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This article is about the electronic protocol. For the ancient King of Denmark, see Harald Bluetooth.
Bluetooth is an industrial specification for wireless personal area networks (PANs). Bluetooth provides a way to connect and exchange information between devices such as mobile phones, laptops, personal computers, printers, digital cameras, and video game consoles over a secure, globally unlicensed short-range radio frequency. The Bluetooth specifications are developed and licensed by the Bluetooth Special Interest Group.
Uses
Bluetooth is a standard and communications protocol primarily designed for low power consumption, with a short range (power-class-dependent: 1 meter, 10 meters, 100 meters) based on low-cost transceiver microchips in each device.[1]
Bluetooth enables these devices to communicate with each other when they are in range. The devices use a radio communications system, so they do not have to be in line of sight of each other, and can even be in other rooms, as long as the received transmission is powerful enough.
It has to be noted that in most cases the effective range of class 2 devices is extended if they connect to a class 1 transceiver, compared to pure class 2 network. This is accomplished by higher sensitivity and transmitter power of the Class 1 device. The higher transmitter power of Class 1 device allows higher power to be received by the Class 2 device. Furthermore, higher sensitivity of Class 1 device allows reception of much lower transmitted power of the Class 2 devices. Thus, allowing operation of Class 2 devices at much higher distances.
Bluetooth profiles
Main article: Bluetooth profile
In order to use Bluetooth, a device must be compatible with certain Bluetooth profiles. These define the possible applications and uses of the technology.
List of applications
More prevalent applications of Bluetooth include:
Wireless control of and communication between a mobile phone and a hands-free headset. This was one of the earliest applications to become popular.
Wireless networking between PCs in a confined space and where little bandwidth is required.
Wireless communications with PC input and output devices, the most common being the mouse, keyboard and printer.
Transfer of files between devices with OBEX.
Transfer of contact details, calendar appointments, and reminders between devices with OBEX.
Replacement of traditional wired serial communications in test equipment, GPS receivers, medical equipment, bar code scanners, and traffic control devices.
For controls where infrared was traditionally used.
Sending small advertisements from Bluetooth enabled advertising hoardings to other, discoverable, Bluetooth devices.
Two seventh-generation game consoles, Nintendo's Wii[2] and Sony's PlayStation 3 use Bluetooth for their respective wireless controllers.
Dial-up internet access on personal computer or PDA using a data-capable mobile phone as a modem.
Bluetooth vs. Wi-Fi in networking
Bluetooth and Wi-Fi have slightly different applications in today's offices, homes, and on the move: setting up networks, printing, or transferring presentations and files from PDAs to computers. Both are versions of unlicensed spread spectrum technology.
Bluetooth differs from Wi-Fi in that the latter provides higher throughput and covers greater distances, but requires more expensive hardware and higher power consumption. They use the same frequency range, but employ different modulation techniques. While Bluetooth is a replacement for a variety of applications, Wi-Fi is a replacement only for local area network access. Bluetooth is often thought of as wireless USB, whereas Wi-Fi is wireless Ethernet, both operating at much lower bandwidth than the cable systems they are trying to replace. However, this analogy is not entirely accurate since any Bluetooth device can, in theory, host any other Bluetooth device—something that is not universal to USB devices, therefore it would resemble more a wireless FireWire.
Bluetooth
Bluetooth exists in many products, such as phones, printers, modems and headsets. The technology is useful when transferring information between two or more devices that are near each other in low-bandwidth situations. Bluetooth is commonly used to transfer sound data with phones (i.e. with a Bluetooth headset) or byte data with hand-held computers (transferring files).
Bluetooth simplifies the discovery and setup of services between devices. Bluetooth devices advertise all of the services they provide. This makes using services easier because there is no longer a need to setup network addresses or permissions as in many other networks.
Wi-Fi
Wi-Fi is more like traditional Ethernet networks, and requires configuration to set up shared resources, transmit files, and to set up audio links (for example, headsets and hands-free devices). It uses the same radio frequencies as Bluetooth, but with higher power resulting in a stronger connection. Wi-Fi is sometimes called "wireless Ethernet." This description is accurate as it also provides an indication of its relative strengths and weaknesses. Wi-Fi requires more setup, but is better suited for operating full-scale networks because it enables a faster connection, better range from the base station, and better security than Bluetooth.
Computer requirements
A personal computer must have a Bluetooth adapter in order to be able to communicate with other Bluetooth devices (such as mobile phones, mice and keyboards). While some desktop computers and most recent laptops come with a built-in Bluetooth adapter, others will require an external one in the form of a dongle.
Unlike its predecessor, IrDA, which requires a separate adapter for each device, Bluetooth allows multiple devices to communicate with a computer over a single adapter.
Operating system support
For more details on this topic, see Bluetooth stack.
Apple has supported Bluetooth since Mac OS X version 10.2 released in 2002.[3]
As for Microsoft platforms, Windows XP Service Pack 2 and later releases have native support for Bluetooth. Previous versions required the users to install their Bluetooth adapter's own drivers, which were not directly supported by Microsoft.[4] Microsoft's own Bluetooth dongles (that are packaged with their Bluetooth computer devices) have no external drivers and thus require at least Windows XP Service Pack 2.
Linux provides two Bluetooth stacks, with the BlueZ stack included with most Linux kernels. It was originally developed by Qualcomm and Affix. BlueZ supports all core Bluetooth protocols and layers.
NetBSD features Bluetooth support since its 4.0 release. Its Bluetooth stack has been ported to FreeBSD and OpenBSD as well.
Specifications and features
The Bluetooth specification was developed in 1994 by Jaap Haartsen and Sven Mattisson, who were working for Ericsson Mobile Platforms in Lund, Sweden.[5] The specification is based on frequency-hopping spread spectrum technology.
The specifications were formalized by the Bluetooth Special Interest Group (SIG), organised by Mohd Syarifuddin. The SIG was formally announced on May 20, 1998. Today it has a membership over 7000 companies worldwide. It was established by Ericsson, Sony Ericsson, IBM, Intel, Toshiba, and Nokia, and later joined by many other companies.
Bluetooth 1.0 and 1.0B
Versions 1.0 and 1.0B had many problems, and manufacturers had difficulty making their products interoperable. Versions 1.0 and 1.0B also included mandatory Bluetooth hardware device address (BD_ADDR) transmission in the Connecting process (rendering anonymity impossible at the protocol level), which was a major setback for certain services planned for use in Bluetooth environments.
Bluetooth 1.1
Ratified as IEEE Standard 802.15.1-2002.
Many errors found in the 1.0B specifications were fixed.
Added support for non-encrypted channels.
Received Signal Strength Indicator (RSSI).
Bluetooth 1.2
This version is backward-compatible with 1.1 and the major enhancements include the following:
Faster Connection and Discovery
Adaptive frequency-hopping spread spectrum (AFH), which improves resistance to radio frequency interference by avoiding the use of crowded frequencies in the hopping sequence.
Higher transmission speeds in practice, up to 721 kbit/s, as in 1.1.
Extended Synchronous Connections (eSCO), which improve voice quality of audio links by allowing retransmissions of corrupted packets.
Host Controller Interface (HCI) support for three-wire UART.
Ratified as IEEE Standard 802.15.1-2005.
Bluetooth 2.0
This version, specified on November 10, 2004, is backward-compatible with 1.1. The main enhancement is the introduction of an Enhanced Data Rate (EDR) of 3.0 Mbit/s. This has the following effects:[6]
Three times faster transmission speed—up to 10 times in certain cases (up to 2.1 Mbit/s).
Lower power consumption through a reduced duty cycle.
Simplification of multi-link scenarios due to more available bandwidth.
The practical data transfer rate is 2.1 megabits per second and the basic signalling rate is about 3 megabits per second.[7] The "Bluetooth 2.0 + EDR" specification given at the Bluetooth Special Interest Group (SIG) includes EDR and there is no specification "Bluetooth 2.0" as used by many vendors. The HTC TyTN pocket PC phone, shows "Bluetooth 2.0 without EDR" on its data sheet.[8] In many cases it is not clear whether a product claiming to support "Bluetooth 2.0" actually supports the EDR higher transfer rate.
Bluetooth 2.1
Bluetooth Core Specification Version 2.1 is fully backward-compatible with 1.1, and was adopted by the Bluetooth SIG on July 26, 2007.[6] This specification includes the following features:
Extended inquiry response: provides more information during the inquiry procedure to allow better filtering of devices before connection. This information includes the name of the device, a list of services the device supports, as well as other information like the time of day, and pairing information.
Sniff subrating: reduces the power consumption when devices are in the sniff low-power mode, especially on links with asymmetric data flows. Human interface devices (HID) are expected to benefit the most, with mouse and keyboard devices increasing the battery life by a factor of 3 to 10.
Encryption Pause Resume: enables an encryption key to be refreshed, enabling much stronger encryption for connections that stay up for longer than 23.3 hours (one Bluetooth day).
Secure Simple Pairing: radically improves the pairing experience for Bluetooth devices, while increasing the use and strength of security. It is expected that this feature will significantly increase the use of Bluetooth.[9]
NFC cooperation: automatic creation of secure Bluetooth connections when NFC radio interface is also available. For example, a headset should be paired with a Bluetooth 2.1 phone including NFC just by bringing the two devices close to each other (a few centimeters). Another example is automatic uploading of photos from a mobile phone or camera to a digital picture frame just by bringing the phone or camera close to the frame.[10][11]
Future of Bluetooth
Broadcast Channel: enables Bluetooth information points. This will drive the adoption of Bluetooth into mobile phones, and enable advertising models based around users pulling information from the information points, and not based around the object push model that is used in a limited way today.
Topology Management: enables the automatic configuration of the piconet topologies especially in scatternet situations that are becoming more common today. This should all be invisible to the users of the technology, while also making the technology just work.
Alternate MAC PHY: enables the use of alternative MAC and PHY's for transporting Bluetooth profile data. The Bluetooth Radio will still be used for device discovery, initial connection and profile configuration, however when lots of data needs to be sent, the high speed alternate MAC PHY's will be used to transport the data. This means that the proven low power connection models of Bluetooth are used when the system is idle, and the low power per bit radios are used when lots of data needs to be sent.
QoS improvements: enable audio and video data to be transmitted at a higher quality, especially when best effort traffic is being transmitted in the same piconet.
High-speed Bluetooth
On 28 March 2006, the Bluetooth Special Interest Group announced its selection of the WiMedia Alliance Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) version of UWB for integration with current Bluetooth wireless technology.
UWB integration will create a version of Bluetooth wireless technology with a high-speed/high-data-rate option. This new version of Bluetooth technology will meet the high-speed demands of synchronizing and transferring large amounts of data, as well as enabling high-quality video and audio applications for portable devices, multi-media projectors and television sets, and wireless VOIP.
At the same time, Bluetooth technology will continue catering to the needs of very low power applications such as mice, keyboards, and mono headsets, enabling devices to select the most appropriate physical radio for the application requirements, thereby offering the best of both worlds.
Bluetooth 3.0
The next version of Bluetooth after v2.1, code-named Seattle (the version number of which is TBD) has many of the same features, but is most notable for plans to adopt ultra-wideband (UWB) radio technology. This will allow Bluetooth use over UWB radio, enabling very fast data transfers of up to 480 Mbit/s, while building on the very low-power idle modes of Bluetooth.
Ultra Low Power Bluetooth
On June 12, 2007, Nokia and Bluetooth SIG announced that Wibree will be a part of the Bluetooth specification as an ultra low power Bluetooth technology.[12] Expected use cases include watches displaying Caller ID information, sports sensors monitoring your heart rate during exercise, as well as medical devices. The Medical Devices Working Group is also creating a medical devices profile and associated protocols to enable this market.
Technical information
Communication and connection
A master Bluetooth device can communicate with up to seven devices. This network group of up to eight devices is called a piconet.
A piconet is an ad-hoc computer network, using Bluetooth technology protocols to allow one master device to interconnect with up to seven active devices. Up to 255 further devices can be inactive, or parked, which the master device can bring into active status at any time.
At any given time, data can be transferred between the master and one other device, however, the devices can switch roles and the slave can become the master at any time. The master switches rapidly from one device to another in a round-robin fashion. (Simultaneous transmission from the master to multiple other devices is possible, but not used much.)
Bluetooth specification allows connecting two or more piconets together to form a scatternet, with some devices acting as a bridge by simultaneously playing the master role and the slave role in one piconet. These devices are planned for 2007.
Many USB Bluetooth adapters are available, some of which also include an IrDA adapter. Older (pre-2003) Bluetooth adapters, however, have limited services, offering only the Bluetooth Enumerator and a less-powerful Bluetooth Radio incarnation. Such devices can link computers with Bluetooth, but they do not offer much in the way of services that modern adapters do.
Setting up connections
Any Bluetooth device will transmit the following information on demand:
Device name.
Device class.
List of services.
Technical information, for example, device features, manufacturer, Bluetooth specification used, clock offset.
Any device may perform an inquiry to find other devices to connect to, and any device can be configured to respond to such inquiries. However, if the device trying to connect knows the address of the device, it always responds to direct connection requests and transmits the information shown in the list above if requested. Use of device services may require pairing or acceptance by its owner, but the connection itself can be initiated by any device and held until it goes out of range. Some devices can be connected to only one device at a time, and connecting to them prevents them from connecting to other devices and appearing in inquiries until they disconnect from the other device.
Every device has a unique 48-bit address. However these addresses are generally not shown in inquiries. Instead, friendly Bluetooth names are used, which can be set by the user. This name appears when another user scans for devices and in lists of paired devices.
Most phones have the Bluetooth name set to the manufacturer and model of the phone by default. Most phones and laptops show only the Bluetooth names and special programs that are required to get additional information about remote devices. This can be confusing as, for example, there could be several phones in range named T610 (see Bluejacking).
Pairing
Pairs of devices may establish a trusted relationship by learning (by user input) a shared secret known as a passkey. A device that wants to communicate only with a trusted device can cryptographically authenticate the identity of the other device. Trusted devices may also encrypt the data that they exchange over the airwaves so that no one can listen in. The encryption can, however, be turned off, and passkeys are stored on the device file system, not on the Bluetooth chip itself. Since the Bluetooth address is permanent, a pairing is preserved, even if the Bluetooth name is changed. Pairs can be deleted at any time by either device. Devices generally require pairing or prompt the owner before they allow a remote device to use any or most of their services. Some devices, such as Sony Ericsson phones, usually accept OBEX business cards and notes without any pairing or prompts.
Certain printers and access points allow any device to use its services by default, much like unsecured Wi-Fi networks. Pairing algorithms are sometimes manufacturer-specific for transmitters and receivers used in applications such as music and entertainment.
Air interface
The protocol operates in the license-free ISM band at 2.4-2.4835 GHz. To avoid interfering with other protocols that use the 2.45 GHz band, the Bluetooth protocol divides the band into 79 channels (each 1 MHz wide) and changes channels up to 1600 times per second. Implementations with versions 1.1 and 1.2 reach speeds of 723.1 kbit/s. Version 2.0 implementations feature Bluetooth Enhanced Data Rate (EDR) and reach 2.1 Mbit/s. Technically, version 2.0 devices have a higher power consumption, but the three times faster rate reduces the transmission times, effectively reducing power consumption to half that of 1.x devices (assuming equal traffic load).
Security
Overview
Bluetooth implements confidentiality, authentication and key derivation with custom algorithms based on the SAFER+ block cipher. In Bluetooth, key generation is generally based on a Bluetooth PIN, which must be entered into both devices. This procedure might be modified if one of the devices has a fixed PIN, e.g. for headsets or similar devices with a restricted user interface. During pairing, an initialization key or master key is generated, using the E22 algorithm.[13] The E0 stream cipher is used for encrypting packets, granting confidentiality and is based on a shared cryptographic secret, namely a previously generated link key or master key. Those keys, used for subsequent encryption of data sent via the air interface, rely on the Bluetooth PIN, which has been entered into one or both devices.
An overview of Bluetooth vulnerabilities exploits has been published by Andreas Becker.[14]
Bluejacking
Bluejacking allows phone users to send business cards anonymously using Bluetooth wireless technology. Bluejacking does NOT involve the removal or alteration of any data from the device. These business cards often have a clever or flirtatious message rather than the typical name and phone number. Bluejackers often look for the receiving phone to ping or the user to react. They then send another, more personal message to that device. Once again, in order to carry out a bluejacking, the sending and receiving devices must be within range of each other, which is typically 10 meters for most mobile devices. Devices that are set in non-discoverable mode are not susceptible to bluejacking. However, the Linux application Redfang claims to find non-discoverable Bluetooth devices.
History of security concerns
2003
In November 2003, Ben and Adam Laurie from A.L. Digital Ltd. discovered that serious flaws in Bluetooth security may lead to disclosure of personal data.[15] It should be noted, however, that the reported security problems concerned some poor implementations of Bluetooth, rather than the protocol itself.
In a subsequent experiment, Martin Herfurt from the trifinite.group was able to do a field-trial at the CeBIT fairgrounds, showing the importance of the problem to the world. A new attack called BlueBug was used for this experiment.[16] This is one of a number of concerns that have been raised over the security of Bluetooth communications.
2004
In 2004 the first purported virus using Bluetooth to spread itself among mobile phones appeared on the Symbian OS.[17] The virus was first described by Kaspersky Lab and requires users to confirm the installation of unknown software before it can propagate. The virus was written as a proof-of-concept by a group of virus writers known as "29A" and sent to anti-virus groups. Thus, it should be regarded as a potential (but not real) security threat to Bluetooth or Symbian OS since the virus has never spread in the wild.
In August 2004, a world-record-setting experiment (see also Bluetooth sniping) showed that the range of Class 2 Bluetooth radios could be extended to 1.78 km (1.08 mile) with directional antennas and signal amplifiers.[18] This poses a potential security threat because it enables attackers to access vulnerable Bluetooth-devices from a distance beyond expectation. The attacker must also be able to receive information from the victim to set up a connection. No attack can be made against a Bluetooth device unless the attacker knows its Bluetooth address and which channels to transmit on.
2005
In April 2005, Cambridge University security researchers published results of their actual implementation of passive attacks against the PIN-based pairing between commercial Bluetooth devices, confirming the attacks to be practicably fast and the Bluetooth symmetric key establishment method to be vulnerable. To rectify this vulnerability, they carried out an implementation which showed that stronger, asymmetric key establishment is feasible for certain classes of devices, such as mobile phones.[19]
In June 2005, Yaniv Shaked and Avishai Wool published a paper describing both passive and active methods for obtaining the PIN for a Bluetooth link. The passive attack allows a suitably equipped attacker to eavesdrop on communications and spoof, if the attacker was present at the time of initial pairing. The active method makes use of a specially constructed message that must be inserted at a specific point in the protocol, to make the master and slave repeat the pairing process. After that, the first method can be used to crack the PIN. This attack's major weakness is that it requires the user of the devices under attack to re-enter the PIN during the attack when the device prompts them to. Also, this active attack probably requires custom hardware, since most commercially available Bluetooth devices are not capable of the timing necessary.[20]
In August 2005, police in Cambridgeshire, England, issued warnings about thieves using Bluetooth-enabled phones to track other devices left in cars. Police are advising users to ensure that any mobile networking connections are de-activated if laptops and other devices are left in this way.[21]
2006
In April 2006, researchers from Secure Network and F-Secure published a report that warns of the large number of devices left in a visible state, and issued statistics on the spread of various Bluetooth services and the ease of spread of an eventual Bluetooth worm.[22]
In October 2006, at the Luxemburgish Hack.lu Security Conference, Kevin Finistere and Thierry Zoller demonstrated and released a remote root shell via Bluetooth on Mac OSX 10.3.9 and 10.4. They also demonstrated the first Bluetooth PIN and Linkkeys cracker, which is based on the research of Wool and Shaked.
Health concerns
Bluetooth uses the microwave radio frequency spectrum in the 2.4 GHz to 2.4835 GHz range. Maximum power output from a Bluetooth radio is 100 mW, 2.5 mW, and 1 mW for Class 1, Class 2, and Class 3 devices respectively, which puts Class 1 at roughly the same level as mobile phones, and the other two classes much lower.[23] Accordingly, Class 2 and Class 3 Bluetooth devices are considered less of a potential hazard than mobile phones, and Class 1 may be comparable to that of mobile phones.
Origin of the name and the logo
Bluetooth was named after a late tenth century king, Harald Bluetooth, King of Denmark and Norway. He is known for his unification of previously warring tribes from Denmark (including now Swedish Scania, where the Bluetooth technology was invented), and Norway. Bluetooth likewise was intended to unify different technologies, such as personal computers and mobile phones.[24]
The name may have been inspired less by the historical Harald than the loose interpretation of him in The Long Ships by Frans Gunnar Bengtsson, a Swedish Viking-inspired novel.
The Bluetooth logo merges the Germanic runes analogous to the modern Latin letter H and B: (for Harald Bluetooth) (Hagall) and (Berkanan) merged together, forming a bind rune.
Bluetooth Special Interest Group
Initially (circa 1996-1997) the technology later known as Bluetooth was an Ericsson-internal project named multi-communicator link or short MC link. Cooperation with Intel was initiated in 1997.[25]
In 1998, Ericsson, IBM, Intel, Toshiba, and Nokia, formed a consortium and adopted the code name Bluetooth for their proposed open specification. In December 1999, 3Com, Lucent Technologies, Microsoft, and Motorola joined the initial founders as the promoter of Bluetooth Special Interest Group (SIG). Since that time, Lucent Technologies transferred their membership to their spinoff Agere Systems, and 3Com has left the promoter group. Agere Systems was later merged with LSI Corporation and left the Bluetooth promoters group in August 2007.
The Bluetooth Special Interest Group (SIG) is a privately held, not-for-profit trade association with headquarters in Bellevue, Washington. As of September 2007 the SIG is composed of over 9,000 member companies that are leaders in the telecommunications, computing, automotive, music, apparel, industrial automation, and network industries, and a small group of dedicated staff in Hong Kong, Sweden, and the USA. SIG members drive the development of Bluetooth wireless technology, and implement and market the technology in their products varying from mobile phones to printers. The Bluetooth SIG itself does not make, manufacture, or sell Bluetooth enabled products.
References
^ How Bluetooth Technology Works. Bluetooth SIG. Retrieved on 2008-02-01.
^ Wii Controller. Bluetooth SIG. Retrieved on 2008-02-01.
^ Apple (2002-07-17). "Apple Introduces "Jaguar," the Next Major Release of Mac OS X". Press release. Retrieved on 2008-02-04.
^ Network Protection Technologies. Changes to Functionality in Microsoft Windows XP Service Pack 2. Microsoft Technet. Retrieved on 2008-02-01.
^ "The Bluetooth Blues", Information Age, 2001-05-24. Retrieved on 2008-02-01.
^ a b Specification Documents. Bluetooth SIG. Retrieved on 2008-02-04.
^ Guy Kewney (2004-11-16). High speed Bluetooth comes a step closer: enhanced data rate approved. Newswireless.net. Retrieved on 2008-02-04.
^ HTC TyTN Specification (PDF). HTC. Retrieved on 2008-02-04.
^ (2006-08-03). "Simple Pairing Whitepaper" (PDF). Version V10r00. Bluetooth SIG. Retrieved on 2007-02-01.
^ Michael Oryl. "Bluetooth 2.1 Offers Touch Based Pairing, Reduced Power Consumption", MobileBurn, 2007-03-15. Retrieved on 2008-02-04.
^ Taoufik Ghanname. "How NFC can to speed Bluetooth transactions-today", Wireless Net DesignLine, 2007-02-14. Retrieved on 2008-02-04.
^ Nokia (2007-06-12). "Wibree forum merges with Bluetooth SIG" (PDF). Press release. Retrieved on 2008-02-04.
^ Juha T. Vainio (2000-05-25). Bluetooth Security. Helsinki University of Technology. Archived from the original on 2006-05-19. Retrieved on 2008-02-04.
^ Andreas Becker (2007-08-16). "Bluetooth Security & Hacks" (PDF). Ruhr-Universität Bochum. Retrieved on 2007-10-10.
^ Bluetooth. The Bunker. Retrieved on 2007-02-01.
^ BlueBug. Trifinite.org. Retrieved on 2007-02-01.
^ John Oates. "Virus attacks mobiles via Bluetooth", The Register, 2004-06-15. Retrieved on 2007-02-01.
^ Long Distance Snarf. Trifinite.org. Retrieved on 2007-02-01.
^ Ford-Long Wong, Frank Stajano, Jolyon Clulow (2005-04). "Repairing the Bluetooth pairing protocol" (PDF). University of Cambridge Computer Laboratory. Retrieved on 2007-02-01.
^ Yaniv Shaked, Avishai Wool (2005-05-02). "Cracking the Bluetooth PIN". School of Electrical Engineering Systems, Tel Aviv University. Retrieved on 2007-02-01.
^ "Phone pirates in seek and steal mission", Cambridge Evening News. Retrieved on 2008-02-04. Archived from the original on 2007-07-17.
^ (2006-05). "Going Around with Bluetooth in Full Safety" (PDF). F-Secure. Retrieved on 2008-02-04.
^ M. Hietanen, T. Alanko (2005-10). Occupational Exposure Related to Radiofrequency Fields from Wireless Communication Systems (PDF). XXVIIIth General Assembly of URSI - Proceedings. Union Radio-Scientifique Internationale. Retrieved on 2007-04-19.
^ About the Bluetooth SIG. Bluetooth SIG. Retrieved on 2008-02-01.
^ Så ska Bluetooth överleva 10 år till. Ny Teknik. Retrieved on 2008-02-27.
External links
http://www.bluetooth.org — Bluetooth Special Interest Group Site (includes specifications)
http://www.bluetooth.com — Official Bluetooth site aimed at users
Categories: Bluetooth Networking standards Mobile computers
วันพฤหัสบดีที่ 28 กุมภาพันธ์ พ.ศ. 2551
Network hub
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A network hub or concentrator is a device for connecting multiple twisted pair or fiber optic Ethernet devices together, making them act as a single network segment. Hubs work at the physical layer (layer 1) of the OSI model, and the term layer 1 switch is often used interchangeably with hub. The device is thus a form of multiport repeater. Network hubs are also responsible for forwarding a jam signal to all ports if it detects a collision.
Hubs also often come with a BNC and/or AUI connector to allow connection to legacy 10BASE2 or 10BASE5 network segments. The availability of low-priced network switches has largely rendered hubs obsolete but they are still seen in older installations and more specialized applications.
Technical information
A hubbed Ethernet network behaves like a shared-medium, that is, only one device can successfully transmit at a time and each host remains responsible for collision detection and retransmission. With 10BASE-T and 100BASE-T links (which generally account for most or all of the ports on a hub) there are separate pairs for transmit and receive but they are used in half duplex mode in which they still effectively behave like shared medium links (See 10BASE-T for the pins specifications)
A network hub, or repeater, is a fairly unsophisticated broadcast device. Hubs do not manage any of the traffic that comes through them, and any packet entering any port is broadcast out on every other port (other than the port of entry). Since every packet is being sent out through every other port, packet collisions result--which greatly impedes the smooth flow of traffic.
The need for hosts to be able to detect collisions limits the number of hubs and the total size of the network. For 10 Mbit/s networks, up to 5 segments (4 hubs) are allowed between any two end stations. For 100 Mbit/s networks, the limit is reduced to 3 segments (2 hubs) between any two end stations, and even that is only allowed if the hubs are of the low delay variety. Some hubs have special (and generally manufacturer specific) stack ports allowing them to be combined in a way that allows more hubs than simple chaining through Ethernet cables, but even so a large Fast Ethernet network is likely to require switches to avoid the chaining limits of hubs.
Most hubs detect typical problems, such as excessive collisions on individual ports, and partition the port, disconnecting it from the shared medium. Thus, hub-based Ethernet is generally more robust than coaxial cable-based Ethernet, where a misbehaving device can disable the entire segment. Even if not partitioned automatically, a hub makes troubleshooting easier because status lights can indicate the possible problem source or, as a last resort, devices can be disconnected from a hub one at a time much more easily than a coaxial cable. They also remove the need to troubleshoot faults on a huge cable with multiple taps.
Dual speed hubs
In their early days, Fast Ethernet switches were relatively expensive . However, hubs suffered from the problem that as simple repeaters they could only support a single speed. Whilst normal PCs with expansion slots could be easily upgraded to Fast Ethernet with a new network card, computers with less common expansion mechanisms, or no expansion bus at all, and other equipment, such as printers, could be expensive or impossible to upgrade. Therefore, a compromise between a hub and a switch appeared known as a "dual speed hub".
Such a device essentially consisted of two hubs (one of each speed) and a two port bridge between them. Devices were connected to the appropriate hub automatically based on their speed and the bridge handled inter-speed traffic. Since the bridge only had two ports and only one of those needed to be 100Mbps it could be much simpler and cheaper than a full fast ethernet switch. Such devices have been rendered obsolete by the decreasing cost of fast ethernet switches.
Uses
Historically, the main reason for purchasing hubs rather than switches was price. This has largely been eliminated by reductions in the price of switches, but hubs can still be useful in special circumstances:
A protocol analyzer connected to a switch does not always receive all the desired packets since the switch separates the ports into different segments. Connecting the protocol analyzer to a hub allows it to see all the traffic on the segment. (Expensive switches can be configured to allow one port to listen in on traffic on another port. This is called port mirroring. However, these cost much more than a hub.)
Some computer clusters require each member computer to receive all of the traffic going to the cluster. A hub will do this naturally; using a switch requires implementing special tricks.
When a switch is accessible for end users to make connections, for example, in a conference room, an inexperienced or careless user (or saboteur) can bring down the network by connecting two ports together, causing a loop. This can be prevented by using a hub, where a loop will break other users on the hub, but not the rest of the network. (It can also be prevented by buying switches that can detect and deal with loops, for example by implementing the Spanning Tree Protocol.)
A cheap hub with a 10BASE2 port is probably the cheapest and easiest way to connect devices that only support 10BASE2 to a modern network (cheap switches don't tend to come with 10BASE2 ports). The same goes for linking in an old thicknet network segment using an AUI port on a hub (individual devices that were intended for thicknet can be linked to modern Ethernet by using an AUI-10BASE-T transceiver).
External links
Hub Reference
Retrieved from "http://en.wikipedia.org/wiki/Network_hub"
Categories: Ethernet Networking hardware Physical layer protocols
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A network hub or concentrator is a device for connecting multiple twisted pair or fiber optic Ethernet devices together, making them act as a single network segment. Hubs work at the physical layer (layer 1) of the OSI model, and the term layer 1 switch is often used interchangeably with hub. The device is thus a form of multiport repeater. Network hubs are also responsible for forwarding a jam signal to all ports if it detects a collision.
Hubs also often come with a BNC and/or AUI connector to allow connection to legacy 10BASE2 or 10BASE5 network segments. The availability of low-priced network switches has largely rendered hubs obsolete but they are still seen in older installations and more specialized applications.
Technical information
A hubbed Ethernet network behaves like a shared-medium, that is, only one device can successfully transmit at a time and each host remains responsible for collision detection and retransmission. With 10BASE-T and 100BASE-T links (which generally account for most or all of the ports on a hub) there are separate pairs for transmit and receive but they are used in half duplex mode in which they still effectively behave like shared medium links (See 10BASE-T for the pins specifications)
A network hub, or repeater, is a fairly unsophisticated broadcast device. Hubs do not manage any of the traffic that comes through them, and any packet entering any port is broadcast out on every other port (other than the port of entry). Since every packet is being sent out through every other port, packet collisions result--which greatly impedes the smooth flow of traffic.
The need for hosts to be able to detect collisions limits the number of hubs and the total size of the network. For 10 Mbit/s networks, up to 5 segments (4 hubs) are allowed between any two end stations. For 100 Mbit/s networks, the limit is reduced to 3 segments (2 hubs) between any two end stations, and even that is only allowed if the hubs are of the low delay variety. Some hubs have special (and generally manufacturer specific) stack ports allowing them to be combined in a way that allows more hubs than simple chaining through Ethernet cables, but even so a large Fast Ethernet network is likely to require switches to avoid the chaining limits of hubs.
Most hubs detect typical problems, such as excessive collisions on individual ports, and partition the port, disconnecting it from the shared medium. Thus, hub-based Ethernet is generally more robust than coaxial cable-based Ethernet, where a misbehaving device can disable the entire segment. Even if not partitioned automatically, a hub makes troubleshooting easier because status lights can indicate the possible problem source or, as a last resort, devices can be disconnected from a hub one at a time much more easily than a coaxial cable. They also remove the need to troubleshoot faults on a huge cable with multiple taps.
Dual speed hubs
In their early days, Fast Ethernet switches were relatively expensive . However, hubs suffered from the problem that as simple repeaters they could only support a single speed. Whilst normal PCs with expansion slots could be easily upgraded to Fast Ethernet with a new network card, computers with less common expansion mechanisms, or no expansion bus at all, and other equipment, such as printers, could be expensive or impossible to upgrade. Therefore, a compromise between a hub and a switch appeared known as a "dual speed hub".
Such a device essentially consisted of two hubs (one of each speed) and a two port bridge between them. Devices were connected to the appropriate hub automatically based on their speed and the bridge handled inter-speed traffic. Since the bridge only had two ports and only one of those needed to be 100Mbps it could be much simpler and cheaper than a full fast ethernet switch. Such devices have been rendered obsolete by the decreasing cost of fast ethernet switches.
Uses
Historically, the main reason for purchasing hubs rather than switches was price. This has largely been eliminated by reductions in the price of switches, but hubs can still be useful in special circumstances:
A protocol analyzer connected to a switch does not always receive all the desired packets since the switch separates the ports into different segments. Connecting the protocol analyzer to a hub allows it to see all the traffic on the segment. (Expensive switches can be configured to allow one port to listen in on traffic on another port. This is called port mirroring. However, these cost much more than a hub.)
Some computer clusters require each member computer to receive all of the traffic going to the cluster. A hub will do this naturally; using a switch requires implementing special tricks.
When a switch is accessible for end users to make connections, for example, in a conference room, an inexperienced or careless user (or saboteur) can bring down the network by connecting two ports together, causing a loop. This can be prevented by using a hub, where a loop will break other users on the hub, but not the rest of the network. (It can also be prevented by buying switches that can detect and deal with loops, for example by implementing the Spanning Tree Protocol.)
A cheap hub with a 10BASE2 port is probably the cheapest and easiest way to connect devices that only support 10BASE2 to a modern network (cheap switches don't tend to come with 10BASE2 ports). The same goes for linking in an old thicknet network segment using an AUI port on a hub (individual devices that were intended for thicknet can be linked to modern Ethernet by using an AUI-10BASE-T transceiver).
External links
Hub Reference
Retrieved from "http://en.wikipedia.org/wiki/Network_hub"
Categories: Ethernet Networking hardware Physical layer protocols
Wi-Fi
From Wikipedia, the free encyclopedia
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The five-layer TCP/IP model
5. Application layer
DHCP · DNS · FTP · Gopher · HTTP · IMAP4 · IRC · NNTP · XMPP · POP3 · SIP · SMTP · SNMP · SSH · TELNET · RPC · RTCP · RTSP · TLS · SDP · SOAP · GTP · STUN · NTP · (more)
4. Transport layer
TCP · UDP · DCCP · SCTP · RTP · RSVP · (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 · (more)
1. Physical layer
Ethernet physical layer · Modems · PLC · SONET/SDH · G.709 · Optical fiber · Coaxial cable · Twisted pair · (more)
Wi-Fi (pronounced wye fye, IPA: /ˈwaɪfaɪ/), a wireless-technology brand owned by the Wi-Fi Alliance, promotes standards with the aim of improving the interoperability of wireless local area network products based on the IEEE 802.11 standards. Common applications for Wi-Fi include Internet and VoIP phone access, gaming, and network connectivity for consumer electronics such as televisions, DVD players, and digital cameras.
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.[1] 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.[2]
Wi-Fi technologies have gone through several generations since their inception in 1998. The Microsoft Windows, Apple Mac OS X and open source Unix and Linux operating systems support Wi-Fi to different extents.
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.[3] Both architectures can operate in community networks.[citation needed]
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 WiFi (Muni-Fi) already has more than 300 projects in process.[4]
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.
Advantages
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.
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 even more devices. Wi-Fi has become widespread in corporate infrastructures, which also helps with the deployment of RFID technology that can piggyback on Wi-Fi.[5]
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 mobile telephones, any standard Wi-Fi device will work anywhere in the world.
Wi-Fi is widely available in more than 250,000[citation needed] public hotspots and tens of millions of homes and corporate and university campuses worldwide. 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.
Disadvantages
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 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 four in Europe: 1, 5, 9, 13. 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, such as 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 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.)
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.
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 also decreases exponentially as the range increases.
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 can cause significant additional interference. General guidance to those who suffer these forms of interference or network crowding is to migrate to a WiFi 5 GHz product, (802.11a or the newer 802.11n IF it has 5GHz/11a 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,[6] 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.
Interoperability issues between non WiFi brands or proprietary deviations from the standard can disrupt connections or lower throughput speeds on all user's devices that are within range, to include the non-WiFi or proprietary product.
Standard devices
Wireless access points 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 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.
Aerials and 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
Distance records include:
June 2007: 382 km (237 mi) is held by Ermanno Pietrosemoli and EsLaRed of Venezuela, transferring about 3 MB of data between mountain tops of El Aguila and Platillon12.
Swedish space agency:310 km (193 mi), but using 6 watt amplifiers to reach an overhead stratospheric balloon.[citation needed]
Embedded systems
Embedded serial to WiFi module
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 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.
Unintended and intended use by outsiders
Main article: Piggybacking (internet 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;[7] 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]
Wikinews has related news:
Florida man charged with stealing WiFi
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 will determine the encryption password in under a second[8]; 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.
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. The universal rule is a Wi-Fi Access Point that has not turned on its security is a service that welcomes its free use, while an access point that has turned its security on does not. The burden is on the access point owner to properly configure and control the access to his internet connection. 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.
Wi-Fi and amateur radio
In the U.S., Canada, Australia and Europe, a portion of the 2.4 GHz Wi-Fi radio spectrum is also allocated to amateur radio users. In the U.S., 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.
Question of health risks
Main article: Wireless electronic devices and health
The UK's Health Protection Agency considers there is no consistent evidence of harm from the low power transmissions of Wi-Fi equipment. Consensus amongst scientists is that there is no evidence of harm, and the continuing calls for more research into the effects on human health remain limited. However, in September 2007, Germany's Environment Ministry announced that its citizens should minimise their exposure to radiation from Wi-Fi by choosing conventional wired connections,[9] without any evidence and contrary to current internationally accepted safety criteria. Dr Michael Clark, of the Health Protection Agency, says published research on mobile phones and masts does not add up to an indictment of Wi-Fi:
All the expert reviews done here and abroad indicate that there is unlikely to be a health risk from wireless networks. … When we have conducted measurements in schools, typical exposures from Wi-Fi are around 20 millionths of the international guideline levels of exposure to radiation. As a comparison, a child on a mobile phone receives up to 50 percent of guideline levels. So a year sitting in a classroom near a wireless network is roughly equivalent to 20 minutes on a mobile. If Wi-Fi should be taken out of schools, then the mobile phone network should be shut down, too—and FM radio and TV, as the strength of their signals is similar to that from Wi-Fi in classrooms.[10]
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 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.[11] 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.
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.
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,[12] 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.[13] Philadelphia is also using Earthlink for its city wide Wi-Fi.[14] New Orleans had free city wide Wi-Fi shortly after Hurricane Katrina.[15] City wide Wi-Fi is available in nine cities in the UK, including Leeds, Manchester and London.[16] 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.
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 conclusion that "Wi-Fi" stands for "Wireless Fidelity".[17][18][19] According to 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 Belanger's words,
Wi-Fi and the yin yang style logo were invented by Interbrand. We [the founding members of the Wireless Ethernet Compatibility Alliance, now called as the Wi-Fi Alliance] 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'.[20]
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."[21] and "A Short History of WLANs." The association created the Wi-Fi logo to indicate that a product had been certified for interoperability.[22]
See also
Electronics Portal
Wikibooks has a book on the topic of
Nets, Webs and the Information Infrastructure
Hotspot
Wireless access point
DTIM (Delivery Traffic Indication Message)
Long-range Wi-Fi
Switched mesh
Public Safety Network
Wireless security
Evil twin phishing
Comparison of wifi handhelds
Nintendo Wi-Fi Connection
Wi-Fi router This page links here and is a redirect with possibilities. You can help by eliminating the redirect command in the redirecting page and expanding it.
iwconfig
Wireless tools for Linux
References
Wikinews has Wi-fi news articles:
Microsoft Pushing Community Wi-Fi
Google formally submits bid to provide free WiFi in San Francisco
Google launches free city wide Wi-Fi in Mountain View, California
^ Wi-Fi Alliance - Get to Know the Alliance. www.wi-fi.org. Retrieved on 2007-11-08.
^ Wi-Fi Alliance - Certified Products. certifications.wi-fi.org. Retrieved on 2007-11-08.
^ Switch on for Square Mile wi-fi. news.bbc.co.uk. Retrieved on 2007-11-08.
^ Muni Wireless
^ Making Business Sense of Real Time Location Systems (RTLS), RFID Radio
^ How Municipal WiFi Works
^ NoCat's goal is to bring you Infinite Bandwidth Everywhere for Free
^ AirSnort home page
^ Germany warns citizens to avoid using Wi-Fi
^ "Wi-fi: should we be worried?", The Times. Retrieved on 2007-09-16.
^ Authorization of Spread Spectrum Systems Under Parts 15 and 90 of the FCC Rules and Regulations (TXT). Federal Communications Commission (June 18, 1985). Retrieved on 2007-08-31.
^ Small Florida Town the First City to Implement FREE Wi-Fi Citywide
^ Corpus Christi WiFi News
^ Update: EarthLink selected for Philadelphia Wi-Fi network
^ Big Easy Gets Free Wi-Fi Network
^ City-wide wi-fi rolls out in UK
^ What is the True Meaning of Wi-Fi?. Teleclick. Retrieved on 2007-08-31.
^ WiFi isn't short for "Wireless Fidelity". Boing Boing. Retrieved on 2007-08-31.
^ Wireless Fidelity' Debunked. Wi-Fi Planet. Retrieved on 2007-08-31.
^ [1] December 2007
^ Enabling the Future of Wi-Fi® Public Access. Wi-Fi.org. Retrieved on 2007-08-31.
^ Securing Wi-Fi Networks with Today's Technologies. Wi-Fi.org. Retrieved on 2007-08-31.
External links
WiFi at the Open Directory Project
Wi-Fi Alliance
[hide]
v • d • eInternet 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
Jump to: navigation, search
The five-layer TCP/IP model
5. Application layer
DHCP · DNS · FTP · Gopher · HTTP · IMAP4 · IRC · NNTP · XMPP · POP3 · SIP · SMTP · SNMP · SSH · TELNET · RPC · RTCP · RTSP · TLS · SDP · SOAP · GTP · STUN · NTP · (more)
4. Transport layer
TCP · UDP · DCCP · SCTP · RTP · RSVP · (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 · (more)
1. Physical layer
Ethernet physical layer · Modems · PLC · SONET/SDH · G.709 · Optical fiber · Coaxial cable · Twisted pair · (more)
Wi-Fi (pronounced wye fye, IPA: /ˈwaɪfaɪ/), a wireless-technology brand owned by the Wi-Fi Alliance, promotes standards with the aim of improving the interoperability of wireless local area network products based on the IEEE 802.11 standards. Common applications for Wi-Fi include Internet and VoIP phone access, gaming, and network connectivity for consumer electronics such as televisions, DVD players, and digital cameras.
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.[1] 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.[2]
Wi-Fi technologies have gone through several generations since their inception in 1998. The Microsoft Windows, Apple Mac OS X and open source Unix and Linux operating systems support Wi-Fi to different extents.
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.[3] Both architectures can operate in community networks.[citation needed]
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 WiFi (Muni-Fi) already has more than 300 projects in process.[4]
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.
Advantages
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.
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 even more devices. Wi-Fi has become widespread in corporate infrastructures, which also helps with the deployment of RFID technology that can piggyback on Wi-Fi.[5]
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 mobile telephones, any standard Wi-Fi device will work anywhere in the world.
Wi-Fi is widely available in more than 250,000[citation needed] public hotspots and tens of millions of homes and corporate and university campuses worldwide. 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.
Disadvantages
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 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 four in Europe: 1, 5, 9, 13. 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, such as 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 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.)
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.
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 also decreases exponentially as the range increases.
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 can cause significant additional interference. General guidance to those who suffer these forms of interference or network crowding is to migrate to a WiFi 5 GHz product, (802.11a or the newer 802.11n IF it has 5GHz/11a 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,[6] 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.
Interoperability issues between non WiFi brands or proprietary deviations from the standard can disrupt connections or lower throughput speeds on all user's devices that are within range, to include the non-WiFi or proprietary product.
Standard devices
Wireless access points 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 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.
Aerials and 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
Distance records include:
June 2007: 382 km (237 mi) is held by Ermanno Pietrosemoli and EsLaRed of Venezuela, transferring about 3 MB of data between mountain tops of El Aguila and Platillon12.
Swedish space agency:310 km (193 mi), but using 6 watt amplifiers to reach an overhead stratospheric balloon.[citation needed]
Embedded systems
Embedded serial to WiFi module
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 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.
Unintended and intended use by outsiders
Main article: Piggybacking (internet 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;[7] 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]
Wikinews has related news:
Florida man charged with stealing WiFi
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 will determine the encryption password in under a second[8]; 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.
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. The universal rule is a Wi-Fi Access Point that has not turned on its security is a service that welcomes its free use, while an access point that has turned its security on does not. The burden is on the access point owner to properly configure and control the access to his internet connection. 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.
Wi-Fi and amateur radio
In the U.S., Canada, Australia and Europe, a portion of the 2.4 GHz Wi-Fi radio spectrum is also allocated to amateur radio users. In the U.S., 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.
Question of health risks
Main article: Wireless electronic devices and health
The UK's Health Protection Agency considers there is no consistent evidence of harm from the low power transmissions of Wi-Fi equipment. Consensus amongst scientists is that there is no evidence of harm, and the continuing calls for more research into the effects on human health remain limited. However, in September 2007, Germany's Environment Ministry announced that its citizens should minimise their exposure to radiation from Wi-Fi by choosing conventional wired connections,[9] without any evidence and contrary to current internationally accepted safety criteria. Dr Michael Clark, of the Health Protection Agency, says published research on mobile phones and masts does not add up to an indictment of Wi-Fi:
All the expert reviews done here and abroad indicate that there is unlikely to be a health risk from wireless networks. … When we have conducted measurements in schools, typical exposures from Wi-Fi are around 20 millionths of the international guideline levels of exposure to radiation. As a comparison, a child on a mobile phone receives up to 50 percent of guideline levels. So a year sitting in a classroom near a wireless network is roughly equivalent to 20 minutes on a mobile. If Wi-Fi should be taken out of schools, then the mobile phone network should be shut down, too—and FM radio and TV, as the strength of their signals is similar to that from Wi-Fi in classrooms.[10]
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 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.[11] 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.
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.
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,[12] 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.[13] Philadelphia is also using Earthlink for its city wide Wi-Fi.[14] New Orleans had free city wide Wi-Fi shortly after Hurricane Katrina.[15] City wide Wi-Fi is available in nine cities in the UK, including Leeds, Manchester and London.[16] 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.
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 conclusion that "Wi-Fi" stands for "Wireless Fidelity".[17][18][19] According to 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 Belanger's words,
Wi-Fi and the yin yang style logo were invented by Interbrand. We [the founding members of the Wireless Ethernet Compatibility Alliance, now called as the Wi-Fi Alliance] 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'.[20]
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."[21] and "A Short History of WLANs." The association created the Wi-Fi logo to indicate that a product had been certified for interoperability.[22]
See also
Electronics Portal
Wikibooks has a book on the topic of
Nets, Webs and the Information Infrastructure
Hotspot
Wireless access point
DTIM (Delivery Traffic Indication Message)
Long-range Wi-Fi
Switched mesh
Public Safety Network
Wireless security
Evil twin phishing
Comparison of wifi handhelds
Nintendo Wi-Fi Connection
Wi-Fi router This page links here and is a redirect with possibilities. You can help by eliminating the redirect command in the redirecting page and expanding it.
iwconfig
Wireless tools for Linux
References
Wikinews has Wi-fi news articles:
Microsoft Pushing Community Wi-Fi
Google formally submits bid to provide free WiFi in San Francisco
Google launches free city wide Wi-Fi in Mountain View, California
^ Wi-Fi Alliance - Get to Know the Alliance. www.wi-fi.org. Retrieved on 2007-11-08.
^ Wi-Fi Alliance - Certified Products. certifications.wi-fi.org. Retrieved on 2007-11-08.
^ Switch on for Square Mile wi-fi. news.bbc.co.uk. Retrieved on 2007-11-08.
^ Muni Wireless
^ Making Business Sense of Real Time Location Systems (RTLS), RFID Radio
^ How Municipal WiFi Works
^ NoCat's goal is to bring you Infinite Bandwidth Everywhere for Free
^ AirSnort home page
^ Germany warns citizens to avoid using Wi-Fi
^ "Wi-fi: should we be worried?", The Times. Retrieved on 2007-09-16.
^ Authorization of Spread Spectrum Systems Under Parts 15 and 90 of the FCC Rules and Regulations (TXT). Federal Communications Commission (June 18, 1985). Retrieved on 2007-08-31.
^ Small Florida Town the First City to Implement FREE Wi-Fi Citywide
^ Corpus Christi WiFi News
^ Update: EarthLink selected for Philadelphia Wi-Fi network
^ Big Easy Gets Free Wi-Fi Network
^ City-wide wi-fi rolls out in UK
^ What is the True Meaning of Wi-Fi?. Teleclick. Retrieved on 2007-08-31.
^ WiFi isn't short for "Wireless Fidelity". Boing Boing. Retrieved on 2007-08-31.
^ Wireless Fidelity' Debunked. Wi-Fi Planet. Retrieved on 2007-08-31.
^ [1] December 2007
^ Enabling the Future of Wi-Fi® Public Access. Wi-Fi.org. Retrieved on 2007-08-31.
^ Securing Wi-Fi Networks with Today's Technologies. Wi-Fi.org. Retrieved on 2007-08-31.
External links
WiFi at the Open Directory Project
Wi-Fi Alliance
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