IEEE 802.11: Wi-Fi Basic Information
Wi-Fi Basic Information
Wi-Fi is a local area wireless technology that allows an electronic device to exchange data or connect to the internet using 2.4 GHz UHF and 5 GHz SHR radio waves. The name "Wi-Fi" is a trademark name that came from a play on the audiophile term "Hi-Fi." The Wi-Fi Alliance defines Wi-Fi as any wireless local area network (WLAN) products that are based on the Institute of Electrical and Electronics Engineers (IEEE) 802.11 standards. Since most modern WLANs are based on these standards, the term "Wi-Fi" is used in general as a synonym for "WLAN." It is important to note that only Wi-Fi products that complete the Wi-Fi Alliance interoperability certification testing successfully may use the "Wi-Fi CERTIFIED" trademark.
Many devices that use Wi-Fi can connect to a network resource through an access point or hotspot. Each of these devices has a range of about 20 meters (66 feet) indoors and much greater outside.
Security
Wi-Fi can be less secure than wired connections since an intruder need not have a physical connection. Since unencrypted internet access can be easily detected by intruders, Wi-Fi has adopted various encryption technologies. The first was WEP, which ended up being easy to break through. More secure protocols such as WPA and WPA2 were then added later to improve the level of security. One optional feature added in 2007, called Wi-Fi Protected Setup (WPS), had a serious flaw that allowed an attacker to recover the router's password.
Advantages
Wi-Fi allows cheaper deployment of local area networks (LANs). It also allows for deployment in areas where cables cannot be run. The price of the chipsets used for Wi-Fi continues to drop making it more economical for manufactures to include them in more devices.
The encryption WPA2 is considered secure provided a strong passphrase is used. Also new protocols make Wi-Fi more suitable for latency-sensitive applications. Power saving mechanisms (WMM Power Save) extend battery life.
Limitations
Spectrum assignments and operational limitations are not consistent worldwide. Australia and Europe allow for an additional two channels beyond those permitted in the United States for the 2.4 GHz band (1-13 instead of 1-11). Japan has one more channel on top of those (1-14).
A Wi-Fi signal occupies five channels in the 2.4 GHz band. The only group of three non-overlapping channels in North America and the United Kingdom is 1, 6, and 11. In Europe and Japan using Channels 1, 5, 9, and 13 create a non-overlapping set of 4 channels.
For 802.11n, the bandwidth is doubled meaning only one non-overlapping channel can be used.
Ultra High Frequency (UHF)
Ultra high frequency (UHF) is a the ITU designation for radio frequencies in the range between 300 MHz and 3 GHz. It is also known as the decimetre band or the decimetre wave was the wavelengths range from one to ten decimetres where 1 decimeter is equal to 1 metre. Super high frequency (SHF) is the next higher band.
Super High Frequency (SHF)
Super high frequency is the ITU designation for radio frequencies in the range between 3 GHz and 30 GHz. This band of frequencies is also known as the centimetre band or the centimetre wave as the wavelengths range from one to ten centimetres. Since these frequencies fall in the microwave band the waves are known as microwaves.
International Telecommunication Union (ITU)
The International Telecommunication Union is a specialized agency of the United Nations (UN) that is responsible for issues that concern information and communication technologies. The ITU coordinates the shared global use of the radio spectrum, promotes international cooperation in assigning satellite orbits, works to improve telecommunication infrastructure in the developing worlds, and assists in the development and coordination of worldwide technical standards.
Wi-Fi Multimedia (WMM)
Also known as Wireless Multimedia Extensions (WME) is a Wi-Fi Alliance interoperability certification based on the IEEE 802.11e standard. It provides basic Quality of Service (QoS) features to IEEE 802.11 networks. WMM prioritizes traffic according to four Access Categories (AC): voice, video, best effort, and background. It does not, however, provide guaranteed throughput. It is suitable for well defined applications that require QoS such as Voice over IP (VoIP) on Wi-Fi phones (VoWLAN).
Power Save Certification
The Wi-Fi Alliance has added Power Save Certification to the WMM specification. Power Save uses mechanisms from 802.11e and legacy 802.11 to save power (for battery powered equipments) and fine-tune power consumption.
The concept of WMM PowerSave is that the station (STA) triggers the release of buffered data from the access point (AP) by sending an uplink data frame. Upon receipt of such a data (trigger) frame the AP releases previously buffered data stored in each of its quotes.