CHAPTER 2: Network Media 46 CABLING AND CONNECTORS OVERVIEW The media that carries data makes up the basic infrastructure of a network. If you consider data as a vehicle that moves between two points; then cabling and connectors are the highways and interchanges that allow data to access and travel across that network. Connectors attached to the ends of the cables are plugged into or coupled in some way with a network card or other device on your network. In doing so, a physical link is created between this device and others on your network. Just as a car uses an on ramp to enter a high- way, the connector provides an access point for data to move along the cable to its intended destination. The purpose of a cable is to carry data across a network. A network card passes an electronic signal onto a cable and a connector is used to connect the cable to the network card or other device to the cable. The data, in the form of an electronic signal, is passed through the connector to a wire or fiber in the cable. Just as the wires in your house carry electricity to the lights and wall sockets in each room, the cable carries these electronic signals to the computers, printers or other network devices meant to receive them. Although local area networks (LANs) of the past often used one type of cabling, many LANs today use a combination of different cable types. This is because different cables will carry the data at varying speeds and distances. Although some cables can carry the data for a hundred meters or so, others can span greater distances, connecting widely spaced areas. In the same way, some cables will allow a network to transfer millions bits data, while others can send a thousand times this amount. As we’ll see later in this chapter, the features of a particular type of cable can vary greatly. Because different types of cabling are available to use, it follows that there are also different types of connectors that may be used. The connectors fit on the ends of the cabling and are designed to hold the wires or fibers within the cabling together, allowing them to make a connection when the connector is plugged into or coupled with a network device. If you think of a cable used on your telephone, each end of the phone cable has a connector that bundles the wires in the cable together in a specific way, so they can make a connec- tion when the cable is plugged into the corresponding telephone or wall jack. The connectors on a network cable are the same, providing an interface for a device to connect to a cable. Fundamentals of Cabling Cabling is the wire or fiber medium that is used to connect computers and other network devices on your network together, and used to carry the data that is transmitted between them. Although we’ll discuss each of the types Cabling and Connectors Overview 47 of cabling in greater detail later in this chapter, be aware that there are three types of physical media that can be used on a network: Coaxial cable Twisted-pair cable Fiber-optic cable Coaxial cable, also referred to as coax, is the same type of cabling you see in most cable television installations today. A single copper wire at the center of the cable core is used to carry the signals and is surrounded by lay- ers of insulation that protect the wire and its transmissions. On networks, there are higher grades and different types of coaxial that may be used: thin (10Base2) or thick (10Base5) are two examples. The thin and thick kinds of coaxial cabling refer to the thickness of the cable. 10Base2 cabling, also known as Thinnet, is 0.25 in. while 10Base5 cabling, also known as Thicknet, is 0.5 in. Because a thicker wire was used in 10Base5, it allows data to travel further than its thinner counterpart. This made 10Base5 ideal as a backbone for early networks, although the increased speeds and distances supported by fiber-optic cabling has become a better solution for modern networks. Twisted-pair cable is a type of cabling that’s used for telephone and net- work communications. When we mentioned the cable used to connect your phone to a wall jack, we were discussing a type of cable called twisted-pair. As shown in Figure 2.1, twisted-pair cables have one or more pairs of copper wires that are insulated and twisted around one another, which prevents the signals on the wires from interfering with one another. Common sources of interference are electromagnetic interference (EMI) and radio fre- quency interference (RFI). Problems may occur such as the untwisting of pairs. In this case, the twisted pairs may open up or loosen and will be more susceptible to EMI and RFI. As we’ll see later in this chapter, there are different categories of Note A backbone segment is made up of high-speed lines and equipment normally located at the very center of your network. FIGURE 2.1 Twisted-Pair Wiring. CHAPTER 2: Network Media 48 twisted-pair cabling, which are used for different purposes and have vary- ing degrees of sensitivity to interference. Twisted-pair cabling may be shielded or unshielded. The difference between unshielded twisted-pair (UTP) and shielded twisted-pair (STP) is that STP has an extra layer of aluminum/polyester between the wire and the plastic covering. This acts as a shield against interference from outside sources that could corrupt data carried on the copper wire. Fiber-optic cabling is different from these other types of cabling, as it doesn’t use copper wires to transmit data. Fiber-optic cables use glass or plastic to transmit light pulses across the network. Because information is transmitted at the speed of light, it can carry more information faster than other types of cabling. Fundamentals of Connectors Connectors are used to hold the ends of the wires or fibers in a cable in place, so that it can then be plugged into a network card or other equipment on your network. As you can see when looking at the cable connectors used for your phone and cable television, these connectors may be plastic or metal and differ greatly in appearance. This makes them easy to identify both in the real world and on the Network exam. There are several different kinds of connectors that may be used with the different types of cabling, which we’ll explain in detail later in this chapter. They are as follows: Bayonet-Neill-Concelman (BNC) is a type of locking connector used  to terminate coaxial cables. BNC is also referred to by many other names such as Bayonet Network Connector, British Naval Connec- tor, or Bayonet Nut Connector. Registered jack (RJ) is used with twisted-pair cables. RJ-11 is used  for phone cables, while RJ-45 is a twisted-pair connector that is commonly used in networks. Standard connector (SC) is used with fiber-optic cabling. Straight tip (ST) is used with fiber-optic cabling. Local connector (LC) is used with fiber-optic cabling. Mechanical transfer registered jack (MTRJ) is used with fiber-optic  cabling. These different types of connectors attach a cable to network cards and other devices in different ways. Some connectors, such as RJ-11, RJ-45, and Media Issues 49 ST, are plugged into a port, whereas others such as BNC and ST connectors have threading that is used to screw the connector into place. To put this into a perspective of something you’re familiar with, the RJ connectors are plugged in just as you would plug your phone cord into the telephone. BNC connectors are screwed onto a corresponding port in the same way you attach the cable used for cable television to the back of your TV. Once the connector is attached to the network card or another device, it provides a connection between the device and the physical media that carries data across your network. MEDIA ISSUES As with anything dealing with networks, there are issues that you’ll need to consider when deciding on what’s best for your organization. The dif- ferent types of physical media available each have their own benefits and vulnerabilities that can affect network performance and the amount of work required to install, troubleshoot, and repair cabling. Some types of cabling can carry more data at faster speeds and over longer distances. Other types are more susceptible to interference that can corrupt data or have security issues that make them more vulnerable to attack. By knowing the issues related to each media type, you can make a better decision on which cabling will best suit the needs of your network. Interference If you’ve ever listened to a radio during a storm, you’ve probably heard the crackles and pops of static when lightning interferes with the radio transmis- sion. Just as the electricity of lightning can interfere with radio signals, simi- lar interference can effect the transmission of data across a network cable. EMI is a low voltage, low current, high-frequency signal that can interfere with the electronic signals transmitted over cabling. Because the EMI signals come from outside sources and interrupt the information sent over cabling, it is often referred to as noise. EMI can result from numerous sources. Power lines, transformers, fluo- rescent lights and fixtures, industrial tools, engines, and other machinery and equipment that run on electricity can emit electromagnetic waves that affect other devices and data transmitted over cabling. The electromagnetic field generated by these devices is a natural byproduct of electricity being passed through the wiring, and its effects are not only seen in cabling, but also in other computer technology. For example, if you place a lamp or fan near your monitor, you may find that the screen flickers because the EMI of the lamp is causing interference with the monitor. CHAPTER 2: Network Media 50 Similar to EMI is RFI, which is caused by electromagnetic radiation in the radio frequency range. RFI can be caused by radio and television broadcast towers, microwave satellite dishes, appliances, and furnaces. Just as with EMI radiation, RFI can result in data being corrupted during transmission. The effects of EMI or RFI can be reduced or eliminated by properly grounding equipment, not placing cables close to sources of EMI or RFI, and using cables that use shielding or are more resistant to EMI/RFI. A shield is a material in the cabling that’s used to absorb EMI/RFI before it reaches the wires that carry data. UTP is the most vulnerable type of cabling because it doesn’t use any shielding to protect the wires in the cable. STP is more resis- tant to EMI/RFI because a layer of aluminum/polyester exists between the wire and the outer plastic covering of the cable. A similar shield is found in coaxial cable, which uses a wire mesh or foil shielding in the cable. The only cabling that is unaffected by EMI/RFI, however, is fiber-optic cabling, which doesn’t contain any copper wiring and uses plastic or glass that is noncon- ductive. Although we’ll discuss the internal components of these cables later in this chapter, using cables that provide shielding or aren’t affected by EMI/ RFI will prevent data from being corrupted during transmission. Another type of interference that can occur in cabling is crosstalk. Cross- talk occurs when the electromagnetic field of one wire interferes with the transmission of another. That is, the signals from one wire essentially bleed onto another wire. You may have experienced this in a telephone system, when you hear someone else’s conversation on your phone line. In networks, this type of interference can cause a loss or corruption of data. Crosstalk can be reduced or eliminated by moving the cables further apart from one another or using cables that use shielding. As with EMI/RFI interference, UTP is the most vulnerable to crosstalk, while STP and coaxial cable have shielding that protects the wire from outside interference. Fiber- optic cabling is immune from crosstalk because it uses light rather than electronic signals to transmit data. Bandwidth Bandwidth is a measurement of the amount of data that can be passed over a cable in a given amount of time. If you compare cabling to a highway, and data to vehicles traveling along the highway, then bandwidth would be the Exam Warning Don’t get crosstalk confused with EMI. Remember that when one cable has its data com- munications bleed onto another cable, it is crosstalk. EMI can come from any number of sources, including florescent lights or machinery. Media Issues 51 amount of traffic supported. Just as too many cars traveling on a highway would cause a traffic jam, there is a limit to the amount of data a cable can support before the network becomes bogged down. Bandwidth is generally measured in increments of bits and bytes. A bit is short for binary digit and is the smallest unit of data on a computer. When information is processed or sent across a wire or circuit board, it is passed as an electric current. The signal is either a high current or low current of electricity and represented digitally by a 1 or 0. Each of these ones and zeros is referred to as a bit, and 8 bits of data make a byte. A word is considered 4 bytes, which is essentially 32 bits … the same length as an IP (Internet Protocol) address, which we will learn about in Chapter 6. The bandwidth capacity of a network cable is usually measured in the number of bits or bytes that can be transferred in a second. In modem con- nections, thousands of bits may be sent, with each thousand referred to as a kilobit per second (Kbps). In network cabling, considerably more data can be sent more quickly. Bandwidth may be measured in megabits per second (Mbps), with each megabit representing a million bits of data transmitted each second, or in the gigabits per second (Gbps), meaning that 1000 mil- lion bits of data are transferred for every 1 gigabit supported. Table 2.1 shows the bandwidth capacity of different media standards, which we’ll discuss in greater detail later in this chapter, and how this capacity varies depending on the media being used. Table 2.1 Bandwidth Capacity of Physical Media Media Standard Cable Type Bandwidth Capacity 10Base2 Coax 10 Mbps 10Base5 Coax 10 Mbps 10BaseT UTP or STP (Category 3 or higher) 10 Mbps 100BaseTX UTP or STP (Category 5 or higher) 100 Mbps 10BaseFL Fiber-optic 10 Mbps 100BaseFX Fiber-optic 100 Mbps 1000BaseT UTP or STP (Category 5 or higher) 1 Gbps (1000 Mbps) 1000BaseSX Fiber-optic 1 Gbps (1000 Mbps) 1000BaseLX Fiber-optic 1 Gbps (1000 Mbps) 1000BaseCX Fiber-optic 1 Gbps (1000 Mbps) 10GbaseSR Fiber-optic 10 Gbps 10GbaseLX4 Fiber-optic 10 Gbps 10GbaseLR Fiber-optic 10 Gbps CHAPTER 2: Network Media 52 If the amount of data exceeds the amount of bandwidth supported, the cabling can become a bottleneck because the transmission speed will be affected. Think about pouring water into a funnel, since the base of the fun- nel is more narrow then the wide mouth on top if you pour the water too quickly it will back up into the mouth of the funnel and spill over. The water moves more slowly through the base since it is a narrower opening forcing you to pour the water slowly. Data transfers work in much the same way. If the data being transmitted on the cable is excessive for the cable’s maxi- mum capability, then the transfer will be slowed. The amount of data being transferred needs to be compatible with the cable type in place, otherwise the outcome is a resulting network bottleneck. It should now make complete sense to you why bandwidth can be precious, especially for your wide area network (WAN) connections (discussed in more detail in Chapter 7). WAN links are costly and you will likely want to use every ounce of bandwidth you can squeeze out of it. To follow a real world example, if 10BaseT UTP cable was used to transfer data between floors of a building, then approximately 10 Mbps of data could be sent per second. If considerably more than this amount was being sent across the network on a routine basis, then cabling that supported a higher bandwidth (such as fiber optic) would be needed. When designing a network, it is important to consider the amount of data that will be transferred so the proper cabling can be initially installed. As the requirements of the network grow, replacing existing cabling with cables that support a higher bandwidth capacity may be necessary. Length Problems The length of cabling is an important consideration when deciding on the cable that will be used for a network. As signals travel the length of a cable, they will weaken over distance. The signals will eventually degrade until they reach the point where the data is lost. When this occurs, it is referred to as attenuation. Test Day Tip An easy way of remembering the maximum bandwidth of the various media standards is to look at the number at the front of the standard, which refers to the number of mega- bits supported. In looking at 10Base5, the 10 symbolizes that the maximum transmission speed is 10 Mbps, while the word Base indicates that it is using a baseband technology (as opposed to broadband). The final portion of the media standard varies in meaning. Originally, the number at the end indicated the maximum distance of the cable. For example, the 5 in 10Base5 indicates that it has a maximum distance of 500 m, while the 2 in 10Base2 was a rounded-up indication of its 185 m maximum distance. This changed, however, with 10BaseT, which signifies that twisted-pair cabling is used. Media Issues 53 Because attenuation can occur, it is important that you don’t exceed the maximum distance of a cable. Table 2.2 shows the maximum lengths of various media standards, which we’ll discuss in greater detail later in this chapter. As you can see, physical media can have a maximum distance ranging from hun- dreds of meters to kilometers in length. If a cable has to be run longer than its maximum distance, then the signal will have to be regenerated. In the past, a device called a repeater performed this task. As we’ll discuss in the next chapter, repeaters aren’t generally found on modern networks, but this same functional- ity is found in other network devices, such as switches, routers, and hubs. Fiber-optic cabling doesn’t suffer from attenuation as copper cabling does. Part of the electric signal passed along a copper wire will be absorbed by the cable and weaken over distance, but since fiber optic uses light passed over glass or plastic fiber it doesn’t suffer from the same problems. Although Table 2.2 Maximum Distance of Physical Media Media Standard Cable Type Maximum Length 10Base2 Coax 185 m 10Base5 Coax 500 m 10BaseT UTP or STP (Category 3 or higher) 100 m 100BaseTX UTP or STP (Category 5 or higher) 100 m 10BaseFL Fiber-optic 2 km 100BaseFX Fiber-optic 400 m (half-duplex) or 2 km (full-duplex) 1000BaseT UTP or STP (Category 5 or higher) 100 m 1000BaseSX Fiber-optic 550 m (MMF) 1000BaseLX Fiber-optic 550 m (MMF) or up to 10 km (SMF) 1000BaseCX Fiber-optic 100 m 10GbaseSR Fiber-optic Up to 300 m over 2000 MHz km MMF 10GbaseLX4 Fiber-optic Up to 10 km over SMF 10GbaseLR Fiber-optic Up to 10 km over SMF Test Day Tip Review the maximum cable lengths and the transmission speeds associated with the dif- ferent media types before going into the exam. To ensure you know them, have someone quiz you on the various elements of each media standard. You can expect to see ques- tions related to these elements of physical media on the exam. CHAPTER 2: Network Media 54 twisted-pair and coaxial cables can span a distance of hundreds of meters, signals will run along fiber-optic cable for kilometers without any noticeable signal degradation. It’s for this reason that fiber-optic cabling is used for con- necting locations of a network that are separated by significant distance. Security Issues The security of cabling is another important issue that should be considered before installing a particular kind of cabling. Different organizations and locations may require different types of cabling to meet the security needs outlined in policies or regulations. In other situations, such as a small office home office (SOHO), security may be a minor issue. Because needs differ, you should try to establish what the security needs are before installation begins. In determining the kind of cable you’ll install, you will also need to be aware of security issues that are inherent to certain types of cabling. If you’ve watched any crime dramas on television, you’ve probably heard of wiretapping. Often, this refers to gaining access and listening to some- one’s telephone line without the person knowing about it. However, as we’ve said, the same or similar cabling used for voice communication is also used in networking. Wiretapping is as much a security risk for network cabling as it is for a business telephone line. Wiretapping involves gaining physical access to a network cable. The cable must be cut or pierced so that the wires inside the cable can be accessed and then spliced or tapped. Because of the shield in STP cabling, this is more difficult to do than with UTP. Older networks that use coaxial cabling often recognize the risk of wiretapping because tapping is required on 10Base5 (Thicknet) cables to add new workstations. A tool called a vampire tap is used to clamp onto the coaxial cable and pierce it. A needle is then dropped into the hole in the cable, so that contact is made with the wire inside of the cable. This tap provides a connection so that 10Base2 cabling can be used to connect a computer to the cable and access data traveling along the cable. Fiber-optic cabling is the least susceptible to wiretapping because of the glass or plastic fibers used to carry the data. It is difficult to tap into the cable without causing damage, although optical vampire taps do exist that allow a tap to be per- formed by clamping onto the cable. Generally though, a tap requires cutting the cable before tapping it, which may provide an obvious clue that a problem exists. Another security issue related to cables is eavesdropping. Eavesdropping is the act of listening to data being sent over the wire without actually pierc- ing the cable. As we learned earlier when we discussed crosstalk and EMI from other cables, the signals of a cable can bleed off and be picked up by other wires in neighboring cables. The same factors that make it possible for EMI to cause interference with cabling also make it possible for someone to obtain data from the cable without piercing it. To minimize the risk of Media Issues 55 eavesdropping, you should use cabling that is less susceptible to EMI (STP or coaxial) or immune to it altogether (fiber optic). Installation The level of difficulty in installing physical media varies depending on the type used and where the cabling is being installed. In some situations, such as a home office, it can be incredibly simple, but in others, such as running cable down an elevator shaft to connect two floors of a building, the instal- lation can be challenging. Depending on the cabling and the location, you may be able to easily install the cabling yourself, or may opt to outsource to a company that specializes in cable installation. Installation of twisted-pair cable is relatively easy. UTP is similar to the cable used for phone lines, so it is thinner and more flexible than other types of cabling, making it easier to get around corners. STP is more difficult than UTP because of the shielding. STP requires an electrical ground with the connec- tors, which is why it is easier to use pre-wired cables that already have the con- nectors installed. It is never recommended that you make cable if you either don’t know how, or don’t have equipment to test the cable that you made. STP is thicker than UTP, making it more rigid, which can make it more difficult to install around corners. Although the shielding provides greater benefits against EMI, the installation of the cabling can be more problem- atic. STP is also more difficult to make and more expensive than UTP. DAMAGE AND DEFENSE… Physical Security Physical security is an important part of any network. In terms of cabling, you should try to keep as much cabling as possible out of public reach. Rather than run- ning cable in the open, or having it accessible in waiting rooms or reception areas, most of your cabling should be run in secured conduits protected from damage behind walls, floors, or ceilings, with wall jacks placed to plug into the network in areas close to desks. Even if you do not use special cable management equipment, you can still keep the cabling neat and secure and out of reach so that you don’t have issues with cut cables, broken cables, and so on. You don’t want members of the public being able to access connections or cabling. You should also perform routine inspections of cabling for physical damage, as this may indicate attempts to tap the wires and acquire data, or just alert you to a simple problem you may be able to proactively take care of before it gets worse. As mentioned in this section, fiber-optic cabling and shielded cable will help to protect your cable from security issues, although fiber-optic cabling is very sensitive to the touch and easy to break if handled incorrectly. It is also very difficult to install and repairs can be difficult and costly. Remember that physical security is important and that in high security areas, more drastic and expen- sive methods are also available to add new levels of security, if needed, such as placing cables in steel con- duits, or using conduits that are pressurized with gas and use monitors to determine pressure changes. This works like an alarm that someone may be attempting to access a cable. . can send a thousand times this amount. As we’ll see later in this chapter, the features of a particular type of cable can vary greatly. Because different types of cabling are available to use,. transmitted between them. Although we’ll discuss each of the types Cabling and Connectors Overview 47 of cabling in greater detail later in this chapter, be aware that there are three types of physical. Because a thicker wire was used in 10Base5, it allows data to travel further than its thinner counterpart. This made 10Base5 ideal as a backbone for early networks, although the increased speeds