#networking lesson 1.9 Wireles Technologies and devises In addition to the wired network, various technologies exist that allow the transmission of information between hosts without cables. These are known as wireless technologies. Wireless technologies use electromagnetic waves to carry information between devices. An electromagnetic wave is the same medium that carries radio signals through the air. The electromagnetic spectrum includes such things as radio and television broadcast bands, visible light, x-rays and gamma-rays. Each of these has a specific range of wavelengths and associated energies as shown in the diagram. Some types of electromagnetic waves are not suitable for carrying data. Other parts of the spectrum are regulated by governments and licensed to various organizations for specific applications. Certain areas of the spectrum have been set aside to allow public use without the restriction of having to apply for special permits. The most common wavelengths used for public wireless communications include the Infrared and part of the Radio Frequency (RF) band. Infrared Infrared (IR) is relatively low energy and cannot penetrate through walls or other obstacles. However, It is commonly used to connect and move data between devices such as Personal Digital Assistants (PDAs) and PCs. A specialized communication port known as an Infrared Direct Access (IrDA) port uses IR to exchange information between devices. IR only allows a one-to-one type of connection. IR is also used for remote control devices, wireless mice, and wireless keyboards. It is generally used for short-range, line-of-sight, communications. However, it is possible to reflect the IR signal off objects to extend the range. For greater ranges, higher frequencies of electromagnetic waves are required. Radio Frequency (RF) RF waves can penetrate through walls and other obstacles, allowing a much greater range than IR. Certain areas of the RF bands have been set aside for use by unlicensed devices such as wireless LANs, cordless phones and computer peripherals. This includes the 900 MHz, 2.4 GHz and the 5 GHz frequency ranges. These ranges are known as the Industrial Scientific and Medical (ISM) bands and can be used with very few restrictions. Bluetooth is a technology that makes use of the 2.4 GHz band. It is limited to low-speed, short-range communications, but has the advantage of communicating with many devices at the same time. This one-to-many communications has made Bluetooth technology the preferred method over IR for connecting computer peripherals such as mice, keyboards and printers. Other technologies that make use of the 2.4 GHz and 5GHz bands are the modern wireless LAN technologies that conform to the various IEEE 802.11 standards. They are unlike Bluetooth technology in that they transmit at a much higher power level, which gives them a greater range By NW-1
Posted on: Sat, 07 Sep 2013 16:29:22 +0000
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