Transmission media

Transmission media are the physical pathways that connect computers, other devices, and people on a network—the highways and byways that comprise the information superhighway. Each transmission medium requires specialized network hardware that has to be compatible with that medium. You have probably heard terms such as Layer 1, Layer 2, and so on. These refer to the OSI reference model, which defines network hardware and services in terms of the functions they perform. (The OSI reference model is discussed in detail in Chapter 5, "Data Communications Basics.") Transmission media operate at Layer 1 of the OSI model: They encompass the physical entity and describe the types of highways on which voice and data can travel.

It would be convenient to construct a network of only one medium. But that is impractical for anything but an extremely small network. In general, networks use combinations of media types. There are three main categories of media types:

Copper cable — Types of cable include unshielded twisted-pair (UTP), shielded twisted-pair (STP), and coaxial cable. Copper-based cables are inexpensive and easy to work with compared to fiber-optic cables, but as you'll learn when we get into the specifics, a major disadvantage of cable is that it offers a rather limited spectrum that cannot handle the advanced applications of the future, such as teleimmersion and virtual reality.

Wireless — Wireless media include radio frequencies, microwave, satellite, and infrared. Deployment of wireless media is faster and less costly than deployment of cable, particularly where there is little or no existing infrastructure (e.g., Africa, Asia-Pacific, Latin America, eastern and central Europe). Wireless is also useful where environmental circumstances make it impossible or cost-prohibitive to use cable (e.g., in the Amazon, in the Empty Quarter in Saudi Arabia, on oil rigs).

There are a few disadvantages associated with wireless, however. Historically, wireless solutions support much lower data rates than do wired solutions, although with new developments in wireless broadband, that is becoming less of an issue (see Part IV, "Wireless Communications"). Wireless is also greatly affected by external impairments, such as the impact of adverse weather, so reliability can be difficult to guarantee. However, new developments in laser-based communications—such as virtual fiber—can improve this situation. (Virtual fiber is discussed in Chapter 15, "WMANs, WLANs, and WPANs.") Of course, one of the biggest concerns with wireless is security: Data must be secured in order to ensure privacy.

Fiber optics — Fiber offers enormous bandwidth, immunity to many types of interference and noise, and improved security. Therefore, fiber provides very clear communications and a relatively noise-free environment. The downside of fiber is that it is costly to purchase and deploy because it requires specialized equipment and techniques.