Media Considerations

Managing a network involves many factors, from configuring the operating system and protocols to monitoring users and network performance. Despite the complexity of networks, it is important not to forget about one of the basics components of a network—the network media.

Choosing the correct network media is an important consideration because the media form the foundation for the entire network. When you're working with any media, you must be aware of the factors that influence its suitability for a given network implementation. Some of the most common media considerations are discussed in the following sections.

Media Interference

As a data signal travels through a specific media, it may be subjected to a type of interference known as electromagnetic interference (EMI).

Many different things cause EMI; common sources include computer monitors and fluorescent lighting fixtures—basically, anything that creates an electromagnetic field. If a network cable is too close to such devices, the signal within the cable can become corrupted. As you might expect, some network media are more susceptible than others to the effects of EMI. Copper-based media are prone to EMI, whereas fiber-optic cable is completely resistant to it.

In most networks, standard cable provides sufficient resistance that EMI isn't a problem. However, you might work in some environments in which interference is a concern. In such environments, it becomes important to understand which media offer the greatest resistance to EMI.

EMI is just one of the threats to network transmissions. Data signals may also be subjected to something commonly referred to as crosstalk, which occurs when signals from two cables in close proximity to one another interfere with each other. As a result, the signals on both cables may become corrupted. When you're troubleshooting intermittent network problems, it might be worth your time to confirm that crosstalk or EMI is not at the root of your problems.

Bandwidth

The term bandwidth is tossed around a lot in the network world, and rightly so—it is a very important consideration. Bandwidth is the transmission capacity of a media or, in other words, the amount of data that a media can carry. Data throughput is measured in bits per second (bps). The speed of modern networks is measured in megabits per second (Mbps) and gigabits per second (Gbps).

The different types of network media vary in the amount of bandwidth they can accommodate. If you're working on a network that accommodates huge amounts of data, then bandwidth is a crucial consideration. In contrast, many older networks in small offices may only occasionally share files and maybe a printer. In such an environment, bandwidth is not a very big issue.

Two rules apply to bandwidth:

• Bigger is better— It seems that there is never enough bandwidth to accommodate the demand placed on networks by many applications.

• You have to pay to play— Understandably, everybody would like more bandwidth, but it can be costly. For organizations that need to surpass the 100Mbps mark, the price can climb quickly.

Media Length

Not all networks have the same design. Some are isolated to a single office building, and others span large distances. For large network implementations, media length (that is, the maximum distance over which a certain type of media can be used) may be a factor in the network administrator's choice of network media. Each media has a recommended maximum length, and surpassing these recommendations can cause unusual network problems that are often difficult to troubleshoot. In some cases, the network simply will not work.

Media have maximum lengths because a signal weakens as it travels farther from its point of origin. If the signal travels far enough, it can weaken so much that it becomes unusable. The weakening of data signals as they traverse the media is referred to as attenuation.

All media are susceptible to attenuation, although each media offers some degree of resistance to weakening signals. Some physical media use a special shielding inside the cable, which increases the distance the signal travels. Another strategy that is commonly employed to compensate for attenuation is signal regeneration. The cable itself does not perform the regeneration process; rather, network devices such as switches or repeaters handle signal regeneration. These devices strengthen the signal as it passes and in doing so, they increase the distance the signal can travel. Network devices, such as hubs, routers, and switches, are covered in Chapter 3, “Networking Components and Devices.”

Some cable types, such as fiber-optic, offer very long media distances; other types, such as twisted-pair, offer very short distances (a fraction of the distance of fiber). Some unbound media (wireless media), don't have an exact figure for the allowable distance because there are so many variables. The next section reviews the different types of network media and compares them according to their resistance to attenuation.

Security

Physical media provide relatively secure transmission because to gain access to the signal on the cable, a person must be able to physically access it—that is, he or she must be able to tap into the cable. Fiber-optic cable is even more difficult to access than other cable types because the light transmissions and glass cable used for fiber make it particularly difficult to tap into.

Wireless media, on the other hand, can be insecure; tapping into, or eavesdropping on, signals is a relatively easy process. For organizations that transmit sensitive data, using wireless media can be a security risk. However, a number of security measures can be employed to secure data as it travels across wireless links.

Installation and Repair

Some network media are easier to manage and install than others. This might seem like a minor consideration, but in real-world applications, it can be very important. For example, fiber-optic cable is far more complex to install and troubleshoot than twisted-pair. It's so complicated, in fact, that special tools and training are often needed to install a fiber network.

Each media has a certain level of handling difficulty. It is important to be aware of what you are in for when it's time to implement or repair the network media.

In addition to the factors already discussed, you need to understand some important concepts before we examine the specific media types; you need to understand baseband and broadband signaling, physical media terminology, and duplexing.