Wi-Fi is a branded standard for wirelessly connecting
electronic devices. A Wi-Fi device, such as a personal
computer, video game console, smartphone, or digital audio
player can connect to the Internet via a wireless network
access point. An access point (or hotspot) has a range of
about 20 meters (65 feet) indoors and a greater range
outdoors. Multiple overlapping access points can cover large
"Wi-Fi" is a trademark of the Wi-Fi Alliance and the brand
name for products using the IEEE 802.11 family of standards.
Wi-Fi is used by over 700 million people, there are over 4
million hotspots (places with Wi-Fi Internet connectivity)
around the world, and about 800 million new Wi-Fi devices
every year. Wi-Fi products that complete the Wi-Fi Alliance
interoperability certification testing successfully can use
the Wi-Fi CERTIFIED designation and trademark.
To connect to a WiFi 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 provides no indication
to the sender about whether 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 channel, so each transmission is noticed. In
order to determine whether the channel is free, the carrier
wave can be sensed by the hardware; if not present the
channel is free for transmission.
A Wi-Fi enabled device such as a personal computer, video
game console, smartphone or digital audio player 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
comprise an area as small as a few rooms or as large as many
square miles. Coverage in the larger area may depend on a
group of access points with overlapping coverage. Wi-Fi
technology has been used in wireless mesh networks, for
example, in London, UK.
In addition to private use in homes and offices, Wi-Fi can
provide public access at Wi-Fi hotspots provided either
free-of-charge or to subscribers to various commercial
services. Organizations and businesses - such as those
running airports, hotels and restaurants - often provide
free-use hotspots to attract or assist clients. Enthusiasts
or authorities who wish to provide services or even to
promote business in selected areas sometimes provide free
Wi-Fi access. As of 2008 more than 300 metropolitan-wide
Wi-Fi (Muni-Fi) projects had started. As of 2010 the Czech
Republic had 1150 Wi-Fi based wireless Internet service
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 premises, can provide Internet access and
internetworking to all devices connected (wirelessly or by
cable) to them. 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 iPhone, Android, Bada and Symbian phones can
create wireless connections.
One can also connect Wi-Fi devices in ad-hoc mode for
client-to-client connections without a router. Wi-Fi also
connects places that would traditionally not have network
access, for example kitchens and garden sheds.
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
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.
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
Wi-Fi operates in more than 220,000 public hotspots and in
tens of millions of homes and corporate and university
campuses worldwide. The current version of Wi-Fi
Protected Access encryption (WPA2) as of 2010 is widely
considered secure, provided users employ a strong passphrase.
New protocols for quality-of-service (WMM) make Wi-Fi more
suitable for latency-sensitive applications (such as voice
and video); and power saving mechanisms (WMM Power Save)
improve battery operation.
Spectrum assignments and operational limitations are not
consistent worldwide: most of Europe allows for an
additional two channels beyond those permitted in the U.S.
for the 2.4 GHz band (1–13 vs. 1–11), while Japan has one
more on top of that (1–14). Europe, as of 2007, was
essentially homogeneous in this respect.
A Wi-Fi signal occupies five channels in the 2.4 GHz band;
any two channels whose channel numbers 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 do, however, comprise 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 compared to 802.11a or 802.11g. This means there
can only be one 802.11n network on 2.4 GHz band without
interference to other WLAN traffic.
The Internet protocol was designed for a wired network in
which packet loss due to noise is very rare and packets are
lost almost exclusively due to congestion. On a wireless
network, noise is common. This difference causes TCP to
greatly slow or break transmission when noise is
significant, even when most packets are still arriving
A small percentage of Wifi users have reported adverse
health issues after repeat exposure and use of Wifi, though
there has been no publication of any effects being
observable in double-blinded studies. The ubiquity of WiFi
has led to calls for more research into the effects of
One study speculated that "laptops (WiFi mode) on the lap
near the testes may result in decreased male fertility".
Another study found decreased working memory among males
during Wi-Fi exposure.
Gro Harlem Brundtland, former Prime Minister of Norway and a
medical doctor, certainly may be the most high profile case
of someone who has suffered from such conditions, and who
has actively called on increase awareness within the medical
In a BBC article, 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