Wi-Fi
From Wikipedia, the free encyclopedia
Wi-Fi or WiFi is a technology for wireless local area networking with devices based on
the IEEE 802.11 standards. Wi-Fiis a trademark of the Wi-Fi Alliance, which restricts the
use of the term Wi-Fi Certified to products that successfully
complete interoperability certification testing.[1]
Devices that can use Wi-Fi technology include personal computers, video-game
consoles, smartphones, digital cameras,tablet computers, digital audio players and
modern printers. Wi-Fi compatible devices can connect to the Internet via a WLAN
network and a wireless access point. Such an access point (or hotspot) has a range of
about 20 meters (66 feet) indoors and a greater range outdoors. Hotspot coverage can
be as small as a single room with walls that block radio waves, or as large as many
square kilometres achieved by using multiple overlapping access points.
Depiction of a device sending information wirelessly to another device, both connected to the local
network, in order to print a document
Wi-Fi most commonly uses the 2.4 gigahertz (12 cm) UHF and 5 gigahertz
(6 cm) SHF ISM radio bands. Having no physical connections, it is more vulnerable to
attack than wired connections, such as Ethernet. Web pages that use Transport Layer
Security (TLS) are secure, but unencrypted Internet access can easily be detected by
intruders. For protection, Wi-Fi has adopted various encryption technologies. The early
encryption Wired Equivalent Privacy (WEP) proved easy to break. Higher quality
protocols, such as Wi-Fi Protected Access (WPA, WPA2) were added later. An optional
feature added in 2007, calledWi-Fi Protected Setup (WPS), had a serious flaw that
allowed an attacker to recover the router's password.[2]
History
In 1971, ALOHAnet connected the Hawaiian Islands with a UHF wireless packet network.
ALOHAnet and the ALOHA protocol were early forerunners to Ethernet, and later
the IEEE 802.11 protocols, respectively.
A 1985 ruling by the U.S. Federal Communications Commission released the ISM
band for unlicensed use.[3] These frequency bands are the same ones used by equipment
such as microwave ovens and are subject to interference.
In 1991, NCR Corporation with AT&T Corporation invented the precursor to 802.11,
intended for use in cashier systems. The first wireless products were under the
name WaveLAN. They are the ones credited with inventing Wi-Fi.
The Australian radio-astronomer John O'Sullivan with his colleagues Terence Percival,
Graham Daniels, Diet Ostry, John Deane[4] developed a key patent used in Wi-Fi as a by-
product of a Commonwealth Scientific and Industrial Research Organisation (CSIRO)
research project, "a failed experiment to detect exploding mini black holes the size of an
atomic particle".[5] In 1992 and 1996, CSIRO obtained patents[6] for a method later used in
Wi-Fi to "unsmear" the signal.[7]
The first version of the 802.11 protocol was released in 1997, and provided up to 2 Mbit/s
link speeds. This was updated in 1999 with 802.11b to permit 11 Mbit/s link speeds, and
this proved to be popular.
In 1999, the Wi-Fi Alliance formed as a trade association to hold the Wi-Fi trademark
under which most products are sold.[8]
Wi-Fi uses a large number of patents held by many different organizations. [9] In April
2009, 14 technology companies agreed to pay CSIRO $250 million for infringements on
CSIRO patents.[10] This led to Australia labeling Wi-Fi as an Australian invention,[11] though
this has been the subject of some controversy.[12][13] 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.[10][14][15] In 2016, the wireless local area network Test Bed was chosen as
Australia's contribution to the exhibition A History of the World in 100 Objects held in
the National Museum of Australia.[16]
Etymology
The name Wi-Fi, commercially used at least as early as August 1999,[17] was coined by
the brand-consulting firm Interbrand. The Wi-Fi Alliance had hired Interbrand to create a
name that was "a little catchier than 'IEEE 802.11b Direct Sequence.' " [18][19] Phil Belanger,
a founding member of the Wi-Fi Alliance who presided over the selection of the name
"Wi-Fi," has stated that Interbrand invented Wi-Fi as a pun upon the word hi-fi.
Interbrand also created the Wi-Fi logo. The yin-yang Wi-Fi logo indicates the certification
of a product for interoperability.[20]
The Wi-Fi Alliance used the nonsense advertising slogan "The Standard for Wireless
Fidelity" for a short time after the brand name was created, leading to the misconception
that Wi-Fi was an abbreviation of "Wireless Fidelity."[18][20][21] The name was however never
officially "Wireless Fidelity".[22] Nevertheless, the Wi-Fi Alliance was also called the
"Wireless Fidelity Alliance Inc" in some publications[23] and the IEEE's own website has
stated "WiFi is a short name for Wireless Fidelity".[24]
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, 4G, and LTE.
The name is often written as WiFi, Wifi, or wifi, but these are not approved by the Wi-Fi
Alliance.
Wi-Fi ad-hoc mode
Wi-Fi nodes operating in ad-hoc mode refers to devices talking directly to each other
without the need to first talk to an access point (also known as base station). Ad-hoc
mode was first invented and realized by Chai K. Toh in his 1996 invention of Wi-Fi ad-
hoc routing, implemented on Lucent WaveLAN 802.11a wireless on IBM ThinkPads over
a size nodes scenario spanning a region of over a mile. The success was recorded in
Mobile Computing magazine and later published formally inIEEE Transactions on
Wireless Communications.[citation needed]
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.[25][26] The Wi-Fi Alliance enforces the use of the Wi-Fi brand to
technologies based on the IEEE 802.11 standards from the IEEE. 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.[27]
Not every Wi-Fi device is submitted for certification. The lack of Wi-Fi certification does
not necessarily imply that a device is incompatible with other Wi-Fi devices. [28] The Wi-Fi
Alliance may or may not sanction derivative terms, such as Super Wi-Fi,[29] coined by the
US Federal Communications Commission (FCC) to describe proposed networking in the
UHF TV band in the US.[30]
IEEE 802.11 standard
This Netgear Wi-Fi router contains dual bands for transmitting the 802.11 standard across the 2.4
and 5 GHz spectrums.
Main article: IEEE 802.11
The IEEE 802.11 standard is a set of media access control (MAC) and physical
layer (PHY) specifications for implementingwireless local area network (WLAN) computer
communication in the 2.4, 3.6, 5, and 60 GHz frequency bands. They are created and
maintained by the IEEE LAN/MAN Standards Committee (IEEE 802). The base version
of the standard was released in 1997, and has had subsequent amendments. The
standard and amendments provide the basis for wireless network products using the Wi-
Fi brand. While each amendment is officially revoked when it is incorporated in the latest
version of the standard, the corporate world tends to market to the revisions because
they concisely denote capabilities of their products.[31] As a result, in the market place,
each revision tends to become its own standard.
Uses
A Japanese sticker indicating to the public that a location is within range of a Wi-Fi network. A dot
with curved lines radiating from it is a common symbol for Wi-Fi, representing a point transmitting a
signal.[32]
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. For all stations that share a single radio frequency communication channel,
transmissions on this channel are received by all stations within range.[33] The
transmission is not guaranteed to be delivered and is therefore a best-effort
delivery mechanism. A carrier wave is used to transmit the data. The data is organised in
packets on an Ethernet link, referred to as "Ethernet frames".[34]
Internet access
Wi-Fi technology may be used to provide Internet access to devices that are within the
range of a wireless network that is connected to the Internet. The coverage of one or
more interconnected access points (hotspots) can extend from an area as small as a few
rooms to as large as many square kilometres. Coverage in the larger area may require a
group of access points with overlapping coverage. For example, public outdoor Wi-Fi
technology has been used successfully in wireless mesh networks in London, UK. An
international example is Fon.
Wi-Fi provides service in private homes, businesses, as well as in public spaces at Wi-Fi
hotspots set up either free-of-charge or commercially, often using a captive
portal webpage for access. 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.
Similarly, battery-powered routers may include a cellular Internet radiomodem and Wi-Fi
access point. When subscribed to a cellular data carrier, they allow nearby Wi-Fi stations
to access the Internet over 2G, 3G, or 4G networks using the tethering technique. Many
smartphones have a built-in capability of this sort, including those based
on Android, BlackBerry, Bada, iOS (iPhone), Windows Phone and Symbian, though
carriers often disable the feature, or charge a separate fee to enable it, especially for
customers with unlimited data plans. "Internet packs" provide standalone facilities of this
type as well, without use of a smartphone; examples include the MiFi- and WiBro-
branded devices. Some laptops that have a cellular modem card can also act as mobile
Internet Wi-Fi access points.
Wi-Fi also connects places that normally don't have network access, such as kitchens
and garden sheds.
City-wide Wi-Fi
In the early 2000s, many cities around the world announced plans to construct citywide
Wi-Fi networks. There are many successful examples; in 2004, Mysore became India's
first Wi-Fi-enabled city. A company called WiFiyNet has set up hotspots in Mysore,
covering the complete city and a few nearby villages.[35]
In 2005, St. Cloud, Florida and Sunnyvale, California, became the first cities in the United
States to offer citywide free Wi-Fi (from MetroFi).[36] Minneapolis has generated $1.2
million in profit annually for its provider.[37]
In May 2010, London, UK, Mayor Boris Johnson pledged to have London-wide Wi-Fi by
2012.[38] Several boroughs including Westminster and Islington[39][40] already had extensive
outdoor Wi-Fi coverage at that point.
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 was to be completed
in 2015.[41]
Campus-Wide Wi-Fi
Many traditional university campuses in the developed world provide at least partial Wi-Fi
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.[42][43][44] By February 1997 the CMU Wi-Fi zone was fully operational. Many
universities collaborate in providing Wi-Fi access to students and staff through
the Eduroam international authentication infrastructure.
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. Thiswireless ad hoc
network mode has proven popular with multiplayer handheld game consoles, such as
the Nintendo DS, PlayStation Portable, digital cameras, and otherconsumer
electronics devices. Some devices can also share their Internet connection using ad hoc,
becoming hotspots or "virtual routers".[45]
Similarly, the Wi-Fi Alliance promotes the specification Wi-Fi Direct for file transfers and
media sharing through a new discovery- and security-methodology.[46]Wi-Fi Direct
launched in October 2010.[47]
Another mode of direct communication over Wi-Fi is Tunneled Direct Link Setup (TDLS),
which enables two devices on the same Wi-Fi network to communicate directly, instead
of via the access point.[48]
A keychain-size Wi-Fi detector
Wi-Fi radio spectrum
802.11b and 802.11g use the 2.4 GHz ISM band, operating in the United States
under Part 15 Rules and Regulations. Because of this choice of frequency band, 802.11b
and g equipment may occasionally suffer interference from microwave ovens, cordless
telephones, and Bluetooth devices.
Spectrum assignments and operational limitations are not consistent worldwide: Australia
and Europe allow for an additional two channels (12, 13) beyond the 11 permitted in the
United States for the 2.4 GHz band, while Japan has three more (12–14). In the US and
other countries, 802.11a and 802.11g devices may be operated without a license, as
allowed in Part 15 of the FCC Rules and Regulations.
A Wi-Fi signal occupies five channels in the 2.4 GHz band. Any two channel 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 North
America and the United Kingdom. In Europe and Japan using Channels 1, 5, 9, and 13
for 802.11g and 802.11n isrecommended.[citation needed]
802.11a uses the 5 GHz U-NII band, which, for much of the world, offers at least 23 non-
overlapping channels rather than the 2.4 GHz ISM frequency band, where adjacent
channels overlap.
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. It is advised to only use channel 1-6-11.
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,[49] and, in some countries, amateur radio, all of which
can cause significant additional interference. It is also an issue when municipalities [50] or
other large entities (such as universities) seek to provide large area coverage.
Service set identifier (SSID)
In addition to running on different channels, multiple Wi-Fi networks can share channels.
A service set is the set of all the devices associated with a particular Wi-Fi network. The
service set can be local, independent, extended or mesh.
Each service set has an associated identifier, the 32-byte Service Set Identifier (SSID),
which identifies the particular network. The SSID is configured within the devices that are
considered part of the network, and it is transmitted in the packets. Receivers ignore
wireless packets from networks with a different SSID.
Throughput
As the 802.11 specifications evolved to support higher throughput, the bandwidth
requirements also increased to support them. 802.11n uses double the radio
spectrum/bandwidth (40 MHz) compared to 802.11a or 802.11g (20 MHz).76 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 limit itself to 20 MHz
bandwidth to prevent interference in dense community.[citation needed]
Many newer consumer devices support the latest 802.11ac standard, which uses the
5 GHz band exclusively and is capable of multi-station WLAN throughput of at least 1
gigabit per second. According to a study, devices with the 802.11ac specification were
expected to be common by 2015 with an estimated one billion spread around the world. [51]
Hardware
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. However, building walls of certain materials, such as stone with high metal
content, can block Wi-Fi signals.
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.[52]
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 backward compatible. Unlike mobile phones, any standard Wi-Fi device will
work anywhere in the world.
Standard devices[edit]
An embedded RouterBoard 112 withU.FL-RSMA pigtail and R52 mini PCIWi-Fi card widely used
by wirelessInternet service providers (WISPs) in the Czech Republic
OSBRiDGE 3GN – 802.11n Access Point and UMTS/GSM Gateway in one device
An Atheros draft-N Wi-Fi adapter with built in Bluetooth on a Sony Vaio E series laptop
USB wireless adapter
A wireless access point (WAP) connects a group of wireless devices to an adjacent
wired LAN. An access point resembles anetwork 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 IProuting, 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 computer, as is the case
with as Apple's AirPort, which is managed with the AirPort Utility on Mac OS X and iOS.[53]
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 or for devices which do not have wireless
networking capability (but have wired networking capability), such as consumer
entertainment devices; alternatively, a wireless bridge can be used to enable a device
which supports a wired connection to operate at a wireless networking standard which is
faster than supported by the wireless network connectivity feature (external dongle or
inbuilt) supported by the device (e.g. enabling Wireless-N speeds (up to the maximum
supported speed on the wired Ethernet port on both the bridge and connected devices
including the wireless access point) for a device which only supports Wireless-G). A dual-
band wireless bridge can also be used to enable 5 GHz wireless network operation on a
device which only supports 2.4 GHz wireless networking functionality and has a wired
Ethernet port.
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, as well as from a reduction in the maximum data throughput that is
available. In addition, the effect of additional users using a network employing wireless
range-extenders is to consume the available bandwidth faster than would be the case
where but a single user migrates around a network employing extenders. For this reason,
wireless range-extenders work best in networks supporting very low traffic throughput
requirements, such as for cases where but a single user with a Wi-Fi equipped tablet
migrates around the combined extended and non-extended portions of the total
connected network. Additionally, a wireless device connected to any of the repeaters in
the chain will have a data throughput that is also limited by the "weakest link" existing in
the chain between where the connection originates and where the connection ends.
Networks employing wireless extenders are also more prone to degradation from
interference from neighboring access points that border portions of the extended network
and that happen to occupy the same channel as the extended network.
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.[54]
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.[55] 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.[56]
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.
In June 2014 Texas Instruments introduced the first ARM Cortex-M4 microcontroller with
an onboard dedicated Wi-Fi MCU, the SimpleLink CC3200. It makes embedded systems
with Wi-Fi connectivity possible to build as single-chip devices, which reduces their cost
and minimum size, making it more practical to build wireless-networked controllers into
inexpensive ordinary objects.[citation needed]
