The difficulty of installing SCS is a factor that givesa distinct advantage to the wireless environment. It can be particularly useful in the following situations:

• in the premisescrouded with people (e.g., in hallways or reception rooms);
• for employeeswithout a fixed work place (e.g. doctors or nurses);
• in the isolated buildings and facilities;
• in the premises withfrequently changing layout;
• in buildings (such as historical sites or architectureattractions), where pulling the cable is not permissible.

Depending on the technology, wireless networks can be divided into three types:

• local area networks — a typical wireless network looks and functions almost the same as a plain cable network, with the exception of the transmission medium. Wireless network adapter with a transceiver is installed in each computer, and users work as if their computers are connected by a cable.
• extandedlocal area networks — some wireless components are able to function in extended local area networks similarly to their counterparts in cable networks. Wireless bridge, for example, is designed to connect networks that are located at a distance up to several kilometers from each other.
• mobile networks (mobile computers) — in wireless mobile networks the transmission media is constituted by telephone systems and public services. It uses batch wireless connection, cellular networks, satellite stations. Employeeswho are constantly on the move, can use this technology with portable computers or PDA, they can exchange e-mail messages, files and other information.

The main differences between these network types are transmission parameters. Local and estendedlocal area networks use transmitters and receivers owned by the organization that operates the network. For laptops the medium of signal transmission are AT&T, MCI, Sprint, local telephone companies and their public services.

Wireless LANs use four methods of data transfer:

• infrared radiation;
• laser;
• narrow band broadcast (single frequency transmission);
• scatteredband broadcast.