From Wikipedia, the free encyclopedia
Wi-Fi (
/ˈwaɪfaɪ/, sometimes 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.
History
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]
The name Wi-Fi
The term
Wi-Fi, first used commercially in August 1999,
[15] was coined by a brand-consulting firm called
Interbrand Corporation that the Alliance had hired 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.
Wi-Fi certification
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 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.
Uses
To 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.
Internet access
A 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.
City-wide Wi-Fi
An outdoor Wi-Fi access point
In the early 2000s, many cities around the world announced plans to
construct city-wide Wi-Fi networks. There are many successful examples;
in 2005
Sunnyvale, California, became the first city in the United States to offer city-wide free Wi-Fi,
[25] and
Minneapolis has generated $1.2 million in profit annually for
its provider.
[26]
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.
[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]
Campus-wide Wi-Fi
Many 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]
Direct computer-to-computer communications
Wi-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]
Advantages and limitations
A keychain-size Wi-Fi detector
Advantages
Wi-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.
Limitations
Spectrum 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.
Range
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. 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 <10m
[40] and so in general have a lower power consumption. Other low-power technologies such as
ZigBee
have fairly long range, but much lower data rate. The high power
consumption of Wi-Fi makes battery life in mobile devices a concern.
Researchers have developed a number of "no new wires" technologies to
provide alternatives to Wi-Fi for applications in which Wi-Fi's indoor
range is not adequate and where installing new wires (such as
CAT-5) is not possible or cost-effective. For example, the
ITU-T G.hn standard for high speed
Local area networks uses existing home wiring (
coaxial cables, phone lines and
power lines). Although
G.hn does not provide some of the advantages of Wi-Fi (such as mobility or outdoor use), it's designed for applications (such as
IPTV distribution) where indoor range is more important than mobility.
Due to the complex nature of
radio propagation
at typical Wi-Fi frequencies, particularly the effects of signal
reflection off trees and buildings, algorithms can only approximately
predict Wi-Fi signal strength for any given area in relation to a
transmitter.
[41] This effect does not apply equally to
long-range Wi-Fi, since longer links typically operate from towers that transmit above the surrounding foliage.
The practical range of Wi-Fi essentially confines mobile use to such
applications as inventory-taking machines in warehouses or in retail
spaces,
barcode-reading
devices at check-out stands, or receiving/shipping stations. Mobile use
of Wi-Fi over wider ranges is limited, for instance, to uses such as in
an automobile moving from one hotspot to another. Other wireless
technologies are more suitable for communicating with moving vehicles.
Data security risks
The most common wireless
encryption-standard,
Wired Equivalent Privacy (WEP), has been
shown to be easily breakable even when correctly configured.
Wi-Fi Protected Access (WPA and WPA2) encryption, which became available in devices in 2003, aimed to solve this problem. Wi-Fi
access points typically default to an encryption-free (
open) mode. Novice users benefit from a zero-configuration device that works out-of-the-box, but this default does not enable any
wireless security,
providing open wireless access to a LAN. To turn security on requires
the user to configure the device, usually via a software
graphical user interface
(GUI). On unencrypted Wi-Fi networks connecting devices can monitor and
record data (including personal information). Such networks can only be
secured by using other means of protection, such as a
VPN or secure
Hypertext Transfer Protocol (
HTTPS) over
Transport Layer Security.
Interference
Wi-Fi connections can be disrupted or the internet speed lowered by
having other devices in the same area. Many 2.4 GHz 802.11b and
802.11g
access-points default to the same channel on initial startup,
contributing to congestion on certain channels. Wi-Fi pollution, or an
excessive number of access points in the area, especially on the
neighboring channel, can prevent access and interfere with other
devices' use of other access points, caused by overlapping channels in
the 802.11g/b spectrum, as well as with decreased
signal-to-noise ratio
(SNR) between access points. This can become a problem in high-density
areas, such as large apartment complexes or office buildings with many
Wi-Fi access points.
Additionally, other devices use the 2.4 GHz band: microwave ovens,
ISM band devices, security cameras,
ZigBee devices, Bluetooth devices,
video senders, cordless phones,
baby monitors, and (in some countries)
Amateur radio all of which can cause significant additional interference. It is also an issue when municipalities
[42] or other large entities (such as universities) seek to provide large area coverage.
Hardware
Standard devices
An
Atheros Wi-Fi N draft adaptor with built in
Bluetooth on a Sony Vaio E series laptop
A
wireless access point (WAP) connects a group of wireless devices to an adjacent wired
LAN. An access point resembles a
network hub, relaying
data
between connected wireless devices in addition to a (usually) single
connected wired device, most often an ethernet hub or switch, allowing
wireless devices to communicate with other wired devices.
Wireless adapters
allow devices to connect to a wireless network. These adapters connect
to devices using various external or internal interconnects such as PCI,
miniPCI,
USB,
ExpressCard, Cardbus and
PC Card. As of 2010, most newer laptop computers come equipped with built in internal adapters.
Wireless routers integrate a Wireless Access Point, ethernet
switch, and internal router firmware application that provides
IP routing,
NAT, and
DNS forwarding through an integrated
WAN-interface.
A wireless router allows wired and wireless ethernet LAN devices to
connect to a (usually) single WAN device such as a
cable modem or a
DSL modem.
A wireless router allows all three devices, mainly the access point and
router, to be configured through one central utility. This utility is
usually an integrated
web server
that is accessible to wired and wireless LAN clients and often
optionally to WAN clients. This utility may also be an application that
is run on a desktop computer, as is the case with as Apple's
AirPort, which is managed with the
AirPort Utility on
Mac OS X and
Microsoft Windows.
[43]
Wireless
network bridges
connect a wired network to a wireless network. A bridge differs from an
access point: an access point connects wireless devices to a wired
network at the
data-link layer.
Two wireless bridges may be used to connect two wired networks over a
wireless link, useful in situations where a wired connection may be
unavailable, such as between two separate homes.
Wireless range-extenders or wireless repeaters can extend the range
of an existing wireless network. Strategically placed range-extenders
can elongate a signal area or allow for the signal area to reach around
barriers such as those pertaining in L-shaped corridors. Wireless
devices connected through repeaters will suffer from an increased
latency for each hop. Additionally, a wireless device connected to any
of the repeaters in the chain will have a throughput limited by the
"weakest link" between the two nodes in the chain from which the
connection originates to where the connection ends.
The security standard,
Wi-Fi Protected Setup,
allows embedded devices with limited graphical user interface to
connect to the Internet with ease. Wi-Fi Protected Setup has 2
configurations: The Push Button configuration and the PIN configuration.
These embedded devices are also called The Internet of Things and are
low-power, battery-operated embedded systems. A number of Wi-Fi
manufacturers design chips and modules for embedded Wi-Fi, such as
GainSpan.
[44]
Distance records
Distance records (using non-standard devices) include 382 km (237 mi)
in June 2007, held by Ermanno Pietrosemoli and EsLaRed of Venezuela,
transferring about 3 MB of data between the mountain-tops of
El Águila and Platillon.
[45][46] The
Swedish Space Agency transferred data 420 km (260 mi), using 6 watt amplifiers to reach an overhead stratospheric balloon.
[47]
Embedded systems
Embedded serial-to-Wi-Fi module
Increasingly in the last few years (particularly as of 2007),
embedded Wi-Fi modules have become available that incorporate a
real-time operating system and provide a simple means of wirelessly
enabling any device which has and communicates via a serial port.
[48]
This allows the design of simple monitoring devices. An example is a
portable ECG device monitoring a patient at home. This Wi-Fi-enabled
device can communicate via the Internet.
[49]
These Wi-Fi modules are designed by
OEMs so that implementers need only minimal Wi-Fi knowledge to provide Wi-Fi connectivity for their products.
Multiple access points
Increasing the number of Wi-Fi access points provides network redundancy, support for fast
roaming and increased overall network-capacity by using more channels or by defining smaller
cells. Wi-Fi implementations have moved toward "thin" access points, with more of the
network intelligence
housed in a centralized network appliance, relegating individual access
points to the role of "dumb" transceivers. Outdoor applications may use
mesh topologies.
Network security
The main issue with wireless network security is its simplified
access to the network compared to traditional wired networks such as
ethernet.
[citation needed]
With wired networking one must either gain access to a building
(physically connecting into the internal network) or break through an
external
firewall.
Most business networks protect sensitive data and systems by attempting
to disallow external access. Enabling wireless connectivity reduces
security if the network uses inadequate or no encryption.
[50]
An attacker who has gained access to a Wi-Fi network router can
initiate a DNS spoofing attack against any other user of the network by
forging a response before the queried DNS server has a chance to reply.
[51]
Securing methods
A common measure to deter unauthorized users involves hiding the access point's name by disabling the
SSID
broadcast. While effective against the casual user, it is ineffective
as a security method because the SSID is broadcast in the clear in
response to a client SSID query. Another method is to only allow
computers with known
MAC addresses to join the network,
[52] but determined eavesdroppers may be able join the network by
spoofing an authorized address.
Wired Equivalent Privacy (WEP) encryption was designed to protect against casual snooping but it is no longer considered secure. Tools such as
AirSnort or
Aircrack-ng can quickly recover WEP encryption keys.
[53] Because of WEP's weakness the
Wi-Fi Alliance approved
Wi-Fi Protected Access (WPA) which uses
TKIP.
WPA was specifically designed to work with older equipment usually
through a firmware upgrade. Though more secure than WEP, WPA has known
vulnerabilities.
The more secure
WPA2 using
Advanced Encryption Standard was introduced in 2004 and is supported by most new Wi-Fi devices. WPA2 is fully compatible with WPA.
[54]
A flaw in a feature added to Wi-Fi in 2007, called
Wi-Fi Protected Setup,
allows WPA and WPA2 security to be bypassed and effectively broken in
many situations. The only remedy as of late 2011 is to turn off Wi-Fi
Protected Setup,
[55] which is not always possible.
Piggybacking
Piggybacking refers to access to a wireless Internet connection by
bringing one's own computer within the range of another's wireless
connection, and using that service without the subscriber's explicit
permission or knowledge.
During the early popular adoption of
802.11, providing open access points for anyone within range to use was encouraged
[by whom?] to cultivate
wireless community networks,
[56] particularly since people on average use only a fraction of their downstream bandwidth at any given time.
Recreational logging and mapping of other people's access points has become known as
wardriving.
Indeed, many access points are intentionally installed without security
turned on so that they can be used as a free service. Providing access
to one's Internet connection in this fashion may breach the Terms of
Service or contract with the
ISP. These activities do not result in sanctions in most jurisdictions; however, legislation and
case law differ considerably across the world. A proposal to leave
graffiti describing available services was called
warchalking.
[57] A
Florida court case determined that owner laziness was not to be a valid excuse.
[citation needed]
Piggybacking often occurs unintentionally, since most access points are configured without encryption by default
[citation needed]
and operating systems can be configured to connect automatically to any
available wireless network. A user who happens to start up a laptop in
the vicinity of an access point may find the computer has joined the
network without any visible indication. Moreover, a user intending to
join one network may instead end up on another one if the latter has a
stronger signal. In combination with automatic discovery of other
network resources (see
DHCP and
Zeroconf) this could possibly lead wireless users to send sensitive data to the wrong middle-man when seeking a destination (
see Man-in-the-middle attack). For example, a user could inadvertently use an insecure network to log in to a
website, thereby making the login credentials available to anyone listening, if the website uses an insecure protocol such as
HTTP.
Health issues
A small percentage of Wi-Fi users have reported adverse health issues after repeat exposure and use of Wi-Fi,
[58] though there has been no publication of any effects being observable in
double-blind studies. A review of studies involving 725 people that claimed
electromagnetic hypersensitivity found no evidence for their claims.
[59] The ubiquity of Wi-Fi has led to calls for more research into the effects of "electronic smog".
[60]
One study speculated that "laptops (Wi-Fi mode) on the lap near the testicles may result in decreased male fertility".
[61] Another study found decreased
working memory among males during Wi-Fi exposure.
[62]
The
World Health Organization (WHO) says "there is no risk from low level, long-term exposure to wi-fi networks" and the United Kingdom's
Health Protection Agency reports that exposure to Wi-Fi for a year results in "same amount of radiation from a 20-minute mobile phone call."
[63][64]
In November 2010 research results were published by
Wageningen University and Research Centre,
the Netherlands, which indicates that electromagnetic radiation may
play a role in a deterioration in the health of trees. In a laboratory
setting it appeared that portions of leaves of Ash saplings, after
having been exposed for over three months to a radiation source similar
to a wifi-access point, withered and died. The authors of the report
noted however that further long-term tests were necessary.
[65]
See also
Notes
References
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Further reading
External links
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