Misplaced Pages

Revision as of 16:15, 7 June 2007

Wi-Fi was originally a brand licensed by the Wi-Fi Alliance to describe the embedded technology of wireless local area networks (WLAN) based on the IEEE 802.11 specifications. Use of the term has broadened over time and is generically used to describe the wireless interface of mobile computing devices, such as laptops in LANs. The term Wi-Fi was chosen as a play on the term "Hi-Fi", but is widely (and incorrectly) thought to be an abbreviation for wireless fidelity. Wi-Fi is widely used for a variety of purposes including Internet and VoIP phone access, gaming, and basic connectivity of consumer electronics such as televisions, DVD players, and digital cameras.

Newer standards in development will allow Wi-Fi to be used by cars on highways in support of an Intelligent Transportation System to increase safety, gather statistics, and enable mobile commerce (see IEEE 802.11p). Wi-Fi and the Wi-Fi CERTIFIED logo are registered trademarks of the Wi-Fi Alliance - the trade organization that tests and certifies equipment compliance with the 802.11x standards. Some concern has been expressed about possible risks to health from Wi-Fi radiation, but so far studies have not confirmed this.

Uses

A person with a Wi-Fi enabled device such as a PC, cell phone or PDA can connect to the Internet when in proximity of an access point. The region covered by one or several access points is called a hotspot. Hotspots can range from a single room to many square miles of overlapping hotspots. Wi-Fi can also be used to create a mesh network. Both architectures are used in community networks.

Wi-Fi also allows connectivity in peer-to-peer (wireless ad-hoc network) mode, which enables devices to connect directly with each other. This connectivity mode is useful in consumer electronics and gaming applications.

When the technology was first commercialized there were many problems because consumers could not be sure that products from different vendors would work together. The Wi-Fi Alliance began as a community to solve this issue so as to address the needs of the end user and allow the technology to mature. The Alliance created the branding Wi-Fi CERTIFIED to show consumers that products are interoperable with other products displaying the same branding.

Wi-Fi at home

Home Wi-Fi clients come in many shapes and sizes, from stationary PCs to digital cameras. The trend today is to incorporate wireless into every electronic where mobility is desired.

Wi-Fi devices in home or consumer-type environments connect in the following ways:

• Via a broadband Internet connection into a single router which can serve both wired and wireless clients
• Ad-hoc mode for client to client connections
• Built into non-computer devices to enable wireless connectivity to other devices or the Internet

Wi-Fi in Business

Business and industrial Wi-Fi has taken off, with the trends in implementation varying greatly over the years. Current technology trends in the corporate wireless world are:

• Dramatically increasing the number of Wi-Fi Access Points in an environment, in order to provide redundancy,support fast roaming and increasing overall network capacity by using more channels and/or creating smaller cells
• Designing for wireless voice applications (VoWLAN or WVOIP)
• Moving toward 'thin' Access Points, with more of the network intelligence housed in a centralized network appliance; relegating individual Access Points to be simply 'dumb' radios
• Outdoor applications utilizing true mesh topologies
• A proactive, self-managed network that functions as a security gateway, firewall, DHCP server, intrusion detection system, and a myriad of other features not previously considered relevant to a wireless network.

Wi-Fi at Hotspots

The most publically visible use of Wi-Fi is at hotspots. These trends include:

• Free Wi-Fi at venues like Panera Bread, It's a Grind Coffee House, and over 100,000 locations in the USA has been growing in popularity. According to a door-to-door survey in San Jose, CA, the number of venues and users is growing fast.
• Paid Wi-Fi at venues like Starbucks, McDonalds, and at hotels. This trend is growing rapidly at venues that require a higher rate of customer churn, such as sit-down restaurants.
• According to Muni Wireless, metropolitan-wide WiFi (Mu-Fi) already has more than 300 projects in process.

Evolution of Wi-Fi standards

Wi-Fi technology has gone through several generations since its inception in 1997.

802.11. The original version of the standard IEEE 802.11 released in 1997 specifies two raw data rates of 1 and 2 megabits per second (Mbps) to be transmitted via infrared (IR) signals or by either frequency hopping or direct-sequence spread spectrum in the Industrial Scientific Medical frequency band at 2.4 GHz. IR remains a part of the standard but has no actual implementations.

802.11a. The 802.11a amendment to the original standard was ratified in 1999. The 802.11a standard uses the same core protocol as the original standard and yields realistic throughput in the mid-20 Mbps. Since the 2.4 GHz band is heavily used, using the 5 GHz band gives 802.11a the advantage of less interference. However, this high carrier frequency also brings disadvantages. It restricts the use of 802.11a to almost line of sight, necessitating the use of more access points.

802.11b. The 802.11b amendment to the original standard was ratified in 1999. 802.11b has a maximum raw data rate of 11 Mbps and uses the same CSMA/CA media access method defined in the original standard. The dramatic increase in throughput of 802.11b (compared to the original standard) along with substantial price reductions led to the rapid acceptance of 802.11b as the definitive wireless LAN technology.

802.11g. In June 2003, a third standard was ratified: 802.11g. This works in the 2.4 GHz band (like 802.11b) but operates at a maximum raw data rate of 54 Mbps, or about 24.7 Mbps net throughputs (like 802.11a). Despite its major acceptance, 802.11g suffers from the same interference as 802.11b in the already crowded 2.4 GHz range. Devices operating in this range include microwave ovens, Bluetooth devices, and cordless telephones.

802.11n. 802.11n builds upon previous standards by adding MIMO (multiple-input multiple-output). MIMO uses multiple transmitter and receiver antennas to allow for increased data throughput through spatial multiplexing and increased range by exploiting the spatial diversity, through coding. On January 19, 2007, the IEEE 802.11 Working Group unanimously approved 802.11n to issue a new Draft 2.0 of the proposed standard.

Manufacturers
There are many vendors now manufacturing and selling 802.11n products. They include:

• Acer
• Airgo Networks
• Apple
• Asus
• Atheros
• Broadcom
• Buffalo Technology
• Dell
• Intel
• Linksys
• Netgear
• U.S. Robotics

References: 80211n.com

Technical information

Wi-Fi: How it Works

Wi-Fi networks use radio technologies called IEEE 802.11 to provide secure, reliable, fast wireless connectivity. A typical Wi-Fi setup contains one or more Access Points (APs) and one or more clients. An AP broadcasts its SSID (Service Set Identifier, "Network name") via packets that are called beacons, which are usually broadcast every 100 ms. The beacons are transmitted at 1 Mbit/s, and are of relatively short duration and therefore do not have a significant effect on performance. Since 1 Mbit/s is the lowest rate of Wi-Fi it assures that the client that receives the beacon can communicate at at least 1 Mbit/s. Based on the settings (e.g. the SSID), the client may decide whether to connect to an AP. If two APs of the same SSID are in range of the client, the client firmware might use signal strength to decide with which of the two APs to make a connection.

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 another. Since Wi-Fi transmits in the air, it has the same properties as a non-switched wired Ethernet network, and therefore collisions can occur. Unlike a wired Ethernet, and like most packet radios, Wi-Fi cannot do collision detection, and instead uses an acknowledgment packet for every data packet sent. If no acknowledgement is received within a certain time a retransmission occurs. Also, a medium reservation protocol can be used when excessive collisions are experienced or expected (RequestToSend/ClearToSend used for Collision Avoidance or CA) in an attempt to try to avoid collisions.

A Wi-Fi network can be used to connect computers to each other to the internet and to wired networks (which use IEEE 802.3 or Ethernet). Wi-Fi networks operate in the unlicensed 2.4 (802.11b/g) and 5 GHz (802.11a/h) radio bands, with an 11 Mbit/s (802.11b) or 54 Mbit/s (802.11a or g) data rate or with products that contain both bands (dual band). They can provide real world performance similar to the basic 10BaseT wired Ethernet networks.

Channels

Except for 802.11a/h, which operates at 5 GHz, Wi-Fi devices historically primarily use the spectrum in 2.4 GHz, which is standardized and unlicensed by international agreement, although the exact frequency allocations and maximum permitted power vary slightly in different parts of the world. Channel numbers, however, are standardized by frequency throughout the world, so authorized frequencies can be identified by channel numbers. The 2.4 GHz band is also used by microwave ovens, cordless phones, baby monitors and Bluetooth devices.

The maximum number of available channels for Wi-Fi enabled devices are:

• 13 for Europe
• 11 for North America. Only channels 1, 6, and 11 are recommended for 802.11b/g to minimize interference from adjacent channels.
• 14 for Japan

Advantages of Wi-Fi

• Allows LANs to be deployed without cabling for client devices, typically 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.
• Built into most modern laptops, getting a laptop without a built in WiFi has become an exception.
• Wi-Fi chipset pricing continues to come down, making Wi-Fi a very economical networking option and driving inclusion of Wi-Fi in an ever-widening array of devices.
• Wi-Fi products are widely available in the market. Different competitive brands of access points and client network interfaces are inter-operable at a basic level of service. Products designated as Wi-Fi CERTIFIED by the Wi-Fi Alliance are backwards inter-operable.
• Wi-Fi is a global set of standards. Unlike cellular carriers, the same Wi-Fi client works in different countries around the world.
• Widely available in more than 250,000 public hot spots and tens of millions of homes and corporate and university campuses worldwide.
• As of 2007, WPA is not easily cracked if strong passwords are used and WPA2 encryption has no known weaknesses.
• New protocols for Quality of Service (WMM) and power saving mechanisms (WMM Power Save) make Wi-Fi even more suitable for latency-sensitive applications (such as voice and video) and small Form-Factor

Disadvantages of Wi-Fi

• Spectrum assignments and operational limitations are not consistent worldwide; most of Europe allows for an additional 2 channels beyond those permitted in the US (1-13 vs 1-11); Japan has one more on top of that (1-14) - 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 Wi-Fi used outside an operator's own premises, or require something akin to an operator registration.
• Equivalent isotropically radiated power (EIRP) in the EU is limited to 20 dBm (0.1 W).
• Power consumption is fairly high compared to some other low bandwidth standards (Zigbee and Bluetooth), making battery life a concern.
• The most common wireless encryption standard, Wired Equivalent Privacy or WEP, has been shown to be easily breakable even when correctly configured. Wi-Fi Protected Access (WPA and WPA2) which began shipping in 2003 aims to solve this problem and is now available on most products.
• Wi-Fi Access Points typically default to an open (encryption-free) mode. Novice users benefit from a zero configuration device that works out of the box but without security enabled providing open wireless access to their LAN. To turn security on requires the user to configure the device, usually via a software GUI.
• Many 2.4 GHz 802.11b and 802.11g Access points default to the same channel on initial start up, contributing to congestion on certain channels. To change the channel of operation for an access point requires the user to configure the device.
• Wi-Fi networks have limited range. A typical Wi-Fi home router using 802.11b or 802.11g with a stock antenna might have a range of 45 m (150 ft) indoors and 90 m (300 ft) outdoors. Range also varies with frequency band. Wi-Fi in the 2.4 GHz frequency block has slightly better range than Wi-Fi in the 5 GHz frequency block. Outdoor range with improved antennas can be several kilometres or more with line-of-sight.
• Wi-Fi pollution, of an excessive number of an access point with other access points in the area, especially on the same or neighboring channel, can prevent access and interfere with the use of other access points by others caused by overlapping channels in the 802.11g/b spectrum as well as with decreased signal-to-noise ratio (SNR) between access points. This can be a problem in high-density areas such as large apartment complexes or office buildings with many Wi-Fi access points. Additionally, other devices use the 2.4 GHz band: microwave ovens, cordless phones, baby monitors, security cameras, and Bluetooth devices can cause significant additional interference.
• It is also an issue when municipalities or other large entities such as universities seek to provide large area coverage. Everyone is considered equal for the base standard without 802.11e/WMM when they use the band. This openness is also important to the success and widespread use of 2.4 GHz Wi-Fi, but makes it unsuitable for "must have" public service functions or where reliability is required. Users sometimes suffer network "frustrations" or a total network breakdown if gaming because a neighbour microwaves some pop corn.
• Interoperability issues between brands or proprietary deviations from the standard can disrupt connections or lower throughput speeds on other user's devices that are within range. And, Wi-Fi devices do not presently pick channels to avoid interference.
• Wi-Fi networks that are open (unencrypted) can be monitored and used to read and copy data (including personal information) transmitted over the network unless another security method is used to secure the data like a VPN or a secure web page.

Standard Devices

Wireless Access Point (WAP)

A wireless access point connects a group of wireless devices to an adjacent wired LAN. An access point is similar to an ethernet hub, relaying data between connected wireless devices in addition to a (usually) single connected wired device, most often an ethernet hub or switch, allowing wireless devices to communicate with other wired devices.

Wireless Adapter

A wireless adapter allows a device to connect to a wireless network. These adapters connect to devices using various external or internal interconnects such as PCI, miniPCI, USB, ExpressCard, Cardbus and PC card. Most newer laptop computers are equipped with internal adapters. Internal cards are generally more difficult to install.

Wireless Router

A wireless router integrates a WAP, ethernet switch, and internal Router firmware application that provides IP Routing, NAT, and DNS forwarding through an integrated WAN interface. A wireless router allows wired and wireless ethernet LAN devices to connect to a (usually) single WAN device such as cable modem or DSL modem. A wireless router allows all three devices (mainly the access point and router) to be configured through one central utility. This utility is most usually an integrated web server which serves web pages to wired and wireless LAN clients and often optionally to WAN clients. This utility may also be an application that is run on a desktop computer such as Apple's AirPort.

Wireless Ethernet Bridge

A wireless Ethernet bridge connects a wired network to a wireless network. This is different from an access point in the sense that an access point connects wireless devices to a wired network at the data-link layer. Two wireless bridges may be used to connect two wired networks over a wireless link, useful in situations where a wired connection may be unavailable, such as between two separate homes.

Range Extender

A wireless range extender or wireless repeater can extend the range of an existing wireless network. Range extenders can be strategically placed to elongate a signal area or allow for the signal area to reach around barriers such as those created in L-shaped corridors. Wireless devices connected through repeaters will suffer from an increased latency for each hop. Additionally, a wireless device at the end of chain of wireless repeaters will have a throughput that is limited by the weakest link within the repeater chain.

Antenna connectors

Most commercial devices (routers, access points, bridges, repeaters) designed for home or business environments use either RP-SMA or RP-TNC antenna connectors. PCI wireless adapters also mainly use RP-SMA connectors.

Most PC card and USB wireless only have internal antennas etched on their printed circuit board while some have MMCX connector or MC-Card external connections in addition to an internal antenna. A few USB cards have a RP-SMA connector.

Most Mini PCI wireless cards utilize Hirose U.FL connectors, but cards found in various wireless appliances contain all of the connectors listed.

Many high-gain (and homebuilt antennas) utilize the Type N connector more commonly used by other radio communications methods.

Non-Standard Devices

DIY Range Optimizations

USB-Wi-Fi adapters, food container "Cantennas", parabolic reflectors, and many other types of self-built antennae are increasingly made by do-it-yourselvers. For minimal budgets, as low as a few dollars, signal strength and range can be improved dramatically.

There is also a type of optimization by polarizing the signal to achieve a planar coverage like a plate. Many of these high-gain aftermarket modifications are technically illegal under FCC and other regulatory guidelines.

Long Range Wi-Fi

Recently, long range Wi-Fi kits have begun to enter the market. Companies like RadioLabs and BroadbandXpress offer long range, inexpensive kits that can be setup with limited knowledge. These kits utilize specialized antennas which increase the range of Wi-Fi dramatically, in the case of the world record 137.2 miles (220 km). These kits are commonly used to get Broadband internet to a place that cannot access the service itself.

The longest link ever achieved was by the Swedish space agency. They attained 310 km, but used 6 watt amplifiers to reach an overhead stratospheric balloon.

The longest link without amplification was 279 km in Venezuela, 2006 Read PDF by www.eslared.org

Wi-Fi and its support by operating systems

There are two sides to Wi-Fi support under an operating system: driver level support, and configuration and management support.

Driver support is usually provided by the manufacturer of the hardware or, in the case of Unix clones such as Linux and FreeBSD, sometimes through open source projects.

Configuration and management support consists of software to enumerate, join, and check the status of available Wi-Fi networks. This also includes support for various encryption methods. These systems are often provided by the operating system backed by a standard driver model. In most cases, drivers emulate an ethernet device and use the configuration and management utilities built into the operating system. In cases where built in configuration and management support is non-existent or inadequate, hardware manufacturers may include their own software to handle the respective tasks.

Microsoft Windows

Microsoft Windows has comprehensive driver-level support for Wi-Fi, the quality of which depends on the hardware manufacturer. Hardware manufactures almost always ship Windows drivers with their products. Windows ships with very few Wi-Fi drivers and depends on the original equipment manufacturers (OEMs)and device manufacturers to make sure users get drivers. Configuration and management depend on the version of Windows.

• Earlier versions of Windows, such as 98, ME and 2000 do not have built-in configuration and management support and must depend on software provided by the manufacturer
• Microsoft Windows XP has built-in configuration and management support. The original shipping version of Windows XP included rudimentary support which was dramatically improved in Service Pack 2. Support for WPA2 and some other security protocols require updates from Microsoft. There are still problems with XP support of Wi-Fi. (One simple interface problem is that if the user makes a mistake in the (case sensitive) passphrase, XP keeps trying to connect but never tells the user that the passphrase is wrong. A second problem is not allowing the user to see different BSSID's for the same ESSID; that is, it provides no way for the user to differentiate access points with the same name.) To make up for Windows’ inconsistent and sometimes inadequate configuration and management support, many hardware manufacturers include their own software and require the user to disable Windows’ built-in Wi-Fi support. See article "Windows XP Bedevils Wi-Fi Users" in Wired News.
• Microsoft Windows Vista has improved Wi-Fi support over Windows XP. The original betas automatically connected to unsecured networks without the user’s approval. The release candidate (RC1 or RC2) does not continue to display this behavior, requiring user permissions to connect to an unsecured network, as long as the user account is in the default configuration with regards to User Account Control.

Apple Mac OS

Apple was an early adopter of Wi-Fi, introducing its AirPort product line, based on the 802.11b standard, in July 1999. Apple then introduced AirPort Extreme as an implementation of 802.11g. All Macs starting with the original iBook included AirPort slots for which an AirPort card can be used, connecting to the computer's internal antenna. All Intel-based Macs either come with built-in Airport Extreme or a slot for an AirPort card. In late 2006, Apple began shipping Macs with Broadcom Wi-Fi chips that also supported the Draft 802.11n standard which can be unlocked through buying a $2 driver released by Apple at the January 2007 Macworld Expo. The driver is also included for free with Apple's 802.11n AirPort Extreme.

Apple makes the Mac OS operating system, the computer hardware, the accompanying drivers, AirPort WiFi base stations, and configuration and management software, simplifying Wi-Fi integration. The built-in configuration and management is integrated throughout many of the operating system's applications and utilities. Mac OS X has Wi-Fi support, including WPA2, and ships with drivers for Apple’s Broadcom-based AirPort cards. Many third-party manufacturers make compatible hardware along with the appropriate drivers which work with Mac OS X’s built-in configuration and management software. Other manufacturers distribute their own software.

Apple's older Mac OS 9 does not have built in support for Wi-Fi configuration and management nor does it ship with Wi-Fi drivers, but Apple provides free drivers and configuration and management software for their AirPort cards for OS 9, as do a few other manufacturers. Versions of Mac OS before OS 9 predate Wi-Fi and do not have any Wi-Fi support, although some third-party hardware manufacturers have made drivers and connection software that allows earlier OSes to use Wi-Fi.

Open source Unix-like systems

Linux, FreeBSD and similar Unix-like clones have much coarser support for Wi-Fi. Due to the open source nature of these operating systems, many different standards have been developed for configuring and managing Wi-Fi devices. The open source nature also fosters open source drivers which have enabled many third party and proprietary devices to work under these operating systems. See Comparison of Open Source Wireless Drivers for more information on those drivers.

• Linux has patchy Wi-Fi support. Native drivers for many Wi-Fi chipsets are available either commercially or at no cost, although some manufacturers don't produce a Linux driver, only a Windows one. Consequently, many popular chipsets either don't have a native Linux driver at all, or only have a half-finished one. For these, the freely available NdisWrapper and its commercial competitor DriverLoader allow Windows x86 and 64 bit variants NDIS drivers to be used on x86-based Linux systems but not on other architectures. As well as the lack of native drivers, some Linux distributions do not offer a convenient user interface and configuring Wi-Fi on them can be a clumsy and complicated operation compared to configuring wired Ethernet drivers. This is changing with NetworkManager, a utility that allows users to automatically switch between networks without using the command line.

• FreeBSD has Wi-Fi support similar to Linux. Support under FreeBSD is best in the 6.x versions, which introduced full support for WPA and WPA2, although in some cases this is driver dependent. FreeBSD comes with drivers for many wireless cards and chipsets, including those made by Atheros, Ralink, Cisco, D-link, Netgear, and many Centrino chipsets, and provides support for others through the ports collection. FreeBSD also has "Project Evil", which provides the ability to use Windows x86 NDIS drivers on x86-based FreeBSD systems as NdisWrapper does on Linux, and Windows amd64 NDIS drivers on amd64-based systems.

• NetBSD, OpenBSD, and DragonFly BSD have Wi-Fi support similar to FreeBSD. Code for some of the drivers, as well as the kernel framework to support them, is mostly shared among the 4 BSDs.

• Haiku has no Wi-Fi support at all as of April 2007.

Embedded systems

Wi-Fi availability in the home is on the increase. This extension of the Internet into the home space will increasingly be used for remote monitoring. Examples of remote monitoring include security systems and tele-medicine. In all these kinds of implementation, if the Wi-Fi provision is provided using a system running one of operating systems mentioned above, then it becomes unfeasible due to weight, power consumption and cost issues.

Increasingly in the last few years (particularly as of early 2007), embedded Wi-Fi modules have become available which come with a real-time operating system and provide a simple means of wireless enabling any device which has and communicates via a serial port.

This allows simple monitoring devices, for example a portable ecg monitor hooked up to a patient in the home, to be created. This Wi-Fi enabled device effectively becomes part of the internet cloud and can communicate with any other node on the internet. The data collected can hop via the home's Wi-Fi access point to anywhere on the internet.

These Wi-Fi modules are designed so that minimal Wi-Fi knowledge is required by designers to wireless enable their product.

Social concerns

Unintended and intended use by outsiders

Measures to deter unauthorized users include suppressing the AP's service set identifier (SSID) broadcast, allowing only computers with known MAC addresses to join the network, and various encryption standards. Access points and computers using no encryption are vulnerable to eavesdropping by an attacker armed with packet sniffer software. If the eavesdropper has the ability to change his MAC address then he can potentially join the network by spoofing an authorised address.

WEP encryption can protect against casual snooping but may also produce a misguided sense of security since freely available tools such as AirSnort can quickly recover WEP encryption keys. Once it has seen 5-10 million encrypted packets, AirSnort will determine the encryption password in under a second. The newer Wi-Fi Protected Access (WPA) and IEEE 802.11i (WPA2) encyption standards do not have the serious weaknesses of WEP encryption, but require strong passphrases for full security.

Recreational exploration of other people's access points has become known as wardriving, and the leaving of graffiti describing available services as warchalking. These activities may be illegal in certain jurisdictions, but existing legislation and case-law is often unclear.

However, it is also common for people to unintentionally use others' Wi-Fi networks without explicit authorization. Operating systems such as Windows XP SP2 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 could possibly lead wireless users to send sensitive data to the wrong destination, as described by Chris Meadows in the February 2004 RISKS Digest.

In Singapore, using another person's Wi-Fi network is illegal under the Computer Misuse Act. A 17 year old has been arrested for simply tapping into his neighbor's wireless Internet connection and faces up to 3 years' imprisonment and a fine.

Wi-Fi vs. amateur radio

In the US, Canada and Australia, a portion of the 2.4 GHz Wi-Fi radio spectrum is also allocated to amateur radio users. In the US, FCC Part 15 rules govern non-licensed operators (i.e. most Wi-Fi equipment users). Under Part 15 rules, non-licensed users must "accept" (i.e. endure) interference from licensed users and not cause harmful interference to licensed users. Amateur radio operators are licensed users, and 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, output power control is required to meet regulations, and the transmission of any encrypted data (for example https) is questionable.

In practice, microwave power amplifiers are expensive. 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 high gain directional antennas, a very narrow beam may be used to construct reliable links with minimal radio frequency interference to other users.

Health risks

There has been some debate about the effects of Wi-Fi transmissions on human health. Although the radiated energy is very low the use of laptops and PDAs may bring the sources very close to parts of the body for prolonged periods of time. In the United Kingdom two media reports, the latest in an episode of the current affairs television program Panorama in May 2007, has led to an unprecedented consumer reaction seeing some families as well as institutions (particularly schools being forced by parents) ordering the removal of their Wi-Fi systems. One authority upon which the reports weigh is Sir William Stewart, chairman of the Health Protection Agency and a former Chief Scientific Adviser to the British Government, however the HPA does not agree with his assessment. Anecdotal stories from individuals of deleterious effects appearing to originate from the low-energy radiation of the Wi-Fi systems have also been reported. These symptoms have included headaches and lethargy; symptoms which reportedly ceased upon the removal of the systems. . Consensus amongst scientists is that there is no evidence of harm, and the continuing calls for more research in the effects on human health remain limited -- many studies (37) have already been conducted that have shown no causal relationship.

History

Wi-Fi uses both single carrier direct-sequence spread spectrum radio technology (part of the larger family of spread spectrum systems) and multi-carrier OFDM (Orthogonal Frequency Division Multiplexing) radio technology. These regulations then enabled the development of Wi-Fi, its onetime competitor HomeRF, and Bluetooth.

Unlicensed spread spectrum was first made available by the Federal Communications Commission in 1985 and these FCC regulations were later copied with some changes in many other countries enabling use of this technology in all major countries. The FCC action was proposed by Michael Marcus of the FCC staff in 1980 and the subsequent controversial regulatory action took 5 more years. It was part of a broader proposal to allow civil use of spread spectrum technology and was opposed at the time by main stream equipment manufacturers and many radio system operators.

The precursor to Wi-Fi was invented in 1991 by NCR Corporation/AT&T (later Lucent & Agere Systems) in Nieuwegein, the Netherlands. It was initially intended for cashier systems; the first wireless products were brought on the market under the name WaveLAN with speeds of 1 Mbit/s to 2 Mbit/s. Vic Hayes, who held the chair of IEEE 802.11 for 10 years and has been named the 'father of Wi-Fi,' was involved in designing standards such as IEEE 802.11b, 802.11a and 802.11g.

Origin and meaning of the term 'Wi-Fi'

Despite the similarity between the terms 'Wi-Fi' and 'Hi-Fi', statements reportedly made by Phil Belanger of the Wi-Fi Alliance contradict the popular conclusion that 'Wi-Fi' stands for 'Wireless Fidelity.' According to Mr. Belanger, the Interbrand Corporation developed the brand 'Wi-Fi' for the Wi-Fi Alliance to use to describe WLAN products that are based on the IEEE 802.11 standards. In Mr. Belanger's words, "Wi-Fi and the yin yang style logo were invented by Interbrand. We 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'."

One possibility for the origin of the actual term is a simplified spelling of "Wi-Phy" or "Wireless Physical Network Layer".

The Wi-Fi Alliance themselves invoked the term 'Wireless Fidelity' with the marketing of a tag line, "The Standard for Wireless Fidelity," but later removed the tag from their marketing. The Wi-Fi Alliance now seems to discourage the propagation of the notion that 'Wi-Fi' stands for 'Wireless Fidelity', but it has been referred to as such by the Wi-Fi Alliance in White Papers currently held in their knowledge base:

"... a promising market for wireless fidelity (Wi-Fi) network equipment."

"A Short History of WLANs... The association created the Wi-Fi (Wireless Fidelity) logo to indicate that a product had been certified for interoperability."

See also

• Hotspot
• Access Point
• DTIM (Delivery Traffic Indication Message)
• Long Range Wi-Fi
• Switched mesh
• Public Safety Network
• Wireless security

References

Template:Wikinewshas

1. Comparing 802.11a, b, and g: Channels and Interference, Que Publishing, September 9, 2005.
2. Table A-2 Cisco
3. How Municipal WiFi Works
4. Reardon, Marguerite (2005-08-16). "New wireless record claimed". Cnet news. Retrieved 2007-01-04. {{cite web}}: Check date values in: |date= (help)
5. http://www.penmachine.com/techie/airport1400.html
6. Move to push Wi-Fi into Linux kernel, Techworld, 3 May 2006
7. Wireless LAN resources for Linux
8. DriverLoader website
9. Quick HOWTO : Ch13 : Linux Wireless Networking, Linux home networking
10. AirSnort home page
11. "Singapore teen faces 3 years' jail for tapping into another's wireless Internet", International Herald Tribune, November 10 2006
12. ^ Lean, Geoffrey (June 3, 2007). "Worried families ditch their Wi-Fi after watchdog voices health concerns". The Independent. Independent News and Media Limited. Retrieved 2007-06-04. {{cite news}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
13. BBC News: Wi-Fi health fears are 'unproven' Accessed 23 April 2007
15. See Teleclick, Boing Boing site and Wi-Fi Planet
16. Wi-Fi.org
17. Wi-Fi.org

External links

• Wi-Fi Alliance

Template:Link FA

• Articles with unsourced statements from January 2007
• Wi-Fi
• 2000s fads