Wi-FiFrom Wikipedia, the free encyclopediaJump to: navigation, search
For the radio station, see WIFI (AM). Wi-Fi logoWi-Fi ( /ˈwaɪfaɪ/, also spelled Wifi or WiFi) is a popular technology that allows an electronic device to exchange data wirelessly (using radio waves) over a computer network, including high-speed Internet connections. 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".[1] However, since most modern WLANs are based on these standards, the term "Wi-Fi" is used in general English as a synonym for "WLAN".

A device that can use Wi-Fi (such as a personal computer, video game console, smartphone, tablet, or digital audio player) can connect to a network resource such as the Internet via a wireless network access point. Such an access point (or hotspot) has a range of about 20 meters (65 feet) indoors and a greater range outdoors. Hotspot coverage can comprise an area as small as a single room with walls that block radio waves or as large as many square miles — this is achieved by using multiple overlapping access points.

"Wi-Fi" is a trademark of the Wi-Fi Alliance and the brand name for products using the IEEE 802.11 family of standards. Only Wi-Fi products that complete Wi-Fi Alliance interoperability certification testing successfully may use the "Wi-Fi CERTIFIED" designation and trademark.

Wi-Fi has had a checkered security history. Its earliest encryption system, WEP, proved easy to break. Much higher quality protocols, WPA and WPA2, were added later. However, an optional feature added in 2007, called Wi-Fi Protected Setup (WPS), has a flaw that allows a remote attacker to recover the router's WPA or WPA2 password in a few hours on most implementations.[2] Some manufacturers have recommended turning off the WPS feature. The Wi-Fi Alliance has since updated its test plan and certification program to ensure all newly-certified devices resist brute-force AP PIN attacks.

Contents [hide]
1 History
1.1 The name
1.2 Wi-Fi certification
2 Uses
2.1 Internet access
2.1.1 City-wide Wi-Fi
2.1.2 Campus-wide Wi-Fi
2.2 Direct computer-to-computer communications
3 Advantages and limitations
3.1 Advantages
3.2 Limitations
3.3 Range
3.4 Data security risks
3.5 Interference
4 Hardware
4.1 Standard devices
4.2 Distance records
4.3 Embedded systems
4.4 Multiple access points
5 Network security
5.1 Securing methods
5.2 Piggybacking
6 Safety
7 See also
8 Notes
9 References
10 Further reading
11 External links

[edit] HistoryMain article: History of IEEE 802.11
802.11 technology has its origins in a 1985 ruling by the US Federal Communications Commission that released the ISM band for unlicensed use.[3] In 1991 NCR Corporation with AT&T invented the precursor to 802.11 intended for use in cashier systems. The first wireless products were under the name WaveLAN.

Vic Hayes has been called the "father of Wi-Fi". He was involved in designing the initial standards within the IEEE.[4][5]

A large number of patents by many companies are used in 802.11 standard.[6] In 1992 and 1996, Australian organisation CSIRO obtained patents for a method later used in Wi-Fi to "unsmear" the signal.[7] In April 2009, 14 tech companies agreed to pay CSIRO $250 million for infringements on CSIRO patents.[8] This led to WiFi being attributed as an Australian invention,[9] though this has been the subject of some controversy.[10][11] CSIRO won a further $220 million settlement for Wi-Fi patent infringements in 2012 with global firms in the United States required to pay the CSIRO licensing rights estimated to be worth an additional $1 billion in royalties.[12][13][8]

In 1999, the Wi-Fi Alliance was formed as a trade association to hold the Wi-Fi trademark under which most products are sold.[14]

[edit] The nameThe term Wi-Fi, first used commercially in August 1999,[15] was coined by a brand-consulting firm called Interbrand Corporation. The Wi-Fi Alliance had hired Interbrand to determine a name that was "a little catchier than 'IEEE 802.11b Direct Sequence'".[16][17][18] Belanger also stated that Interbrand invented Wi-Fi as a play on words with Hi-Fi, and also created the Wi-Fi logo.

The Wi-Fi Alliance initially used an advertising slogan for Wi-Fi, "The Standard for Wireless Fidelity",[16] but later removed the phrase from their marketing. Despite this, some documents from the Alliance dated 2003 and 2004 still contain the term Wireless Fidelity.[19][20] There was no official statement related to the dropping of the term.

The yin-yang Wi-Fi logo indicates the certification of a product for interoperability.[19]

Non-Wi-Fi technologies intended for fixed points such as Motorola Canopy are usually described as fixed wireless. Alternative wireless technologies include mobile phone standards such as 2G, 3G or 4G.

[edit] Wi-Fi certificationSee also: Wi-Fi Alliance
The IEEE does not test equipment for compliance with their standards. The non-profit Wi-Fi Alliance was formed in 1999 to fill this void — to establish and enforce standards for interoperability and backward compatibility, and to promote wireless local-area-network technology. As of 2010[update] the Wi-Fi Alliance consisted of more than 375 companies from around the world.[21][22] The Wi-Fi Alliance enforces the use of the Wi-Fi brand to technologies based on the IEEE 802.11 standards from the Institute of Electrical and Electronics Engineers. This includes wireless local area network (WLAN) connections, device to device connectivity (such as Wi-Fi Peer to Peer aka Wi-Fi Direct), Personal area network (PAN), local area network (LAN) and even some limited wide area network (WAN) connections. Manufacturers with membership in the Wi-Fi Alliance, whose products pass the certification process, gain the right to mark those products with the Wi-Fi logo.

Specifically, the certification process requires conformance to the IEEE 802.11 radio standards, the WPA and WPA2 security standards, and the EAP authentication standard. Certification may optionally include tests of IEEE 802.11 draft standards, interaction with cellular-phone technology in converged devices, and features relating to security set-up, multimedia, and power-saving.[23]

Not every Wi-Fi device is submitted for certification. The lack of Wi-Fi certification does not necessarily imply a device is incompatible with other Wi-Fi devices. If it is compliant or partly compatible, the Wi-Fi Alliance may not object to its description as a Wi-Fi device[citation needed] though technically only certified devices are approved. Derivative terms, such as Super Wi-Fi, coined by the US Federal Communications Commission (FCC) to describe proposed networking in the UHF TV band in the US, may or may not be sanctioned.

Wi-Fi Signal logo[edit] UsesTo connect to a Wi-Fi LAN, a computer has to be equipped with a wireless network interface controller. The combination of computer and interface controller is called a station. All stations share a single radio frequency communication channel. Transmissions on this channel are received by all stations within range. The hardware does not signal the user that the transmission was delivered and is therefore called a best-effort delivery mechanism. A carrier wave is used to transmit the data in packets, referred to as "Ethernet frames". Each station is constantly tuned in on the radio frequency communication channel to pick up available transmissions.

[edit] Internet accessA Wi-Fi-enabled device can connect to the Internet when within range of a wireless network connected to the Internet. The coverage of one or more (interconnected) access points — called hotspots — can extend from an area as small as a few rooms to as large as many square miles. Coverage in the larger area may require a group of access points with overlapping coverage. Outdoor public Wi-Fi technology has been used successfully in wireless mesh networks in London, UK.

Wi-Fi provides service in private homes, high street chains and independent businesses, as well as in public spaces at Wi-Fi hotspots set up either free-of-charge or commercially. Organizations and businesses, such as airports, hotels, and restaurants, often provide free-use hotspots to attract customers. Enthusiasts or authorities who wish to provide services or even to promote business in selected areas sometimes provide free Wi-Fi access.

Routers that incorporate a digital subscriber line modem or a cable modem and a Wi-Fi access point, often set up in homes and other buildings, provide Internet access and internetworking to all devices connected to them, wirelessly or via cable. With the emergence of MiFi and WiBro (a portable Wi-Fi router) people can easily create their own Wi-Fi hotspots that connect to Internet via cellular networks. Now Android, Bada, iOS (iPhone), and Symbian devices can create wireless connections.[24] Wi-Fi also connects places that normally don't have network access, such as kitchens and garden sheds.

[edit] City-wide Wi-FiFurther information: Municipal wireless network An outdoor Wi-Fi access pointIn the early 2000s, many cities around the world announced plans to construct city-wide Wi-Fi networks. There are many successful examples; in 2004, Mysore became India's first Wi-fi-enabled city and second in the world after Jerusalem. A company called WiFiyNet has set up hotspots in Mysore, covering the complete city and a few nearby villages.[25]

In 2005 Sunnyvale, California, became the first city in the United States to offer city-wide free Wi-Fi,[26] and Minneapolis has generated $1.2 million in profit annually for its provider.[27]

In May 2010, London, UK, Mayor Boris Johnson pledged to have London-wide Wi-Fi by 2012.[28] Several boroughs including Westminster and Islington[29][30] already have extensive outdoor Wi-Fi coverage.

Officials in South Korea's capital are moving to provide free Internet access at more than 10,000 locations around the city, including outdoor public spaces, major streets and densely populated residential areas. Seoul will grant leases to KT, LG Telecom and SK Telecom. The companies will invest $44 million in the project, which will be completed in 2015.[31]

[edit] Campus-wide Wi-FiMany traditional college campuses in the United States provide at least partial wireless Wi-Fi Internet coverage. Carnegie Mellon University built the first campus-wide wireless Internet network, called Wireless Andrew at its Pittsburgh campus in 1993 before Wi-Fi branding originated.[32][33][34]

In 2000, Drexel University in Philadelphia became the United States's first major university to offer completely wireless Internet access across its entire campus.[35]

[edit] Direct computer-to-computer communicationsWi-Fi also allows communications directly from one computer to another without an access point intermediary. This is called ad hoc Wi-Fi transmission. This wireless ad hoc network mode has proven popular with multiplayer handheld game consoles, such as the Nintendo DS, Playstation Portable, digital cameras, and other consumer electronics devices. Some devices can also share their Internet connection using ad-hoc, becoming hotspots or "virtual routers".[36]

Similarly, the Wi-Fi Alliance promotes a specification called Wi-Fi Direct for file transfers and media sharing through a new discovery- and security-methodology.[37] Wi-Fi Direct launched in October 2010.[38]

[edit] Advantages and limitations
A keychain-size Wi-Fi detector[edit] AdvantagesWi-Fi allows cheaper deployment of local area networks (LANs). Also spaces where cables cannot be run, such as outdoor areas and historical buildings, can host wireless LANs.

Manufacturers are building wireless network adapters into most laptops. The price of chipsets for Wi-Fi continues to drop, making it an economical networking option included in even more devices.[citation needed]

Different competitive brands of access points and client network-interfaces can inter-operate at a basic level of service. Products designated as "Wi-Fi Certified" by the Wi-Fi Alliance are backwards compatible. Unlike mobile phones, any standard Wi-Fi device will work anywhere in the world.

Wi-Fi Protected Access encryption (WPA2) is considered secure, provided a strong passphrase is used. New protocols for quality-of-service (WMM) make Wi-Fi more suitable for latency-sensitive applications (such as voice and video). Power saving mechanisms (WMM Power Save) extend battery life.

[edit] LimitationsSpectrum assignments and operational limitations are not consistent worldwide: most of Europe allows for an additional two channels beyond those permitted in the US for the 2.4 GHz band (1–13 vs. 1–11), while Japan has one more on top of that (1–14). As of 2007, Europe, is essentially homogeneous in this respect.

A Wi-Fi signal occupies five channels in the 2.4 GHz band. Any two channels numbers that differ by five or more, such as 2 and 7, do not overlap. The oft-repeated adage that channels 1, 6, and 11 are the only non-overlapping channels is, therefore, not accurate. Channels 1, 6, and 11 are the only group of three non-overlapping channels in the U.S.

Equivalent isotropically radiated power (EIRP) in the EU is limited to 20 dBm (100 mW).

The current 'fastest' norm, 802.11n, uses double the radio spectrum/bandwidth (40MHz) compared to 802.11a or 802.11g (20MHz). This means there can be only one 802.11n network on the 2.4 GHz band at a given location, without interference to/from other WLAN traffic. 802.11n can also be set to use 20MHz bandwidth only to prevent interference in dense community.

[edit] RangeSee also: Long-range Wi-Fi
Wi-Fi networks have limited range. A typical wireless access point using 802.11b or 802.11g with a stock antenna might have a range of 32 m (120 ft) indoors and 95 m (300 ft) outdoors. IEEE 802.11n, however, can more than double the range.[39] Range also varies with frequency band. Wi-Fi in the 2.4 GHz frequency block has slightly better range than Wi-Fi in the 5 GHz frequency block which is used by 802.11a and optionally by 802.11n. On wireless routers with detachable antennas, it is possible to improve range by fitting upgraded antennas which have higher gain in particular directions. Outdoor ranges can be improved to many kilometers through the use of high gain directional antennas at the router and remote device(s). In general, the maximum amount of power that a Wi-Fi device can transmit is limited by local regulations, such as FCC Part 15 in the US.

Due to reach requirements for wireless LAN applications, Wi-Fi has fairly high power consumption compared to some other standards. Technologies such as Bluetooth (designed to support wireless PAN applications) provide a much shorter propagation range of