Wi-Fi

The old Wi-Fi Alliance logo
Introduced	September 1998; 20 years ago (1998-09)
Compatible hardware	Personal computers, gaming consoles, televisions, printers, mobile phones

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v t e

Wi-Fi (/ˈwaɪfaɪ/)^[1] is technology for radio wireless local area networking of devices based on the IEEE 802.11 standards. Wi‑Fi is 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.^[2]

Devices that can use Wi-Fi technologies include desktops and laptops, video game consoles, smartphones and tablets, smart TVs, digital audio players, cars and modern printers. Wi-Fi compatible devices can connect to the Internet via a WLAN 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

Different versions of Wi-Fi exist, with different ranges, radio bands and speeds. Wi-Fi most commonly uses the 2.4 gigahertz (12 cm) UHF and 5.8 gigahertz (5 cm) SHF ISM radio bands; these bands are subdivided into multiple channels. Each channel can be time-shared by multiple networks. These wavelengths work best for line-of-sight. Many common materials absorb or reflect them, which further restricts range, but can tend to help minimise interference between different networks in crowded environments. At close range, some versions of Wi-Fi, running on suitable hardware, can achieve speeds of over 1 Gbit/s.

Anyone within range with a wireless network interface controller can attempt to access a network; because of this, Wi-Fi is more vulnerable to attack (called eavesdropping) than wired networks. Wi-Fi Protected Access (WPA) is a family of technologies created to protect information moving across Wi-Fi networks and includes solutions for personal and enterprise networks. Security features of WPA have included stronger protections and new security practices as the security landscape has changed over time.

History[edit]

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, under the name WaveLAN.

The Australian radio-astronomer Dr John O'Sullivan with his colleagues Terence Percival, Graham Daniels, Diet Ostry, and 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] Dr O'Sullivan and his colleagues are credited with inventing Wi-Fi.^[6][7] In 1992 and 1996, CSIRO obtained patents^[8] for a method later used in Wi-Fi to "unsmear" the signal.^[9]

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.^[10]

Wi-Fi uses a large number of patents held by many different organizations.^[11] In April 2009, 14 technology companies agreed to pay CSIRO $1 billion for infringements on CSIRO patents.^[12] This led to Australia labeling Wi-Fi as an Australian invention,^[13] though this has been the subject of some controversy.^[14][15] 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][16][17] 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.^[18]

Etymology[edit]

The name Wi-Fi, commercially used at least as early as August 1999,^[19] 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'."^[20][21] 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 on the word hi-fi.^[22]

Interbrand also created the Wi-Fi logo. The yin-yang Wi-Fi logo indicates the certification of a product for interoperability.^[23]

The Wi-Fi Alliance used the nonsense advertising slogan "The Standard for Wireless Fidelity" for a short time after the brand name was created.^[20][23][24] The name was, however, never officially "Wireless Fidelity".^[25] Nevertheless, the Wi-Fi Alliance was also called the "Wireless Fidelity Alliance Inc" in some publications^[26]

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 sometimes written as WiFi, Wifi, or wifi, but these are not approved by the Wi-Fi Alliance. IEEE is a separate, but related organization and their website has stated "WiFi is a short name for Wireless Fidelity".^[27][28]

Wi-Fi ad-hoc mode[edit]

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 Keong Toh in his 1996 invention^[29] 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 (1999)^[30] and later published formally in IEEE Transactions on Wireless Communications, 2002^[31] and ACM SIGMETRICS Performance Evaluation Review, 2001.^[32]

Wi-Fi certification[edit]

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.^[33][34] 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.^[35]

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.^[36] The Wi-Fi Alliance may or may not sanction derivative terms, such as Super Wi-Fi,^[37] coined by the US Federal Communications Commission (FCC) to describe proposed networking in the UHF TV band in the US.^[38]

Terminology[edit]

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.^[39]

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 controllers 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.^[40] 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".^[41]

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.

Versions[edit]

There are many different versions of Wi-Fi: 802.11a, 802.11b, 802.11g, 802.11n (Wi-Fi 4^[42]), 802.11h, 802.11i, 802.11-2007, 802.11n, 802.11-2012, 802.11ac (Wi-Fi 5^[42]), 802.11ad, 802.11af, 802.11-2016, 802.11ah, 802.11ai, 802.11aj, 802.11aq, 802.11ax (Wi-Fi 6^[42]), 802.11ay.

Equipment frequently support multiple versions of Wi-Fi. To communicate, devices must use a common Wi-Fi version. The versions differ between the radio wavebands they operate on, the radio bandwidth they occupy, the maximum data rates they can support and other details. In general, lower frequencies have better range but have less capacity. Some versions permit the use of multiple antennas, which permits greater speeds as well as reduced interference.

Historically, equipment has listed the versions of Wi-Fi that it supports, but the Wi-Fi alliance has now standardised generational numbering so that equipment can indicate that it supports Wi-Fi 4 (if the equipment supports 802.11n), Wi-Fi 5 (802.11ac) and Wi-Fi 6 (802.11ax). The alliance have stated that the generational level 4, 5, or 6 can be indicated in the user interface when connected, along with the signal strength.^[42]

Uses[edit]

Internet access[edit]

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 radio modem 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.

Google is intending to use the technology to allow rural areas to enjoy connectivity by utilizing a broad mix of projection and routing services. Google also intends to bring connectivity to Africa and some Asian lands by launching blimps that will allow for internet connection with Wi-Fi technology.^[43]

City-wide Wi-Fi[edit]

An outdoor Wi-Fi access point

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 (Mysuru) 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.^[44]

In 2005, St. Cloud, Florida and Sunnyvale, California, became the first cities in the United States to offer citywide free Wi-Fi (from MetroFi).^[45]Minneapolis has generated $1.2 million in profit annually for its provider.^[46]

In May 2010, London mayor Boris Johnson pledged to have London-wide Wi-Fi by 2012.^[47] Several boroughs including Westminster and Islington ^[48][49] already had extensive outdoor Wi-Fi coverage at that point.

Officials in South Korea's capital Seoul 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.^[50]

Campus-wide Wi-Fi[edit]

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.^[51][52][53] 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.

Wi-Fi ad hoc versus Wi-Fi direct[edit]

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".^[54]

Similarly, the Wi-Fi Alliance promotes the specification Wi-Fi Direct for file transfers and media sharing through a new discovery- and security-methodology.^[55] Wi-Fi Direct launched in October 2010.^[56]

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.^[57]

A keychain-size Wi-Fi detector

Wi-Fi radio spectrum[edit]

The 802.11 standard provides several distinct radio frequencies ranges for use in Wi-FI communications: 900 MHz, 2.4 GHz, 3.6 GHz, 4.9 GHz, 5 GHz, 5.9 GHz, and 60 GHz bands.^[58][59][60] Each range is divided into a multitude of channels. Countries apply their own regulations to the allowable channels, allowed users and maximum power levels within these frequency ranges. The ISM band ranges are also often used.^[61]

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, USB3.0 hubs, 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. However, channels that are four apart interfere a negligible amount, much less than reusing channels.^[62] In Europe and Japan where channel 13 is available, using Channels 1, 5, 9, and 13 for 802.11g and 802.11n is recommended.

802.11a/n/ac use the 5 GHz U-NII band, which, for much of the world, offers at least 23 non-overlapping 20 MHz channels rather than the 2.4 GHz ISM frequency band, where the channels are only 5MHz wide. The 5GHz bands are more strongly absorbed by common building materials, and usually give shorter range.

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.^[63]

Communications protocol[edit]

USB wireless adapter

The Wi-Fi protocols are in the IEEE 802 family which includes Ethernet, and are designed to interwork.

Whereas Ethernet media are not usually shared, and have essentially negligible error rates, wireless communication media are subject to significant interference and have multiple users. Because of this, for Wi-Fi, the Logical Link Control (LLC) specified by IEEE 802.2 employs Wi-Fi's media access control (MAC) protocols to manage retries without relying on higher levels of the protocol stack.

Wi-Fi's MAC and physical layer (PHY) specifications are defined by IEEE 802.11 for implementing wireless local area network (WLAN) computer communication in the infrared, and 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.^[64] As a result, in the market place, each revision tends to become its own standard.

Performance[edit]

Parabolic dishes transmit and receive the radio waves only in particular directions and can give much greater range than omnidirection antennas

Yagi-Uda antennas, widely used for television reception, are relatively compact at Wi-Fi wavelengths

Wi-Fi operational range depends on factors such as the frequency band, radio power output, receiver sensitivity, antenna gain and antenna type as well as the modulation technique. In addition, propagation characteristics of the signals can have a big impact.

At longer distances, and with greater signal absorption, speed is usually reduced.

Transmitter power[edit]

Compared to cell phones and similar technology, Wi-Fi transmitters are low power devices. 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. Equivalent isotropically radiated power (EIRP) in the European Union is limited to 20 dBm (100 mW).

To reach requirements for wireless LAN applications, Wi-Fi has higher power consumption compared to some other standards designed to support wireless personal area network (PAN) applications. For example, Bluetooth provides a much shorter propagation range between 1 and 100 m^[65] 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 some mobile devices a concern.

Antenna[edit]

An access point compliant with either 802.11b or 802.11g, using the stock omnidirectional antenna might have a range of 100 m (0.062 mi). The same radio with an external semi parabolic antenna (15 dB gain) with a similarly equipped receiver at the far end might have a range over 20 miles.

Higher gain rating (dBi) indicates further deviation (generally toward the horizontal) from a theoretical, perfect isotropic radiator, and therefore the antenna can project a usable signal further in particular directions, as compared to a similar output power on a more isotropic antenna.^[66] For example, an 8 dBi antenna used with a 100 mW driver will have a similar horizontal range to a 6 dBi antenna being driven at 500 mW. Note that this assumes that radiation in the vertical is lost; this may not be the case in some situations, especially in large buildings or within a waveguide. In the above example, a directional waveguide could cause the low power 6 dBi antenna to project much further in a single direction than the 8 dBi antenna which is not in a waveguide, even if they are both being driven at 100 mW.

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).

MIMO[edit]

This Netgear Wi-Fi router contains dual bands for transmitting the 802.11 standard across the 2.4 and 5 GHz spectrums and supports MIMO.

Some standards, such as IEEE 802.11n and IEEE 802.11ac for Wi-Fi allow a device to have multiple antennas. Multiple antennas enable the equipment to focus on the far end device, reducing interference in other directions, and giving a stronger useful signal. This greatly increases range and network speed without exceeding the legal power limits.

IEEE802.11n can more than double the range.^[67] 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 used by 802.11a (and optionally by 802.11n).

Under optimal conditions, IEEE802.11ac can achieve communication rates of 1Gbit/s.

Radio propagation[edit]

With Wi-Fi signals line-of-sight usually works best, but Wi-Fi signals can be affected by absorption, reflection, and diffraction through and around structures.

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.^[68]
This effect does not apply equally to long-range Wi-Fi, since longer links typically operate from towers that transmit above the surrounding foliage.

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.

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.^[69][70]
The Swedish Space Agency transferred data 420 km (260 mi), using 6 watt amplifiers to reach an overhead stratospheric balloon.^[71]

Radio bands[edit]

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, and a single station throughput of at least 500 Mbit/s. In the first quarter of 2016, The Wi-Fi Alliance certifies devices compliant with the 802.11ac standard as "Wi-Fi CERTIFIED ac". This new standard uses several advanced signal processing techniques such as multi-user MIMO and 4X4 Spatial Multiplexing streams, and large channel bandwidth (160 MHz) to achieve the Gigabit throughput. According to a study by IHS Technology, 70% of all access point sales revenue In the first quarter of 2016 came from 802.11ac devices.^[72]

Interference[edit]

Wi-Fi connections can be disrupted or the Internet speed lowered by having other devices in the same area. Wi-Fi protocols are designed to share channels reasonably fairly, and will often work with little to no disruption. However, 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, can prevent access and interfere with other devices' use of other access points as well as with decreased signal-to-noise ratio (SNR) between access points. In addition interference can be caused by overlapping channels in the 802.11g/b spectrum. These issues can become a problem in high-density areas, such as large apartment complexes or office buildings with many Wi-Fi access points.

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,^[73] and, in some countries, amateur radio, all of which can cause significant additional interference. It is also an issue when municipalities^[74] or other large entities (such as universities) seek to provide large area coverage.

To minimise collisions with Wi-Fi and non Wi-Fi devices, Wi-Fi employs Carrier-sense multiple access with collision avoidance (CSMA/CA), where transmitters listen before transmitting, and delay transmission of packets if they detect that other users are active on the channel.

These bands are allowed to be used with low power transmitters, without requiring a license and with few restrictions. However, while unintended interference is common, users that have been found to knowingly cause deliberate interference to other users (particularly for attempting to locally monopolise these bands for commercial purposes) have been handed large fines.^[75]

Throughput[edit]

Graphical representation of Wi-Fi application specific (UDP) performance envelope 2.4 GHz band, with 802.11g

Graphical representation of Wi-Fi application specific (UDP) performance envelope 2.4 GHz band, with 802.11n with 40 MHz

Various layer 2 variants of IEEE 802.11 has different characteristics. Across all flavours of 802.11, maximum achievable throughputs are either given based on measurements under ideal conditions or in the layer 2 data rates. This, however, does not apply to typical deployments in which data are being transferred between two endpoints of which at least one is typically connected to a wired infrastructure and the other endpoint is connected to an infrastructure via a wireless link.

This means that typically data frames pass an 802.11 (WLAN) medium and are being converted to 802.3 (Ethernet) or vice versa.

Due to the difference in the frame (header) lengths of these two media, the packet size of an application determines the speed of the data transfer. This means that an application which uses small packets (e.g. VoIP) creates a data flow with a high overhead traffic (e.g. a low goodput).

Other factors which contribute to the overall application data rate are the speed with which the application transmits the packets (i.e. the data rate) and the energy with which the wireless signal is received. The latter is determined by distance and by the configured output power of the communicating devices.^[76][77]

The same references apply to the attached throughput graphs which show measurements of UDP throughput measurements. Each represents an average throughput of 25 measurements (the error bars are there, but barely visible due to the small variation), is with a specific packet size (small or large), and with a specific data rate (10 kbit/s – 100 Mbit/s). Markers for traffic profiles of common applications are included as well. This text and measurements do not cover packet errors but information about this can be found at the above references. The table below shows the maximum achievable (application specific) UDP throughput in the same scenarios (same references again) with various different WLAN (802.11) flavours. The measurement hosts have been 25 meters apart from each other; loss is again ignored.

Multiple access points[edit]

Increasing the number of Wi-Fi access points for a network provides redundancy, better range, support for fast roaming and increased overall network-capacity by using more channels or by defining smaller cells. Except for the smallest implementations (such as home or small office networks), 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.

An Extended Service Set may be formed by deploying multiple access points that are configured with the same SSID and security settings. Wi-Fi client devices will typically connect to the access point that can provide the strongest signal within that service set.

Hardware[edit]

An embedded RouterBoard 112 with U.FL-RSMA pigtail and R52 mini PCI Wi-Fi card widely used by wireless Internet service providers (WISPs) in the Czech Republic

OSBRiDGE 3GN – 802.11n Access Point and UMTS/GSM Gateway in one device

Wi-Fi allows wireless 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.

Since the early 2000s 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.^[78]

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 AirPort wireless G Wi-Fi adapter from an Apple MacBook.

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^[update], 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 computer, as is the case with as Apple's AirPort, which is managed with the AirPort Utility on macOS and iOS.^[79]

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 whereby 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 whereby a single user with a Wi-Fi equipped tablet migrates around the combined extended and non-extended portions of the total connected network. Also, a wireless device connected to any of the repeaters in the chain will have a data throughput that is limited by the "weakest link" existing in the chain between where the connection originates and where the connection ends. Networks employing wireless extenders are 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.

Embedded systems[edit]

Embedded serial-to-Wi-Fi module

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.^[80]

Increasingly in the last few years (particularly as of 2007^[update]), 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.^[81]
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.^[82]

Wireless network interface controller Gigabyte GC-WB867D-I.

Antenna of wireless network interface controller Gigabyte GC-WB867D-I.

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]}

Network security[edit]

The main issue with wireless network security is its simplified access to the network compared to traditional wired networks such as Ethernet. With wired networking, one must either gain access to a building (physically connecting into the internal network), or break through an external firewall. To enable Wi-Fi, one merely needs to be within the range of the Wi-Fi network. 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.^[83][84][85]

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.^[86]

Securing methods[edit]

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,^[87]
but determined eavesdroppers may be able to 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.^[88] 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.^[89] In 2017 a flaw in the WPA2 protocol was discovered, allowing a key replay attack, known as KRACK.^[90][91]

A flaw in a feature added to Wi-Fi in 2007, called Wi-Fi Protected Setup (WPS), 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,^[92] which is not always possible.

Security researcher (Jens 'Atom' Steube) has revealed a new WiFi hacking technique that makes it easier for hackers to crack WiFi passwords of most modern routers.^[93]

Virtual Private Networks are often used to secure Wi-Fi.^{[citation needed]}

Data security risks[edit]

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The older 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 over Transport Layer Security (HTTPS).

Wi-Fi Protected Access encryption (WPA2) is considered secure, provided a strong passphrase is used. In 2018, WPA3 was announced as a replacement for WPA2, increasing security;^[94] it rolled out on June 26.^[95]

Piggybacking[edit]

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,^[96] 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.^[97] A Florida court case determined that owner laziness was not to be a valid excuse.^{[citation needed]}

Piggybacking often occurs unintentionally – a technically unfamiliar user might not change the default "unsecured" settings to their access point 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 unsecure network to log into a website, thereby making the login credentials available to anyone listening, if the website uses an unsecure protocol such as plain HTTP without TLS (HTTPS).

An unauthorized user can obtain security information (factory preset passphrase and/or Wi-Fi Protected Setup PIN) from a label on a wireless access point can use this information (or connect by the Wi-Fi Protected Setup pushbutton method) to commit unauthorized and/or unlawful activities.

Health concerns[edit]

The World Health Organization (WHO) says "no health effects are expected from exposure to RF fields from base stations and wireless networks", but notes that they promote research into effects from other RF sources.^[98] Although the WHO's International Agency for Research on Cancer (IARC) later classified radio-frequency electromagnetic fields (EMFs) as "possibly carcinogenic to humans (Group 2B)"^[99] (a category used when "a causal association is considered credible, but when chance, bias or confounding cannot be ruled out with reasonable confidence"),^[100] this was based on risks associated with wireless phone use rather than Wi-Fi networks.

The United Kingdom's Health Protection Agency reported in 2007 that exposure to Wi-Fi for a year results in the "same amount of radiation from a 20-minute mobile phone call".^[101]

A review of studies involving 725 people who claimed electromagnetic hypersensitivity, "...suggests that 'electromagnetic hypersensitivity' is unrelated to the presence of an EMF, although more research into this phenomenon is required."^[102]

Alternatives[edit]

A number other "wireless" technologies provide alternatives to Wi-Fi in some cases:

• Bluetooth, short distance network


• 
  Bluetooth Low Energy, a low-power variant


• 
  Zigbee, low-power, low data rate, and close proximity


• Cellular networks, as used by smartphones


• 
  WiMax, provide wireless internet connection from outside individual homes

Some alternatives are "no new wires", re-using existing cable:

• 
  G.hn over existing home wiring, such as phone and power lines
  

There are also several wired technologies for computer networking which in some cases will be viable alternatives, in particular:

• Ethernet over twisted pair

See also[edit]

• 
  Gi-Fi — a term used by some trade press to refer to faster versions of the IEEE 802.11 standards


• Indoor positioning system


• Li-Fi


• List of WLAN channels


• Operating system Wi-Fi support


• San Francisco Digital Inclusion Strategy


• WiGig


• Wireless Broadband Alliance

References[edit]

Further reading[edit]

• 
  The WNDW Authors (1 March 2013). Butler, Jane, ed. Wireless Networking in the Developing World (Third Edition) (PDF)|format= requires |url= (help). ISBN 978-1-4840-3935-9.