WIRELESS TECHNOLOGIES

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.
Wireless technologies and devices
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.
Advantages of wireless Technology
Wireless technology offers many advantages compared to traditional wired networks.
One of the main advantages is the ability to provide anytime, anywhere connectivity. The widespread implementation of wireless in public locations, known as hotspots, allows people to easily connect to the Internet to download information and exchange emails and files.
Wireless technology is fairly easy and inexpensive to install. The cost of home and business wireless devices continues to decrease. Yet, despite the decrease in cost, the data rate and capabilities of these devices have increased, allowing faster, more reliable wireless connections.
Wireless technology enables networks to be easily expanded, without the limitations of cabled connections. New and visiting users can join the network quickly and easily.
Disadvantages of Wireless Technologies
Despite the flexibility and benefits of wireless, there are some limitations and risks.
First, Wireless LAN (WLAN) technologies make use of the unlicensed regions of the RF spectrum. Since these regions are unregulated, many different devices make use of them. As a result, these regions are congested and signals from different devices often interfere with each other. In addition, many devices such as microwave ovens and cordless phones use these frequencies and can interfere with WLAN communications.
Second, a major concern with wireless is security. Wireless provides ease of access. It does this by broadcasting data in a manner that allows anyone the ability to access it. However, this same feature also limits the amount of protection wireless can provide for the data. It allows anyone to intercept the communication stream, even unintended recipients. To address these security concerns, techniques have been developed to help secure wireless transmissions including encryption and authentication.
Types of wireless Technologies
Wireless networks are grouped into three major categories: Wireless Personal Area networks (WPAN), Wireless Local Area networks (WLAN), and Wireless Wide Area networks (WWAN).
Despite these distinct categories, it is difficult to place boundary limitations on a wireless implementation. This is because, unlike a wired network, wireless networks do not have precisely defined boundaries. The range of wireless transmissions can vary due to many factors. Wireless networks are susceptible to outside sources of interference, both natural and man-made. Fluctuations in temperature and humidity can greatly alter the coverage of wireless networks. Obstacles within the wireless environment can also affect the range.



WPAN
This is the smallest wireless network used to connect various peripheral devices such as mice, keyboards and PDAs to a computer. All of these devices are dedicated to a single host with usually use IR or Bluetooth technology.
WLAN
WLAN is typically used to extend the boundaries of the local wired network (LAN). WLANs use RF technology and conform to the IEEE 802.11 standards. They allow many users to connect to a wired network through a device known as an Access Point (AP). An Access Point provides a connection between wireless hosts and hosts on an Ethernet wired network.
WWAN
WWAN networks provide coverage over extremely large areas. A good example of a WWAN is the cell phone network. These networks use technologies such as Code Division Multiple Access (CDMA) or Global System for Mobile Communication (GSM) and are often regulated by government agencies.
Wireless Technologies standarads
A number of standards have been developed to ensure that wireless devices can communicate. They specify the RF spectrum used, data rates, how the information is transmitted, and more. The main organization responsible for the creation of wireless technical standards is the IEEE.
The IEEE 802.11 standard governs the WLAN environment. There are four amendments to the IEEE 802.11 standard that describe different characteristics for wireless communications. The currently available amendments are 802.11a, 802.11b, 802.11g and 802.11n. (802.11n is not ratified at the time of this writing.) Collectively these technologies are referred to as Wi-Fi, Wireless Fidelity.
Another organization, known as the Wi-Fi Alliance, is responsible for testing wireless LAN devices from different manufacturers. The Wi-Fi logo on a device means that this equipment meets standards and should interoperate with other devices of the same standard.