With wired networks, planning the installation of cabling is fairly straightforward. You can survey the site and look for routes where installers can run the cable. You can measure the distances and quickly determine whether cable runs are possible. If some users are too far away from the network, you can design a remote networking solution or extend the length of the cable by using repeaters. When the design is complete, installers can run the cables, and the cable plant almost always supports the transmission of data as planned.
A WLAN installation is not as predictable. It is difficult if not impossible to design a WLAN by merely inspecting the facility. Predicting the way in which the contour of the building will affect the propagation of radio waves is difficult. As Chapter 2, “Radio Wave Fundamentals,” explains, omnidirectional antennas propagate radio waves in all directions if nothing gets in the way. Walls, ceilings, and other obstacles attenuate the signals more in some directions than others and even cause radio waves to change their paths of transmission. Even the opening of a bathroom door can change the propagation pattern. These events cause the actual radiation pattern to distort, taking on a jagged appearance, as shown in Figure 4-13.
Figure 4-13 The Radiation Pattern of an Omnidirectional Antenna Within an Office Building Is Irregular and Unpredictable
To avoid installation problems, an organization should perform a thorough wireless site survey to assess the coverage of the network. Neglecting to do so might leave some users in a coverage hole without reliable connections to the network. Propagation tests give you the information necessary to plan optimum installation locations for access points, allowing coverage over required areas.