Wi-Fi

From Wikipedia, the free encyclopedia

The five-layer TCP/IP model
5. Application layer
DHCP · DNS · FTP · Gopher · HTTP · IMAP4 · IRC · NNTP · XMPP · POP3 · RTP · SIP · SMTP · SNMP · SSH · TELNET · RPC · RTCP · RTSP · TLS (and SSL) · SDP · SOAP · GTP · STUN · NTP · (more)
4. Transport layer
TCP · UDP · DCCP · SCTP · RSVP · ECN · (more)
3. Network/internet layer
IP (IPv4 · IPv6) · OSPF · IS-IS · BGP · IPsec · ARP · RARP · RIP · ICMP · ICMPv6 · IGMP · (more)
2. Data link layer
802.11 (WLAN) · 802.16 · Wi-Fi · WiMAX · ATM · DTM · Token ring · Ethernet · FDDI · Frame Relay · GPRS · EVDO · HSPA · HDLC · PPP · PPTP · L2TP · ISDN · ARCnet · LLTD · (more)
1. Physical layer
Ethernet physical layer · RS-232 · SONET/SDH · G.709 · Optical fiber · Coaxial cable · Twisted pair · (more)
This box: view • talk • edit

Wi-Fi (IPA: /ˈwaɪfaɪ/) is the trade name for a popular wireless technology used in home networks, mobile phones, video games and more. Wi-Fi is supported by nearly every modern personal computer operating system and most advanced game consoles.

Contents 1 Purpose 2 Uses 3 Balancing effort, advantages and challenges 3.1 Operational advantages 3.2 Limitations 3.3 Reach 3.4 Threats to security 3.5 Population 3.6 Pollution 4 Hardware 4.1 Standard devices 4.2 Distance records 4.3 Embedded systems 5 Network security 6 History 7 City wide Wi-Fi 8 Origin and meaning of the term "Wi-Fi" 9 Wi-Fi Alliance 10 See also 11 References 12 External links

[edit] Purpose

The purpose of Wi-Fi is to hide complexity by enabling wireless access to applications and data, media and streams. The main aims of Wi-Fi are to:

• facilitate access to information
• ensure compatibility and coexistence
• eliminate cabling and wiring
• eliminate switches, adapters, plugs and connectors.

[edit] Uses

A Wi-Fi enabled device such as a PC, game console, cell phone, MP3 player or PDA can connect to the Internet when within range of a wireless network connected to the Internet. The coverage of one or more interconnected access points — called a hotspot — can comprise an area as small as a single room with wireless-opaque walls or as large as many square miles covered by overlapping access points. Wi-Fi technology has served to set up mesh networks, for example, in London.^[1] Both architectures can operate in community networks.

In addition to restricted use in homes and offices, Wi-Fi can make access publicly available at Wi-Fi hotspots provided either free of charge or to subscribers to various providers. Organizations and businesses such as airports, hotels and restaurants often provide free hotspots to attract or assist clients. Enthusiasts or authorities who wish to provide services or even to promote business in a given area sometimes provide free Wi-Fi access. Metropolitan-wide Wi-Fi (Muni-Fi) already has more than 300 projects in process.^[2]

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 can prove useful in consumer electronics and gaming applications.

When wireless networking technology first entered the market many problems ensued for consumers who could not rely on products from different vendors working together. The Wi-Fi Alliance began as a community to solve this issue — aiming to address the needs of the end-user and to allow the technology to mature. The Alliance created the branding Wi-Fi CERTIFIED to reassure consumers that products will interoperate with other products displaying the same branding.

Many consumer devices use Wi-Fi. Amongst others, personal computers can network to each other and connect to the Internet, mobile computers can connect to the Internet from any Wi-Fi hotspot, and digital cameras can transfer images wirelessly.

Routers which incorporate a DSL-modem or a cable-modem and a Wi-Fi access point, often set up in homes and other premises, provide Internet-access and internetworking to all devices connected (wirelessly or by cable) to them. One can also connect Wi-Fi devices in ad-hoc mode for client-to-client connections without a router.

As of 2007 Wi-Fi technology had spread widely within business and industrial sites. In business environments, just like other environments, increasing the number of Wi-Fi access-points provides redundancy, support for fast roaming and increased overall network-capacity by using more channels or by defining smaller cells. Wi-Fi enables wireless voice-applications (VoWLAN or WVOIP). Over the years, Wi-Fi implementations have moved toward "thin" access-points, with more of the network intelligence housed in a centralized network appliance, relegating individual access-points to the role of mere "dumb" radios. Outdoor applications may utilize true mesh topologies. As of 2007 Wi-Fi installations can provide a secure computer networking gateway, firewall, DHCP server, intrusion detection system, and other functions.

[edit] Balancing effort, advantages and challenges

As in all aspects of life and technology arguing advantages and disadvantages is a question of views and aspects. The baseline must be to balance cost and benefit. There is no addressing of advantages without addressing the aspect and view on the subject first.

[edit] Operational advantages

Wi-Fi allows LANs (Local Area Networks) 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.

As of 2007, wireless network adapters are built into most modern laptops. The price of chipsets for Wi-Fi continues to drop, making it an economical networking option included in ever more devices. Wi-Fi has become widespread in corporate infrastructures.

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 compatible. Wi-Fi is a global set of standards. Unlike mobile telephones, any standard Wi-Fi device will work anywhere in the world.

Wi-Fi is widely available in more than 220,000 public hotspots and tens of millions of homes and corporate and university campuses worldwide.^[3] WPA is not easily cracked if strong passwords are used and WPA2 encryption has no known weaknesses. New protocols for Quality of Service (WMM) make Wi-Fi more suitable for latency-sensitive applications (such as voice and video), and power saving mechanisms (WMM Power Save) improve battery operation.

[edit] Limitations

Spectrum assignments and operational limitations are not consistent worldwide. Most of Europe allows for an additional 2 channels beyond those permitted in the U.S. for the 2.4 GHz band. (1–13 vs. 1–11); Japan has one more on top of that (1–14). Europe, as of 2007, was essentially homogeneous in this respect. A very confusing aspect is the fact that a Wi-Fi signal actually occupies five channels in the 2.4 GHz band resulting in only three non-overlapped channels in the U.S.: 1, 6, 11, and three or four in Europe: 1, 5, 9, 13 can be used if all the equipment on a specific area can be granted not to use 802.11b at all, even as fallback or beacon. Equivalent isotropically radiated power (EIRP) in the EU is limited to 20 dBm (0.1 W).

[edit] Reach

Due to reach requirements for wireless LAN applications, power consumption is fairly high compared to some other low-bandwidth standards. Especially Zigbee and Bluetooth supporting wireless PAN applications refer to much lesser propagation range of <10m (ref. e.g. IEEE Std. 802.15.4 section 1.2 scope). Range is always making battery life a concern.

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 32 m (120 ft) indoors and 95 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 (directional) antennas can be several kilometres or more with line-of-sight.

Wi-Fi performance decreases roughly quadratically as the range increases at constant radiation levels.

[edit] Threats to security

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 this default is without any wireless security enabled, providing open wireless access to their LAN. To turn security on requires the user to configure the device, usually via a software graphical user interface (GUI). 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, such as a VPN or a secure web page. (See HTTPS/Secure Socket Layer.)

[edit] Population

Many 2.4 GHz 802.11b and 802.11g Access points default to the same channel on initial startup, contributing to congestion on certain channels. To change the channel of operation for an access point requires the user to configure the device. Yet, this default use of channels 1, 6 and 11 gives better performance than "advanced" users choosing channels 2, 5, 7 and 9 as "unused, free".

[edit] Pollution

Standardization is a process driven by market forces. Interoperability issues between non-Wi-Fi brands or proprietary deviations from the standard can still disrupt connections or lower throughput speeds on all user's devices that are within range, to include the non-Wi-Fi or proprietary product. Moreover, the usage of the ISM band in the 2.45 GHz range is also common to Bluetooth, WPAN-CSS, ZigBee and any new system will take its share.

Wi-Fi pollution, or an excessive number of 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, security cameras, Bluetooth devices and (in some countries) Amateur radio, video senders, cordless phones and baby monitors, all of which can cause significant additional interference. General guidance to those who suffer these forms of interference or network crowding is to migrate to a Wi-Fi 5 GHz product, (802.11a, or the newer 802.11n if it has 5 GHz support) as the 5 GHz band is relatively unused and there are many more channels available. This also requires users to set up the 5 GHz band to be the preferred network in the client and to configure each network band to a different name (SSID). It is also an issue when municipalities,^[4] or other large entities such as universities, seek to provide large area coverage. This openness is also important to the success and widespread use of 2.4 GHz Wi-Fi.

[edit] Hardware

[edit] Standard devices

A wireless access point connects a group of wireless devices to an adjacent wired LAN. An access point is similar to a network 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 adapters allow devices 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 routers integrate 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 network bridges connect 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.

Wireless range extenders or wireless repeaters 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 connected to any of the repeaters in the chain will have a throughput that is limited by the weakest link between the two nodes in the chain from which the connection originates to where the connection ends.

[edit] Distance records

Distance records (using non-standard devices) include 382 km (237 mi) in June 2007, held by Ermanno Pietrosemoli and EsLaRed of Venezuela, transferring about 3 MB of data between mountain tops of El Aguila and Platillon.^[5][6] The Swedish Space Agency transferred data 310 km (193 mi), using 6 watt amplifiers to reach an overhead stratospheric balloon. ^[7] However, striving for records does not comply with common license-free usage of WiFi equipment under regulated power level restrictions.

[edit] Embedded systems

Wi-Fi availability in the home is on the increase.^{[citation needed]} This extension of the Internet into the home space will increasingly be used for remote monitoring.^{[citation needed]} 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.^[8] This allows simple monitoring devices – for example, a portable ECG monitor hooked up to a patient in their 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 designers need minimal Wi-Fi knowledge to wireless-enable their products.

[edit] Network security

Main article: Piggybacking (internet access)

There is an ongoing search for optimizing between efforts, risks and benefits. As any common dissemination of information, also WiFi transmission may be subject of unwanted access.

During the early popular adoption of 802.11, providing open access points for anyone within range to use was encouraged to cultivate wireless community networks;^[9] particularly since people on average use only a fraction of their upstream bandwidth at any given time. Later, equipment manufacturers and mass-media advocated isolating users to a predetermined whitelist of authorized users—referred to as "securing" the access point.^{[dubious – discuss]}

Measures to deter unauthorized users include suppressing the AP's SSID broadcast, allowing only computers with known MAC addresses to join the network, and various encryption standards. Suppressed SSID and MAC filtering are ineffective security methods as the SSID is broadcast in the open in response to a client SSID query and a MAC address can easily be spoofed. If the eavesdropper has the ability to change his MAC address, then he can potentially join the network by spoofing an authorized address.

WEP encryption can protect against casual snooping, but may also produce a misguided sense of security since freely available tools such as AirSnort or aircrack can quickly recover WEP encryption keys. Once it has seen 5-10 million encrypted packets, AirSnort can determine the encryption password in under a second;^[10] newer tools such as aircrack-ptw can use Klein's attack to crack a WEP key with a 50% success rate using only 40,000 packets. The newer Wi-Fi Protected Access (WPA) and IEEE 802.11i (WPA2) encryption standards do not have any of the serious weaknesses of WEP encryption.

One serious issue with wireless network security is not just encryption, but access to the network (signal reception). With wired networking it is necessary to get past either a firewall or the security guard & locked doors. With wireless it is only necessary to get reception and spend as long as you want, comfortably out of (easy) reach of the network owner. Most business networks protect sensitive data and systems by attempting to disallow external access. Thus being able to get wireless reception (and thus possibly break the encryption) becomes an attack vector on the network as well.^[11]

Recreational logging and mapping of other people's access points has become known as wardriving. It is also common for people to use open (unencrypted) Wi-Fi networks as a free service, termed piggybacking. Indeed, many access points are intentionally installed without security turned on so that they can be used as a free service. These activities do not result in sanctions in most jurisdictions, however legislation and case law differ considerably across the world. A proposal to leave graffiti describing available services was called warchalking. In a Florida court case^{[citation needed]}, owner laziness was determined not to be a valid excuse.

Piggybacking is often unintentional. Most access points are configured without encryption by default, and operating systems such as Windows XP SP2 and Mac OS X may be configured to automatically connect to any available wireless network. 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 middle man when seeking a destination (see Man-in-the-middle attack). For example, a user could inadvertently use an insecure network to login to a website, thereby making the login credentials available to anyone listening, if the website is using an insecure protocol like HTTP, rather than a secure protocol like HTTPS.

[edit] 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. The regulations for unlicensed spread spectrum enabled the development of Wi-Fi, its onetime competitor HomeRF, Bluetooth, and many other products such as some types of cordless telephones.

Unlicensed spread spectrum was first made available in the US 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.^[12] The FCC action was proposed by Michael Marcus of the FCC staff in 1980 and the subsequent 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.^[13]

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, and 802.11a.

[edit] City wide Wi-Fi

Further information: Municipal wireless network

St. Cloud, Florida became the first city in the United States to offer city wide free Wi-Fi,^[14] although many others have plans to offer the service. Corpus Christi, Texas had offered free Wi-Fi until May 31, 2007 when the network was purchased by Earthlink.^[15] Philadelphia is also using Earthlink for its city wide Wi-Fi.^[16] New Orleans had free city wide Wi-Fi shortly after Hurricane Katrina.^[17] City wide Wi-Fi is available in nine cities in the UK, Newcastle Upon Tyne being the first UK city host, others include Leeds, Liverpool, Manchester, Norwich and London.^[18] Other cities, such as the Minneapolis metro area, have a large number of Wi-Fi hotspots so you can receive good signals anywhere, even if from different sources. In Europe, the City of Luxembourg has a city-wide Wi-Fi network.

In Latin America, Mexico City downtown has a public Wi-Fi network. Also, many public squares in towns of Puerto Rico are offering Wi-Fi Internet access.

As compared to Wireless Mesh, WiMax provides over 4 times the number of subcarriers over a variable bandwidth of 1 to 28 MHz. With more subcarriers and a variable length guard interval, the spectral efficiency has increased from 15% to 40% compared to Wireless Mesh. The error vector magnitude of Wireless Mesh is higher than WiMax. This makes WiMax have a longer range. Wireless Mesh transmits and receives functions on the same channel where as WiMax transmits and receives functions at a different channel and at a different time. In Wireless Mesh the output power is virtually fixed however in WiMax the devices closer to the base stations emit less output power whereas the ones further away emit maximum output power.

Wi-Fi can overpower WiMax if the city is meshed with hot spots. A very easy way to do it would be if mobile carriers integrate hot spots with their mobile base stations as WiMax chips are not as integrated as the Wi-Fi chips.

[edit] Origin and meaning of the term "Wi-Fi"

The term "Wi-Fi" suggests "Wireless Fidelity", comparing with the long-established audio recording term "High Fidelity" or "Hi-Fi", and "Wireless Fidelity" has often been used in an informal way, even by the Wi-Fi Alliance itself, but officially the term does not mean anything.

"Wi-Fi" was coined by a brand consulting firm called Interbrand Corporation that had been hired by the Alliance to determine a name that was "a little catchier than 'IEEE 802.11b Direct Sequence'."^[19][20][21]Interbrand invented "Wi-Fi" as simply a play-on-words with "Hi-Fi", as well as creating the yin yang style Wi-Fi logo.

The Wi-Fi Alliance initially complicated matters by stating that it actually stood for "Wireless Fidelity", as with the slogan "The Standard for Wireless Fidelity",^[20] but later removed the phrase from their marketing. The Wi-Fi Alliance's early White Papers still held in their knowledge base: "… a promising market for wireless fidelity (Wi-Fi) network equipment."^[22] and "A Short History of WLANs." The yin yang logo indicates that a product had been certified for interoperability.^[23]

The Alliance has since downplayed the connection to "Hi-Fi". Their official position is that it is merely a brand name that stands for nothing in particular, and they now discourage the use of the term "Wireless Fidelity".

[edit] Wi-Fi Alliance

Main article: Wi-Fi Alliance

The Alliance promotes standards with the aim of improving the interoperability of wireless local area network products based on the IEEE 802.11 standards. The Wi-Fi Alliance, a consortium of separate and independent companies, agrees on a set of common interoperable products based on the family of IEEE 802.11 standards.^[24] The Wi-Fi Alliance certifies products via a set of defined test-procedures to establish interoperability. Those manufacturers with membership of Wi-Fi Alliance and whose products pass these interoperability tests can mark their products and product packaging with the Wi-Fi logo.^[25]

[edit] See also

[edit] References

[edit] External links

• Wi-Fi Alliance

v • d • e Internet access methods Wired Dial-up · ISDN · DSL · Cable · Fiber optic · Power-line Wireless Wi-Fi · Bluetooth · DECT · WiBro · WiMAX · UMTS-TDD · HSPA · EV-DO · Satellite · IR