Wi-Fi (or Wi-fi, WiFi, Wifi, wifi), short for "Wireless Fidelity", is a set of standards for wireless local area networks (WLAN) currently based on the IEEE 802.11 specifications. New standards beyond the 802.11 specifications, such as 802.16 are currently in the works, they offer many enhancements, anywhere from longer range to greater transfer speeds.
Wi-Fi was intended to be used for wireless devices and LANs, but is now often used for Internet access. It enables a person with a wireless-enabled computer or personal digital assistant to connect to the Internet when in proximity of an access point 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 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. Despite such problems, companies like Zyxel, SocketIP and Symbol Technologies are offering telephony platforms (Central Office replacements and terminals (phones)) that use Wi-Fi transport.
Many operators are now selling mobile internet products that link cellular wireless and Wi-Fi 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 term 4G is occasionally used for Wi-Fi, the implication being that the bandwidth and capabilities offered are already greater than those promised by the 3G cellular telephone standards.
The main difference between cellular and Wi-Fi is that cellular system use licensed spectrum, and Wi-Fi is implemented in unlicensed bands. The economic basis for their implementation is therefore completely different. The success of Wi-Fi has made many people look to unlicensed spectrum as the future of wireless access, rather than spectrum licensed and controlled by large corporations.
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:
- T-Mobile provides hotspots in many Starbucks in the U.S;
- 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;
- Sify, an Indian internet service provider, has set up 120 wireless access points in Bangalore, India in hotels, malls and government offices.
- Vex (http://www.pointernetworks.com.br) offers a big network of hotspots spread over Brazil. Telefónica Speedy WiFi (http://www.speedywifi.com.br) has started its services in a new and growing network distributed over the state of São Paulo.
While commercial services attempt to move existing business models to Wi-Fi many groups and communities have set up free use Wi-Fi networks. Many have adopted a common Peering agreement (http://www.freenetworks.org/peering.html) in order that each network can openly share with each other.
Many municipalities have joined with the local community groups to help grow the free Wi-Fi network, many have not. Some community groups have built their Wi-Fi networks 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 protocol 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 countries, such as Estonia  (http://www.wifi.ee/?p=area&lang=eng) and the Kingdom of Tonga, provide free Wi-Fi access to the internet to all of their inhabitants.
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.
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 100mWatt limit and one accepts interference from other; including interference which causes your devices to no longer function.
- 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, require a 'general authorization' for any WiFi used outside the owned premises; or require something akin to an operator registration. For Europe; consult http://www.ero.dk for an anual 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 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.
- 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 150 ft (46 m) indoors and 300 ft (92 m) outdoors. But about 10 US$ and an hour of building will get you an antenna that can go much further.
- Rogue access points could be used to steal information transmitted from Wi-Fi users.
Wi-Fi and free software
- BSD (FreeBSD, NetBSD, OpenBSD) have had support for most Adapters since late 98. 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.
- Linux: As of version 2.6, little Wi-Fi hardware is supported by the Linux kernel. However, see the Adapters section below for pointers.
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 use by outsiders
Many business and residential users do not bother to protect their network, which can therefore also be used by people just outside the building, see warchalking and wardriving. Configuration is not hard, and used to require both knowledge and effort. Many users of wireless networks won't even realize they are "trespassing" since the drivers on their laptops automatically seek out the nearest access point. Early attempts to provide security included changing or suppressing the Service Set Identifier (SSID), and only allowing wireless cards with specific MAC addresses to connect. These methods were easily defeated by hackers armed with packet sniffers and MAC address spoofing cards. Today owners of access points use one of the many encryption standards available to protect their network (for example, WEP).
Examples of external antennas to increase the range beyond the nominated distances. These can be home made and hence be of interest for hobbyists and community wireless networks. Popular examples are the so called "spider omni" (http://flakey.info/antenna/omni/quarter/) and "waveguide cantenna" (http://flakey.info/antenna/waveguide/).
See also: Wikibooks: Building a Wifi antenna (http://en.wikibooks.org/wiki/Building_a_Wifi_antenna).
Adapters with free, open drivers