Editing Wi-Fi (section)

== Operational principles ==
Wi-Fi stations communicate by sending each other [[data packet]]s, blocks of data individually sent and delivered over radio on various channels. As with all radio, this is done by the [[modem|modulation and demodulation]] of [[carrier wave]]s. Different versions of Wi-Fi use different techniques, 802.11b uses [[direct-sequence spread spectrum]] on a single carrier, whereas 802.11a, Wi-Fi 4, 5 and 6 use [[orthogonal frequency-division multiplexing]].<ref>Cisco Systems, Inc. White Paper Capacity, Coverage, and Deployment Considerations for IEEE 802.11g</ref><ref name="oreilly-802.11ac">{{cite web |url=http://chimera.labs.oreilly.com/books/1234000001739/ch04.html |work=802.11ac: A Survival Guide |first1=Matthew S. |last1=Gast |date=2013 |title=Chapter 4. Beamforming in 802.11ac |publisher=O'Reilly Atlas |access-date=17 April 2014 |archive-url=https://web.archive.org/web/20170703105148/http://chimera.labs.oreilly.com/books/1234000001739/ch04.html |archive-date=3 July 2017 |url-status=dead }}</ref>

Channels are used [[half duplex]]<ref>{{Cite web|date=23 January 2020|title=Why can't WiFi work as full duplex while 3G and 4G can|url=https://community.meraki.com/t5/Wireless-LAN/Why-can-t-WiFi-work-as-full-duplex-while-3G-and-4G-can/m-p/74017#M11290|access-date=19 September 2020|website=Meraki Community |language=en|archive-date=17 October 2021|archive-url=https://web.archive.org/web/20211017103935/https://community.meraki.com/t5/Wireless-LAN/Why-can-t-WiFi-work-as-full-duplex-while-3G-and-4G-can/m-p/74017#M11290|url-status=live}}</ref><ref>{{Cite web|title=Bad Info Is Nothing New for WLAN- Don't Believe "Full Duplex" in Wi-Fi 6|url=https://www.toolbox.com/tech/it-strategy/blogs/bad-info-is-nothing-new-for-wlan-dont-believe-full-duplex-in-wi-fi-6-082619/ |date= August 26, 2019 |first1=Lee |last1=Badman |access-date=19 September 2020|website=Toolbox|language=en-US|archive-date=19 November 2021|archive-url=https://web.archive.org/web/20211119071542/https://www.toolbox.com/tech/it-strategy/blogs/bad-info-is-nothing-new-for-wlan-dont-believe-full-duplex-in-wi-fi-6-082619/|url-status=live}}</ref> and can be [[Time-division multiple access|time-shared]] by multiple networks. Any packet sent by one computer is locally received by stations tuned to that channel, even if that information is intended for just one destination.{{Efn|This ''one speaks, all listen'' property is a security weakness of shared-medium Wi-Fi since a node on a Wi-Fi network can eavesdrop on all traffic on the wire if it so chooses.}} Stations typically ignore information not addressed to them.{{Efn|name=promiscuous|Unless it is put into [[promiscuous mode]].}} The use of the same channel also means that the data bandwidth is shared, so for example, available throughput to each device is halved when two stations are actively transmitting.

As with other IEEE 802 LANs, stations come programmed with a globally unique 48-bit MAC address.{{Efn|In some cases, the factory-assigned address can be overridden, either to avoid an address change when an adapter is replaced or to use [[locally administered address]]es.}} The MAC addresses are used to specify both the destination and the source of each data packet. On the reception of a transmission, the receiver uses the destination address to determine whether the transmission is relevant to the station or should be ignored.

A scheme known as [[carrier-sense multiple access with collision avoidance]] (CSMA/CA) governs the way stations share channels. With CSMA/CA stations attempt to avoid collisions by beginning transmission only after the channel is sensed to be idle,<ref name="federalstandard">{{cite web |url=http://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm |title=Federal Standard 1037C |website=Institute for Telecommunication Sciences |date=August 7, 1996 |access-date=9 September 2012 |archive-date=2 March 2009 |archive-url=https://web.archive.org/web/20090302235918/http://www.its.bldrdoc.gov/fs-1037/fs-1037c.htm |url-status=dead }}</ref><ref name="atis">{{cite web |url=http://www.atis.org/tg2k/ |title=ATIS Telecom Glossary 2007 |id=ATIS-0100523.2007 |website=Alliance for Telecommunications Industry Solutions |access-date=9 September 2012 |url-status=dead |archive-url=https://web.archive.org/web/20080302071329/http://www.atis.org/tg2k/ |archive-date=2 March 2008 }}</ref> but then transmit their packet data in its entirety. CSMA/CA cannot completely prevent collisions, as two stations may sense the channel to be idle at the same time and thus begin transmission simultaneously. A collision happens when a station receives signals from multiple stations on a channel at the same time. This corrupts the transmitted data and can require stations to re-transmit. The lost data and re-transmission reduces throughput, in some cases severely.

=== Waveband ===
{{Main|List of WLAN channels}}

The 802.11 standard provides several distinct [[radio frequency]] ranges for use in Wi-Fi communications: 900&nbsp;[[MHz]], 2.4&nbsp;GHz, 3.6&nbsp;GHz, 4.9&nbsp;GHz, 5&nbsp;GHz, 6&nbsp;GHz and 60&nbsp;GHz [[band (radio)|bands]].<ref>{{Cite web |url=https://www.radio-electronics.com/info/wireless/wi-fi/80211-channels-number-frequencies-bandwidth.php |title=Wi-Fi Channels, Frequencies, Bands & Bandwidths |website=Electronics Notes |language=en |access-date=18 August 2018 |archive-date=16 February 2018 |archive-url=https://web.archive.org/web/20180216081725/https://www.electronics-notes.com/articles/connectivity/wifi-ieee-802-11/channels-frequencies-bands-bandwidth.php |url-status=live }}</ref><ref>{{cite book | url=https://ieeexplore.ieee.org/document/7786995 | publisher=[[IEEE]] | date=14 December 2016 | doi=10.1109/IEEESTD.2016.7786995| isbn=978-1-5044-3645-8 | title=IEEE Standard for Information technology—Telecommunications and information exchange between systems Local and metropolitan area networks—Specific requirements - Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications }}</ref><ref>{{Cite news|url=https://www.lifewire.com/wireless-standards-802-11a-802-11b-g-n-and-802-11ac-816553|title=802.11 WiFi Standards Explained|work=Lifewire|access-date=18 August 2018|language=en|archive-date=12 December 2018|archive-url=https://web.archive.org/web/20181212063416/https://www.lifewire.com/wireless-standards-802-11a-802-11b-g-n-and-802-11ac-816553|url-status=live}}</ref> Each range is divided into a multitude of [[Channel (communications)|channels]]. In the standards, channels are numbered at 5&nbsp;MHz spacing within a band (except in the 60&nbsp;GHz band, where they are 2.16&nbsp;GHz apart), and the number refers to the centre frequency of the channel. Although channels are numbered at 5&nbsp;MHz spacing, transmitters generally occupy at least 20&nbsp;MHz, and standards allow for neighbouring channels to be bonded together to form a wider channel for higher throughput.

Countries apply their own regulations to the allowable channels, allowed users and maximum power levels within these frequency ranges. 802.11b/g/n can use the 2.4&nbsp;GHz band, operating in the United States under FCC [[Part 15]] rules and regulations. In this frequency band, equipment may occasionally suffer [[Interference (communication)|interference]] from microwave ovens,<ref name="scienceabc" /> [[cordless telephone]]s, [[USB 3.0]] hubs,<ref>{{cite web |url= http://www.usb.org/developers/docs/whitepapers/327216.pdf |title=USB 3.0 Radio Frequency Interference Impact on 2.4&nbsp;GHz Wireless Devices |website=USB.org |publisher=USB Implementers Forum |date=April 2012 |access-date=14 October 2019}}</ref> [[Bluetooth]] and other devices.<ref name="wired">{{Cite magazine|url=https://www.wired.com/2010/09/wireless-explainer/|title=Why Everything Wireless Is 2.4&nbsp;GHz|magazine=WIRED|access-date=18 August 2018|language=en-US|archive-date=26 July 2018|archive-url=https://web.archive.org/web/20180726115300/https://www.wired.com/2010/09/wireless-explainer/|url-status=live}}</ref>

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&nbsp;GHz band, while Japan has three more (12–14).

802.11a/h/j/n/ac/ax can use the [[U-NII|5&nbsp;GHz U-NII band]], which, for much of the world, offers at least 23 non-overlapping 20&nbsp;MHz channels. This is in contrast to the 2.4&nbsp;GHz frequency band where the channels are only 5&nbsp;MHz wide. In general, lower frequencies have longer range but have less capacity. The 5&nbsp;GHz bands are absorbed to a greater degree by common building materials than the 2.4&nbsp;GHz bands and usually give a shorter range.

As 802.11 specifications evolved to support higher throughput, the protocols have become much more efficient in their bandwidth use. Additionally, they have gained the ability to [[Link aggregation|aggregate]] channels together to gain still more throughput where the bandwidth for additional channels is available. 802.11n allows for double radio spectrum bandwidth (40&nbsp;MHz) per channel compared to [[802.11a]] or 802.11g (20&nbsp;MHz). 802.11n can be set to limit itself to 20&nbsp;MHz bandwidth to prevent interference in dense communities.<ref>{{Cite web|url=https://www.cisco.com/c/en/us/products/collateral/wireless/aironet-1250-series/design_guide_c07-693245.html#_Toc309331071|title=802.11n Data Rates Dependability and scalability|publisher=[[Cisco]]|archive-url=https://web.archive.org/web/20170705034144/http://www.cisco.com/c/en/us/products/collateral/wireless/Aironet-1250-series/design_guide_c07-693245.html#_Toc309331071|archive-date=5 July 2017|url-status=live|access-date=20 November 2017}}</ref> In the 5&nbsp;GHz band, 20&nbsp;MHz, 40&nbsp;MHz, 80&nbsp;MHz, and 160&nbsp;MHz channels are permitted with some restrictions, giving much faster connections.

{|style="margin: 0 auto;"
| [[File:2.4 GHz spectrum example Screenshot.png|thumb|An example of 2.4&nbsp;GHz Wi-Fi spectrum]]
| [[File:5 GHz Wi-Fi spectrum screenshot.png|thumb|An example of 5&nbsp;GHz Wi-Fi spectrum]]
| [[File:Netgear-Nighthawk-AC1900-WiFi-Router.jpg|thumb|upright| This [[Netgear]] Wi-Fi router contains dual bands for transmitting the 802.11 standards across the 2.4 and 5&nbsp;GHz spectrums and supports MIMO.]]
| [[File:Huawei 4G+ Modem.jpg|thumb|upright| A dual-band cellular 4G+ Wi-Fi modem by Huawei]]
|}

=== Communication stack ===
{{Main|IEEE 802|IEEE 802.11}}
[[File:802.11 frame.png|alt=|right|frameless|622x622px|Generic 802.11 Frame]]

Wi-Fi is part of the IEEE 802 protocol family. The data is organized into [[802.11 frame types|802.11 frames]] that are very similar to [[Ethernet frame]]s at the data link layer, but with extra address fields. MAC addresses are used as [[network address]]es for routing over the LAN.<ref name="IEEE 802.3 Clause 3.1.1">{{cite web| url = http://standards.ieee.org/getieee802/download/802.3-2012_section1.pdf| title = 3.1.1 Packet format| work = IEEE Standard for Ethernet, 802.3-2012 – section one| date = 28 December 2012| access-date = 6 July 2014| page = 53| url-status=dead| archive-url = https://web.archive.org/web/20141021020414/http://standards.ieee.org/getieee802/download/802.3-2012_section1.pdf| archive-date = 21 October 2014}}</ref>

Wi-Fi's MAC and [[physical layer]] (PHY) specifications are defined by IEEE 802.11 for modulating and receiving one or more carrier waves to transmit the data in the infrared, and 2.4, [[IEEE 802.11y-2008|3.6]], 5, 6, or [[IEEE 802.11ad|60&nbsp;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 many 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 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.<ref>{{cite web|url=http://www.gadgetreview.com/what-is-wifi-what-does-wifi-stand-for-how-does-it-work|title=What Does WiFi Stand For and How Does Wifi Work?|last=Stobing|first=Chris|date=17 November 2015|website=GadgetReview|archive-url=https://web.archive.org/web/20151201045951/http://www.gadgetreview.com/what-is-wifi-what-does-wifi-stand-for-how-does-it-work|archive-date=1 December 2015|url-status=live|access-date=18 November 2015}}</ref> As a result, in the market place, each revision tends to become its own standard.

In addition to 802.11, the IEEE 802 protocol family has specific provisions for Wi-Fi. These are required because Ethernet's cable-based media are not usually shared, whereas with wireless all transmissions are received by all stations within the range that employ that radio channel. While Ethernet has essentially negligible error rates, wireless communication media are subject to significant interference. Therefore, the accurate transmission is not guaranteed so delivery is, therefore, a [[best-effort delivery]] mechanism. 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.<ref>{{cite book|last1=Geier|first1=Jim|title=Overview of the IEEE 802.11 Standard|url=http://www.informit.com/articles/article.aspx?p=24411&seqNum=7|publisher=InformIT|access-date=8 April 2016|url-status=live|archive-url=https://web.archive.org/web/20160420043213/http://www.informit.com/articles/article.aspx?p=24411&seqNum=7|archive-date=20 April 2016|date=6 December 2001}}</ref>

For internetworking purposes, Wi-Fi is usually [[protocol layering|layered]] as a [[link layer]]{{efn|The link layer is equivalent to the physical and data link layers of the [[OSI model]].}} below the [[internet layer]] of the [[Internet Protocol]]. This means that nodes have an associated [[internet address]] and, with suitable connectivity, this allows full Internet access.

===Modes===

====Infrastructure====
[[File:Wi-Fi.gif|thumb|A Wi-Fi network in infrastructure mode. The print job is sent from the computer via the AP to the printer.]]

In infrastructure mode, which is the most common mode used, all communications go through a base station. For communications within the network, this introduces an extra use of the airwaves but has the advantage that any two stations that can communicate with the base station can also communicate through the base station, which limits issues associated with the [[hidden node problem]] and simplifies the protocols.

==== Ad hoc and Wi-Fi direct ====
Wi-Fi also allows communications directly from one computer to another without an access point intermediary. This is called [[wireless ad hoc network|''ad hoc'' Wi-Fi transmission]]. Different types of ad hoc networks exist. In the simplest case, network nodes must talk directly to each other. In more complex protocols nodes may forward packets, and nodes keep track of how to reach other nodes, even if they move around.

Ad hoc mode was first described by [[Chai Keong Toh]] in his 1996 patent of wireless ad hoc routing,<ref>{{Cite patent|country=US|number=5987011|title=Routing Method for Ad-Hoc Mobile Networks|status=|pubdate=16 November 1999|gdate=|invent1=Toh|inventor1-first=Chai Keong|inventorlink=Chai Keong Toh}}</ref> implemented on Lucent WaveLAN 802.11a wireless on IBM [[ThinkPad]]s over a size nodes scenario spanning a region of over a mile. The success was recorded in ''Mobile Computing'' magazine (1999)<ref>{{Cite web|url=http://www.mobileinfo.com/education/magazines.htm|title=Mobile Computing Magazines and Print Publications|website=www.mobileinfo.com|url-status=live|archive-url=https://web.archive.org/web/20160426220723/http://www.mobileinfo.com/education/magazines.htm|archive-date=26 April 2016|access-date=19 December 2017}}</ref> and later published formally in ''[[IEEE Transactions on Wireless Communications]]'', 2002<ref>{{cite journal|last1=Toh|first1=C.-K|author-link=Chai Keong Toh|last2=Delwar|first2=M.|last3=Allen|first3=D.|date=7 August 2002|title=Evaluating the Communication Performance of an Ad Hoc Mobile Network|journal=[[IEEE Transactions on Wireless Communications]]|volume=1|issue=3|pages=402–414|doi=10.1109/TWC.2002.800539}}</ref> and ''ACM SIGMETRICS Performance Evaluation Review'', 2001.<ref>{{cite journal|last1=Toh|first1=C.-K|author-link=Chai Keong Toh|last2=Chen|first2=Richard|last3=Delwar|first3=Minar|last4=Allen|first4=Donald|date=2001|title=Experimenting with an Ad Hoc Wireless Network on Campus: Insights & Experiences|url=http://ftp.math.utah.edu/pub/tex/bib/toc/sigmetrics.html|journal=ACM SIGMETRICS Performance Evaluation Review|volume=28|issue=3|pages=21–29|doi=10.1145/377616.377622|s2cid=1486812|access-date=8 October 2021|archive-date=2 December 2021|archive-url=https://web.archive.org/web/20211202183049/http://ftp.math.utah.edu/pub/tex/bib/toc/sigmetrics.html|url-status=live}}</ref>

This wireless ad hoc network mode has proven popular with [[multiplayer video game]]s on [[handheld game console]]s, such as the [[Nintendo DS]] and [[PlayStation Portable]]. It is also popular on [[digital camera]]s, and other [[consumer electronics devices]]. Some devices can also share their Internet connection using ad hoc, becoming hotspots or [[virtual router]]s.<ref>{{cite web|url=https://techsansar.com/internetworking/wireless-home-networking-virtual-wifi-hotspot/|title=Wireless Home Networking with Virtual WiFi Hotspot|last=Subash|date=24 January 2011|website=Techsansar|archive-url=https://web.archive.org/web/20110830150439/http://techsansar.com/internetworking/wireless-home-networking-virtual-wifi-hotspot-2946/|archive-date=30 August 2011|url-status=live|access-date=14 October 2011}}</ref>

Similarly, the Wi-Fi Alliance promotes the specification [[Wi-Fi Direct]] for file transfers and media sharing through a new discovery and security methodology.<ref>{{cite web|url=http://www.networkworld.com/news/2009/101409-wi-fi-direct.html?hpg1=bn|title=Wi-Fi Direct allows device-to-device links|last=Cox|first=John|date=14 October 2009|website=[[Network World]]|archive-url=https://web.archive.org/web/20091023052219/http://www.networkworld.com/news/2009/101409-wi-fi-direct.html?hpg1=bn|archive-date=23 October 2009|url-status=dead}}</ref> Wi-Fi Direct launched in October 2010.<ref>{{cite web|url=http://www.wi-fi.org/news-events/newsroom/wi-fi-gets-personal-groundbreaking-wi-fi-direct-launches-today|title=Wi-Fi gets personal: Groundbreaking Wi-Fi Direct launches today|date=25 October 2010|publisher=[[Wi-Fi Alliance]]|archive-url=https://web.archive.org/web/20150626120701/http://www.wi-fi.org/news-events/newsroom/wi-fi-gets-personal-groundbreaking-wi-fi-direct-launches-today|archive-date=26 June 2015|url-status=live|access-date=25 June 2015}}</ref>

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.<ref>{{cite web|url=http://www.wi-fi.org/knowledge-center/faq/what-is-wi-fi-certified-tdls|title=What is Wi-Fi Certified TDLS?|publisher=[[Wi-Fi Alliance]]|archive-url=https://web.archive.org/web/20141108145755/http://www.wi-fi.org/knowledge-center/faq/what-is-wi-fi-certified-tdls|archive-date=8 November 2014|url-status=dead}}</ref>

=== Multiple access points ===
[[File:802.11 Beacon frame.gif|thumb|Access points send out [[beacon frame]]s to announce the presence of networks.]]

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 typically connect to the access point that can provide the strongest signal within that service set.<ref>{{citation
|last=Edney
|first=Jon
|year=2004
|chapter=What is an ESS?
|title=IEEE 802 LAN/MAN Standards Committee Meeting, July 2004
|location=Piscataway, New Jersey
|publisher=Institute of Electrical and Electronics Engineers
|chapter-url=http://www.ieee802.org/21/doctree/2004_Meeting_Docs/2004-07_meeting_docs/21-04-0105-00-0000-what_ess.ppt
|page=8}}</ref>

Increasing the number of Wi-Fi access points for a network provides [[Redundancy (engineering)|redundancy]], better range, support for fast [[handover]], and increased overall network capacity by using more channels or by defining smaller [[cellular network|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 networking|mesh]] topologies.<ref>{{cite web|url=https://newscutzy.com/windows/fix-wifi-connected-but-no-internet-access/|title=Fix WiFi Connected But No Internet Access On Windows 11/10/8/7|access-date=25 June 2020|publisher=newscutzy.com|date=3 December 2021|language=english|author=Mohsin Beg|archive-date=24 June 2021|archive-url=https://web.archive.org/web/20210624202339/https://newscutzy.com/windows/fix-wifi-connected-but-no-internet-access/|url-status=live}}</ref>