The term wireless, quite simply, means any communication what does not have a physically wired medium (e.g., coax cable, twisted pair, optical fiber, etc.). The transmission is carried optically (light) or using electromagnetic waves of energy (radio frequency) through space itself.
There are a vast number of wireless technologies that range from such things as Bluetooth, an RF wireless technology designed PAN applications, to Wi-Fi, an RF-based technology designed for (LAN) applications, to EV-DO and GSM, technologies designed for wide area cellular applications. Other wireless worlds include microwave, satellite, broadcast radio and television, and a wide variety of medical, industrial, and scientific applications.
Because the frequencies in use are in the public domain, it is vital that wireless applications be engineered so as to avoid interference with one another. To this end, the spectrum is typically controlled by the local government, and international issues are dealt with by international bodies, such as the United Nations. In the United States, the Federal Communications Commission (FCC) oversees spectrum usage.
Another critical issue in wireless technologies is privacy. Again, because the transmission path is often in the public right of way, any receiver can tap into the transmission stream and receive the signals. To protect wireless transmissions, some form of encryption is required. Many wireless standards also include specifications for how to authenticate and authorize receivers, and how to encrypt traffic during the transmission.
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