Telecommunications channels make use of a variety of telecommunications media. These include twisted-pair wire, coaxial cables, and fiber-optic cables, all of which physically link the devices in a network. In addition, there are infrared systems, which use infrared light to transmit and receive data.
Twisted-Pair Wire ü Ordinary telephone wire
ü Copper wire is twisted into pairs
ü Cheap and easy to install
Coaxial Cableü Sturdy copper or aluminum wire wrapped with spacers to insulate and protect it
ü Commonly used in television cable
Fiber-Optic Cableü One or more hair-thin filaments of glass fiber wrapped in a protective jacket
ü Less susceptible to interference and more secure
Wireless telecommunications technologies rely on radio wave, microwave, infrared, and visible light pulses to transport digital communications without wires between communications devices. Wireless technologies include terrestrial microwave, communications satellites, cellular and PCS telephone and pager systems, mobile data radio, wireless LANs, and various wireless Internet technologies. Each technology utilizes specific ranges within the electromagnetic spectrum (in megahertz) of electromagnetic frequencies that are specified by national regulatory agencies to minimize interference and encourage efficient telecommunications.
Wireless access to the Internet, intranets, and extranets is growing as more Web-enabled information appliances proliferate. Smart telephones, pagers, PDAs, and other portable communications devices have become very thin clients in wireless networks. Agreement on a standard wireless application protocol (WAP) has encouraged the development of many wireless Web applications and services. The telecommunications industry continues to work on third generation (3G) wireless technologies whose goal is to raise wireless transmission speeds to enable streaming video and multimedia applications on mobile devices.
Figure above illustrates the wireless application protocol that is the foundation of wireless mobile Internet and Web applications. The WAP standard specifies how Web pages in HTML or XML are translated into a wireless markup language (WML) by filter software and preprocessed by proxy software to prepare the Web pages for wireless transmission from a Web server to a Web-enabled wireless device [16].
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