Section 4.2. Wired Links and Transmission

4.2. Wired Links and Transmission

Wired links provide a physical path for signals to propagate. Three types of wired links are twisted pair , coaxial cable , and optical fiber .

4.2.1. Twisted-Pair Links

A twisted-pair link is the simplest form of guided medium used for data transmission. A twisted pair is normally manufactured using copper and consists of two insulated wires. The twisting action on wires reduces the cross-talk interferences generated between each two pairs of transmission links. To increase the capacity of transmission cables, especially for long-distance applications, several pairs of such links are bundled together and wrapped in a protective sheath. One of the most common applications of the twisted-pair link is for telephone network transmission links. The frequency range of twisted-pair cables is approximately 0 to 1 MHz.

4.2.2. Coaxial Cable

A higher data rate for longer-distance applications can be achieved with coaxial cable , a hollow outer cylindrical conductor surrounding an inner wire. The outer conductor is spaced tightly with inner wire by a solid dielectric material. The outer conductor is also shielded from outside. This concentric construction makes coaxial cables susceptible to interference. Coaxial cables have a wide variety of applications, such as cable television distribution, long-distance telephone transmission, and local area networks. The frequency range that coaxial cables can carry is 0 to 750 MHz.

4.2.3. Optical Fiber

Remarkably higher-bandwidth communication links can be achieved using optical fibers. An optical fiber is a thin glass or plastic wire that can guide an optical ray. One of the best substances used to make optical fibers is ultrapure fused silica . These fibers are, however, more expensive than regular glass fibers. Plastic fibers are normally used for short-distance links where higher losses are tolerable.

Similar to coaxial cables, optical fiber cables have a cylindrical layout. The three concentrics are the core , the cladding , and the jacket . The core consists of several very thin fibers, each of which is surrounded by its own cladding. Each cladding also has a glass or plastic coating but different from those of the core. This difference is the key mechanism that confines the light in the cable. Basically, the boundary between the core and cladding reflects the light into the core and runs it through the cable.

The combined core and cladding is surrounded by a jacket. Jackets are made of materials that can protect the cable against interference and damage. Optical fibers are superior to coaxial cables mainly because of their higher bandwidths, lighter weights, lower signal attenuation, and lower impact by external interferences. Optical fiber links are used in all types of data communication LAN and WAN applications. The frequency range of fiber optics is approximately 180 THz to 330 THz.