1.5. Recognizing Media Types

The media is the wired or wireless connection that allows one computer to communicate with another computer. When you choose a cable standard and a connector type, you are also choosing a media type. It's important that you understand your choices in regard to connector type and media type.

1.5.1. Critical Information

You should be able to recognize the most common media types and describe their use. In this section we discuss each media type and its most common use.

1.5.1.1. Category 3, 5, 5e, and 6 Twisted-Pair Cables

The category of a twisted-pair cable indicates the tightness of the twist applied to the wire pairs in the cable. The twist in wire pairs prevents an electrical interference called crosstalk from affecting the communication. Crosstalk occurs when a signal bleeds over from one wire to another (even through the insulation of the wire). The tighter the twist, the faster you can transmit information through a cable without suffering from crosstalk. Table 1.9 shows the maximum speed of the main cable categories.

Category 5e (enhanced) is the cable type that is currently recommended as a minimum for all new installations. Cable is generally used to connect each computer to a central point, typically a hub or a switch, that is contained in a network closet. Ensuring that each computer has its own cable creates redundancy in the network and thereby provides fault tolerance.

1.5.2. UTP

Unshielded twisted-pair (UTP) cable is the most common type of cable used today. UTP is offered for all of the categories of cable that we have discussed. It is most often used because it is far easier to install than STP (which we will discuss next). The only protection from electrical interference provided by UTP is the fact that the pairs of wires within the cable are twisted, which is usually enough.

1.5.3. STP

Shielded twisted-pair (STP) resembles UTP except that it includes a foil shield that covers the wires and adds another layer of protection against outside magnetic interference. In order for this protection to be effective, the connections have to be properly grounded. This adds to the complexity of installations, so most organizations have opted to use fiberoptic cable instead of STP when electromagnetic interference is a problem. For example, if a cable is passing by a large electrical motor or fluorescent light ballast, STP might be used to provide greater resistance from electromagnetic interference (EMI). STP cable was often used for communication connections through elevator shafts, prior to fiberoptic cable. Figure 1.14 shows an STP cable.

Figure 1.14. An STP cable

1.5.3.1. Coaxial Cable

In the late 1980s, coaxial cable was used as the backbone of network segments and to connect computers to the bus topology that made up the network. Coaxial cable is rarely used anymore for network backbones or to connect computers, but it is being used today to connect cable modems to the cable provider's connection to provide a computer with a broadband Internet connection. Coaxial cable consists of an inner core wire and an outer braid of insulating wire. The entire signal is carried by the inner core wire. Figure 1.15 shows the components that make up a coaxial cable.

Figure 1.15. A coaxial cable

1.5.3.2. Single-Mode Fiber

Single-mode fiberoptic cable (SMF) is a very high speed and very high distance media. It consists of a single strand of fiberglass that carries the signals. The light source that is generally used with single-mode fiber is a laser, although light-emitting diodes (LEDs) might also be used. With single-mode fiber, a single light source is transmitted from end to end and pulsed to create communication. Single-mode fiber is used for long runs because it can transmit data 50 times further than multimode fiber and at a faster rate. For example, single-mode fiber might be used on an organization's corporate campus between buildings. Since the transmission media is glass, the installation of single-mode fiber can be a bit tricky. There are other layers protecting the glass core, but the cable still should not be crimped or pinched around any tight turns. It is, however, completely immune to electrical interference since light is used instead of electrical signals. Figure 1.16 illustrates the layers included in single-mode fiberoptic cable

1.5.3.3. Multimode Fiber

Multimode fiberoptic cable (MMF) also uses light to communicate a signal, but the light is dispersed into numerous paths as it travels through the core and is reflected back by cladding that lines the core. Multimode fiber provides high bandwidth at high speeds over medium distances (up to about 3000 feet) but can be inconsistent for very long runs. Because of this, multimode fiber is generally used within a smaller area of a building whereas single mode might be used between buildings. Multimode fiber is available in glass or in a plastic version that makes installation easier and increases installation flexibility. As with single-mode fiber, multimode fiber can be used when electrical interference is present, since it is completely immune to that inter-ference. For example, multimode fiber might be used today to provide communication connections in a building that go through an elevator shaft. Figure 1.17 shows the how light is split into multiple paths in a multimode fiber-optic cable.

Figure 1.16. Single-mode fiber-optic cable

Figure 1.17. A multimode fiber-optic cable

1.5.4. Exam Essentials

Know and be able to recognize common media types. The most common media types are twisted-pair cable, coaxial cable, and fiber optic cable. You should be able to recognize the most common media types given a picture or description.

Describe how common media types are used. You should know how the most common media types are used to transfer data throughout the network. You should be able to differen-tiate between copper based twisted-pair cables and fiber-optic cables. You should also know how each type might be used in a network.

Know the characteristics of Category 3 cable. Category 3 cable is a copper twisted-pair cable that can carry signal at a maximum of 10Mbps without suffering from crosstalk. This type of cable is rarely used in networks today.

Describe the characteristics of Category 5 cable. Category 5 cable, the most common cable type today, is a copper twisted-pair cable that can carry signals at a maximum rate of 100Mbps without suffering from crosstalk. Category 5 cable is used to connect computers and many other devices within a LAN.

List the characteristics of Category 5e cable. Category 5e cable is a copper twisted-pair cable that can carry signals at a maximum rate of 1000Mbps without suffering from crosstalk. This is one of the most commonly installed cables today.

Know the characteristics of Category 6 cable. Category 6 cable is a copper twisted-pair cable that can carry signals at maximum rate of 1000Mbps without suffering from crosstalk. This is also one of the most commonly installed cables today.

Describe the characteristics of UTP. Unshielded twisted-pair (UTP) cable is the most common type of cable used today. It does not provide any shielding other than the fact that the wires are twisted. Most of the cable standards include the UTP type of cable.

Know the characteristics of STP. Shielded twisted-pair (STP) cable is used to reduce the effect of EMI on cables in environments that contain large sources of EMI, such as electric motors or fluorescent light ballasts. STP includes a foil shield that provides that added protection. STP is rarely used in today's networks because it has been replaced by fiber-optic cable.

List the characteristics of coaxial cable. Coaxial cable was used for backbone segments and for bus topology networks in the late 1980s. The entire signal on a coaxial cable is transmitted through the core wire in the center of the cable. The main use for coaxial cable today is to connect cable modems to the cable provider's connection.

Know the characteristics of single-mode fiber. Single-mode fiber optic cable is a very high speed and high distance media. It generally uses a laser beam to concentrate and pulse light on a single strand of fiber. Single-mode fiber is typically used to provide a backbone for buildings on an organization's campus.

List the characteristics of multimode fiber. Multimode fiber-optic cable also uses light to transmit a signal, but the light is dispersed within the cable, causing it to travel numerous paths called modes. Each of these modes is part of the communication process that is used. Multimode fiber can provide very high bandwidth for short distances, but it can become inconsistent for very long runs, over 3000 feet. This fiber is most often used as a backbone for a LAN within a single building.