Wi-Fi

Wi-Fi (or Wi-fi, WiFi, Wifi, wifi), short for "Wireless Fidelity", is a set of product compatibility standards for wireless local area networks (WLAN) based on the IEEE 802.11 specifications. There are currently four deployed 802.11 variations: 802.11a, 802.11b, 802.11g, and 802.11n.

The b standard permits up to 11Megabits/second, while both a and g allow up to 54Mbs. The new n specification will allow even higher speeds (up to 100Mbs and beyond). The 802.11a standard works in the 5GHz frequency band, and the others work in the 2.4GHz band. In fact, n is a superset of g, and g is a superset of b, so there is some interoperability among them. In most of the world, these freqencies do not require user licenses from local regulators (eg, the Federal Communications Commission in the US). In all areas, the maximum radio transmitter power and the maximum effective radiated power (essentially the power output at the antenna) are strictly limited. In the US, maximum transmitter power is 1 watt, and maximum effective radiated power is 4 watts; in Europe these limits are somewhat lower. An antenna which concentrates 1 watt of transmitter energy into 1/4 of an 'omnidirectional' sphere will achieve 4 watts of effective power. Most WiFi equipment (eg, PCMCIA or Cardbus cards for laptops, PCI cards for desktop equivalent computers, or standalone units often with other functions included) has transmitter power levels of between 15mw and perhaps 200mw, so antennas with some gain are permissible.

New standards beyond the 802.11 specifications, such as 802.16(WiMAX, with ranges of several miles and data rates of 70Mbs or so), are currently in the works and offer many enhancements, anywhere from longer range to greater transfer speeds. 802.16a permits operation between 2 and 11 GHz, so there may eventually be some interoperability between 802.11 units and some 802.16a units.

Wi-Fi was intended to be used for mobile devices and LANs, but is now often used for Internet and wireless VoIP phone access. It enables a person with a wireless-enabled computer, a personal digital assistant (PDA), or a wireless VoIP phone 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.

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

Wi-Fi vs. cellular

Some argue that Wi-Fi and related consumer technologies will replace cellular telephone networks such as 3G and GSM. The current generation of Wi-Fi is still lacking roaming and authentication features (see 802.1x, SIM cards and RADIUS) and the limited range of Wi-Fi as well as the narrowness of the available spectrum are holding back its proliferation as 3G replacement.

However, the bandwith and overall capabilities of Wi-Fi are already exceeding those once promised by 3G cellular telephone standards which lead to the use of the term 4G being used for Wi-Fi.

Companies like Zyxel, SocketIP and Symbol Technologies are already offering telephony platforms (Central Office replacements and terminals (phones)) that use Wi-Fi VoIP.

Many vendors are now selling mobile Internet products that link Wi-Fi and cellular radio system in a more or less transparent way to take advantage of the benefits of both systems. Future wireless systems are expected to routinely switch between a variety of radio systems.

The main difference between cellular and Wi-Fi is that the cellular system uses the licensed spectrum, and Wi-Fi is implemented in unlicensed bands. The economic basis for its implementation is therefore completely different. The success of Wi-Fi has made many people look to the unlicensed spectrum as the future of wireless access, rather than the spectrum licensed and controlled by large corporations.

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 still patchy:

• WiSE Technologies provides commercial hotspots for airports, universities, and independent cafes in the US;
• T-Mobile provides Wi-Fi service in over 6000 HotSpot locations which includes many Starbucks, Borders, Fed-Ex/Kinkos, Airline Clubs, Airports and Hotes in the U.S and UK;[1]
• Pacific Century Cyber Works 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;
• Wayport provides access to an ever-increasing number of Wireless McDonald'slocations;
• 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
• Airborne Access provides commercial hotspots for a lot of areas in the Philippines and other cities and countries around the world.

Free Wi-Fi

While commercial services attempt to move existing business models to Wi-Fi, many groups, communities, cities, and individuals have already 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; other, such as Wireless Leiden rely completely on OSPF. 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 free 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.

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.

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. One such example is AnchorFree Wireless in Sunnyvale, CA. AnchorFree provides free Wi-Fi access in Silicon Valley and San Francisco. In February of 2005 FreeFi launched a nationwide network of free, advertising-sponsored hotspots.

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.
• Many 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 local regulatory limits and one provided one accepts interference from other sources, including interference which causes your devices to no longer function. It is alleged, wrongly, that Amateur Radio operators have permission to boost the power on their WiFi transmitters up to the legal maximum for their Amateur Radio license class, which can be as high as 1500 watts (roughly 15,000 times higher than typical WiFi equipment).
• Legislation is not consistent worldwide; most of Europe allows for an additional 2 channels; 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 the owned premises; or required something akin to an operator registration. For Europe; consult http://www.ero.dk for an annual report on the additional restriction each European country imposes.
• The 802.11b and 802.11g flavors of Wi-Fi use the 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 to avoid interference 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 these microwave frequencies can also cause degradation in performance.
• Power consumption is fairly high compared to 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 easily breakable even when correctly configured. Although newer wireless products are slowly providing support for the Wi-Fi Protected Access (WPA) protocol, many older access points will have to be replaced to support it. The adoption of the 802.11i (aka WPA2) standard in June 2004 makes available a rather better security scheme for future use — when properly configured. In the meantime, many enterprises have had to deploy 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. 802.11a equipment, using a higher frequency, has reduced range, all other things being equal.
• 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.
• WiFi equipment could be used to steal personal information (passwords, financial information, identity information, ...) transmitted from Wi-Fi users, if sensible protections are not used. WEP is not sensible protection for it is easily evaded. The 802.11i standard (partially implemented in some equipment as W(ireless)P(rotected)A(ccess) will be a substantial improvement if properly configured at both ends.
• Free access points (or improperly configured access points) may be used by a hacker to anonymously initiate an attack that would be impossible to track beyond the owner of the access point.

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 is mostly shared between the 3 BSDs. Darwin and Mac OS X, despite their overlap with FreeBSD, have their own unique implementation. In OpenBSD 3.7, there are more wireless chipsets that 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 be implemented by other BSDs if they do not already exists. The ndiswrapper is also available for FreeBSD.
• Linux: As of version 2.6, most Wi-Fi hardware is supported natively by 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 proprietory closed source drivers provided by the manufacturer and open source drivers written by the community. Atheros and Ralink RT2x00 are supported through open source projects. Support for other more exotic wireless devices is available through use of the ndiswrapper driver, which allows Linux compiled for the Intel x86 architecture to "wrap" a Windows driver for direct use.

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. Most Wi-Fi community networks are based on free access and freely sharing bandwith.

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. Harmless recreational exploration of other people's access points has become known as wardriving, and the leaving of graffiti describing available services as warchalking.

It is also common for people to unintentionally use others' Wi-Fi networks without specific authorization. Operating systems such as Windows XP and Mac OS X automatically connect to any nearby 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 a 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 could theoretically lead wireless users to send sensitive data to the wrong destination, as described by Chris Meadows in the February 2004 RISKS Digest. [2]

See also

• OSGi Alliance
• WiMAX
• Liquid crystal display television with integrated WiFi port
• Wikibooks: Building a Wifi antenna
• Wireless mesh network
• Wireless LAN
• Wardriving

External links

Wikibooks has more about this subject:

Wifi

• WiFi Tutorial Includes information on Architecture, Standards, Security and Comparisons
• JiWire The Largest Directory Of Public Hotspots Worldwide
• MetroFreefi The Largest Directory Of US free Wi-Fi Hotspots
• Auscillate.com Free WiFi Lists Community-compiled lists of free wifi sites in various large US cities.
• Wireless Libraries
• WiFiMaps.com Maps of Wi-Fi installations across the US submitted by users' findings
• FreeNetworks A volunteer association dedicated to education, collaboration, and advocacy for the creation of free WiFi networks
• LocustWorld WiFi mesh networking projects
• WEP Cracking, the FBI Way A brief guide in cracking WEP enabled networks as demonstrated by the FBI.
• WiGLE Worldwide database and mapping of wireless networks.
• Wifi-Forum Worldwide discussion forum on Wi-Fi technology