast as a radio frequency might. So the same signal that we can send over 100 meters of a copper network might be able to be sent over kilometers if you were using fiber optics. And, of course, light is not susceptible to any type of radio frequency interference. And if you’re working in an environment where there is interference, you might want to use fiber optics to avoid any type of problem with your network.

Just as there are many different standards and many different connectors for copper based networks, there are also many different standards and connectors for fiber optic networks as well. So you’ll want to check the configuration and documentation of your devices and make sure that the fiber optics that you’re connecting are using the right type of fiber and the right type of connector.

If we were to deconstruct a fiber optic cable, you would have something very similar to this. On one side of the cable is the light source. This might be an LED or a laser. And on the other side is the receiver. This LED is sending a light through this fiber optic and that consists of a core that is very reflective, and you can see the light bouncing through this core as it receives on the other side. Around the core is a low reflective cladding, and the entire fiber optic run is protected with a buffer coating around the outside.

Here’s the connector that’s at the end of a fiber optic cable. It has a protective ferrule around the outside of the fiber. And if you look very closely at the very middle of this connection, you can just barely make out the core of the fiber that’s in the middle. I’ll highlight it here so that you can really see where that happens to be. Let’s remove that highlight. Now you can start to see that discoloration where the fiber is connected on the end of that cable.

We will generally install one of two different types of fiber optic cables. One is a multi-mode fiber and the other is a single-mode fiber. Multi-mode fiber is commonly used for relatively short range communication. This would be up to around 2 kilometers in distance. And often this uses an inexpensive light source, such as a light emitting diode or an LED.

The core of the fiber optic is relatively large, certainly larger than the wavelength of the light. And because of that, the light itself can use different modes to be able to transmit through that fiber. And you can see the different modes bouncing off the edges of the fiber optic cable itself. Because there are different modes that are being communicated through this fiber, we refer to that as multi-mode fiber.

If we’re communicating over a much longer distance, we may want to use single-mode fiber. Some standards of fiber based ethernet can communicate up to 100 kilometers without a need to regenerate the signal. Because we’re going a longer distance, we may be using a very bright and intense LED or we may be using laser to be able to extend this signal much further. A single-mode fiber also has a smaller core, which can only allow a single mode of light to propagate through the fiber.

Cabling is the foundation of everything we do in networking. Whether you’re using a router, a switch, a wireless access point, or any other infrastructure device, cabling is going to be a critical part of that communication. Once the cabling is installed, it’s very difficult to uninstall or remove that cabling and replace it with something else. So make sure you’re using the right cabling for the right infrastructure.

And even if your network happens to be mostly wireless, eventually that wireless connection will need to connect to a cable. So you need to make sure you have the right cables installed in the right place to be able to provide the best possible throughput of your network.

One of the most common cable types is the twisted pair copper cable. This is something we use for practically all wired ethernet connections, and it usually consists of multiple wires twisted together within a single sheath. You’ll often see that the cables themselves are paired together. That’s because there’s often one type of signal on one of the wires and a reverse of that signal on the other wire. You may see this written as transmit plus or transmit minus or receive plus and receive minus.

The reason that we have the same signal being sent in different forms is so that we can recognize and correct if there happens to be any type of interference. This twist in these two wires means that at least one of these wires will always be moving away from interference. This allows us to compare these signals on the receiving end to determine what the actual signal should look like.

Another interesting part is that the different cable pairs have different twist rates. So if you look very carefully at an individual cable, you’ll notice that some pairs of cables are twisted much tighter than other pairs. One common misnomer that I often hear about cables is that a certain cable has a particular speed. But in reality, the cable doesn’t have any speed at all. The copper is literally just sitting there in the cable.

The cable itself is supporting a signal, and that signal is allowing us to send a certain amount of data over that particular type of connection. The specific ethernet standard that you’re sending over that wire determines just how much data you’ll be able to move across that particular cable.

If you’re ever wondering what type of cable you should be using for the type of ethernet network that you have, you should go back to the 802.3 standards. Those standards will specify the minimum cable type that’s allowed for that particular standard, and it will specify the type of signal and the total throughput expected over that cable.

To be able to easily determine the type of cable that’s appropriate for a specific ethernet standard. We’ve created a set of standards for the cables themselves. We refer to these standards as a category of cable. For example, you might find category 5, category 6, or category 7.

If you check the ethernet standard, it will specify the minimum category of cable that is required for that particular standard. For example, if you’re using 1000BASE-T, you can look at the 1000BASE-T standards from the IEEE, and it will tell you that the minimum cable category for that specific ethernet standard is a category 5 cable. If you install category 5 cable or anything above category 5, it will work properly with the 1000BASE-T standard.

Although twisted pair wiring is very common for our local area networks, another type of ethernet cable that’s very often used is a coaxial cable. This describes a cable where two or more forms within that cable share a common axis. For example, you can see the single wire conductor that’s in the middle of this coaxial cable. There’s also an insulator, a shielding, and a jacket that are also sharing that same axis.

One common type of coaxial cable, especially on our ethernet and internet connections, is an RG-6 cable. If you have a cable modem or you’re bringing in a cable modem connection into your data center, it’s probably being brought in on a coaxial cable.

If we put two conductors inside of this cable type, then we have a twin axial cable. We often refer to this as simply twinax. Twinax is a type of cable that you can commonly associate with 10 gigabit per second ethernet. It’s often installed as part of an SFP+ interface. This allows for full duplex communication over a single cable, but it limits the amount of distance that you can send this signal to about 5 meters. This has a relatively low cost when associated with fiber optics. And very often, it has a much lower latency when you compare it to using something like a twisted pair connection.

If you’re at work and you look at the ceiling, you may notice that you’re not seeing the actual ceiling of that floor. Instead, you’re seeing a drop ceiling and something like acoustic tiles that is sitting above the actual ceiling. There is a space between this drop ceiling and the actual ceiling, and we refer to that space as the plenum. Inside the plenum, we may have network cables, there might be heat sensors, you might have cables for power. And there may be other pieces of the infrastructure that run inside the plenum as well.

In some environments, there may be a drop ceiling, and above the drop ceiling may be ductwork where all of the air supply happens to flow. You may have air supplied as part of a heating or cooling system in that ductwork, and there may be return air that’s using additional duct work to go back to that heating or cooling system.

Since a plenum implies that there is a shared air space in a configuration such as this where only duct work is used to transfer the air, there would be no plenum. But if there’s no duct work and we share this same air space with all of our networking cables, then we need to consider that we’re using the proper type of network cables in that shared plenum.

This would obviously be a concern in a fire, especially if we’re using a network cable type that produces a large amount of smoke or perhaps even hazardous fumes if it was to catch on fire. If this was in a plenum, that smoke and those fumes would be distributed to everyone in the building. This means we need to make sure we’re installing the correct type of cable if we happen to be installing this into a shared plenum.

Ethernet cables have a jacket on the outside of the cable, and many of those ethernet cables are manufactured with a Polyvinyl Chloride, or PVC, manufacturing. If you’re putting this cable into a plenum, then you need a plenum-rated cable. And that cable is usually manufactured with a Fluorinated Ethylene Polymer, FEP, or a low-smoke Polyvinyl Chloride, PVC.

This plenum-rated cable is designed to be much safer in a fire than one that is not designed for a plenum. One challenge when working with plenum-rated cable is it may not be quite as flexible as non-plenum-rated cable. So if you’re going around a lot of twists and turns, it may be a bit more of a challenge to install that cable into the plenum. So if you’re installing cable into a new building or you’re replacing cable in an existing building, make sure you see where that cable is being run and you use the correct type of cable for that location.