Common Network Cable

Having now examined some of the general considerations that surround network media, the next step is to look at the different types of media available. The network media are not the most glamorous part of computer networking, but they are important both for the Network+ exam and the real world. Besides, who said networking was glamorous?

Network media can be divided into two distinct categories: cable and wireless, sometimes referred to as bound and unbound media. Cable media come in three common types: twisted-pair, coaxial, and fiber-optic. Wireless media has another range. The following sections identify the characteristic of each type of media.

Cable Media

Working with today's networks, you are more likely to be working with cable media than with any wireless alternative. Cable media provides a physical connection between networked devices—for example, a copper cable running from a desktop computer to a hub in the server room. Data transmissions pass through the cable to their destination.

There are two types of cable media: metal and optical-based cable. Copper-based cable is widely used to connect LANs and wide area networks (WANs), and optical cable is mainly used for large-scale network implementations. The following sections review the various types of cable media and the networks on which they are used.

Coaxial Cable

At one time, almost all networks used coaxial cable. Times have changed, and coax has fallen out of favor, giving way to faster and more durable cable options. That is not to say that you won't be working with coax at some point. Many environments have been using coax and continue to do so because their network needs do not require an upgrade to another media—at least not yet. Many small offices continue to use coax on their networks, so we'll include it in our discussion.

Coaxial cable resembles standard TV cable and is constructed using an outside insulation cover, braided metal shielding, and a copper wire at the center. The shielding and insulation help combat attenuation, crosstalk, and EMI. Some coax is available with dual and even quad shielding.

Two types of coax are used in networking: thin coax and thick coax. Neither is particularly popular anymore, but you are most likely to encounter thin coax. Figure 2.1 shows the construction of a standard coaxial cable.

Thin Coax

Thin coax is by far the most widely used type of coax. As the name suggests, it is thin—at least compared to other forms of available coax. Thin coax, also called Thinnet, is only .25 inches in diameter, making it fairly easy to install; it has a maximum cable length of 185 meters (that is, just over 600 feet). If longer lengths of thin coax are used, data signals sent along the cable will suffer from attenuation, compromising data integrity. Table 2.1 summarizes the types of thin coax cable.

Table 2.1. Thin Coax Types

Cable Type	Description
RG-58 /U	Has a solid copper core
RG-58 A/U	Has a stranded wire core
RG-58 C/U	Used for military specifications
RG-59	Often used for cable TV and cable modems
RG-62	Used for ARCnet specifications

Thin coax typically runs from computer to computer and uses British Naval connectors (BNCs) to connect to network devices. Figure 2.2 shows BNC T connectors and terminators, which are often used with thin coax.

Thick Coax

Thick coax is indeed thicker than thin coax. The popularity of thick coax has fallen due to its implementation difficulty and low network speeds. In its day, thick coax found its niche as a backbone for network environments because of its better-than-average resistance to attenuation and EMI.

Unlike thin coax, which connects to individual network devices via BNCs, thick coax requires an extra length of cable that runs from it to the networked system. Thick coax networks use a device called a tap to connect a smaller cable to the thick coax backbone. Taps are simple devices that penetrate the outer insulation and create a connection directly to the inside wire.

It is unlikely that you will be involved in designing and implementing a network with thick coax. However, you might work with a network that has an existing thick coax infrastructure.

Twisted-Pair

Now and for the foreseeable future, twisted-pair cable is the network media of choice. It is relatively inexpensive, easy to work with, and well suited to the needs of the modern network. There are two distinct types of twisted-pair cable: unshielded twisted-pair (UTP) and shielded twisted-pair (STP). UTP is the most common implementation of twisted-pair cable, and it is used for both telephone systems and computer networks.

STP, as its name implies, adds extra shielding within the casing, so it copes with interference and attenuation better than regular UTP. Because of this shielding, cable distances for STP can be greater than for UTP; but, unfortunately, the additional shielding also makes STP considerably more costly than regular UTP.

The Electronic Industries Association/Telecommunications Industry Association (EIA/TIA) has specified five categories of twisted-pair cable:

• Category 1— Voice-grade UTP telephone cable. Due to its susceptibility to interference and attenuation and its low bandwidth capability, Category 1 UTP is not practical for network applications.

• Category 2— Data-grade cable that is capable of transmitting data up to 4Mbps. Category 2 cable is, of course, too slow for networks. It is unlikely that you will encounter Category 2 used on any network today.

• Category 3— Data-grade cable that is capable of transmitting data up to 10Mbps. A few years ago, Category 3 was the cable of choice for twisted-pair networks. As network speeds pushed the 100Mbps speed limit, Category 3 became ineffective.

• Category 4— Data-grade cable that has potential bandwidth of 16Mbps. Category 4 cable was often implemented in the IBM Token Ring networks.

• Category 5— Data-grade cable that is capable of transmitting data at 100Mbps. Category 5 is the cable of choice on twisted-pair networks and is associated with Fast Ethernet technologies.

To keep pace with today's faster network speeds, twisted-pair categories beyond 5 have been developed. Because not all Category 5 cable is suitable for Gigabit Ethernet applications, an enhanced version of Category 5 has been developed: Category 5e. Category 6 supports data throughput up to three times greater than that of Category 5, but it costs considerably more. In fact, the price of Category 6 might be close enough to fiber that companies will probably choose fiber-optic cable instead. Stay tuned for further developments.

Fiber-optic Cable

Fiber-optic cable is a newcomer on the networking scene compared to the other network cable media, and it is perhaps the most interesting. Unlike standard networking cables, which use electric signals to send data transmissions, fiber uses light. As a result, fiber-optic transmissions are not susceptible to EMI or crosstalk, giving fiber cable an obvious advantage over copper-based media. In addition, fiber-optic cable is highly resistant to attenuation, allowing data signals to travel distances measured in kilometers rather than meters, as with copper-based media. Further advantages of fiber cable include the fact that it's small in diameter, it's lightweight, and it offers significantly faster transmission speeds than other cable media. Quite simply, fiber beats twisted-pair from almost every angle. So, why aren't all networks using fiber cable? The same reason we don't all drive Porsches: cost.

A few things will continue to ensure that there is room for twisted-pair and copper-based media in network environments. First, a fiber solution is very costly, eliminating it from many small- to mid-sized companies that simply do not have the budget to support a fiber-optic solution. The second drawback of fiber is the complexity of its installation and maintenance. Working with fiber-optic cable often requires trained professionals and specialized tools. Third, fiber technology is incompatible with much of the existing electronic network infrastructure, meaning that to use fiber-optic cable, much of the current network hardware needs to be retrofitted or upgraded, and that can be a very costly commitment.

A fiber-optic cable consists of several components, including the optic core at the center, an optic cladding, insulation, and an outer jacket. The optic core is responsible for carrying the light signal and is commonly constructed of plastic or glass. Figure 2.3 shows an example of the components of a fiber-optic cable.

Two types of optical fiber are available: single-mode and multimode. Multimode fiber has a larger core than single-mode. This larger core allows hundreds of light rays to flow through the fiber simultaneously. Single-mode fiber, on the other hand, has a small core that allows only a single light beam to pass. The light transmissions in single-mode fiber pass through the core in a direct line, like a flashlight beam. The numerous light beams in multimode fiber bounce around inside the core, inching toward their destination. Because light beams bounce within the core, the light beams slow down, reduce in strength, and take some time to travel along the cable. For this reason, single-mode fiber's speed and distance are superior to those of multimode.

Fiber cable can also have a variety of internal compositions (glass or plastic core), and the size of the core inside the cable, measured in microns, can vary. Some of the common types of fiber-optic cable include the following:

• 62.5 micron core/125 micron cladding multimode

• 50 micron core/125 micron cladding multimode

• 100 micron core/140 micron cladding multimode

• 8.3 micron core/125 micron cladding single mode

REVIEW BREAK: Cable Summary

Be prepared: The CompTIA Network+ exam will require you to identify the basic characteristics of each cable type discussed in this section. In particular, you will be expected to know which cables offer the greatest resistance to interference and attenuation, and you must be able to identify which type of cable is best suited for a particular network environment. Table 2.2 summarizes the characteristics of the various cable media.

Table 2.2. Cable Media Characteristics

Media	Resistance to Attenuation	Resistance to EMI/Crosstalk	Cost of Implementation	Difficulty of Implementation
Thin coax	Moderate	Moderate	Low	Low
Thick coax	High	High	Moderate	Moderate
UTP	Low	Low	Low	Low
STP	Moderate	Moderate	Moderate	Low
Fiber-optic	Very high	Very high	Very high	Extremely difficult

Wireless Media

If you looked at the back of your computer right now, you'd no doubt see wires of all shapes and sizes coming out in all directions. Wouldn't it be nice if these unsightly and cumbersome cables were not needed? It is the goal of wireless communications to one day make this possible. As far as networking is concerned, it is possible to have at least one fewer cable hanging from your system.

Wireless is the alternative to cable-based media. Wireless networks do not use standard cable per se, but they still require a media for signal transmission. Wireless communications connect sending and receiving devices by transmitting signals through the atmosphere. These signals take the form of waves inside the electromagnetic spectrum. Located in this electromagnetic spectrum are the frequency ranges, or bands, commonly associated with wireless data transmissions. These include radio, microwave, and infrared.

Radio

Radio frequency (RF) sits somewhere between 10KHz and 1GHz on the electromagnetic spectrum. Networks can take advantage of radio transmissions within this range to send and receive data. Three types of RF transmissions can be used: single-frequency low-power RF, single-frequency high-power RF, and spread-spectrum.

Single-frequency low-power RF transmissions are used where the data has to travel a limited distance. Single-frequency RF transmissions do not require a line of sight between communicating devices; however, structures such as walls or buildings can completely or partially block signals between the sending and receiving devices.

The downside of single-frequency low-power RF transmissions is that the distance a signal can travel is very limited. The distance depends on many factors, but 50 to 70 meters is generally the maximum distance. A second drawback is that the speeds of single-frequency low-power RF signal transmission hover between 1Mbps and 10Mbps. This might be fine to transmit small files, but as the amount of data transmitted increases, transmission slows down—it's akin to trying to download MP3s using a 14.4Kbps modem.

A final, and perhaps most important, consideration that affects RF transmissions (and any other wireless broadcast transmission, for that matter) is the security risk involved. Interrupting or intercepting transmissions is possible, so any sensitive data being transmitted is potentially at risk. Because the signals do not travel far for single-frequency low-power RF, eavesdropping on the transmission must be done from close range.

Single-frequency high-power RF transmissions can be transmitted significantly farther than can single-frequency low-power RF. The devices required to create the increased distance capability also increase the cost, making the single-frequency high-power RF much more expensive than the single-frequency low-power RF. High-power RF is also much more complicated than low-power RF; skilled technicians are often required to install and configure it. Like the low-power RF, high-power RF is susceptible to eavesdropping, and because the signals travel so much farther than low-power RF signals, the signal can be tampered with from far away.

High-power RF maintains the same transmission rates as low-power RF: 1Mbps to 10Mbps.

Spread-spectrum is an improvement over the single-frequency transmissions because it uses multiple frequencies simultaneously. This strategy makes transmissions more reliable, decreases the potential of eavesdropping, and reduces the susceptibility to interference. All this is accomplished by using two kinds of spread-spectrum communication: frequency hopping and direct sequence modulation.

Frequency hopping is the technique of switching data between multiple frequencies. Direct sequence modulation breaks data into segments called chips and sends the chips on multiple frequencies.

Frequency hopping is perhaps the most cost-effective type of wireless LAN media to deploy—that is, if you can live with network speeds of 2Mbps or less. Direct sequence provides increased data rates and may be worth the cost for a network that uses bandwidth-intensive applications.

Table 2.3 compares the various RF transmission methods.

Table 2.3. Comparison of RF Transmission Methods

Characteristic	Low-Power Single-Frequency RF	High-Power Single-Frequency RF	Spread-spectrum
Distance	Short distances; 50 to 70 meters	Very long distances; often several miles	N/A
Bandwidth	1Mbps to 10Mbps	1Mbps to 10Mbps	1Mbps to 2Mbps for frequency hopping, 2Mbps to 6Mbps for direct sequence
Installation	Easy	Difficult; requires trained technicians	Moderate to difficult
Interference	Highly susceptible to interference	Highly susceptible to interference	Moderately resistant to interference
Cost	Moderate compared to other technologies	Very expensive	Moderate
Security	Eavesdropping possible from within close within close	Eavesdropping possible from close and distant sources	Highly resistant to eavesdropping

Microwave

Unlike the RF wireless communications, microwave requires a line of sight between the sending and receiving devices. Microwave communication is typically able to reach higher transmission speeds on average than its RF counterparts, but the associated costs, including that of licensing frequencies, are higher as well. Microwave data communication is available in two types: terrestrial (earth-based) and satellite systems. Each of these is discussed in the following sections.

Terrestrial Microwave

Terrestrial microwave transmissions are line-of-sight transmissions between microwave towers or microwave transmitters. Microwave transmitters are typically mounted in high locations such as mountaintops or tall buildings, to help ensure a clean line of sight between the transmitters.

Terrestrial microwave is commonly implemented to connect buildings where traditional cable would be too complicated or costly to set up. The cost of a microwave solution depends largely on the distance required for transmission. Microwave solutions for limited distances, usually only a few hundred meters, are comparatively inexpensive. Microwave solutions requiring data transmission distances measured in kilometers are very costly.

As with radio wave transmissions, data transfer speeds for terrestrial microwave are limited (somewhere between 1Mbps and 10Mbps), and transmissions are susceptible to interference and eavesdropping. Attenuation in microwave transmissions is more of an issue for long distances than for short distances.

Satellite Microwave

Satellite transmissions require a device on earth and a geosynchronous orbiting satellite. These satellites hover some 23,000 miles above the earth, so you can expect transmission delays with satellite microwave. These delays typically range between .5 and 5 seconds; given the distance the signal is traveling, that delay is definitely acceptable.

Very few companies and fewer individuals can afford to launch their own satellite to send and receive data; rather, satellite services can be purchased from vendors. Satellite microwave solutions have transfer speeds comparable to those of terrestrial microwave and are also susceptible to atmospheric interference and eavesdropping. Installing a satellite microwave system requires exact configurations on the earth-bound system; but, thankfully, you are not required to launch into space to configure things at the other end.

Infrared Wireless Networking

Infrared wireless networking uses infrared beams to send data transmissions between devices. Infrared wireless networking offers higher transmission rates than the other wireless technologies, reaching 10Mbps to 16Mbps.

There are two types of infrared transmissions: broadcast and point-to-point. The broadcast method disperses the infrared beam in a wider area. Point-to-point infrared transmissions use a more focused beam between devices. Point-to-point infrared transmissions offer higher transfer speeds and are less susceptible to interference.

However, point-to-point is harder to configure than broadcast because it requires a much more finely tuned line-of-sight configuration than broadcast.