Twisted Pair

The most common type of cable used in today’s networks is twisted pair. It is referred to as twisted pair because the copper wires inside of the cable are twisted together into pairs throughout the entire length of the cable. Regularly, admins use UTP cable, short for unshielded twisted pair. Typical versions of twisted pair include Category 6 and Category 5e (often abbreviated to just Cat 6 or Cat 5e). Table 9.1 shows the various categories of twisted pair you should know for the exam and the networks they are rated for.

Data transfer rate (also known as speed or bandwidth) is normally measured in bits because networks usually transfer data serially, or one bit at a time. 100 Mbps is 100 megabits per second. 1 Gbps is equal to 1 gigabit per second (known as a gigabit network), or 1000 Mbps. 10 Gbps is equal to 10 gigabits per second. Now, a cable might be rated for 10-Gbps networks (such as Cat 6), but you probably won’t attain that speed over the cable. Typically, the actual speed (known as throughput) might be 250 Mbps, 500 Mbps, 1 Gbps, and possibly more. That depends on many factors, including the frequency of the cable (for example, Cat 6 is 250 MHz and Cat 6a is 500 MHz), the technology used to send data, the encoding rate, whether duplexing is involved, the length of the cable, the quality of the installation, and so on. So, it’s difficult to put a specific number to each category of cable—just remember what network speeds each category of cable is rated for.

The Telecommunications Industry Association (TIA) defines standards for cabling and wiring, such as the 568A and 568B standards. Generally speaking, the most common standard you see is the 568B standard. Table 9.2 shows the color sequence for each of the eight wires (or pins) for the 568B and 568A standards. Figure 9.1 shows a close-up of the wires organized for a 568B connection.

Any physical cabling equipment used in the network must comply with this standard. This includes cables, patch panels, jacks, and even connectors. The connector used with twisted-pair networks is known colloquially as the RJ45 (more specifically, the 8P8C connector). RJ45 plugs connect to each end of the cable, and these cables connect to RJ45 sockets within network adapters and on network switches.

As you can see in Figure 9.2, RJ45 plugs look a lot like the plugs that connect your telephone (known as RJ11). However, the RJ45 plug is larger and contains eight wires, whereas the RJ11 plug holds only a maximum of six wires (and normally only uses four).

A standard twisted-pair patch cable that you would use to connect a computer to a switch or RJ45 jack is wired for 568B on each end. That makes it a straight-through cable. However, if you wanted to connect a computer directly to another computer, you would need to use a crossover cable. This type of cable is wired for 568B on one end and 568A on the other. You can see in Table 9.2 that certain pins are “crossed” to each other from 568B to 568A. Pin 1 on 568B crosses to pin 3 on 568A, and pin 2 crosses to 6. You can also use a crossover cable to connect one switch to another; though this is usually not necessary nowadays because most switches will auto-sense the type of cable you plug into them.

UTP has a few disadvantages:

• ▸ It can be run only 100 meters (328 feet) before signal attenuation occurs, which is the weakening or degrading of signal.

• ▸ Its outer jacket is made of plastic and it has no shielding, making it susceptible to electromagnetic interference (EMI) and vulnerable to unauthorized network access in the form of wiretapping.

Because the UTP cable jacket is made of PVCs (plastics) that can be harmful to humans when they catch on fire, most municipalities require that plenum-rated cable be installed in any area that cannot be reached by a sprinkler system. A plenum is an enclosed space used for airflow. For example, if cables are run above a drop ceiling, building code requires that they are plenum-rated. This means that the cable has a special Teflon coating or is a special low-smoke variant of twisted pair, reducing the amount of PVC chemicals that are released into the air in the case of fire.

Because UTP is susceptible to EMI, a variant was developed known as STP or shielded twisted pair. This includes metal shielding over each pair of wires, reducing external EMI and the possibility of unauthorized network access. A couple of disadvantages of STP include higher cost of product and installation and the fact that the shielding needs to be grounded to work effectively. Keep in mind that all server room and wiring closet equipment—such as patch panels, punch blocks, and wiring racks—should be permanently grounded before use.

Coaxial

Coaxial cable is another way to transfer data over a network. This cable has a single conductor surrounded by insulating material, which is then surrounded by a copper screen and, finally, an outer plastic sheath. Some networking technologies still use coaxial cable; for example, cable Internet connections use RG-6 coaxial cable (and possibly the older RG-59 cable). This cable screws on to the terminal of a cable modem using an F-connector. It is the same cable and connector used with cable TV set-top boxes (STB) and DVRs.

Generally, RG-6 cable can be run as far as 500 to 1000 feet. The maximum distance varies because several factors play into how far the data can travel before attenuation (for example, the frequency used, protocol used, and so on). Its speed also varies depending on what type of transmission is sent over it. A typical RG-6 cable has a minimum bandwidth of 1 GHz, which can loosely translate to 1 Gbps, but the data throughput will most likely be capped at some number below that. For example, cable Internet providers will often cap that at 30 Mbps to 50 Mbps, and some fiber optic providers (who change the cable type from fiber optic to coaxial at the house or business) might cap it at anywhere between 100 Mbps and 500 Mbps. This all varies according to the provider and how many services are being transmitted over the same line.

There are two derivatives of RG-6 that you should know: RG-6/U, which is double-shielded, and the more common RG-6/UQ, which is quadruple-shielded and is often referred to as “quad shield.” It is a better option if you are running RG-6 in ceilings or near any electrical appliances.

Fiber Optic

Fiber optic is fast and, when dealing with EMI, it’s a better option than copper-based cables. Because fiber optic cables transmit data by way of light instead of electricity, they can send signals much faster and further than copper wires, and EMI doesn’t even play into the equation. Plus, fiber optic cables are difficult to splice into, unlike copper-based cables. Due to these reasons, fiber optic cable is the most secure type of cable.

You might encounter single-mode and multimode fiber; for the most part, single-mode fiber is used over longer distances, but both types are easily capable of supporting 1000-Mbps and 10-Gbps networks and can be run farther than twisted-pair cable. A couple types of connectors used with fiber include ST and SC, as shown in Figure 9.3. Another connector is LC, which looks quite similar to SC.

Multimode cables have a larger core diameter than single-mode cables. It is the more commonly used fiber optic cable in server rooms and when making network backbone connections between buildings in a campus. It transmits data approximately 600 meters. Single-mode, on the other hand, is used for longer distance runs, perhaps from one city to the next (as far as thousands of kilometers). At shorter distances, single-mode cable can go beyond 10 Gbps.

USB

USB ports are used by many devices, including keyboards, mice, printers, flash drives, and much more. The USB port enables data transfer between the device and the computer and usually powers the device as well. The speed of a USB device’s data transfer depends on the version of the USB port, as shown in Table 9.4.

There are various plugs used for the different types of USB connections. Figure 9.5 displays an illustration of these connectors.

Type A and Type B connectors are commonly used for printers and other larger devices. Mini- and micro-connectors are often used for handheld computers, smartphones, mice, digital cameras, portable music players, and cell phones. USB-C is used for newer smartphones and other devices developed after 2017. However, some companies create proprietary cables and connectors for their devices based off of the USB specifications. These devices will not connect properly to Type A, Type B, and mini- or micro-connectors.

Lightning and Thunderbolt

Lightning is a proprietary port built into Apple devices such as the iPad and iPhone. It’s an 8-pin connector that replaced the 30-pin dock predecessor. As with USB-C, the Lightning connector can be inserted face up or face down. It supports USB 3.0 speeds.

Thunderbolt is a high-speed hardware interface developed by Intel. As of the writing of this book, this is used primarily by Apple computers. It combines elements of PCI Express and DisplayPort technologies. Versions 1 and 2 use the Mini DisplayPort connector and version 3 uses the USB Type-C connector. Thunderbolt 2 gives access to 4K monitors. Because Thunderbolt is based on DisplayPort technology, it provides native support for the Apple Thunderbolt Display and Mini DisplayPort displays.

Thunderbolt can be used to transfer data at high rates to external storage devices or to displays (or both; up to six devices can be daisy-chained, meaning wired together in sequence). If you look at the ports of the computer and see the thunderbolt icon next to the Mini DisplayPort port, then it is meant to be used for data transfer to peripherals. If you see a display icon, then it can be used with a monitor. While you can physically connect a Thunderbolt device to a Mac with DisplayPort, the device will not work, but if you connect a DisplayPort device to a Mac with Thunderbolt, the device will work. Table 9.5 describes the different versions of Thunderbolt.

Serial

The term serial is used with many technologies: USB, Serial-attached SCSI, bit streams over network cables, and so on; but generally, if a person refers to serial connections for peripheral devices, that person is talking about the Recommended Standard 232 (RS-232) data transmission standard. Though it is an old technology, it is still used in many environments. For example, the RS-232 standard describes how DTEs (computers) and DCEs (dial-up modems) communicate using serial ports.

RS-232 communicates via serial cables that have either 9 wires (DE-9, also known as DB-9) or 25 wires (DB-25). RS-232 has been used for many years, and that will most likely continue. That is because of its simple design, and the vast array of devices out there that use RS-232 interfaces such as handheld and mountable terminals, networking equipment, industrial machines, and analytical instruments. Because of this, you can still find motherboards with a built-in RS-232 port—usually a DE-9. If a computer does not have one, and you need to access RS-232-based equipment, there are PCIe add-on cards. And for laptops and other mobile devices, there are USB to RS-232 converters. RS-232 and other Recommended Standards (such as RS-422 and RS-485) are published by the TIA, the same organization that publishes the standard for 568B.