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Module 6:Connecting Networks with Cables and Connectors

1. 6.0 Connecting Networks with Cables and Connectors

At this point in the course, you've learned a lot, as you know, about the components of a network. different topologies for interconnecting those components, but we've not spent much time talking about the actual media that's going to be used to do those interconnections. Well, that's great news. We're going to be covering that in this module. We're going to be contrasting five- and 10-gauge copper cables and connectors. We'll take a look at the colour coding being used in that network cable plugged into the back of your computer right now. We'll take a look at a bunch of Ethernet standards. Now let's get started with copper cabling and see what's up with all of those twists that we have in those copper wires.

2. 6.1 Copper Cables

In this video, let's talk about some of the different types of copper cabling we might find in a network. And we have two specific types we're going to focus on: coaxial cable and twisted pair cable. First, let's focus on coaxial cable. If you look at the tip of that cable, you can see a wire coming out. Well, that little wire that's inside the cable is surrounded by insulation, so it's not touching that outer metal braiding that you see, and then you see the insulation around that braiding.

But we have two conductors. We've got that inner wire and the braiding. And the reason it's designed this way is to help prevent EMI (electromagnetic interference). That's what happens when one transmission gets carried over into another transmission. You might have experienced this on an old telephone line. You were talking on the phone, but you could faintly hear somebody else. And that was because your telephone cables and your neighbors' telephone cables were going back to the central office side by side, and the electromagnetic field created by their telephone wire was induced on your telephone wire, and you could hear them somewhat.

We don't want that in the networking world. We don't want our wires to become an antenna where we could transmit and interfere with someone else, or where we could become an antenna and receive interference from someone else. So we want shielding. And the way this gives a shield is by surrounding that inner conductor with the outer conductor. And that design is based on Maxwell's equations, which say that a radio wave cannot pass through a perfect conductor. But this design, even though the braiding is not a perfect conductor, is really, really good. That's going to help prevent anything from going through that braiding and getting to the inner conductor.

And the coaxial cables are measured by impedance. And the two main impedances we have are 75 ohm and 50 ohm. In your home, if you have cable television or cablemodem, you're likely to have 75-ohm coaxial cable, either RG-59 or the newer and better RG six.I say RG-6 is newer and better because it is less lossy. You can go a longer distance with less loss. And in the early days of Ethernet networking, we used 50-ohm coaxial cables to carry packets around the network. RG-58 was a thin coaxial cable, and that Ethernet technology was called "ten base 2," or "thinnet," and it ran at ten megabits per second. RG-8, you say, was a thicker coaxial cable, and that's what was used for ten-based five or thicknet networks. And with the thin-net networks, you had these little twists on coaxial connectors where you could connect a computer to the cable by tapping into the cable.

Or we actually had something called "vampire taps," something that would penetrate that outer insulation and get into the interconnector for the thick net. But we don't see coaxial cable used for networks much these days, and think about the name "coaxial." We have two conductors, an outer conductor and an interconnector, and they have the same centerpoint, or they have the same axis. That's why we call it coaxial. The twin axial cable, on the other hand, is a more recent variant. Here we have two interconnectors, each on their own axis. And this type of cable has several different use cases. But primarily, we use twin axial cable today for data centers because, in data centers, we typically don't need really long runs.

So if we need to interconnect a couple of components in a data center and we don't need to exceed 7 meters, an axial cable might be the solution for us. And it typically runs in a data centre at either 40 gigabits per second or 100 gigabits per second. And again, that's with a seven-metre limitation. But outside of our data center, we're typically going to see some sort of twisted pair cabling used in our networks with distances less than 100 meters. And you might wonder how we're protecting ourselves from EMI if there's no shielding. When it comes to higher speed transmissions, some twisted pair cable does have shielding, but we also have unshielded twisted pair cables, or UTP. And the way that we prevent or reduce EMI with an unshielded twisted pair is by twisting pairs of wires together. By twisting those wires, we have copper crossing over copper at a distance that's less than one fourth of the wavelength that's being transmitted down that cable, and that's going to prevent it from becoming an antenna.

So by tightly twisting the wires, that is going to provide us with some EMI protection. However, in environments with a lot of interference or when we want to have higher speeds on the order of ten gigabits per second or maybe even 40 gigabits per second on twisted pair cabling, in that case, we might have shielded twisted pair. And when I say shielded, you might see this in a couple of different forms. You may see foil used frequently. Each pair of wires will have foil wrapped around them. And then you might also see braiding, much like we see in the coaxial cable, that surrounds all eight conductors in this twisted pair cable. Oh, and one other variant of twisted pair cabling I want you to know about is plenty-rated twisted pair cabling. Consider running cable in a data center, where you're running cable beneath the raised floor, or in an office with a drop ceiling and you're throwing cable across the ceiling above the drop ceiling.

Well, are those areas used for the HVAC system's cold air return? If so, you don't want to put regular cable in those areas being used for the air return. Those areas are called plenum areas if they're being used by the HVAC system. And the reason I say you don't want to use regular cabling is that regular insulation on cabling is exposed to extreme heat. If there were a fire in the datacenter, it could start to release toxic fumes. You don't want toxic fumes being pumped through your building by the HVAC system. As a result, you should use plenum-rated cable, which has insulation that will not emit toxic fumes in the event of extreme heat. Now let's consider some different types of twisted pair cabling; these are called different categories of twisted pair cable. PBX systems—private branch exchanges—are phone systems. Within companies, they commonly use category three.

And in the early days of networking, I remember that we would use existing PBX Category 3 wiring to connect devices to the network. And we did that at ten megabits per second. You could use all four pairs in the wire, which would give you 100 megabits per second. That was called 100 base T four and was rarely used, though normally we would use just two of the four pairs to get ten base T. And the distance limitation was 100 meters. And when fast Ethernet came around and lots of people wanted to do 100 megabits per second, category three was not going to do a great job of that. So instead, we started installing Category 5 or Cat 5 cable. This would do 100 base T, or 100 megabits per second, which uses just two of the four pairs. It specifically uses pins 1, 2, 3, and 6 of a connector's eight different pins.

And category five can also do 1000 b/t using all eight wires. That's one gigabit per second. Now, category five E does not provide much more speed or distance, but it does provide better electrical characteristics, and it is recommended over category five. But both of these have distance limitations of 100 meters, and they can be used for 100-base TX or 1000-base T communication. When we go up to category six, not only can we do 1000 base T—one gigabit per second—but we can also do something called a 5G base T—five gigabits per second—or even a 10 G base T—ten gigabits per second. Be aware, though, that with category six, if you're doing ten G-based Ts, you're limited to 55 metres as opposed to 100 meters. You can overcome that 55-meter limitation, though, by going from category six to category six a, which will give you the same speeds, but even tenG base T can go 100 meters.

Category seven can support 5G base T (10 GB T). Or you might want to use that cable to support POTs, plain old telephone service, CATV, community, antenna, television, or, in other words, cable TV and your phone system, plus gigabit Ethernet. So you can have voice, video, and data all running side by side on your category 7 cable with a distance limitation of 100 meters. In a data center, where cable lengths are typically shorter, you may encounter category eight, which can do 25 G based T or even 40 G based T at 40 gigabits per second. However, the distance limitation is going to be in the range of about 30 to 36 meters. Again, this is intended for datacenter use, not building infrastructure cabling. Because of that distance limitation

3. 6.2 Fiber Cables

One of the enemies that we're always fighting against with copper cabling is EMI, or electromagnetic interference. The great news is that with fiberoptic cabling, we're immune from EMI. The reason is that, with fibre optics, we don't use electromagnetic waves to carry data. We use light. And in this video, I want you to be able to distinguish between a couple of types of fibre optic cabling: singlemode fiber, or SMF, and multimode fiber, or MMF. Here's how that works:

Think of putting a straw into a glass of water. Have you ever noticed that it looks like the straw is bending when you do that? Well, the straw is not bending. The light is bending. The reason that the light bends is because water and air have their own index of refraction. What I mean by that is that light travels a little bit slower in water as compared to air. And when we go from air into water, those different indices of refraction cause the light to bend. That's how fibre optics work. If you look at the glass inside a fibre optic strand, that glass is really made up of two kinds of glass.

There's an inner core, and then that's surrounded by another type of glass called the cladding. And these two types of glass have different indices of refraction. When this cable was manufactured, the manufacturer put different dyes in the core as compared to the cladding, and they have very different indices of refraction.

It doesn't just bend the light a little bit, like putting a straw into a glass of water. The light can actually bend back on itself. And as a result, we can keep the light inside the core and prevent it from escaping out into the cladding. And with multimode fiber, the diameter of the core you can see is a bit larger than the diameter of the core with single-mode fiber. And when we say mode, we're talking about a path that life takes. Let's say that one path is coming in at an angle like this. We see that we hit the cladding, and because the cladding has a different index of refraction, the light bends back into the core. So there was a little bit of bouncing. Maybe another beam of light came in, and it did not bounce very much. It didn't come in at a very steep angle, but another black beam came in at a very steep angle, and it hit the cladding, and it went bounce, bounce, bounce, bounce, bounce, until it finally came out the other end.

Can you see that over a long distance? This could corrupt data if I had a binary one that went into this fibre optic cable first, but it's using that red path of light where it's bouncing a lot. And then I had a binary zero that used the green path of light that's not bouncing much at all over a long distance. Can you see that? That binary zero using the green path of light could actually pass the binary one using the red path because the red path is spending all that time going back and forth, back and forth, back and forth. It could actually be passed up by that green path. So instead of the data coming out as "one followed by zero," it could come out as "zero followed by one." It could corrupt our data. That's called multimode delay distortion. And as a result, a lot of fiberoptic cables are limited to about 2 miles of distance.

The good news is that with single-mode fiber, we don't have that issue of multimode distortion because, as the name suggests, we don't have multiple modes; we have a single mode. Specifically, that core has such a small diameter that it only permits one path of light to go through the cable. And that single mode of light is going to prevent one binary bit from bouncing back and forth and the other one from going straight down the middle. Well, there's not going to be one bit passing up another bit because we only have one allowable path. And that's a look at the distinction between multimode fibre and single-mode fiber.

4. 6.3 Copper Connectors

In this video, we're going to take a look at a few different types of copper connectors that go on the ends of copper cabling. It might be twisted pair cabling, or it might be coaxial cabling. First, let's consider the RJ-11 and the RJ-45 connectors. Where RJ? By the way, that stands for registered jack. and an RJ-45 connector that you see on the left. We typically see that on the end of an Ethernet cable.

That's what you'll probably be using to plug in PCs, printers, and network devices. And if you look really closely at the graphic, you're going to see that there are eight different slots where there can be a conductor. And each of those slots on this little connector has a conductor in it. So it's referred to as an eight-position, eight-conductor cable. Now compare that to an RJ 11. An RJ Eleven is physically a bit smaller than an RJ 45. You might see an RJ-11 jack on telephones, modems, fax machines, and pretty much anything going back to the local telephone company.

Now, technically, an RJ-11 has six positions. You might be able to see that in the graphic. In other words, there are six slots where we could have a connector, but an RJEleven connector only has two conductors. Now you might be looking at that graphic and saying, "Whoa, that's got four conductors on it." If you notice that, you've made a fantastic catch. What happens is that we commonly refer to this connector that we see on screen as an RJ Eleven. But I want you to understand that technically, RJ-11 only has two conductors.

Although the cables and connectors that we typically use have four conductors, those four conductors allow us to have two different telephone lines coming over the same cable. We have an inner pair of wires; they work together as one line. We have an outer pair of wires; they work together as a separate line. And those pairs are made up of conductors that we refer to as tip and ring. And what we're actually seeing onscreen is an RJ-14 connector. However, if you were to see this on an exam, I would recommend that you say it's an RJ-11 connector because those two terms are used interchangeably a lot. RJ 14, on the other hand, is a connector with six positions and four conductors. But again, we would probably refer to that as an RJ Eleven.

Two other types of connectors that I would want you to know about are the DB-9 and DB-25 connectors. The D comes from the shape of the connector. If you look at it on its side, it looks sort of like a D, and it's called a D subminiature connection. And there are a series of these connectors with a different number of pins in the different connectors. The DB9 has nine pins. As you can see, the DB 25 connector has 25 pins; however, if you counted them, the DB 25 connector has 26 pins. And this is another case where the naming has become popular but is not technically correct.

There was an A-D-A-A-A-A DB, a DC, a DD, and a DE. And the DB nine, as we call it, is technically a de nine. That's what it calls it in the official literature. But we'll typically call it a DB-9 because that DB acronym caught on so much after the DB-25 connector got so popular years ago. So commonly, we're going to see these called DB-25 and DB-9 connectors, and they're going to be used with serial connections, usually. For example, I've connected these types of connectors to modems and serial printers. I had a few Unix hosts with asynchronous terminals that used these types of serial connectors to connect to the Unix host. I've even had computer mice in the past that would connect using a DB-9 connector going into a serial port on the back of a PC.

Now, I haven't seen a mouse that uses that to connect to a PC in many, many years, but it used to be one of the valid uses of a DB nine. And finally, in this video, we want to talk about a couple of coaxial connectors, the F-Type connector and the BNC connector. The F-Type connector is commonly used to connect to devices such as cable modems, cable TV, cable boxes, and DVRs. And the type of cable that this is terminating is usually an RG-6 or an RG-59 coaxial cable. A, B, and C are three other types of coaxial connectors. And by the way, in the name Band C, the B stands for bayonet. Notice the extending interconnector that is spreading out from the center.

That's sort of like a bayonet sticking out of the center. So we say that's a bayonet connector, and the N and the C and B and C are the initials of the creators of BNC. The N is for Neil, and the C is for Consulman. So it's Bayonet Neil Consulman. That's what a BNC connector is. Now, some people will call it a British Naval Connector, and they'll say that's what BNC stands for. So it really depends on what literature you read. And this is commonly used to transport radio frequencies for a variety of applications. I've used it a lot for electronic test equipment. This type of connector was also used with 10-base-2 or thin networks. But we don't see this type of connector much in networking anymore. This connector was more popular back in the 1980s and 1990s for connecting to a network. That concludes our look at six different types of copper connectors that we may encounter. You.

5. 6.4 Fiber Connectors

As we're interconnecting our network devices with fibre optic cabling, we need to be familiar with some of the different types of fibre connectors that are out there. And in this video, we're going to take a look at four of the more popular connectors that you're likely to see. The first one is an ST connector. This is known by a couple of different names. "St" could stand for a straight tip connector. You see, the fibre is actually in that white piece of plastic that extends beyond the connector.

So we could call it a straight tip or a bayonet connector because it looks kind of like a bayonet. And if we're using this to connect into a piece of equipment, we're going to be using two of these connectors like we see on screen. One is going to be for receiving data, one is for transmitting data, and the connector has a spring in it. You might be able to see that in the graphic. And to connect it, you push it into the device you're reconnecting it with, twist, and release, and the tension in the spring holds that connector in place. Another type of fibre connector is an LC connector.

And depending on what literature you read, you might see it called a loose connector, a local connector, or even a little connector. The LC connector, on the other hand, has a tab on it that you push down to release it so you can unplug it from a port. And one thing you'll notice about the LC connector is that it's a little bit smaller. It's got a smaller form factor, in other words, than an ST connector, which is going to allow us to have a higher density of cabling in the same physical space in a fibre patch panel. A third type of fibre connector is an SC connector. And again, the literature varies depending on what the SC stands for.

You might see it referred to as a subscriber connector, a standard connector, or, since it's square, you might see it called a square connector. And for the St connector, the SC connector, and the LC connector, these different types of connectors are going to require that we have a couple of different fibre strands, each with a connector on each end, because one connector only has one fibre strand used for either transmitting or receiving.

Typically, however, you might run into an Mtrj connector, and if you look really closely, you might be able to see that there are actually two fibres in this one connector that's going to give us a lot more port density than any of the other options because we have both the transmit and receive fibre strands in that same very small connector. And the literature might say that MTRJ stands for media termination. Recommended jack. Or you might see it as a mechanical transfer register. Jack And when you're looking at different types of fibre connectors, you might see an acronym after one of these types.

For example, you might see APC or UPC. Well, let's take a look at what those acronyms mean. First, let's consider the core of the fibre in this connector. Recall that this is an ST connector. And inside of that plastic bayonet sticking out, we have a fibre strand. And that fibre strand has a core piece of glass that's surrounded by another piece of glass called the cladding.

And the index of refraction is so different between the core and the cladding that we're able to keep light inside the core if we don't come into that core using our laser light at too steep an angle. And on screen, that grey rectangle that I've shown you represents the core of this fiber. And we want to think about what happens when we connect two fibres together at the ends like this. If we stick with fibres until the end, that could be what we're doing in a fibre optic patch panel. We might have a coupler that ties those together.

When we do that, there's going to be some loss. The laser light is not going to pass through 100% from the first fibre to the second fiber. That means we're going to have some reflection at the boundary. Let's say that the laser light comes in and hits the boundary. Most of it, hopefully, is going to pass through the boundary. But there's a little bit of reflection that happens. And as a result, some of that light, that laser light, goes back in the other direction. And sometimes the strength of that laserlight might actually damage the transmitter.

And this type of connection, where we're sticking these two fibres against one another and the surfaces are actually touching on both fibre strands, is called an ultra-physical contact connection. And again, as we just saw, it could result in some of the laser light reflecting back to the laser transmitter and maybe damaging it. And the way that we might help mitigate a situation like that is to use, instead of a UPC connector, an APC connector.

That is an oblique physical contact. Here, there's an eight-degree angle sort of shaved off of that fibre strand. So when we join this with another fibre optic cable, it's not going to be a flat surface against a flat surface. There's a bit of an air gap. And as a result, when the laser light comes in again, we're hoping that most of it is going to be transmitted into the other fiber.

And the portion that does get reflected is not going to be reflected straight down the cable. It's going to be reflected at an angle. And as a result, at the degree that it hits that cladding, a lot of that light is going to be going out into the cladding.

And yes, it's possible that a portion of that reflection could keep bouncing back and forth off of the cladding all the way back down to the transmitting laser, but we'll have a significant loss of power that's going to help reduce the probability that this will damage the transmitting laser. And again, this is called an APC, or an angled physical contact.

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