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What is Wi-Fi?

2006-02-05 00:00wikipedia
Internet protocol suite
Layer Protocols
Application DNS, FTP, HTTP, IMAP, IRC, NNTP, POP3, SIP, SMTP, SNMP, SSH, TELNET, BitTorrent, …
Transport DCCP, SCTP, TCP, RTP, UDP, IL, RUDP, …
Network IPv4, IPv6, …
Link Ethernet, Wi-Fi, Token ring, MPLS, PPP, …

Wi-Fi (also WiFi, Wi-fi, Wifi, or wifi) is a set of product compatibility standards for wireless local area networks (WLAN) based on the IEEE 802.11 specifications. New standards beyond the 802.11 specifications, such as 802.16(WiMAX), are currently in the works and offer many enhancements, anywhere from longer range to greater transfer speeds.

Wi-Fi was intended to be used for mobile devices and LANs, but is now often used for Internet access. It enables a person with a wireless-enabled computer or personal digital assistant (PDA) to connect to the Internet when in proximity of an access point. The geographical region covered by one or several access points is called a hotspot.

Contrary to popular belief, Wi-Fi did not originally stand for Wireless-Fidelity. The term "Wi-Fi" was developed by the Wi-Fi Alliance along with the Interbrand Corporation (here) to describe WLAN products that are based on the IEEE 802.11 standards. Phil Belanger of the Wi-Fi Alliance quoted, "Wi-Fi and the yin yang style logo were invented by Interbrand. We (the founding members of the Wireless Ethernet Compatibility Alliance, now called the Wi-Fi Alliance) hired Interbrand to come up with the name and logo that we could use for our interoperability seal and marketing efforts. We needed something that was a little catchier than “IEEE 802.11b Direct Sequence”. Later, the term "Wireless Fidelity" was coined with the marketing of a new tag line, "The Standard for Wireless Fidelity." But that was soon dropped due to confusion among customers and consumers.

Certified products can use the official Wi-Fi logo, which indicates that the product is interoperable with any other product also showing the logo.

History

Back in 1991 Wi-Fi was invented by NCR Corporation/AT&T (later on Lucent & Agere Systems) in Nieuwegein, the Netherlands. Initially meant for cashier systems the first wireless products were brought on the market under the name WaveLAN with speeds of 1Mbps/2Mbps. Vic Hayes who is the inventor of Wi-Fi has been named 'father of Wi-Fi' and was with his team involved in designing standards such as IEEE 802.11b, 802.11a and 802.11g. In 2003, Vic retired from Agere Systems. Agere Systems suffered from strong competition in the market even though their products were cutting edge, as many opted for cheaper Wi-Fi solutions. Agere's 802.11abg all-in-one chipset (code named: WARP) never hit the market, Agere Systems decided to quit the Wi-Fi market in late 2004.

Wi-Fi: How it works

The typical Wi-Fi setup contains one or more Access Points (AP's) and one or more clients. An AP broadcasts its SSID (Service Set Identifier, Network name) via packets that are called beacons, which are broadcasted every 100ms. The beacons are transmitted at 1Mbps, and are relatively short and therefore are not of influence on performance. Since 1Mbps is the lowest rate of Wi-Fi it assures that client who receives the beacon can communicate at at least 1Mbps. Based on the settings (i.e. the SSID), the client may decide whether to connect to an AP. Also the firmware running on the client Wi-Fi card is of influence. Say two AP's of the same SSID are in range of the client, the firmware may decide based on signal strength (Signal-to-noise ratio) to which of the two AP's it will connect. The Wi-Fi standard leaves connection criteria and roaming totally open to the client. This is a strength of Wi-Fi, but also means that one wireless adapter may perform substantially better than the other. Since Windows XP there is a feature called zero configuration which makes the user show any network available and let the end user connect to it on the fly. In the future wireless cards will be more and more controlled by the operating system. Microsoft's newest feature called SoftMAC will take over from on-board firmware. Having said this, roaming criteria will be totally controlled by the operating system. Wi-Fi transmits in the air, it has the same properties as a non-switched ethernet network. Even collisions can therefore appear like in non-switched ethernet LAN's.

Wi-Fi vs. cellular

Some argue that Wi-Fi and related consumer technologies hold the key to replacing cellular telephone networks such as GSM. Some obstacles to this happening in the near future are missing roaming and authentication features (see 802.1x, SIM cards and RADIUS), the narrowness of the available spectrum and the limited range of Wi-Fi. It is more likely that WiMax could compete to other cellular phone protocols such as GSM, UMTS or CDMA. However Wi-Fi is ideal for VoIP applications like in a corporate LAN or SOHO environment. Early adopters were already available in the late 90's. Though the market exploded in 2005. Companies such as Zyxell, UT Starcomm, Samsung, Hitachi and many more are offering VoIP Wi-Fi phones for reasonable prices.

Anno 2005 ADSL ISP providers start to offer VoIP services to their customers (i.e. the dutch ISP XS4All did to all of their customers). Since calling via VoIP is cheap, more often just free, VoIP enabled ISP's will open the VoIP market. GSM phone with integrated Wi-Fi & VoIP capabilities start to take off. One day they might replace the landline-phone.

The question whether Wi-Fi will compete against cellular does not seem to be right. Devices capable of multiple standards will definetly dominate market. Wi-Fi-only phones have a very limited range, setting up a global covering network would be too expensive. Therefore they are only good for local networks such as a corporate network.

Commercial Wi-Fi

Commercial Wi-Fi services are available in places such as Internet cafes, coffee houses and airports around the world (commonly called Wi-Fi-cafés), although coverage is patchy in comparison with cellular:

Ozone and OzoneParis In France, in September 2003, Ozone started deploying the OzoneParis network across the city of lights. The objective: to construct a wireless metropolitan network with full Wi-Fi coverage of Paris. Ozone Pervasive Network philosophy is based on a nationwide scale.
WiSE Technologies provides commercial hotspots for airports, universities, and independent cafes in the US;
T-Mobile provides hotspots in many Starbucks in the U.S, and UK;
Pacific Century Cyberworks provides hotspots in Pacific Coffee shops in Hong Kong;
a Columbia Rural Electric Association subsidiary offers 2.4 GHz Wi-Fi service across a 3,700 mi² (9,500 km²) region within Walla Walla and Columbia counties in Washington and Umatilla County, Oregon;
Other large hotspot providers in the U.S. include Boingo, Wayport and iPass;
Sify, an Indian internet service provider, has set up 120 wireless access points in Bangalore, India in hotels, malls and government offices.

Vex offers a big network of hotspots spread over Brazil. Telefónica Speedy WiFi has started its services in a new and growing network distributed over the state of São Paulo.
Link repository on Wi-Fi topics at AirHive Net

Free Wi-Fi

While commercial services attempt to move existing business models to Wi-Fi, many groups, communities, cities, and individuals have set up free Wi-Fi networks, often adopting a common peering agreement in order that networks can openly share with each other. Free wireless mesh networks are often considered the future of the internet.

Many municipalities have joined with local community groups to help expand free Wi-Fi networks. Some community groups have built their Wi-Fi networks entirely based on volunteer efforts and donations.

For more information, see wireless community network, where there is also a list of the free Wi-Fi networks one can find around the globe.

OLSR is one of the protocols used to set up free networks. Some networks use static routing; others, rely completely on OSPF. Wireless Leiden developed their own routing software under the name LVrouteD for community wi-fi networks that consist of a completely wireless backbone. Most networks rely heavily on open source software, or even publish their setup under an open source license.

Some smaller countries and municipalities already provide free Wi-Fi hotspots and residential Wi-Fi internet access to everyone. Examples include the Kingdom of Tonga or Estonia which have already a large number of free Wi-Fi hotspots throughout their countries.

In Paris France, OzoneParis offers free Internet access for life to anybody who contributes to the Pervasive Network’s development by making their rooftop available for the WiFi Network.

Many universities provide free WiFi internet access to their students, visitors, and anyone on campus. Similarly, some commercial entities such as Panera Bread offer free Wi-Fi access to patrons. McDonald's Corporation also offers Wi-Fi access, often branded 'McInternet'. This was launched at their flagship restaurant in Oak Brook, Illinois and is also available in many branches in London, UK.

However, there is also a third subcategory of networks set up by certain communities such as universities where the service is provided free to members and guests of the community such as students, yet used to make money by letting the service out to companies and individuals outside. An example of such a service is Sparknet in Finland. Sparknet also supports OpenSparknet, a project where people can name their own wireless access point as a part of Sparknet in return for certain benefits.

Recently commercial Wi-Fi providers have built free Wi-Fi hotspots and hotzones. These providers hope that free Wi-Fi access would equate to more users and significant return on investment.

Advantages of Wi-Fi

Unlike packet radio systems, Wi-Fi uses unlicensed radio spectrum and does not require regulatory approval for individual deployers.

Allows LANs to be deployed without cabling, potentially reducing the costs of network deployment and expansion. Spaces where cables cannot be run, such as outdoor areas and historical buildings, can host wireless LANs.
Wi-Fi products are widely available in the market. Different brands of access points and client network interfaces are interoperable at a basic level of service.

Competition amongst vendors has lowered prices considerably since their inception.
Wi-Fi networks support roaming, in which a mobile client station such as a laptop computer can move from one access point to another as the user moves around a building or area.
Many access points and network interfaces support various degrees of encryption to protect traffic from interception.
Wi-Fi is a global set of standards. Unlike cellular carriers, the same Wi-Fi client works in different countries around the world.

Disadvantages of Wi-Fi

Use of the 2.4 GHz Wi-Fi band does not require a license in most of the world provided that one stays below the 100 mW limit and one accepts interference from other sources; including interference which causes your devices to no longer function. Some believe, wrongly, that Amateur Radio operators are an exception to the otherwise limited power output ceilings. The claim is that they may boost power output from their WiFi routers up to the legal maximum for their Amateur Radio license class, often 100 watts for spread spectrum operation (roughly 1,000 times that of a normal router).
Spectrum assignments and operational limitations are not consistent worldwide; most of Europe allows for an additional 2 channels beyond those permitted in the US; Japan has one more on top of that - and some countries, like Spain, prohibit use of the lower-numbered channels. Furthermore some countries, such as Italy, used to require a 'general authorization' for any WiFi used outside an operator's own premises, or require something akin to an operator registration. For Europe; consult http://www.ero.dk for an annual report on the additional restrictions each European country imposes.
The 802.11b and 802.11g flavors of Wi-Fi use the unlicensed 2.4 GHz spectrum, which is crowded with other devices such as Bluetooth, microwave ovens, cordless phones (900 MHz or 5.8 GHz are, therefore, alternative phone frequencies one can use if one has a Wi-Fi network), or video sender devices, among many others. This may cause a degradation in performance. Other devices which use microwave frequencies such as certain types of cell phones can also cause degradation in performance. Lots of Wi-Fi cards have Microwave-robustness algorithms on-board which makes the problems in almost all cases non-existent.

Power consumption is fairly high compared to some other standards, making battery life and heat a concern.
The most common wireless encryption standard, Wired Equivalent Privacy or WEP, has been shown to be breakable even when correctly configured (caused by weak-key generation). Although most newer wireless products support the much improved Wi-Fi Protected Access (WPA) protocol, many first-generation access points cannot be upgraded in the field and have to be replaced to support it. The adoption of the 802.11i (aka WPA2) standard in June 2004 makes available a still further improved security scheme, which is becoming available on the latest equipment. Both schemes require stronger passwords in personal mode than most users typically employ. Many enterprises have deployed additional layers of encryption (such as VPNs) to protect against interception.

Wi-Fi networks have limited range. A typical Wi-Fi home router using 802.11b or 802.11g might have a range of 45 m (150 ft) indoors and 90 m (300 ft) outdoors. Range also varies, as WiFi is no exception to the physics of radio wave propagation, with frequency band. WiFi in the 2.4 GHz frequency block has better range than WiFi in the 5 GHz frequency block, and less range than the oldest WiFi (and pre-WiFi) 900 MHz block.

Interference of a closed or encrypted access point with other open access points on the same or a neighboring channel can prevent access to the open access points by others in the area. This can pose a problem in high-density areas such as large apartment buildings where many residents are operating Wi-Fi access points.
Access points could be used to steal personal information transmitted from Wi-Fi users.

Interoperability issues between brands or deviations in the standard can cause limited connection or lower throughput speeds.

Free access points (or improperly configured access points) may be used by the malicious to anonymously initiate an attack that would be impossible to track beyond the owner of the access point.

Wi-Fi gaming

Wi-Fi is compatible with gaming consoles and handhelds. They are mainly exhibited in Nintendo systems such as the Nintendo DS and going to be included in the Nintendo Revolution.

The Nintendo DS was the first to have Wi-Fi which is used for Mario Kart DS, Animal Crossing: Wild World and Tony Hawk's American Sk8land. More Wi-Fi compatible games, such as Metroid Prime Hunters are planned for future release Iwata, the President of Nintendo announced the Nintendo Revolution will be Wi-Fi compatible, also saying that titles like Super Smash Brothers will be playable.

The Sony PSP comes with WLAN which can be turned on by the switch of a button to connect to WI-FI hotspots or wireless connections. It can also be switched to off to save battery life. There is a built in mode that lets the user scan the local area for any connections that may be there. The PSP also features a web browser that allows a user to browse most websites, albeit without external plugins such as Macromedia Flash.

Many games have their own servers for gamers to connect and play in an online world against other human players. Games include Madden 2006, SOCOM 3: U.S. Navy Seals, and NBA Live 2006.

Wi-Fi and free software

BSDs (FreeBSD, NetBSD, OpenBSD) have had support for most adapters since late 1998. Code for Atheros, Prism, Harris/Intersil and Aironet chips (from assorted WiFi vendors) is mostly shared among the 3 BSDs. Darwin and Mac OS X, despite their overlap with FreeBSD, have their own unique implementation. In OpenBSD 3.7, more drivers for wireless chipsets are available, including RealTek RTL8180L, Ralink RT25x0, Atmel AT76C50x, and Intel 2100 and 2200BG/2225BG/2915ABG, due to at least in part of the OpenBSD's effort to push for open source drivers for wireless chipsets. It is possible that such drivers may be implemented by other BSDs if they do not already exist. The ndiswrapper is also available for FreeBSD.

Linux: As of version 2.6, some Wi-Fi hardware is supported natively in the Linux kernel. Support for Orinoco, Prism, Aironet and Atmel are included in the main kernel tree, while ADMtek and Realtek RTL8180L are both supported by closed source drivers provided by the manufacturer and open source drivers written by the community. Intel Calexico radios are supported by open sourced drivers available at Sourceforge. Atheros and Ralink RT2x00 are supported through open source projects. Otherwise, support for other wireless devices is available through use of the open source ndiswrapper driver, which allows Linux running on the Intel x86 architecture to "wrap" a vendor's Windows driver for direct use. At least one commercial implementation of the idea is also available. The FSF has some recommended cards and more information can be found through the searchable Linux wireless site.

Trademark

Wi-Fi is a trademark of the Wi-Fi Alliance (formerly the Wireless Ethernet Compatibility Alliance), the trade organization that tests and certifies equipment compliance with the 802.11x standards.

Unintended and intended use by outsiders

The default configuration of most Wi-Fi access points provides no protection from unauthorized use of the network. Many business and residential users do not intend to secure their access points by leaving them open to users in the area. It has become etiquette to leave access points open for others to use just as one can expect to find open access points while on the road.

Measures to deter unauthorized users include suppressing

the AP's service set identifier (SSID) broadcast, only allowing computers with known MAC addresses to join the network, and various encryption standards. Older access points frequently do not support adequate security measures to protect against a determined attacker armed with a packet sniffer and the ability to switch MAC addresses. Recreational exploration of other people's access points has become known as wardriving, and the leaving of graffiti describing available services as warchalking.

However, it is also common for people to unintentionally use others' Wi-Fi networks without authorization. Operating systems such as Windows XP and Mac OS X automatically connect to an available wireless network, depending on the network configuration. 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's signal is stronger. In combination with automatic discovery of other network resources (see DHCP and Zeroconf) this can lead wireless users to send sensitive data to the wrong destination, as described by Chris Meadows in the February 2004 RISKS Digest.

[Read the article about Wi-Fi in Chinese]
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