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25 janvier 2011 2 25 /01 /janvier /2011 05:12

In telecommunications, wireless communication may be used to transfer information over short distances (a few meters as in television remote control) or long distances (thousands or millions of kilometers for radio communications). The term is often shortened to "wireless"   (Dell XPS M1210 Batteryhttp://www.hdd-shop.co.uk .

It encompasses various types of fixed, mobile, and portable two-way radios, cellular telephones, personal digital assistants (PDAs), and wireless networking. Other examples of wireless technology include GPS units, garage door openers and or garage doors, wireless computer mice, keyboards and headsets,satellite television and cordless telephones (Dell Studio XPS 1640 Battery)  .

Wireless operations permits services, such as long range communications, that are impossible or impractical to implement with the use of wires. The term is commonly used in the telecommunications industry to refer to telecommunications systems (e.g. radio transmitters and receivers, remote controls, computer networks, network terminals, etc   (Dell Vostro 1710 Battery)      .

which use some form of energy (e.g. radio frequency (RF), infrared light, laser light, visible light, acoustic energy, etc.) to transfer information without the use of wires. Information is transferred in this manner over both short and long distances   Dell KM958 battery .

he term "wireless" has become a generic and all-encompassing word used to describe communications in which electromagnetic waves or RF (rather than some form of wire) carry a signal over part or the entire communication path. Common examples of wireless equipment in use today include  Dell Studio 1555 battery :

  • Professional LMR (Land Mobile Radio) and SMR (Specialized Mobile Radio) typically used by business, industrial and Public Safety entities.
  • Consumer Two way radio including FRS Family Radio Service, GMRS (General Mobile Radio Service) and Citizens band ("CB") radios  Sony VGP-BPS13 battery .
  • The Amateur Radio Service (Ham radio).
  • Consumer and professional Marine VHF radios.
  • Cellular telephones and pagers: provide connectivity for portable and mobile applications, both personal and business  Sony VGP-BPS13/B battery .
  • Global Positioning System (GPS): allows drivers of cars and trucks, captains of boats and ships, and pilots of aircraft to ascertain their location anywhere on earth.
  • Cordless computer peripherals: the cordless mouse is a common example; keyboards and printers can also be linked to a computer via wireless        Sony VGP-BPS13/S battery .
  • Cordless telephone sets: these are limited-range devices, not to be confused with cell phones.
  • Satellite television: Is broadcast from satellites in geostationary orbit. Typical services use digital broadcasting to provide multiple channels to viewers        Sony VGP-BPS13A/B battery .
  • Wireless gaming: new gaming consoles allow players to interact and play in the same game regardless of whether they are playing on different consoles. Players can chat, send text messages as well as record sound and send it to their friends. Controllers also use wireless technology        Sony VGP-BPS13B/B battery .
  • They do not have any cords but they can send the information from what is being pressed on the controller to the main console which then processes this information and makes it happen in the game. All of these steps are completed in milliseconds       Sony VGP-BPL9 battery .

Wireless networks

Wireless networking (i.e. the various types of unlicensed 2.4 GHz WiFi devices) is used to meet many needs. Perhaps the most common use is to connect laptop users who travel from location to location   Sony VGP-BPS13B/B battery .

Another common use is for mobile networks that connect via satellite. A wireless transmission method is a logical choice to network a LAN segment that must frequently change locations. The following situations justify the use of wireless technology   Sony VGP-BPL15 battery :

  • To span a distance beyond the capabilities of typical cabling,
  • To provide a backup communications link in case of normal network failure,
  • To link portable or temporary workstations        Dell Inspiron E1505 battery ,
  • To overcome situations where normal cabling is difficult or financially impractical, or
  • To remotely connect mobile users or networks.

Modes

  • radio frequency communication      Dell Latitude E6400 battery ,
  • microwave communication, for example long-range line-of-sight via highly directional antennas, or short-range communication, or
  • infrared (IR) short-range communication, for example from remote controls or via Infrared Data Association (IrDA).

Applications may involve point-to-point communication, point-to-multipoint communication, broadcasting, cellular networks and other wireless networks   HP Pavilion dv6000 Battery .

Cordless

The term "wireless" should not be confused with the term "cordless", which is generally used to refer to powered electrical or electronic devices that are able to operate from a portable power source (e.g. a battery pack) without any cable or cord to limit the mobility of the cordless device through a connection to the mains power supply  SONY VAIO VGN-FZ Battery .

Some cordless devices, such as cordless telephones, are also wireless in the sense that information is transferred from the cordless telephone to the telephone's base unit via some type of wirelesscommunications link. This has caused some disparity in the usage of the term "cordless", for example in Digital Enhanced Cordless Telecommunications   SONY VAIO VGN-FZ18 Battery .

History

Photophone

The world's first, wireless telephone conversation occurred in 1880, when Alexander Graham Bell and Charles Sumner Tainter invented and patented the photophone, a telephone that conducted audio conversations wirelessly over modulated light beams (which are narrow projections of electromagnetic waves)  SONY VAIO VGN-FZ21E Battery .

In that distant era when utilities did not yet exist to provide electricity, and lasers had not even been conceived of in science fiction, there were no practical applications for their invention, which was highly limited by the availability of both sunlight and good weather       SONY VAIO VGN-FW21E Battery .

Similar to free space optical communication, the photophone also required a clear line of sight between its transmitter and its receiver. It would be several decades before the photophone's principles found their first practical applications in military communications and later in fiber-optic communications  SONY VAIO VGN-NR11S/S Battery .

Early wireless work

David E. Hughes, eight years before Hertz's experiments, transmitted radio signals over a few hundred yards by means of a clockwork keyed transmitter      SONY VAIO VGN-NR11M/S Battery .

As this was before Maxwell's work was understood, Hughes' contemporaries dismissed his achievement as mere "Induction". In 1885, T. A. Edison used a vibrator magnet for induction transmission. In 1888, Edison deployed a system of signaling on the Lehigh Valley Railroad        SONY VAIO VGN-NR11Z/S Battery .

In 1891, Edison obtained the wireless patent for this method using inductance (U.S. Patent 465,971).

In the history of wireless technology, the demonstration of the theory of electromagnetic waves by Heinrich Hertz in 1888 was important       SONY VAIO VGN-NR11Z/T Battery .

The theory of electromagnetic waves was predicted from the research of James Clerk Maxwell and Michael Faraday. Hertz demonstrated that electromagnetic waves could be transmitted and caused to travel through space at straight lines and that they were able to be received by an experimental apparatus        Sony VAIO VGN-FZ21E Battery .

The experiments were not followed up by Hertz. Jagadish Chandra Bose around this time developed an early wireless detection device and helped increase the knowledge of millimeter length electromagnetic waves.Practical applications of wireless radio communication and radio remote control technology were implemented by later inventors, such as Nikola Tesla  Sony VAIO VGN-FW21E Battery .

Radio

The term "wireless" came into public use to refer to a radio receiver or transceiver (a dual purpose receiver and transmitter device), establishing its usage in the field of wireless telegraphy early on; now the term is used to describe modern wireless connections such as in cellular networks and wireless broadband Internet  Sony VAIO VGN-NR11S/S Battery .

It is also used in a general sense to refer to any type of operation that is implemented without the use of wires, such as "wireless remote control" or "wireless energy transfer", regardless of the specific technology (e.g. radio, infrared, ultrasonic) used. Guglielmo Marconi andKarl Ferdinand Braun were awarded the 1909 Nobel Prize for Physics for their contribution to wireless telegraphy  Sony VAIO VGN-NR11Z/S Battery .

The electromagnetic spectrum

Light, colors, AM and FM radio, and electronic devices make use of the electromagnetic spectrum. In the US, the frequencies that are available for use for communication are treated as a public resource and are regulated by the Federal Communications Commission  Sony VAIO VGN-NR11M/S Battery .

This determines which frequency ranges can be used for what purpose and by whom. In the absence of such control or alternative arrangements such as a privatized electromagnetic spectrum, chaos might result if, for example, airlines didn't have specific frequencies to work under and an amateur radio operator were interfering with the pilot's ability to land an airplane  Sony VAIO VGN-NR11Z/T Battery .

Wireless communication spans the spectrum from 9 kHz to 300 GHz. (Also see Spectrum management)

Applications of wireless technology

Security systems

Wireless technology may supplement or replace hard wired implementations in security systems for homes or office buildings  SONY VAIO VGN-FZ180E Battery .

Cellular telephone (phones and modems)

Perhaps the best known example of wireless technology is the cellular telephone and modems. These instruments use radio waves to enable the operator to make phone calls from many locations worldwide       SONY VAIO VGN-FZ220E Battery .

They can be used anywhere that there is a cellular telephone site to house the equipment that is required to transmit and receive the signal that is used to transfer both voice and data to and from these instruments.

Wi-Fi

Wi-Fi is a wireless local area network that enables portable computing devices to connect easily to the Internet  SONY VAIO VGN-FZ340E Battery .

Standardized as IEEE 802.11 a,b,g,n, Wi-Fi approaches speeds of some types of wiredEthernet. Wi-Fi hot spots have been popular over the past few years. Some businesses charge customers a monthly fee for service, while others have begun offering it for free in an effort to increase the sales of their goods      SONY VAIO VGN-FZ430E Battery .

Wireless energy transfer

Wireless energy transfer is a process whereby electrical energy is transmitted from a power source to an electrical load that does not have a built-in power source, without the use of interconnecting wires        SONY VAIO VGN-FZ460E Battery .

Computer interface devices

Answering the call of customers frustrated with cord clutter, many manufactures of computer peripherals turned to wireless technology to satisfy their consumer base          SONY VAIO VGN-FZ480E Battery .

Originally these units used bulky, highly limited transceivers to mediate between a computer and a keyboard and mouse, however more recent generations have used small, high quality devices, some even incorporating Bluetooth. These systems have become so ubiquitous that some users have begun complaining about a lack of wired peripherals   SONY VAIO VGN-FZ4000 Battery .

Wireless devices tend to have a slightly slower response time than their wired counterparts, however the gap is decreasing. Initial concerns about the security of wireless keyboards have also been addressed with the maturation of the technology   SONY VAIO VGN-FZ31E Battery .

In computer networking, a wireless access point (WAP) is a device that allows wireless devices to connect to a wired network using Wi-Fi, Bluetooth or related standards. The WAP usually connects to a router (via a wired network), and can relay data between the wireless devices (such as computers or printers) and wired devices on the network   SONY VAIO VGN-FZ31B Battery .

Industrial grade WAPs are rugged, with a metal cover and a DIN rail mount. During operations they can tolerate a wider temperature range, high humidity and exposure to water, dust, and oil. Wireless security includes: WPA-PSK, WPA2, IEEE 802.1x/RADIUS, WDS, WEP, TKIP, and CCMP (AES) encryption    SONY VAIO VGN-FZ31J Battery .

Unlike home consumer models, industrial wireless access points can also be used as a bridge, router, or a client.

Introduction

Prior to wireless networks, setting up a computer network in a business, home, or school often required running many cables through walls and ceilings in order to deliver network access to all of the network-enabled devices in the building   SONY VAIO VGN-FZ31M Battery .

With the advent of the Wireless Access Point, network users are now able to add devices that access the network with few or no cables. Today's WAPs are built to support a standard for sending and receiving data using radio frequencies rather than cabling. Those standards, and the frequencies they use are defined by the IEEE       SONY VAIO VGN-FZ31Z Battery .

Most WAPs use IEEE 802.11 standards.

Common WAP Applications

A typical corporate use involves attaching several WAPs to a wired network and then providing wireless access to the office LAN. The wireless access points are managed by a WLAN Controller which handles automatic adjustments to RF power, channels, authentication, and security      SONY VAIO VGN-FZ38M Battery .

Further, controllers can be combined to form a wireless mobility group to allow inter-controller roaming. The controllers can be part of a mobility domain to allow clients access throughout large or regional office locations. This saves the clients time and administrators overhead because it can automatically re-associate or re-authenticate        SONY VGP-BPS8 Battery .

A Hot Spot is a common public application of WAPs, where wireless clients can connect to the Internet without regard for the particular networks to which they have attached for the moment. The concept has become common in large cities, where a combination of coffeehouses       SONY VGP-BPS13 Battery ,

libraries, as well as privately owned open access points, allow clients to stay more or less continuously connected to the Internet, while moving around. A collection of connected Hot Spots can be referred to as a lily-pad network.

The majority of WAPs are used in Home wireless networks SONY VGP-BPS13/S Battery .

Home networks generally have only one WAP to connect all the computers in a home. Most are wireless routers, meaning converged devices that include the WAP, a router, and, often, an ethernet switch. Many also include a broadband modem   SONY VGP-BPS13A/B Battery .

In places where most homes have their own WAP within range of the neighbors' WAP, it's possible for technically savvy people to turn off their encryption and set up a wireless community network, creating an intra-city communication network without the need of wired networks       SONY VGP-BPS13B/B Battery .

A WAP may also act as the network's arbitrator, negotiating when each nearby client device can transmit. However, the vast majority of currently installedIEEE 802.11 networks do not implement this, using a distributed pseudo-random algorithm called CSMA/CA instead       SONY VGP-BPS13A/S Battery .

Wireless Access Point vs. Ad Hoc Network

Some people confuse Wireless Access Points with Wireless Ad Hoc networks. An Ad Hoc network uses a connection between two or more devices without using a wireless access point: the devices communicate directly when in range    SONY VGP-BPS13AS Battery.

An Ad Hoc network is used in situations such as a quick data exchange or a multiplayer LAN game because setup is easy and does not require an access point. Due to its peer-to-peer layout, Ad Hoc connections are similar to Bluetooth ones and are generally not recommended for a permanent installation    Dell Inspiron 1320n Battery .

Internet access via Ad Hoc networks, using features like Windows' Internet Connection Sharing, may work well with a small number of devices that are close to each other, but Ad Hoc networks don't scale well. Internet traffic will converge to the nodes with direct internet connection, potentially congesting these nodes      Dell Inspiron 1464 Battery .

For internet-enabled nodes, Access Points have a clear advantage, with the possibility of having multiple access points connected by a wired LAN.

Limitations

One IEEE 802.11 WAP can typically communicate with 30 client systems located within a radius of 100 m    Dell Inspiron 1564 Battery .

However, the actual range of communication can vary significantly, depending on such variables as indoor or outdoor placement, height above ground, nearby obstructions, other electronic devices that might actively interfere with the signal by broadcasting on the same frequency, type of antenna, the current weather, operating radio frequency, and the power output of devices  Dell Inspiron 1764 Battery .

Network designers can extend the range of WAPs through the use of repeaters and reflectors, which can bounce or amplify radio signals that ordinarily would go un-received. In experimental conditions, wireless networking has operated over distances of several hundred kilometers     Dell Studio 1450 Battery .

Most jurisdictions have only a limited number of frequencies legally available for use by wireless networks. Usually, adjacent WAPs will use different frequencies (Channels) to communicate with their clients in order to avoid interference between the two nearby systems      Dell Studio 1457 Battery .

Wireless devices can "listen" for data traffic on other frequencies, and can rapidly switch from one frequency to another to achieve better reception. However, the limited number of frequencies becomes problematic in crowded downtown areas with tall buildings using multiple WAPs       Dell Latitude D610 Battery .

In such an environment, signal overlap becomes an issue causing interference, which results in signal droppage and data errors.

Wireless networking lags behind wired networking in terms of increasing bandwidth and throughput   Toshiba NB100 Battery .

While (as of 2010) typical wireless devices for the consumer market can reach speeds of 300 Mbit/s (megabits per second) (IEEE 802.11n) or 54 Mbit/s (IEEE 802.11g), wired hardware of similar cost reaches 1000 Mbit/s (Gigabit Ethernet). One impediment to increasing the speed of wireless communications comes from Wi-Fi's use of a shared communications medium  Toshiba Satellite M65 battery ,

so a WAP is only able to use somewhat less than half the actual over-the-air rate for data throughput. Thus a typical 54 MBit/s wireless connection actually carries TCP/IP data at 20 to 25 Mbit/s. Users of legacy wired networks expect faster speeds, and people using wireless connections keenly want to see the wireless networks catch up  Toshiba Satellite M60 battery .

By 2008 draft 802.11n based access points and client devices have already taken a fair share of the market place but with inherent problems integrating products from different vendors.

Security

Wireless access has special security considerations        Dell Latitude D830 Battery .

Many wired networks base the security on physical access control, trusting all the users on the local network, but if wireless access points are connected to the network, anyone on the street or in the neighboring office could connect.

The most common solution is wireless traffic encryption. Modern access points come with built-in encryption   Dell Latitude D620 Battery .

The first generation encryption scheme WEP proved easy to crack; the second and third generation schemes, WPA and WPA2, are considered secure if a strong enough password or passphrase is used.

Some WAPs support hotspot style authentication using RADIUS and other authentication servers  Dell Inspiron Mini 10 Battery .

A wireless local area network (WLAN) links two or more devices using some wireless distribution method (typically spread-spectrum or OFDM radio), and usually providing a connection through an access point to the wider internet. This gives users the mobility to move around within a local coverage area and still be connected to the network  Sony VGN-FW11S Battery .

Wireless LANs have become popular in the home due to ease of installation, and the increasing popularity of laptop computers. Public businesses such as coffee shops and malls have begun to offer wireless access to their customers; often for free. Large wireless network projects are being put up in many major cities       Sony VGN-FW11M Battery :

New York City, for instance, has begun a pilot program to cover all five boroughs of the city with wireless Internet access.

In 1970 Norman Abramson, a professor at the University of Hawaii, developed the world’s first wireless computer communication network, ALOHAnet, using low-cost ham-like radios        Sony VGN-FW139E/H battery .

The system included seven computers deployed over four islands to communicate with the central computer on the Oahu Island without using phone lines.

"In 1979, F.R. Gfeller and U. Bapst published a paper in the IEEE Proceedings reporting an experimental wireless local area network using diffused infrared communications         Dell Latitude E5400 Battery .

Shortly thereafter, in 1980, P. Ferrert reported on an experimental application of a single code spread spectrumradio for wireless terminal communications in the IEEE National Telecommunications Conference. In 1984, a comparison between infrared and CDMA spread spectrum communications for wireless office information networks was published by Kaveh Pahlavan in IEEE Computer Networking Symposium which appeared later in the IEEE Communication Society Magazine       Dell Latitude E4200 Battery .

In May 1985, the efforts of Marcus led the FCC to announce experimental ISM bands for commercial application of spread spectrum technology. Later on, M. Kavehrad reported on an experimental wireless PBX system using code division multiple access      Dell Inspiron 300M Battery .

These efforts prompted significant industrial activities in the development of a new generation of wireless local area networks and it updated several old discussions in the portable and mobile radio industry.

The first generation of wireless data modems was developed in the early 1980s by amateur radio operators, who commonly referred to this as packet radio        Dell Vostro A840 Battery .

They added a voice band data communication modem, with data rates below 9600-bit/s, to an existing short distance radio system, typically in the two meter amateur band. The second generation of wireless modems was developed immediately after the FCC announcement in the experimental bands for non-military use of the spread spectrum technology   Dell Studio 1737 battery .

These modems provided data rates on the order of hundreds of kbit/s. The third generation of wireless modem then aimed at compatibility with the existing LANs with data rates on the order of Mbit/s. Several companies developed the third generation products with data rates above 1 Mbit/s and a couple of products had already been announced by the time of the first IEEE Workshop on Wireless LANs       Dell Inspiron E1505 battery ."

"The first of the IEEE Workshops on Wireless LAN was held in 1991. At that time early wireless LAN products had just appeared in the market and the IEEE 802.11 committee had just started its activities to develop a standard for wireless LANs. The focus of that first workshop was evaluation of the alternative technologies          Dell RM791 battery .

By 1996, the technology was relatively mature, a variety of applications had been identified and addressed and technologies that enable these applications were well understood. Chip sets aimed at wireless LAN implementations and applications, a key enabling technology for rapid market growth, were emerging in the market      Dell XPS M1530 battery .

Wireless LANs were being used in hospitals, stock exchanges, and other in building and campus settings for nomadic access, point-to-point LAN bridges, ad-hoc networking, and even larger applications through internetworking. The IEEE 802.11 standard and variants and alternatives      Dell XPS M2010 battery ,

such as the wireless LAN interoperability forum and the European HiperLAN specification had made rapid progress, and the unlicensed PCS Unlicensed Personal Communications Services and the proposed SUPERNet, later on renamed as U-NII, bands also presented new opportunities       Acer Aspire One battery ."

WLAN hardware was initially so expensive that it was only used as an alternative to cabled LAN in places where cabling was difficult or impossible. Early development included industry-specific solutions and proprietary protocols, but at the end of the 1990s these were replaced by standards          Toshiba Satellite P10 Battery ,

primarily the various versions of IEEE 802.11 (commonly misunderstood as equal to trademark Wi-Fi of Wi-Fi_Alliance). An alternative ATM-like 5 GHz standardized technology, HiperLAN/2, has so far not succeeded in the market, and with the release of the faster 54 Mbit/s 802.11a (5 GHz) and 802.11g (2.4 GHz) standards, almost certainly never will   SONY VGN-FZ210CE Battery .

Stations

All components that can connect into a wireless medium in a network are referred to as stations.

All stations are equipped with wireless network interface cards (WNICs).

Wireless stations fall into one of two categories: access points, and clients          Dell Precision M70 Battery .

Access points (APs), normally routers, are base stations for the wireless network. They transmit and receive radio frequencies for wireless enabled devices to communicate with.

Wireless clients can be mobile devices such as laptops, personal digital assistants, IP phones and other smartphones, or fixed devices such as desktops and workstations that are equipped with a wireless network interface           Toshiba Satellite L305 Battery .

Basic service set

The basic service set (BSS) is a set of all stations that can communicate with each other.

There are two types of BSS: Independent BSS (also referred to as IBSS), and infrastructure BSS   Toshiba Satellite T4900 Battery .

Every BSS has an identification (ID) called the BSSID, which is the MAC address of the access point servicing the BSS.

An independent BSS (IBSS) is an ad-hoc network that contains no access points, which means they can not connect to any other basic service set              Toshiba PA3399U-2BRS battery .

An infrastructure can communicate with other stations not in the same basic service set by communicating through access points.

Extended service set

An extended service set (ESS) is a set of connected BSSes. Access points in an ESS are connected by a distribution system. Each ESS has an ID called the SSID which is a 32-byte (maximum) character string         Toshiba Satellite A200 Battery .

Distribution system

A distribution system (DS) connects access points in an extended service set. The concept of a DS can be used to increase network coverage through roaming between cells           Toshiba Satellite 1200 Battery .

DS can be wired or wireless. Current wireless distribution systems are mostly based on WDS or MESH protocols, though other systems are in use, too.

Peer-to-peer

Peer-to-Peer or ad-hoc wireless LAN

An ad-hoc network is a network where stations communicate only peer to peer (P2P)          Toshiba Satellite M300 Battery .

There is no base and no one gives permission to talk. This is accomplished using the Independent Basic Service Set (IBSS).

A peer-to-peer (P2P) network allows wireless devices to directly communicate with each other. Wireless devices within range of each other can discover and communicate directly without involving central access points  SONY VGP-BPS13A/Q Battery .

This method is typically used by two computers so that they can connect to each other to form a network.

If a signal strength meter is used in this situation, it may not read the strength accurately and can be misleading, because it registers the strength of the strongest signal, which may be the closest computer        SONY VGP-BPS13A/Q Battery .

IEEE 802.11 define the physical layer (PHY) and MAC (Media Access Control) layers based on CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance). The 802.11 specification includes provisions designed to minimize collisions, because two mobile units may both be in range of a common access point, but out of range of each other        SONY VGP-BPS13B/Q Battery .

The 802.11 has two basic modes of operation: Ad hoc mode enables peer-to-peer transmission between mobile units. Infrastructure mode in which mobile units communicate through an access point that serves as a bridge to a wired network infrastructure is the more common wireless LAN application the one being covered       SONY VGP-BPS13B/Q Battery .

Since wireless communication uses a more open medium for communication in comparison to wired LANs, the 802.11 designers also included shared-key encryption mechanisms: Wired Equivalent Privacy (WEP), Wi-Fi Protected Access (WPA, WPA2), to secure wireless computer networks        SONY VGP-BPS13/Q Battery .

Bridge

A bridge can be used to connect networks, typically of different types. A wireless Ethernet bridge allows the connection of devices on a wired Ethernet network to a wireless network. The bridge acts as the connection point to the Wireless LAN       SONY VGP-BPS13/Q Battery .

Wireless distribution system

A Wireless Distribution System is a system that enables the wireless interconnection of access points in an IEEE 802.11 network. It allows a wireless network to be expanded using multiple access points without the need for a wired backbone to link them, as is traditionally required            SONY VGP-BPS21A/B Battery .

The notable advantage of WDS over other solutions is that it preserves the MAC addresses of client packets across links between access points.

An access point can be either a main, relay or remote base station. A main base station is typically connected to the wired Ethernet  SONY VGP-BPS21/S Battery .

A relay base station relays data between remote base stations, wireless clients or other relay stations to either a main or another relay base station. A remote base station accepts connections from wireless clients and passes them to relay or main stations. Connections between "clients" are made using MAC addresses rather than by specifying IP assignments  SONY VGP-BPS21B Battery .

All base stations in a Wireless Distribution System must be configured to use the same radio channel, and share WEP keys or WPA keys if they are used. They can be configured to different service set identifiers. WDS also requires that every base station be configured to forward to others in the system       SONY VGP-BPS21A Battery .

WDS may also be referred to as repeater mode because it appears to bridge and accept wireless clients at the same time (unlike traditional bridging). It should be noted, however, that throughput in this method is halved for all clients connected wirelessly  SONY VGP-BPS21 Battery .

When it is difficult to connect all of the access points in a network by wires, it is also possible to put up access points as repeaters.

Roaming

There are 2 definitions for wireless LAN roaming:

  • Internal Roaming (1): The Mobile Station (MS) moves from one access point (AP) to another AP within a home network because the signal strength is too weak       Sony VGP-BPS21A/B Battery .
  • An authentication server (RADIUS) assumes the re-authentication of MS via 802.1x (e.g. with PEAP). The billing of QoS is in the home network. A Mobile Station roaming from one access point to another often interrupts the flow of data between the Mobile Station and an application connected to the network   Sony VGP-BPS21/S Battery .
  • The Mobile Station, for instance, periodically monitors the presence of alternative access points (ones that will provide a better connection). At some point, based upon proprietary mechanisms, the Mobile Station decides to re-associate with an access point having a stronger wireless signal         Sony VGP-BPS21B Battery .
  • The Mobile Station, however, may lose a connection with an access point before associating with another access point. In order to provide reliable connections with applications, the Mobile Station must generally include software that provides session persistence       Sony VGP-BPS21A Battery .
  • External Roaming (2): The MS(client) moves into a WLAN of another Wireless Internet Service Provider (WISP) and takes their services (Hotspot). The user can independently of his home network use another foreign network, if this is open for visitors. There must be special authentication and billing systems for mobile services in a foreign network  Sony VGP-BPS21 Battery .

Wireless network refers to any type of computer network that is not connected by cables of any kind. It is a method by which telecommunications networks and enterpise (business), installations avoid the costly process of introducing cables into to a building, or as a connection between various equipment locations   Sony Vaio PCG-5G2L Battery .

Wireless telecommunications networks are generally implemented and administered using a transmission system called radio waves. This implementation takes place at the physical level, (layer), of the network structure.

Wireless PAN

Wireless Personal Area Networks (WPANs) interconnect devices within a relatively small area, generally within a persons reach  Sony Vaio PCG-5G3L Battery .

For example, both Bluetooth radio and invisible Infrared light provides a WPAN for interconnecting a headset to a laptop. ZigBee also supports WPAN applications. Wi-Fi PANs are becoming commonplace (2010) as equipment designers start to integrate Wi-Fi into a variety of consumer electronic devices      Sony Vaio PCG-5J1L Battery .

Intel "My WiFi" and Windows 7 "virtual Wi-Fi" capabilities have made Wi-Fi PANs simpler and easier to set up and configure.

Wireless LAN

A wireless local area network (WLAN) links two or more devices using a wireless distribution method, providing a connection through an access point to the wider internet      Sony Vaio PCG-5K2L Battery .

The use of spread-spectrumor OFDM technologies also gives users the mobility to move around within a local coverage area, and still remain connected to the network.

  • Wi-Fi: "Wi-Fi" is a term used to describe 802.11 WLANs, although it is technically a declared standard of interoperability between 802.11 devices      Sony Vaio PCG-5J2L Battery .
  • Fixed Wireless Data: This implements point to point links between computers or networks at two distant locations, often using dedicated microwave or modulated laser light beams over line of sightpaths. It is often used in cities to connect networks in two or more buildings without installing a wired link   Sony Vaio PCG-5K1L Battery .

Wireless MAN

Wireless Metropolitan Area Networks are a type of wireless network that connects several Wireless LANs.

Wireless WAN

wireless wide area networks are wireless networks that typically cover large outdoor areas. These networks can be used to connect branch offices of business or as a public internet access system         Sony Vaio PCG-6S2L Battery .

They are usually deployed on the 2.4 GHz band. A typical system contains base station gateways, access points and wireless bridging relays. Other configurations are mesh systems where each access point acts as a relay also. When combined with renewable energy systems such as photo-voltaic solar panels or wind systems they can be stand alone systems       Sony Vaio PCG-6S3L Battery .

Mobile devices networks

With the development of smart phones, cellular telephone networks routinely carry data in addition to telephone conversations:

  • Global System for Mobile Communications (GSM): The GSM network is divided into three major systems: the switching system, the base station system, and the operation and support system      Sony Vaio PCG-6V1L Battery .
  • The cell phone connects to the base system station which then connects to the operation and support station; it then connects to the switching station where the call is transferred to where it needs to go. GSM is the most common standard and is used for a majority of cell phones      Sony Vaio PCG-6W1L Battery .
  • Personal Communications Service (PCS): PCS is a radio band that can be used by mobile phones in North America and South Asia. Sprint happened to be the first service to set up a PCS.
  • D-AMPS: Digital Advanced Mobile Phone Service, an upgraded version of AMPS, is being phased out due to advancement in technology. The newer GSM networks are replacing the older system           Sony Vaio PCG-6W2L Battery .

Uses

An embedded RouterBoard 112 withU.FL-RSMA pigtail and R52 mini PCI Wi-Ficard widely used by wireless Internetservice providers (WISPs) in the Czech Republic        Sony Vaio PCG-6W3L Battery .

Wireless networks continue to develop, usage has grown in 2010. Cellular phones are part of everyday wireless networks, allowing easy personal communications. Inter-continental network systems use radio satellites to communicate across the world. Emergency services such as the police utilize wireless networks to communicate effectively      Sony Vaio PCG-7111L Battery .

Individauls and businesses use wireless networks to send and share data rapidly, whether it be in a small office building or across the world.

Another use for wireless networks is a cost effective means to connect to the Internet, in regions where the telecommunications infrastructure is both poor and lacking in resources, typically in rural areas and developing countries  Sony Vaio PCG-7112L Battery .

Compatibility issues also arise when dealing with wireless networks. Different devices may have compatibility issues, or might require modifications to solve these issues. Wireless networks are often typically slower than those found in modern versions of Ethernet cable connected installations     Sony Vaio PCG-7113L Battery .

A wireless network is more vulnerable, because anyone can intercept and sometimes divert a network broadcasting signal when point to point connections are used. Many wirless networks use WEP - Wired Equivalent Privacy - security systems. These have been found to be still vulnerable to intrusion      Sony Vaio PCG-7133L Battery .

Though WEP does block some intruders, the security problems have caused some businesses to continue using wired networks until a more suitable security system can be introduced. The use of suitable firewalls overcome some security problems in wireless networks that are vulnerable to attempted unauthorised access    Sony Vaio PCG-7Z2L Battery .

Environmental concerns and health hazard

Starting around 2009, there have been increased concerns about the safety of wireless communications, despite little evidence of health risks so far      Sony Vaio PCG-8Y1L Battery .

The president of Lakehead University refused to agree to installation of a wireless network citing a California Public Utilities Commission study which said that the possible risk of tumors and other diseases due to exposure to electromagnetic fields (EMFs) needs to be further investigated        Sony Vaio PCG-8Y2L Battery .

Wireless community networks or wireless community projects are the organizations that attempt to take a grassroots approach to providing a viable alternative to municipal wireless networks for consumers.

Because of evolving technology and locales, there are at least four different types of solution  Sony Vaio PCG-8Z1L Battery :

  • Cluster: Advocacy groups which simply encourage sharing of unmetered internet bandwidth via Wi-Fi, may also index nodes, suggest uniform SSID (for low-quality roaming), supply equipment, dns services, etc.
  • Mesh: Technology groups which coordinate building a mesh network to provide Wi-Fi access to the internet   Sony Vaio PCG-8Z2L Battery
  • WISP: A mesh that forwards all traffic back to consolidated link aggregation point(s) that have centralized access to the internet
  • WUG: A wireless user group run by wireless enthusiasts. An open network not used for the reselling of internet. Running a combination of various off the shelf WIFI hardware running in the license free ISM bands 2.4 GHz/5.8 GHz Sony VAIO PCG-5G2L Battery

Certain countries regulate the selling of internet access, requiring a license to sell internet access over a wireless network. In South Africa it is regulated byICASA .They require that WISP's apply for a VANS or ECNS/ECS license before being allowed to resell internet access over a wireless link            Sony VAIO PCG-5G3L Battery .

The cluster and mesh approaches are more common but rely primarily on the sharing of unmetered residential and business DSL and cable Internet. This sort of usage might be non-compliant with the Terms of Service (ToS) of the typical local providers that deliver their service via the consumer phone and cable duopoly       Sony VAIO PCG-5J1L Battery .

Wireless community network sometimes advocate complete freedom from censorship, and this position may be at odds with the Acceptable Use Policies of some commercial services used. Some ISPs do allow sharing or reselling of bandwidth       Sony VAIO PCG-5K2L Battery .

History

These projects are in many senses an evolution of amateur radio, and more specifically packet radio, as well as an outgrowth of the free software community (which in itself substantially overlaps with amateur radio) Sony VAIO PCG-5J2L Battery .

The key to using standard wireless networking devices designed for short-range use for multi-kilometre Long Range Wi-Fi linkups is the use of high-gain directional antennas. Rather than purchasing commercially available units, such groups sometimes advocate homebuilt antenna construction          Sony VAIO PCG-5K1L Battery .

Examples include the cantenna, which is typically constructed from aPringles potato chip can, and RONJA, an optical link that can be made from a smoke flue and LEDs, with circuitry and instructions released under the GFDL. As with other wireless mesh networks, three distinct generations of mesh networks are used in wireless community networks      Sony VAIO PCG-5L1L Battery .

In particular, in the 2004 timeframe, some mesh projects suffered poor performance when scaled up.

Organization

Organizationally, a wireless community network requires either a set of affordable commercial technical solutions or a critical mass of hobbyists willing to tinker to maintain operations        Sony VAIO PCG-6S2L Battery .

Mesh networks require that a high level of community participation and commitment be maintained for the network to be viable. The mesh approach currently requires uniform equipment. One market-driven aspect of the mesh approach is that users who receive a weak mesh signal can often convert it to a strong signal by obtaining and operating a repeater node, thus extending the mesh networkSony VAIO PCG-6S3L Battery .

Such volunteer organizations focusing in technology that is rapidly advancing sometimes have schisms and mergers. The Wi-Fi service provided by such groups is usually free and without the stigma ofpiggybacking (internet access). An alternative to the voluntary model is to use a co-operative structure     Sony VAIO PCG-6V1L Battery .

One issue with corporate wireless networks in general, and WLANs in particular, involves the need for security. Many early access points could not discern whether or not a particular user had authorization to access the network    Sony VAIO PCG-6W1L Battery .

Although this problem reflects issues that have long troubled many types of wired networks (it has been possible in the past for individuals to plug computers into randomly available Ethernet jacks and get access to a local network), this did not usually pose a significant problem, since many organizations had reasonably good physical security   Sony VAIO PCG-6W2L Battery .

However, the fact that radio signals bleed outside of buildings and across property lines makes physical security largely irrelevant to Piggybackers. Such corporate issues are covered in wireless security         Sony VAIO PCG-6W3L Battery .

Concerns

Anyone within the geographical network range of an open, unencrypted wireless network can 'sniff' or record the traffic, gain unauthorized access to internal network resources as well as to the internet, and then possibly send spam or do other illegal actions using the wireless network's IP address, all of which are rare for home routers but may be significant concerns for office networksSony VAIO PCG-7111L Battery .

If router security is not activated or if the owner deactivates it for convenience, it creates a free hotspot. Since most 21st century laptop PCs have wireless networking built in (cf. Intel 'Centrino' technology), they don't need a third-party adapter such as a PCMCIA Card or USB dongle     Sony VAIO PCG-7112L Battery .

Built in wireless networking might be enabled by default, without the owner realizing it, thus broadcasting th

e laptop's accessibility to any computer nearby.

Modern operating systems such as Mac OS, or Microsoft Windows make it fairly easy to set up a PC as a wireless LAN 'base station' using Internet Connection Sharing, thus allowing all the PCs in the home to access the Internet via the 'base' PC Sony VAIO PCG-7113L Battery .

However, lack of knowledge about the security issues in setting up such systems often means that someone nearby may also use the connection. Such "piggybacking" is usually achieved without the wireless network operators knowledge; it may even be without the knowledge of the intruding user if their computer automatically selects a nearby unsecured wireless network to use as an access point   Sony VAIO PCG-7133L Battery .

Security options

There are three principal ways to secure a wireless network.

  • For closed networks (like home users and organizations) the most common way is to configure access restrictions in the access points. Those restrictions may include encryption and checks onMAC address           Sony VAIO PCG-7Z1L Battery .
  • Another option is to disable ESSID broadcasting, making the access point difficult for outsiders to detect. Wireless Intrusion Prevention Systems can be used to provide wireless LAN security in this network model    Sony VAIO PCG-7Z2L Battery .
  • For commercial providers, hotspots, and large organizations, the preferred solution is often to have an open and unencrypted, but completely isolated wireless network. The users will at first have no access to the Internet nor to any local network resources           Sony VAIO PCG-8Y1L Battery .
  • Commercial providers usually forward all web traffic to a captive portal which provides for payment and/or authorization. Another solution is to require the users to connect securely to a privileged network using VPN.
  • Wireless networks are less secure than wired ones        Sony VAIO PCG-8Y2L Battery .
  • in many offices intruders can easily visit and hook up their own computer to the wired network without problems, gaining access to the network, and it's also often possible for remote intruders to gain access to the network through backdoors like Back Orifice       Sony VAIO PCG-8Z1L Battery .
  • One general solution may be end-to-end encryption, with independent authentication on all resources that shouldn't be available to the public.

Access Control at the Access Point level

One of the simplest techniques is to only allow access from known, approved MAC addresses   Sony VAIO PCG-8Z2L Battery .

However, this approach gives no security against sniffing, and client devices can easily spoof MAC addresses, leading to the need for more advanced security measures.

Some access points can also support "AP isolation" which isolates all wireless clients and wireless devices on the network from each other   WD passport essential (500GB/640GB) .

Wireless devices will be able to communicate with the gateway but not with each other in the network.

Another very simple technique is to have a secret ESSID (id/name of the wireless network), though anyone who studies the method will be able to sniff the ESSID      WD passport essential (250GB/320GB) .

Today all (or almost all) access points incorporate Wired Equivalent Privacy (WEP) encryption and most wireless routers are sold with WEP turned on. However, security analysts have criticized WEP's inadequacies, and the U.S. FBI has demonstrated the ability to break WEP protection in only three minutes using tools available to the general public (see aircrack)  WD  passport essential SE (750GB/1TB)   .

The Wi-Fi Protected Access (WPA and WPA2) security protocols were later created to address these problems. If a weak password, such as a dictionary word or short character string is used, WPA and WPA2 can be cracked. Using a long enough random password (e.g. 14 random letters) or passphrase (e.g. 5 randomly chosen words) makes pre-shared key WPA virtually uncrackable  WD  passport elite(250GB/320GB) .

The second generation of the WPA security protocol (WPA2) is based on the final IEEE 802.11i amendment to the 802.11 standard and is eligible for FIPS 140-2 compliance. With all those encryption schemes, any client in the network that knows the keys can read all the traffic       WD passport elite(500GB/640GB) .

Restricted access networks

Solutions include a newer system for authentication, IEEE 802.1x, that promises to enhance security on both wired and wireless networks. Wireless access points that incorporate technologies like these often also have routers built in, thus becoming wireless gateways      WD  passport studio for Mac(320GB/500GB) .

End-to-End encryption

One can argue that both layer 2 and layer 3 encryption methods are not good enough for protecting valuable data like passwords and personal emails. Those technologies add encryption only to parts of the communication path, still allowing people to spy on the traffic if they have gained access to the wired network somehow     WD  passport studio for Mac(500GB/640GB) .

The solution may be encryption and authorization in the application layer, using technologies like SSL, SSH, GnuPG, PGP and similar.

The disadvantage with the end to end method is, it may fail to cover all traffic. With encryption on the router level or VPN, a single switch encrypts all traffic, even UDP and DNS lookups         WD  Elements series(250GB/320GB) .

With end-to-end encryption on the other hand, each service to be secured must have its encryption "turned on," and often every connection must also be "turned on" separately. For sending emails, every recipient must support the encryption method, and must exchange keys correctly         WD  Elements SE(500GB/640GB) .

For Web, not all web sites offer https, and even if they do, the browser sends out IP addresses in clear text.

The most prized resource is often access to Internet. An office LAN owner seeking to restrict such access will face the non trivial enforcement task of having each user authenticate himself for the router     WD Elements SE(750GB/1TB) .

Open Access Points

Today, there is almost full wireless network coverage in many urban areas - the infrastructure for the wireless community network (which some consider to be the future of the internet) is already in place        WD  Elements desktop(500GB/640GB) .

One could roam around and always be connected to Internet if the nodes were open to the public, but due to security concerns, most nodes are encrypted and the users don't know how to disable encryption. Many people consider it proper etiquette to leave access points open to the public, allowing free access to Internet       WD  Elements desktop(750GB/1TB) .

Others think the default encryption provides substantial protection at small inconvenience, against dangers of open access that they fear may be substantial even on a home DSL router.

The density of access points can even be a problem - there are a limited number of channels available, and they partly overlap   WD  Elements desktop(1.5 TB/2TB) .

Each channel can handle multiple networks, but places with many private wireless networks (for example, apartment complexes), the limited number of Wi-Fi radio channels might cause slowness and other problems       WD  passport essential SE (750GB/1TB)--USB 3.0)   .

According to the advocates of Open Access Points, it shouldn't involve any significant risks to open up wireless networks for the public:

  • The wireless network is after all confined to a small geographical area         WD  passport essential (500GB/640GB) .
  • A computer connected to the Internet and having improper configurations or other security problems can be exploited by anyone from anywhere in the world, while only clients in a small geographical range can exploit an open wireless access point. Thus the exposure is low with an open wireless access point, and the risks with having an open wireless network are small  WD  passport for Mac(320GB/500GB) .
  • However, one should be aware that an open wireless router will give access to the local network, often including access to file shares and printers.
  • The only way to keep communication truly secure is to use end-to-end encryption     WD  passport for Mac(640GB/1TB) .
  • For example, when accessing an internet bank, one would almost always use strong encryption from the web browser and all the way to the bank - thus it shouldn't be risky to do banking over an unencrypted wireless network. The argument is that anyone can sniff the traffic applies to wired networks too         My book essential 4 generation  (640GB/1TB) ,
  • where system administrators and possible crackers have access to the links and can read the traffic. Also, anyone knowing the keys for an encrypted wireless network can gain access to the data being transferred over the network   WD  My book essential 4 generation( 1.5TB/2TB) .
  • If services like file shares, access to printers etc. are available on the local net, it is advisable to have authentication (i.e. by password) for accessing it (one should never assume that the private network is not accessible from the outside). Correctly set up, it should be safe to allow access to the local network to outsiders   WD  My book elite( 1TB/1.5TB) .
  • With the most popular encryption algorithms today, a sniffer will usually be able to compute the network key in a few minutes.
  • It is very common to pay a fixed monthly fee for the Internet connection, and not for the traffic - thus extra traffic will not hurtWD  My book studio(1TB/2TB) .
  • Where Internet connections are plentiful and cheap, freeloaders will seldom be a prominent nuisance  WD  My book essential 4 generation( 1.5TB/2TB) .

On the other hand, in some countries including Germany, persons providing a n open access point may be made (partially) liable for any illegal activity conducted via this access point. Also, many contracts with ISPs specify that the connection may not be shared with other persons      WD  My book elite(640GB/2TB) .

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