Wi-Fi

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Wi-Fi (sometimes written Wi-fi, WiFi, Wifi, wifi) is a trademark for sets of product compatibility standards for wireless local area networks (WLANs). Wi-Fi was intended to allow mobile devices, such as laptop computers and personal digital assistants (PDAs) to connect to local area networks, but is now often used for Internet access and wireless VoIP phones. Desktop computers can use Wi-Fi too, allowing offices and homes to be networked without expensive wiring. Many computers are sold today with Wi-Fi built-in; others require adding a Wi-Fi network card. Other devices, such as digital cameras, are sometimes equipped with Wi-Fi.

A person with a Wi-Fi-enabled device is able to connect to a local area network when near one of the network's access points. The connection is made by radio signals; there is no need to plug the device into the network. If the local area network is connected to the Internet, the Wi-Fi device can have Internet access as well. The geographical region covered by one or several access points is called a hotspot. The range of an access point varies. The access point built into a typical Wi-Fi home router might have a range of 45 m (150 ft) indoors and 90 m (300 ft) outdoors.

Wi-Fi logo

The Wi-Fi trademark is controlled by the Wi-Fi Alliance (formerly the Wireless Ethernet Compatibility Alliance), the trade organization that tests and certifies equipment compliance with the IEEE 802.11 standards. Apple Computer sells Wi-Fi products under its AirPort trademark. Certified products can use the official Wi-Fi logo, which indicates that the product is interoperable with any other product also showing the logo.

Contents

Specifications

Wi-Fi is 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 specification was used in the first Wi-Fi products. The g and n variants are the ones most often sold as of 2005.

Wi-Fi specifications
Specification Speed Frequency
Band
Compatible
with
802.11b 11 Mb/s 2.4 GHz b
802.11a 54 Mb/s 5 GHz a
802.11g 54 Mb/s 2.4 GHz b, g
802.11n 100 Mb/s 2.4 GHz b, g, n

In most of the world, the frequencies used by Wi-Fi do not require user licenses from local regulators (eg, the Federal Communications Commission in the US). 802.11a equipment, using a higher frequency, has reduced range, all other things being equal.

The most widespread version of Wi-Fi in the US market today (based in IEEE 802.11b/g) operates in the 2,400 MHz to 2,483.50 MHz. It allows operation in 11 channels (5 MHz each), centered on the following frequencies:

  • Channel 1 - 2,412 MHz;
  • Channel 2 - 2,417 MHz;
  • Channel 3 - 2,422 MHz;
  • Channel 4 - 2,427 MHz;
  • Channel 5 - 2,432 MHz;
  • Channel 6 - 2,437 MHz;
  • Channel 7 - 2,442 MHz;
  • Channel 8 - 2,447 MHz;
  • Channel 9 - 2,452 MHz;
  • Channel 10 - 2,457 MHz;
  • Channel 11 - 2,462 MHz

Europe, France, Spain and Japan have adopted their own allowed channels sets. 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 most of 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, MiniPCI, Cardbus, PCMCIA 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 are currently in the works and offer many enhancements, anywhere from longer range to greater transfer speeds. One example is WiMAX, with a range of several miles and data rates of up to 70Mbs. 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 vs. cellular

Some expect that Wi-Fi and related consumer technologies will replace cellular telephone networks such as 3G and GSM. The current generation of Wi-Fi still lacks 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 BroadVoice, UTStarcom, Zyxel, SocketIP and Symbol Technologies are already offering Wi-Fi VoIP phones and 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 Internet access

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

Free Wi-Fi

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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. Philadelphia is one of the largest cities to have embarked on a city owned and operated WiFi network for free public use. Many other cities such as San Francisco have plans to create free Wi-Fi community networks.

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, or in the case of Wireless Leiden developed their own router software called LVrouted. 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.

Japan has been the first country to utilize public Wi-Fi support in select regions. Grand Haven, Michigan has been the first US city to utilize city-wide Wi-Fi support.

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 (although may require some software configuration).

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 provided one accepts interference from other sources, including interference which causes your devices to no longer function.
  • Legislation/regulation is not consistent worldwide; most of Europe allows for an additional 2 channels over those allowed for b and g; 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 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 equipment such as Bluetooth devices, 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.
  • Closed access points can interfere with properly configured open access points on the same frequency, preventing use of open access points by others.
  • Power consumption is fairly high compared to other standards, making battery life and heat a concern.

Wi-Fi and amateur radio

In the US, the 2.4 GHz Wi-Fi radio spectrum is also allocated to amateur radio users. FCC Part 15 rules govern non-licenced operators (i.e. most Wi-Fi equipment users). Amateur operators retain what the FCC terms "primary status" on the band under a distinct set of rules (Part 97). Under Part 97, licensed amateur operators may construct their own equipment, use very high-gain antennas, and boost output power to 100 watts on frequencies covered by Wi-Fi channels 2-6. However, Part 97 rules mandate using only the minimum power necessary for communications, forbid obscuring the data, and require station identification every 10 minutes. Therefore, expensive automatic power-limiting circuitry is required to meet regulations, and the transmission of any encrypted data (for example https) is questionable.

In practice, microwave power amplifiers are expensive and decrease receive-sensitivity of link radios. On the other hand, the short wavelength at 2.4 GHz allows for simple construction of very high gain directional antennas. Although Part 15 rules forbid any modification of commercially constructed systems, amateur radio operators may modify commercial systems for optimized construction of long links, for example. Using only 200 mW link radios and two 24 dB gain antennas, an effective radiated power of many hundreds of watts in a very narrow beam may be used to construct reliable links of over 100 km with little radio frequency interference to other users.

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 available, including RealTek RTL8180L, Ralink RT25x0, Atmel AT76C50x, and Intel 2100/2200BG/2225BG/2915ABG, due at least in part to 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 exist. 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 proprietary 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. Starting with Linux 2.6.14, the Intel Pro Wireless driver (mostly for centrino laptops) is included in the main kernel tree. As with some Prism cards, you need to download a closed-source binary firmware.

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 chalk 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]

Security

WiFi equipment could be used to steal personal information (passwords, financial information, identity information, and so on) transmitted from Wi-Fi users, if sensible protections are not used.

The first and most commonly used wireless encryption standard, Wired Equivalent Privacy or WEP, has been shown to be easily breakable even when correctly configured. Most wireless products now on the market support the Wi-Fi Protected Access (WPA) encryption protocol, which is considered much stronger, though some older access points have to be replaced to support it. The adoption of the 802.11i standard (marketed as WPA2) makes available a rather better security scheme — when properly configured. As of mid-2005, both Microsoft Windows XP and Mac OS X support WPA2, but on newer equipment only. While waiting for better standards to be available, many enterprises have chosen to deploy additional layers of encryption (such as VPNs) to protect against interception.

Some report that 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.

Large corporations are often concerned about the security risk posed to a secure company network by an unauthorized wireless access point, also known as a rogue access point. With the advent of inexpensive wireless routers available at consumer electronics stores, employees sometimes connect an unauthorized access point out of ignorance or malice, thereby exposing the secure corporate network to anyone who may be "wardriving" nearby. To alleviate the potential risk of rogue access points, some large organizations have begun (as of 2005) to install wireless intrusion detection systems. These systems are designed to monitor the premises for wireless signals and immediately report the presence of any unauthorized access points.

See also

External links

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