Network Cabling and Data Threats
Regardless of the type of computers, network design, or network architecture used, each computer on a network has to be connected using some form of network cabling. Common network implementations use copper-based cable, fiber cable, and even wireless technologies such as radio waves. However, the increasing availability of wireless technology means that computers are breaking free of the traditional network attachment methods. That said, today, only a very small percentage of organizations use wireless networking. Before we jump into describing more of the various cables used to create today’s networks, we thought it wise to first review some of the terms and considerations you will have to know about when discussing network cabling. We’ll start by discussing one of the most common terms, bandwidth.
Bandwidth
Bandwidth is one of those terms that is thrown around a lot in the computer world—usually, in the form of a complaint about not enough of it. As it relates to cabling, bandwidth basically refers to the transmission capacity or throughput of the cable. You are most likely going to hear bandwidth speed measured in megabits per second (Mbps), meaning that a cable with a bandwidth of 10 Mbps can transmit 10 million bits per second. Sound fast? At one point it may have been, but in today’s demanding network environments, it isn’t. Today’s networks typically transmit at speeds of 100 Mbps, which is still too slow for many organizations.
The need for speed has created the pursuit of technologies to increase bandwidth. Some strategies commonly used to increase bandwidth include replacing hubs with switches (discussed in the Ethernet section later in this chapter) and replacing traditional copper-based networking cable with fiber-optic solutions. Although there is some debate as to what the actual maximum speed of fiber optic cable is, it is generally accepted that the maximum is 100 gigabits per second (Gbps), which represents a staggering 100 billion bits per second. But as you might expect, the faster you go, the more you have to pay. Technologies such as fiber optics are often out of the reach of many businesses; there is a fine line between performance and finances.
Attenuation
Network cabling can only be of a certain length before the data signals that pass through them weaken. The degradation of data signals as they pass through a particular network cable is referred to as attenuation and it is a major consideration when designing or troubleshooting a network.
Distance is one of the factors that defines what types of cabling can be used for a particular network. For example, in environments where a cable must run great distances, fiber-optic cable can be used up to 50 km, depending on frequency, before the data signal weakens, which is longer than any other physical cable. Other network cabling, such as the widely used unshielded twisted-pair, can only be run in distances of 100 meters before the data signal fades.
TIP
In the networking world, there is an exception to pretty much every rule. In this case, the maximum distance for a cable can be increased using devices called repeaters, which regenerate data signals as they pass along the network media. With the signals regenerated, the set distance limits no longer apply.
Interference
Attenuation is one of the threats to the integrity of data signals on network cabling, but there is another common one. As signals pass through twisted-pair or coaxial network cables, they can be subjected to particular interference known as electromagnetic interference (EMI).
There are many devices in and around an office that can cause EMI, including computer monitors, fluorescent lighting units, and even refrigerators. EMI can weaken the signal within the cable and make it unreadable by the receiving device. Some cable types are more susceptible to EMI than others, and as you might expect, the more money spent on cabling, the better the resistance to EMI. In terms of EMI resistance, fiber-optic cable is completely resistant as it uses light instead of copper as a transmission medium.
In addition to EMI, another type of interference known as crosstalk can cause problems. Crosstalk refers to the interference from other wires around or within the cable. For example, if two wires are run very close together, the signals in both wires may interfere with each other. Crosstalk is typically combated by twisting the wires within the cable. If you ever have the opportunity to look inside some cable, such as UTP network cable, you will see that the wires are twisted around each other. This twisting helps prevents crosstalk.
TEST SMART
Before taking the exam, be sure you understand the three common threats to data signals: attenuation, crosstalk, and EMI.
RS-232
Before reading the CompTIA objectives, had you ever heard of RS-232 cable? As in “Hey Mike, pass me a section of that RS-232.” Probably not because it doesn’t exist. The CompTIA A+ objectives include RS-232 in the cabling category, but in reality, RS-232 is not cabling at all. Actually, RS-232 (Recommended Standard-232) is a TIA/EIA standard for serial transmission between computers and peripheral devices such as modems, mice, and keyboards. In the real world, referring to serial communication as RS-232 is a little like referring to Sting as Gordon Sumner; it may be technically accurate, but no one will know who or what you are talking about.
NOTE
Serial connections send data over the cable one bit at a time. It is a simple way to send information in or out of the computer, but it’s not as fast as other ways the computer can communicate. Parallel communication is faster than serial because it sends several bits at a time in parallel instead of single bits in sequence, as with serial communication. Parallel communication is often associated with printers or removable storage devices, which need faster speeds.
The RS-232 standard was introduced way back in the 1960s, and is still the most widely used communication protocol in use today. It is simple, inexpensive to implement, and though relatively slow, more than adequate for most simple serial communication devices such as keyboards and mice. RS-232 commonly uses a 25-pin DB-25 or 9-pin DB-9 connector, such as with a serial mouse. Wireless technologies can also use RS-232 serial communication. In a normal environment, RS-232 has a limitation of 50 feet and offers slow data rates of 20 Kbps.
Infrared
Infrared communication is not foreign to any of us who have used a TV or stereo remote control, but in terms of networking, infrared technology has been largely ignored. This is likely a result of the emergence of other, faster technologies such as the newer radio wave–based 802.11b wireless Ethernet networking standard. Infrared is often referred to as IrDA, named after the Infrared Data Association, which holds the responsibility for developing standards for wireless infrared transmissions.
The function of IrDA is to provide cable-free communication for a range of devices including laptops, PDAs, keyboards, mice, digital cameras, printers, and so on. Basically, if something works over a wire/cable connection, it will work over the IrDA infrared data link. The convenience of not having to work with cables has a downside, and that is performance. IrDA transmissions are limited to 115 Kbps, depending on the device. This slow speed is due partly to the fact that IrDA uses a half duplex communication method. There are developments under way and IrDA 2.0, the latest version, boasts speeds of 4 Mbps—OK, but too slow for many of today’s data transfers. You could grow old waiting to get all of the high-resolution pics out of your digital camera. As a comparison, consider that your USB 2.0 devices can transfer at speeds up to 480 Mbps and IEEE 1394 (FireWire) gets as high as 400 Mbps. Considering the speed difference, a cable here and there is a reasonable trade-off.
In addition to the speed being a problem, the fact that IrDA is a point-to-point technology can also be an issue. Point-to-point communication works in the same way your TV remote would; you need to point the device directly at the other device to have it function. Ever try to change the channel when someone is standing in the way? The same effect happens when the transmission is interrupted between computer components; put your bag of Doritos in the wrong spot and you lose your connectivity. In addition, the maximum distance between the sending and receiving devices for an infrared data transmission is normally limited to between 1 and 3 meters. Given the transmission speeds, the line-of-sight requirement, and distance restrictions, infrared does not make for an ideal network connectivity solution. Why is it included in the A+ objectives under networking hardware? We will leave that one to you to try and figure out.
NOTE
IrDA communication uses half-duplex communication. This means it is able to send and receive data but not at the same time.
IrDA is supported across several platforms; it is very much integrated with newer Windows platforms and has been available since Windows 95. Infrared is also supported by the mainstream Linux distributions as well as Macintosh systems. Support from these operating systems usually makes setting up IrDA devices a painless process.
Fiber-Optic Cable
There is a constant demand for faster networking speeds, and fiber-optic cable was introduced to help meet this need. Compared with the other types of cabling discussed here, fiber-optic cable is a relative newcomer to the world of corporate networking. Unlike the other transmission types, fiber-optic cable uses light instead of electrical signals and so is not susceptible to interference as is copper wire. Fiber-optic cable has a central glass core, which is surrounded by a glass cladding and protected by an outer sheath. Although the cable is designed to be durable and easy to work with, special attention is needed when you’re working with fiber-optic cabling. In many cases, special tools and skills are required for installing fiber optics, though as the technology becomes more popular, simplified methods are being introduced. Figure 6-8 shows an example of fiber-optic cabling.
Figure 6-8. Fiber-optic cable
Because it transmits light, fiber-optic cable is capable of transmitting long distances at very high speeds. In terms of performance, fiber-optic cable has no match, being able to transfer data at speeds of 100 Mbps to beyond 1Gbps. However, when it comes to cost and difficulty of installation, fiber-optic cable becomes less attractive.
TEST SMART
If you need to run network cable over long distances or require high speeds and increased resistance to EMI and crosstalk, fiber-optic cabling is your best choice.
Media Characteristics Summary
Understanding the basic characteristics of network cable types is an important skill for anyone working with or supporting networks. Table 6-2 summarizes the cable types discussed in this section.
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Table 6-2. Summary of Cable Types |
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|
Cable Type |
Susceptibility to Interference |
Transmission Speed |
Maximum Distance |
Installation Difficulty |
|
Thin coax |
Low |
10 Mbps |
185 meters |
Low |
|
Thick coax |
Very low |
10 Mbps |
500 meters |
Difficult |
|
UTP |
High |
10 to 100 Mbps |
100 meters |
Easy |
|
STP |
Low |
10 to 500 Mbps |
90 meters |
Moderate |
|
RS-232 |
N/A |
20 Kbps |
50 Feet |
N/A |
|
Infrared |
High |
115 Kbps-4 Mbps |
1 meter |
Easy |
|
Fiber-optic |
None |
100 Mbps to 1Gbps and beyond |
Up to 30 miles |
Difficult |
SEE ALSO
Pictures and descriptions of the connectors used with the various cables can be found in Chapter 1.
