The A+ Certification & PC Repair Handbook (Charles River Media Networking/Security)

There are more than 2,500 types of cable in use for connecting computers and peripherals. The majority of computers today still use some type of wire or cable to transmit data from one system to another. There are three main types of network cables in use that you need to be familiar with for the Core exam: coaxial, twisted pair, and fiber optic. Each of these cable types has characteristics that set it apart from the others, such as cost, distance limitations, data transfer methods, data transfer rates, and installation methods used. The exam will focus on your ability to identify which technology is used by a certain cable category, and which cable medium should be used to connect two or more specific devices.

Coaxial Cable

Coaxial cable is a type of copper cabling that is often times used for Ethernet local area network and cable TV connections. There are two common types of coaxial cable, they are thicknet and thinnet which are described next.

Thicknet

Thicknet coaxial cable, also known as 10Base5, is approximately half an inch thick; it is a heavy type of cable with a copper core, which was used with early mainframe computers and early networks. Thicknet coaxial still exists, but it is very limited in its ability to achieve the high data transfer rates that are needed to support today’s bandwidth-hungry computers and applications.

Thicknet coaxial cable has the ability to carry 10Mb (megabits) of data a total distance of 500 meters, or approximately 1,500 feet. Thus, the naming convention scheme of 10Base5 has been established for coaxial cable. In other words, 10Base5 means that 10Mb of information can travel over a baseband medium, or base, a total of 500 meters (the naming convention drops the last two zeros): 5 100 = 1,500 feet; the true measurement is closer to 1,640 feet.

Thicknet coaxial cable was and sometimes still is used as a backbone connection that connects to a small thinnet cable by use of a vampire tap and an Attachment Unit Interface (AUI) connector.

Thinnet

Thinnet coaxial cable, also known as 10Base2, is approximately a quarter-inch thick. It is a thinner, more flexible type of coaxial cable that is usually connected directly to an NIC with a BNC or BNC T-connector. Figure 21.8 displays a BNC and BNC T-connector. Thinnet is much easier to install and work with than thicknet, but thinnet only carries a data signal the distance of 185 meters, or approximately 607 feet.

Figure 21.8: A BNC and BNC T-connector.

Both thicknet and thinnet coaxial can make up a network referred to as a bus network. (Bus networks are described in Chapter 22.) A bus network must be terminated at both ends of a cable, or the bus network will fail. Thus, thicknet and thinnet both require terminators at both cable ends.

Twisted-Pair Cable

Twisted-Pair (TP) cable arose from the need to replace the distance and other limitations associated with coaxial-type cable. TP is referred to as 10BaseT. Once again, the 10 refers to the transmission rate of data, Base refers to a baseband media type, and the T refers to the twisted pair, or wiring twists in the cable itself.

There are two types of twisted-pair wiring: Shielded Twisted Pair (STP) and Unshielded Twisted Pair (UTP).

Shielded Twisted Pair

STP is basically the same type of wire as UTP, with the exception that STP uses a woven copper braided shielding and foil wrapping that protect the twisted wire pairs from outside interference, such as Electromagnetic Interference (EMI). This shielding makes an STP wire less susceptible to cross-talk from other wires. STP is more expensive than unshielded twisted pair, based on its extra protection and ability to transmit a data signal over a greater distance than UTP.

Unshielded Twisted Pair

UTP is also a 10Mbps baseband cable. UTP, generally referred to as 10BaseT, is the most common type of Ethernet cable in use today and is found mostly in what is called a star typology network. (Star typology networks are discussed in detail in Chapter 22.) UTP in its simplest form is two insulated copper wires that can carry a data signal 100 meters, or approximately 328 feet.

To keep wiring standards uniform, there are five categories of UTP wiring, as specified by the Electronics Industries Association (EIA) and the Telecommunications Industries Association (TIA):

Category 1 (CAT1): CAT1 is the original implementation of UTP used for telephone cable. It is capable of transmitting voice, but not data. This type of phone wire was installed before the mid-1980s.

Category 2 (CAT2): CAT2 is a UTP cable type made up of four twisted pairs of wires. It supports transmission rates up to 4Mbps.

Category 3 (CAT3): CAT3 can transmit data up to 10Mbps. It has four twisted pairs that are twisted three times per foot.

Category 4 (CAT4): CAT4 cable is capable of data transmissions up to 16Mbps. It has four twisted pairs of wire.

Category 5 (CAT5): CAT5 cable is capable of data transmission rates of up to 100Mbps. It is also made of four twisted pairs of wire. CAT5 UTP is also referred to as 100BaseT or 100BaseTX. It carries a data signal 100 meters, or approximately 328 feet.

Category 5e (CAT5e): Otherwise known as “Enhanced” CAT 5 cable, CAT5e is capable of data transmission rates of up to 350Mbps. Like CAT5, CAT5e can carry a data signal up to 100 meters, or 328 feet, without a bridge or other form of amplification. Also like CAT5, CAT5e is made of four twisted pairs of wire. The difference here is that CAT5e was created to support high-speed gigabit Ethernet devices and technology, such as ATM (Asynchronous Transfer Mode). CAT5e has better performance, resistance, and suffers less from attenuation than traditional CAT5.

CAT5 and CAT5e both have 100-ohm impedance and are terminated with RJ45 connectors.

CAT5e is backward compatible with traditional CAT5.

CAT5e is built using a 24-gauge conducting wire

The “enhanced” electrical technology built into CAT5e makes it possible for CAT5e cable to support additional bandwidth needed for such technology as gigabit Ethernet.

Category 6 (CAT6): The CAT6 cabling standard is rated up to 550M or 1000Mbps.

CAT6 cabling is built using 23-gauge conductor wire.

CAT6 has a better performance rating than CAT5e and suffers less from cross talk and noise.

CAT6 is more expensive to install support than CAT5 or CAT5e.

To keep you sharp for the exam, here are the updated IEEE standard requirements for UTP cabling:

10BaseT: IEEE standard for requirements of sending data at 10Mbps over unshielded twisted-pair cable.

100BaseT: IEEE standard for requirements of sending data at 100Mbps over unshielded twisted-pair cable.

1000BaseT (also known as gigabit Ethernet): IEEE standard for requirements of sending data at 1,000Mbps over unshielded twisted-pair cable.

Twisted-Pair Connectors

There are two types of UTP connectors you need to know about for the test: RJ-11 connectors and RJ-45 connectors.

An RJ-11 phone connector was used for early categories of UTP to connect a modem to a typical phone jack, or your phone to a phone jack. In technical circles, an RJ-11 wire is a simple phone wire that houses four wires or connections. See Figure 21.9 for an RJ-11 connector.

Figure 21.9: An RJ-11 connector.

An RJ-45 connector is the most common type of TP data cable connector in use. It houses eight wire traces. The RJ-45 connector on one end of a TP wire plugs into an NIC that is installed into a system. The RJ-45 connector on the other end of the TP cable plugs into a network hub, router, or RJ-45 wall jack. Figure 21.10 shows an RJ-45 connector.

Figure 21.10: An RJ-45 connector.

Crossover Cable

A crossover cable is a type of Ethernet TP cable that is commonly used to connect two computers in a peer-to-peer fashion. The crossover cable switches the transmit and receive lines of the cable, which allows two computers to communicate directly with each other without the use of a hub or router. If you want an inexpensive alternative to purchasing a hub, a crossover cable is the way to go to connect two computers.

A null modem cable can also be used as a crossover cable to network two computers. A null modem cable is serial cable that is connected to the serial ports of two system units.

Fiber-Optic Cable

Fiber-optic cable, otherwise known as 10BaseFL, is the network wire of choice. It is capable of extremely fast transmission rates over long distances, without interference.

A fiber-optic cable has a core that is composed of plastic or glass. A glass cladding or sheath covers the core. Finally, a Kevlar fiber jacket surrounds the entire wire. Data can be transmitted through a fiber-optic cable with a laser or LED at a rate of 2GBps or higher. The data signal on a fiber-optic wire can travel up to a distance of 100 kilometers (about 60 miles), depending on which technology is being implemented with the fiber and if a repeater is used. Fiber-optic cables use special ST- and SC-type connectors to attach to NICs and fiber-optic ports. These connectors are precisely crafted and specially designed to suit fiber-optic cable connection requirements.

Fiber-optic cable needs great care and consideration when being installed. Specially trained, certified fiber installers are usually employed to carry out this task. Because of its high transmission speeds and specialized installation methods, fiber-optic technology is quite expensive.

Next we will discuss the two fiber-optic cable mode technologies that you will need to be familiar with for the exam.

Single-Mode (SM)

Single-mode fiber optic, also referred to as monomode fiber, is a fiber technology meant for very long distance data transmissions. With single-mode fiber, a laser is used to generate a single pulse of light, or ‘mode of light,’ into the fiber media. This light is used as a data transmission carrier for a very long distance. Photodiodes are used to receive the transmission sent over the fiber-optic media.

Multi-Mode (MM)

Multi-mode fiber uses LEDs (Light Emitting Diodes) to generate signals of light into the core fibers for transmission over fiber media. This mode of fiber is designed to carry many light signal rays, or ‘modes,’ at the same time over a shorter distance than single mode. If the light rays, or ‘modes of light,’ have to travel too far with this mode, modal dispersion occurs and transmission fails. The core of the fiber media used with multi-mode is larger than with single mode; thus, the accepting photodiodes have a much larger circumference.

Here are some key points:

The core of single-mode fiber is much smaller than the core used multi-mode type fiber.

Single mode fiber has greater distance and bandwidth capabilities than multi-mode.

Single-mode fiber is more expensive than multi-mode.

It is much more difficult to repair breaks in single-mode fiber optic media.

Multi-mode fiber uses LEDs (light emitting diodes) to generate signals of light.

With single-mode fiber a laser is used to generate a single pulse of light

Bridged media connectors (converters) are available, which enable Ethernet connections to be converted to fiber and fiber connections to be converted to Ethernet. Multi-mode fiber converters can support distances up to 2 Km. Single-mode fiber converters support distances of up to 60 Km.

Refer to Table 21.2 for a comparison chart of the major networking cables described in this chapter.

IDC (Insulation Displacement Connector)

An insulation displacement connector is a connector that is used in various different types of network termination media or connection equipment. An IDC connector removes the insulation on a cable or wire when a connection is made. It works by piercing, or ‘crimping’ the insulation around the cable’s wires with a special tool called an IDC crimper. This technique is used to push or ‘force’ a single wire between two pieces of plastic, or ‘blades,’ that are part of a connector, such as an RJ-45 patch. An IDC assists with the process of timely termination and makes for an effective and reliable connection.