Chapter 3

Networking Topologies, Connectors, and Wiring Standards

The Following CompTIA Network+ Exam Objectives Are Covered in This Chapter:

• 3.1 Categorize standard media types and associated properties.
  • Fiber:
• Multimode
• Singlemode
• Copper:
• UTP
• STP
• CAT3
• CAT5
• CAT5e
• CAT6
• CAT6a
• Coaxial
• Crossover
• T1 Crossover
• Straight-through
• Plenum vs. non-plenum
• Media converters:
• Singlemode fiber to Ethernet
• Multimode fiber to Ethernet
• Fiber to Coaxial
• Singlemode to multimode fiber
• Distance limitations and speed limitations
• Broadband over powerline
• 3.2 Categorize standard connector types based on network media.
  • Fiber:
• ST
• SC
• LC
• MTRJ
• Copper:
• RJ-45
• RJ-11
• BNC
• F-connector
• DB-9 (RS-232)
• Patch panel
• 110 block (T568A, T568B)
• 3.8 Identify components of wiring distribution.
  • IDF
  • MDF
  • Demarc
  • Demarc extension
  • Smart jack
  • CSU/DSU

The idea of connecting a bunch of computers together hasn’t changed a whole lot since the mid-1980s, but how we go about doing that certainly has. Like everything else, the technologies and devices we create our networks with have evolved dramatically and will continue to do so in order to keep up with the ever-quickening pace of life and the way we do business.

When you connect computers together to form a network, you want error-free, blazingly fast communication, right? Although “error-free” and reality don’t exactly walk hand in hand, keeping lapses in communication to a minimum and making that communication happen really fast is definitely possible. But it isn’t easy, and understanding the types of media and network topologies used in networking today will go far in equipping you to reach these goals. So will being really knowledgeable about and familiar with the array of components and devices used to control network traffic.

All of these networking ingredients are going to be the focus of this chapter. In it, I’ll cover different types of networking media, discuss common topologies and devices, and compare the features that they all bring into designing a solid network that’s as problem free and turbo charged as possible.

Physical Media

A lot of us rely on wireless networking methods that work using technologies like radio frequency and infrared, but even wireless depends on a physical media backbone in place somewhere. And the majority of installed LANs today communicate via some kind of cabling, so let’s take a look at the three types of popular cables used in modern networking designs:

• Coaxial
• Twisted-pair
• Fiber optic

Coaxial Cable

Coaxial cable, referred to as coax, contains a center conductor made of copper that’s surrounded by a plastic jacket with a braided shield over it. A plastic such as polyvinyl chloride (PVC) or fluoroethylenepropylene (FEP, commonly known as Teflon) covers this metal shield. The Teflon-type covering is frequently referred to as a plenum-rated coating, and it’s definitely expensive but often mandated by local or municipal fire code when cable is hidden in walls and ceilings. Plenum rating applies to all types of cabling and is an approved replacement for all other compositions of cable sheathing and insulation like PVC-based assemblies.

The difference between plenum and non-plenum cable comes down to how each is constructed and where you can use it. Many large multistory buildings are designed to circulate air through the spaces between the ceiling of one story and the floor of the next; this space between floors is referred to as the plenum. And it just happens to be a perfect spot to run all the cables that connect the legions of computers that live in the building. Unless there’s a fire—if that happens, the plenum cable becomes a serious hazard because its insulation gives off poisonous smoke that gets circulated throughout the whole building. Plus, plenum cables can actually become “wicks” for the fire, helping it quickly spread from room to room and floor to floor—yikes!

Because it’s a great goal to prevent towering infernos, the National Fire Protection Association (NFPA) demands that cables run within the plenum have been tested and guaranteed as safe. They must be fire retardant and create little or no smoke and poisonous gas when burned. This means you absolutely can’t use a non-plenum-type cable in the plenum, but it doesn’t mean you can’t use it in other places where it’s safe. And because it’s a lot cheaper, you definitely want to use it where you can.

Thin Ethernet, also referred to as thinnet or 10Base2, is a thin coaxial cable. It is basically the same as thick coaxial cable except it’s only about ¼ inch in diameter. Thin Ethernet coaxial cable is Radio Grade 58, or just RG-58. Figure 3-1 shows an example of thinnet. This connector resembles the coaxial connector used for cable TV which is called an F connector.

Oh, by the way, if you use thinnet cable, you’ve got to use BNC connectors to attach stations to the network, as shown in Figure 3-2.

You can attach a BNC connector with a crimper that looks like a weird pair of pliers and has a die to crimp the connector. A simple squeeze crimps the connector to the cable. You can also use a screw-on connector, but I avoid doing that because it’s not very reliable.

Table 3-1 lists some specifications for the different types of coaxial cable, but understand that we use only RG-59 and RG-6 in today’s world.

Table 3-1: Coaxial cable specifications

Twisted-Pair Cable

Twisted-pair cable consists of multiple individually insulated wires that are twisted together in pairs. Sometimes a metallic shield is placed around them, hence the name shielded twisted-pair (STP). Cable without outer shielding is called unshielded twisted-pair (UTP), and it’s used in twisted-pair Ethernet (10BaseT, 100BaseTX, 1000BaseTX) networks.

Ethernet Cable Descriptions

Ethernet cable types are described using a code that follows this format: N<Signaling>X. The N refers to the signaling rate in megabits per second, <Signaling> stands for the signaling type—either baseband or broadband—and the X is a unique identifier for a specific Ethernet cabling scheme.

Here’s a common example: 100BaseX. The 100 tells us that the transmission speed is 100Mb, or 100 megabits. The X value can mean several different things, and the T is short for twisted-pair. This is the standard for running 100-Megabit Ethernet over two pairs (four wires) of Category 5, 5e, or 6 UTP.

So why are the wires in this cable type twisted? Because when electromagnetic signals are conducted on copper wires in close proximity—like inside a cable—it causes interference called crosstalk. Twisting two wires together as a pair minimizes interference and even protects against interference from outside sources. This cable type is the most common today for the following reasons:

• It’s cheaper than other types of cabling.
• It’s easy to work with.
• It allows transmission rates that were impossible 10 years ago.

UTP cable is rated in these categories:

Category 1 Two twisted wire pairs (four wires). It’s the oldest type and is only voice grade—it isn’t rated for data communication. People refer to it as plain old telephone service (POTS). Before 1983, this was the standard cable used throughout the North American telephone system. POTS cable still exists in parts of the Public Switched Telephone Network (PSTN) and supports signals limited to the 1MHz frequency range.

Category 2 Four twisted wire pairs (eight wires). It handles up to 4Mbps, with a frequency limitation of 10MHz, and is now obsolete.

Category 3 Four twisted wire pairs (eight wires) with three twists per foot. This type can handle transmissions up to 16MHz. It was popular in the mid-1980s for up to 10Mbps Ethernet, but it’s now limited to telecommunication equipment and, again, is obsolete for networks.

Category 4 Four twisted wire pairs (eight wires), rated for 20MHz. Also obsolete.

Category 5 Four twisted wire pairs (eight wires), rated for 100MHz. But why use Cat 5 when you can use Cat 5e for the same price? I am not sure you can even buy plain Cat 5 anymore!

Category 5e (enhanced) Four twisted wire pairs (eight wires), rated for 100MHz, but capable of handling the disturbance on each pair that’s caused by transmitting on all four pairs at the same time—a feature that’s needed for Gigabit Ethernet. Any category below 5e shouldn’t be used in today’s network environments.

Figure 3-3 shows a basic Cat 5e cable with the four wire pairs twisted to reduce crosstalk.

Category 6 Four twisted wire pairs (eight wires), rated for 250MHz. Cat 6 became a standard back in June 2002. You would usually use it as riser cable to connect floors together. If you’re installing a new network in a new building, there’s no reason to use anything but Category 6 UTP cabling as well as running fiber runs between floors.

Category 6a (Augmented) Basic category 6 cable has a reduced maximum length when used for 10GBaseT; however, Category 6a cable, or Augmented Category 6, is characterized to 500MHz and has improved crosstalk characteristics, which allows10GBaseT to be run for up to 100 meters. The most important point is a performance difference between ISO/IEC and EIA/TIA component specifications for the NEXT (near-end crosstalk) transmission parameter. Running at a frequency of 500MHz, an ISO/IEC Cat 6a connector provides double the power (3db) of a Cat 6A connector that conforms with the EIA/TIA specification. Note that 3 dB equals a 100 percent increase of a near-end crosstalk noise reduction. This is our future cable indeed!

Connecting UTP

BNC connectors won’t fit very well on UTP cable, so you need to use a registered jack (RJ) connector, which you’re familiar with because most telephones connect with them. The connector used with UTP cable is called RJ-11 for phones that use four wires; RJ-45 has four pairs (eight wires), as shown in Figure 3-4.

Figure 3-5 shows the pin-outs used in a typical RJ-45 connector. Looking from the bottom of the connector, pin 1 would be on the left.

Most of the time, UTP uses RJ connectors; you use a crimper to attach them to a cable, just as you would with BNC connectors. The only difference is that the die that holds the connector is a different shape. Higher-quality crimping tools have interchangeable dies for both types of cables. We do not use RJ-11 for local area networks (LANs), but we do use them for our home Digital Subscriber Line (DSL) connections.

Fiber-Optic Cable

Because fiber-optic cable transmits digital signals using light impulses rather than electricity, it’s immune to EMI and RFI.

Anyone who’s seen a network’s UTP cable run down an elevator shaft would definitely appreciate this fiber feature. Fiber cable allows light impulses to be carried on either a glass or a plastic core. Glass can carry the signal a greater distance, but plastic costs less. Whichever the type of core, it’s surrounded by a glass or plastic cladding with a different refraction index that reflects the light back into the core. Around this is a layer of flexible plastic buffer that can be wrapped in an armor coating that’s usually Kevlar, which is then sheathed in PVC or plenum.

The cable itself comes in either single-mode fiber (SMF) or multimode fiber (MMF); the difference between them is in the number of light rays (the number of signals) they can carry. Multimode fiber is most often used for shorter-distance applications and single-mode fiber for spanning longer distances.

Although fiber-optic cable may sound like the solution to many problems, it has pros and cons just like the other cable types.

Here are the pros:

• It’s completely immune to EMI and RFI.
• It can transmit up to 40 kilometers (about 25 miles).

And here are the cons:

• It’s difficult to install.
• It’s more expensive than twisted-pair.
• Troubleshooting equipment is more expensive than twisted-pair test equipment.
• It’s harder to troubleshoot.

Single-Mode Fiber

Single-mode fiber-optic cable (SMF) is a very high-speed, long-distance media that consists of a single strand—sometimes two strands—of glass fiber that carries the signals. Light-emitting diodes (LEDs) and laser are the light sources used with SMF. The light source is transmitted from end to end and pulsed to create communication. This is the type of fiber cable employed to span really long distances because it can transmit data 50 times further than multimode fiber at a faster rate.

Clearly, because the transmission media is glass, the installation of SMF can be a bit tricky. Yes, there are outer layers protecting the glass core, but the cable still shouldn’t be crimped or pinched around any tight corners.

Multimode Fiber

Multimode fiber-optic cable (MMF) also uses light to communicate a signal, but with it, the light is dispersed on numerous paths as it travels through the core and is reflected back. A special material called cladding is used to line the core and focus the light back onto it. MMF provides high bandwidth at high speeds over medium distances (up to about 3,000 feet), but beyond that it can be really inconsistent. This is why MMF is most often used within a smaller area of one building; SMF can be used between buildings.

MMF is available in glass or in a plastic version that makes installation a lot easier and increases the installation’s flexibility.

Fiber-Optic Connectors

A whole bunch of different types of connectors are available to use with fiber-optic cables, but the two most popular are the straight tip (ST) and subscriber (or square) connector (SC). The ST fiber-optic connector (developed by AT&T) is one of the most widely used fiber-optic connectors; it uses a BNC attachment mechanism similar to thinnet’s that makes connections and disconnections fairly frustration free. In fact, this is the feature that makes this connector so popular. Figure 3-6 shows an example of an ST connector. Notice the BNC attachment mechanism.

The SC connector is another type of fiber-optic connector. As you can see in Figure 3-7, SC connectors are latched—a mechanism holds the connector in securely and prevents it from falling out.

SC connectors work with either single-mode or multimode optical fibers and will last for around 1,000 matings. They’re being used more now but still aren’t nearly as popular as ST connectors for LAN connections.

Small Form Factor Fiber-Optic Connectors

Another cool fiber-optic connector is the small form factor (SFF) connector, which allows more fiber-optic terminations in the same amount of space than its standard-sized counterparts. The two most popular versions are the mechanical transfer registered jack (MT-RJ or MTRJ), designed by AMP, and the Local Connector (LC), designed by Lucent.

The MT-RJ fiber-optic connector was the first small form factor fiber-optic connector to be widely used, and it’s only one-third the size of the SC and ST connectors it most often replaces. It offers these benefits:

• Small size
• TX and RX strands in one connector
• Keyed for single polarity
• Pre-terminated ends that require no polishing or epoxy
• Easy to use

Figure 3-8 shows an example of an MT-RJ fiber-optic connector.

LC is a newer style of SFF fiber-optic connector that’s pulling ahead of the MT-RJ. It is especially popular for use with Fibre-Channel adapters (FCs) and is a standard used for fast storage area networks and Gigabit Ethernet adapters. Figure 3-9 depicts an example of the LC connector.

It has similar advantages to MT-RJ and other SFF-type connectors but is easier to terminate. It uses a ceramic insert just as standard-sized fiber-optic connectors do.

Media Converters

There may be instances where you need to convert from one media type to another. It could be that you need to go from one mode of fiber to another mode, or it could be more extreme and you need to go from fiber to Ethernet. Here are some of the more common media converters:

Single-mode fiber to Ethernet These devices accept a fiber connector and an Ethernet connector and convert the signal from Ethernet and single-mode fiber (see Figure 3-10).

Multimode fiber to Ethernet These devices accept a fiber connector and an Ethernet connector and convert the signal from Ethernet and multi-mode fiber (see Figure 3-11).

Fiber to coaxial These devices accept a fiber connector and a coaxial connector and convert digital signals from optical to coax (see Figure 3-12).

Singlemode to multimode fiber These devices accept a single-mode fiber connector and a multimode fiber connector and convert the signals between the two (see Figure 3-13).

Broadband over Power Line

In February 2011, the IEEE finally published a standard for Broadband over Power Line (BPL) called IEEE 1901; this is also referred to as Power Line Communication (PLC) or even Power Line Digital Subscriber Line (PDSL). Although this technology has been available for decades in theory, without an IEEE standard it was just not adopted as an alternative to other high-speed media.

However, it is highly likely that this technology will really start to see some traction, especially from the power companies who will be able to gather data from every device in your house and specifically tell you how much power is being used by your refrigerator, washers and dryers, and especially your computer and televisions, among all the other devices plugged into a wall power outlet.

BPL will allow you to just plug a computer into a wall power socket and have more than 500Mbps (in the future) for up to 1,500 meters.

Near my home in Boulder, Colorado, Xcel Energy is using BPL in combination with radio links for its SmartGridCity pilot project, which will send data from power meters, hot water heaters, thermostats, and more.

An example of an adaptor is shown in Figure 3-14.

This technology can be used to deliver Internet access to the home as well. For a computer (or any other device), you would need only to plug a BPL modem into any outlet in an equipped building to have high-speed Internet access. The basic BPL installation is shown in Figure 3-15.

After the gateway is connected through the coupler to the meter bank for the building, any electrical outlet can be used with the BPL modem to receive the ISP connection to the Internet. Challenges that still exist include (1) the fact that power lines are typically noisy and (2) the frequency at which the information is transmitted is used by shortwave and the unshielded power lines can act as antennas, thereby interfering with shortwave communications.

Serial Cables

Except for multimode fiber, all the cable flavors I’ve talked about so far are considered serial cable types. In network communications, serial means that one bit after another is sent out onto the wire or fiber and interpreted by a network card or other type of interface on the other end.

Each 1 or 0 is read separately and then combined with others to form data. This is very different from parallel communication where bits are sent in groups and have to be read together to make sense of the message they represent. A good example of a parallel cable is an old printer cable—which has been replaced by USB, as I’ll get to in a minute.

RS-232

Recommended Standard 232 (RS-232) was a cable standard commonly used for serial data signals connecting data-terminal equipment and data-communications equipment, such as computer’s serial port to an external modem.

Figure 3-16 shows an example of one of the many types of RS-232 cables. These cables normally connect to a connector on the device called a DB-9.

Because most laptops don’t even come with these types of connectors anymore, they’ve pretty much been replaced by things like USB and FireWire.

Universal Serial Bus

Universal Serial Bus (USB) is now the built-in serial bus du jour of most motherboards. You usually get a maximum of 4 external USB interfaces, but add-on adapters can take that up to as many as 16 serial interfaces. USB can actually connect a maximum of 127 external devices, and it’s a much more flexible peripheral bus than either serial or parallel.

We use USB to connect printers, scanners, and a host of other input devices like keyboards, joysticks, and mice. When connecting USB peripherals, you’ve got to connect them either directly to one of the USB ports (as shown in Figure 3-17) on the PC or to a USB hub that is connected to one of those USB ports.

Hubs can be chained together to provide multiple USB connections, but even though you can connect up to 127 devices, it’s really not practical to go there. Each device has a USB plug, as shown in Figure 3-18.

Cable Properties

The reason we use so many different types of cables in a network is that each type has its own set of properties that specifically make it the best to use for a particular area or purpose. Different types vary in transmission speeds, distance, duplex, noise immunity, and frequency, and I’ll cover each of these next.

Transmission Speeds

Based on the type of cable or fiber you choose and the network that it’s installed in, network administrators can control the speed of a network to meet the network’s traffic demands. Admins usually permit, or would like to have, transmission speeds of up to 10Gbps or higher on the core areas of their networks that connect various network segments. In the distribution and access areas, where users connect to switches, it’s typically 100Mbps per connection, but transmission speeds are creeping up because the traffic demand is getting higher.

Distance

A deciding factor used in choosing what cable type to use is often the topology of a network and the distance between its components. Some network technologies can run much further than others without communication errors, but all network communications technologies are prone to attenuation—the degradation of signal due to the medium itself and the distance signals have to travel. Some cable types suffer from attenuation more than others. For instance, any network using twisted-pair cable should have a maximum segment length of only 328 feet (100 meters).

Duplex

All communications are either half duplex or full duplex. The difference is whether the communicating devices can “talk” and “listen” at the same time.

During half-duplex communication, a device can either send communication or receive communication, but not both at the same time. Think walkie-talkie—when you press the button on the walkie-talkie, you turn the speaker off and you can’t hear anything the other side is saying.

In full-duplex communication, both devices can send and receive communication at the same time. This means that the effective throughput is doubled and communication is much more efficient. Full-duplex is typical in most of today’s switched networks. I’ll discuss both full and half duplex in more detail in Chapter 4, “The Current Ethernet Specifications.”

Noise Immunity (Security, EMI)

Any time electrons are pushed through two wires next to each other, it creates a magnetic current. And we can create a current in the wires. This is good because without magnetic flux, we wouldn’t be using computers—the power that surges through them is a result of it. The bad news is that it also creates two communications issues.

First, because the wire is creating a current based on the 1s and 0s coursing through it, with the right tools in hand, people can read the message in the wire without cutting it or even removing the insulation. You’ve heard of this—it’s called tapping the wire, and it’s clearly a valid security concern. In ancient history, high-security installations like the Pentagon actually encased communication wires in lead shielding to prevent them from being tapped. STP wires make tapping a little harder, but not hard enough.

The best way to solve the magnetic-flux problem caused by electricity is to not use these wires at all. As I said, fiber-optic cables carry the signal as light on a glass or a really pure plastic strand, and light is not susceptible to magnetic flux, making fiber optics a whole lot harder to tap. It’s still not impossible—you can do it at the equipment level, but you have to actually cut and then repair the cable to do that, which isn’t likely to go unnoticed.

The second magnetic-flux issue comes from the outside in instead of from the inside out. Because wires can take on additional current if they’re near any source of magnetism, you’ve got to be really careful where you run your cables. You can avoid EMI by keeping copper cables away from all powerful magnetic sources like electric motors, speakers, amplifiers, fluorescent light ballasts, and so on. Just keep them away from anything that can generate a magnetic field!

Frequency

Each cable type has a specified maximum frequency that gives you the transmission bandwidth it can handle. Cat 5e cable is tested to 100MHz maximum frequency and can run 1Gbps signals for relatively short distances. That’s maxing it out, but it’s still good for connecting desktop hosts at high speeds. On the other hand, Cat 6 is a 250MHz cable that can handle 1Gbps data flow all day long with ease. Cat 6 has a lot more twists and thicker cables, so it is best used when connecting floors of a building.

Wiring Standards

Ethernet cabling is an important thing to understand, especially if you’re planning to work on any type of LAN. There are different types of wiring standards available:

• 568A
• 568B
• Straight-through
• Crossover

We will look into each one of these, and then I’ll end this discussion with some examples for you.

568A vs. 568B

If you look inside a network cable, you will find four pairs of wires twisted together to prevent crosstalk; they’re also twisted like this to help prevent EMI and tapping. The same pins have to be used on the same colors throughout a network to receive and transmit, but how do you decide which color wire goes with which pin? The good news is that you don’t have to decide—at least not completely.

Two wiring standards have surfaced that have been agreed on by over 60 vendors, including AT&T, 3Com, and Cisco (although there isn’t 100 percent agreement). In other words, over the years, some network jacks have been pinned with the 568A standard and some have used the 568B standard, which can cause a bit of confusion if you don’t know what you’re looking at in your network.

568A By looking at Figure 3-19, you can see that the green pair is used for pins 1 and 2 but the orange pair is split to pins 3 and 6, separated by the blue pair.

568B Now take a look at Figure 3-20. The orange pair is pins 1 and 2 and the green pair is pins 3 and 6, again separated by the blue pair.

If you’re thinking, “What’s the difference, and why does it matter?” the answer is the position of four wires on one side of the cable—that’s it! There are eight wires in each UTP cable; pins 4, 5, 7, and 8 aren’t used in either standard.

This only leaves the wire pairs to connect to pins 1, 2, 3, and 6. Remember, if we connect the green-white, green, orange-white, and orange wires to pins 1, 2, 3, and 6, respectively, on both sides of the cable, we’re using the 568A standard and creating the kind of straight-through cable that’s regularly implemented as a regular patch cable for most networks. On the other hand, if we switch from pin 1 to pin 3 and from pin 2 to pin 6 on one side only, we’ve created a crossover cable for most networks. Let’s take a look.

Straight-Through Cable

The straight-through cable is used to connect a host to a switch or hub or a router to a switch or hub.

Four wires are used in straight-through cable to connect Ethernet devices. It’s really pretty simple to do this; Figure 3-21 depicts the four wires used in a straight-through Ethernet cable.

Notice that only pins 1, 2, 3, and 6 are used. Connect 1 to 1, 2 to 2, 3 to 3, and 6 to 6, and you’ll be up and networking in no time. Just remember that this would be a 10/100 Ethernet-only cable, and it wouldn’t work with 1000Mbps Ethernet, voice, Token Ring, ISDN, and so on.

Crossover Cable

The same four wires are used in this cable, and just as with the straight-through cable, you just connect the different pins together. Crossover cables can be used to connect these devices:

• Switch to switch
• Hub to hub
• Host to host
• Hub to switch
• Router direct to host

Check out Figure 3-22, which demonstrates how each of the four wires are used in a crossover Ethernet cable.

Okay—did you notice that instead of connecting 1 to 1, 2 to 2, and so on, we connected pins 1 to 3 and 2 to 6 on each side of the cable? A crossover cable is typically used to connect two switches together, but it can also be used to test communications between two workstations directly, bypassing the switch.

A crossover cable is used only in Ethernet UTP installations. You can connect two workstation NICs or a workstation and a server NIC directly with it.

If you are trying to match the straight-through and crossover cables with the 568A and 568B standard, here is how it would look:

568A+568A = straight through

568B+568B = straight through

568A+568B = crossover

It’s really cool that you can carry a crossover cable with you in your tool bag along with your laptop—then, if you want to ensure that a server’s NIC is functioning correctly, you can just connect your laptop directly to the server’s NIC using your handy crossover cable. You should be able to log in to the server if both NICs are configured correctly.

Use a cable tester to make sure that what you’re dealing with is in fact a crossover cable. The tester can also tell you if there’s a problem with the cable. Figure 3-23 shows an inexpensive cable tester for UTP.

This cost-effective little tool will tell you beyond a shadow of a doubt if you have a straight-through or crossover cable—or even if there’s a problem with the cable.

T1 Crossover Cable

In Chapter 5 you will be introduced to a device called the CSU/DSU. This device may be your connection to the Internet for the enterprise. The type of cable you use to connect to this device from your router depends on the interface types that are available on the router.

The router may connect with several types of serial cables if a T1 connection is not built into the router. If a T1 connection is built into the router, you will use an Ethernet cable. Figure 3-24 shows a T1 crossover cable connected to a T568B connection.

In rare instances you may have the need to run a cable between two CSU/DSUs. In that case you will need a T1 crossover cable. A T1 cable uses T568B pairs 1 and 2, so to connect two T1 CSU/DSU devices back-to-back requires a crossover cable that swaps these pairs. Specifically, pins 1, 2, 4, and 5 are connected to 4, 5, 1, and 2, respectively.

Installing Wiring Distributions

By now, you’re probably getting the idea that there are a lot more components in the average computer networks than meets the eye, right? If this isn’t exactly a news bulletin to you, then you either already are, or have been, involved in the initial installation of the network. If the latter describes you, you probably will be, or already are, involved in the purchase and installation of the components that will connect the computers throughout your organization’s building. And it may also be up to you to verify that all of the network components have been installed properly and tested. So, let’s go over each of these components and the process of verifying their proper installation.

MDF/IDF

The main distribution frame (MDF) is a wiring point that’s generally used as a reference point for telephone lines. It’s also considered the WAN termination point. It’s installed in the building as part of the prewiring, and the internal lines are connected to it. After that, all that’s left is to connect the external (telephone company) lines to the other side to complete the circuit. Often, another wire frame called an intermediate distribution frame (IDF) is located in an equipment or telecommunications room. It is connected to the MDF and is used to provide greater flexibility for the distribution of all the communications lines to the building. It is typically (and better be) a sturdy metal rack designed to hold the bulk of cables coming from all over the building!

25 Pair

A 25-pair cable consists of 25 individual pairs of wires all inside one common insulating jacket. It’s not generally used for data cabling, just for telephone cabling, and especially for backbone and cross-connect cables because it reduces the cable clutter significantly. This type of cable is often referred to as a feeder cable because it supplies signal to many connected pairs.

110 Block

A newer type of wiring distribution point called a 110 block has replaced most telephone wire installations and is also used for computer networking. On one side, wires are punched down; the other side has RJ-11 (for phone) or RJ-45 (for network) connections.

You’ll find 110 blocks in sizes from 25 to more than 500 wire pairs, and some are capable of carrying 1Gpbs connections when used with Category 6 cables. The hitch is that using Cat 6 with the 110 block is really difficult because of the size of the Cat 6 wiring.

Demarc/Demarc Extension

The demarc (short for demarcation) is the last point of responsibility of the service provider. It’s often at the MDF in your building connection (if your building is large), but it’s usually just an RJ-45 jack that your channel service unit/data service unit (CSU/DSU) connects into from your router to wide area network (WAN) connections (CSU/DSUs are explained in detail in Chapter 16 “Wide Area Networks”).

When troubleshooting, network admins often test for connectivity on both sides of the demarc to determine if the problem is internal or external. The length of copper or fiber that begins after the demarc but still doesn’t reach all the way up to your office is referred to as a demarc extension.

Smart Jack

A smart jack, also called a network interface device (NID) or network interface unit, is owned by the PSTN and is a special network interface that’s often used between the service provider’s network and the internal network. You can’t physically test to an actual demarc because it is just an RJ-45 jack, but the service provider may install a NID that has power and can be looped for testing purposes.

The smart-jack device may also provide for code and protocol conversion, making the signal from the service provider usable by the devices on the internal network like the CSU/DSU.

Summary

I know getting through this chapter probably wasn’t the most fun you’ve had recently. But understanding all those types of wires and cabling, along with their unique capacities, their associated standards, and the right connectors to use with them plus where to place them is integral to having a solid, foundational understanding of the things that make a great network run quickly and reliably.

It’s critical for you to grasp the basics of networking. Having the facts about how a good network is designed and implemented and what goes into that process will make you an effective and efficient technician—and maybe, some day, a highly paid system administrator.

Exam Essentials

Understand the various types of cables used in today’s networks. Coaxial (other than for cable modems) is rarely used, but twisted-pair and fiber optic cable are very common in today’s networks.

Understand the various types of ends that are used on each type of cable. Coax uses BNC; twisted-pair uses RJ-11 for voice and RJ-45 for data; and fiber uses various ends, depending on its use.

Describe the various types of media converters that are available. These include single mode fiber to Ethernet, multimode fiber to Ethernet, fiber to coaxial, and single mode to multimode fiber.

Understand what a 568A to 568A cable is. A 568A to 568A cable is also known as an Ethernet straight-through cable and is used to connect hosts to switches, for example.

Understand what a 568A to 568B cable is. A 568A to 568B cable is also known as an Ethernet crossover cable and is used to connect switches to switches, for example.

Define the function of a T1 crossover cable. In rare instances, you may have the need to run a cable between two CSU/DSUs. In that case, you will need a T1 crossover cable. A T1 cable uses T568B pairs 1 and 2, so to connect two T1 CSU/DSU devices back-to-back requires a crossover cable that swaps these pairs. Specifically, pins 1, 2, 4, and 5 are connected to 4, 5, 1, and 2, respectively.

Describe the operation of Broadband over Power Line. BPL allows for the transmission of data over existing power lines, both for networking home computers and for receiving Internet access to a building.

Written Lab

In this section, write the answers to the following questions:

1. Which UTP wiring uses four twisted wire pairs (eight wires) and is rated for 250MHz?

2. The point at which the operational control or ownership changes from your company to a service provider is referred to as ___________________.

3. Which type of cable will you use to connect switches?

4. Which RG rating of coax is used for cable modems?

5. Which UTP uses four twisted wire pairs (eight wires), is rated for 100MHz, and is capable of handling the disturbance on each pair caused by transmitting on all four pairs at the same time?

6. You want to connect a host to a switch port. What type of Ethernet cable will you use?

7. In what instance would you use T1 crossover cable?

8. 568A uses which pins to make a connection?

9. 568B uses which pins to make a connection?

10. What are two advantages of fiber-optic cabling?

You can find the answers in Appendix B.

Review Questions

You can find the answers in Appendix A.

1. Why would a network administrator use plenum-rated cable during an installation? (Choose two.)

A. Low combustion temperature

B. High combustion temperature

C. Reduces toxic gas released during a fire

D. Is not susceptible to any interference

2. Which of the following Ethernet Unshielded twisted-pair cabling types are commonly used?

A. 10BaseT

B. 100BaseTX

C. 1000BaseTX

D. All of the above

3. In which of the following categories is UTP cable not rated?

A. Category 2

B. Category 3

C. Category 5e

D. Category 8

4. What type of connector does UTP cable typically use?

A. BNC

B. ST

C. RJ-45

D. SC

5. Which of the following provides the longest cable run distance?

A. Single-mode fiber

B. Multimode fiber

C. Category 3 UTP

D. Coax

6. You need to crimp on a connector using an RJ-45 connector. Which pin-out configuration would you use to connect a host into a switch?

A. UTP

B. Straight-through

C. Crossover

D. Rolled

7. Fiber-optic cable is immune to electromagnetic interference (EMI) and radio frequency interference (RFI) because it ___________________ .

A. Transmits analog signals using electricity

B. Transmits analog signals using light impulses

C. Transmits digital signals using light impulses

D. Transmits digital signals using electricity

8. What type of cable transmits lights from end to end?

A. Coax

B. Fiber-optic

C. UTP

D. Category 2

9. What is the main difference between single-mode fiber (SMF) and multimode fiber (MMF)?

A. Electrical signals.

B. Number of light rays.

C. Number of digital signals.

D. Signal-mode can be run a shorter distance.

10. What type of cable should be used if you need to make a cable run longer than 100 meters?

A. Category 5e

B. Category 6

C. Fiber-optic

D. Coaxial

11. Which of the following are fiber-optic connectors? (Select three.)

A. BNC

B. ST

C. RJ-11

D. SC

E. LC

F. RJ-45

12. You need to connect two devices on a vertical connect and they need to send voice traffic. Which of the following cable will you use?

A. Cat 3

B. Cat 5

C. Cat 8

D. Rolled

13. How many hosts on a half-duplex segment can talk at one time?

A. 0

B. 1

C. 2

D. Unlimited

14. Which type of cable does EMI have the least effect on?

A. Coax

B. Fiber-optic

C. UTP

D. STP

15. How many devices can be connected to a full-duplex segment?

A. 0

B. 1

C. 2

D. 4

16. How many wires are used in a 100 Mbps UTP transmission?

A. 2

B. 4

C. 6

D. 8

17. A crossover cable is used to connect all of the following except ___________________.

A. Switch to switch

B. Host to host

C. Hub to switch

D. Host to switch

18. How is a T1 crossover cable crosses wired?

A. Pins 1, 2, 4, and 5 are connected to 4, 5, 1, and 2.

B. Pins 2, 3, 4, and 5 are connected to 4, 5, 1, and 2.

C. Pins 1, 2, 4, and 5 are connected to 3, 4, 5,and 6.

D. Pins 4, 5, 6, and 7 are connected to 4, 5, 1, and 2.

19. The purpose of the demarcation point is to separate the customer from whom?

A. The branch office

B. Headquarters

C. The data center

D. The service provider

20. You need to make a 568B cable for a FastEthernet link. How many pairs will you use?

A. 1

B. 2

C. 3

D. 4