A wireless Wireless network refers to any type of computer network that is wireless, and is commonly associated with a telecommunications network whose interconnections between nodes is implemented without the use of wires. Wireless telecommunications networks are generally implemented with some type of remote information transmission system that uses local area network A local area network is a computer network covering a small physical area, like a home, office, or small groups of buildings, such as a school, or an airport. The defining characteristics of LANs, in contrast to wide area networks (WANs), include their usually higher data-transfer rates, smaller geographic area, and lack of a need for leased (WLAN) links devices via a wireless distribution method (typically spread-spectrum Spread-spectrum techniques are methods by which a signal generated in a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth. These techniques are used for a variety of reasons, including the establishment of secure communications, increasing resistance to natural interference and or OFDM Orthogonal frequency-division multiplexing , essentially identical to coded OFDM (COFDM) and discrete multi-tone modulation (DMT), is a frequency-division multiplexing (FDM) scheme utilized as a digital multi-carrier modulation method. A large number of closely-spaced orthogonal sub-carriers are used to carry data. The data is divided into several) and usually provides 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.

Wireless LANs have become popular in the home due to ease of installation and the increasing popularity of laptop A laptop is a personal computer designed for mobile use and small and light enough to sit on a person's lap while in use. A laptop integrates most of the typical components of a desktop computer, including a display, a keyboard, a pointing device , speakers, and usually including a battery, into a single small and light unit. The rechargeable computers. Public businesses such as coffee shops and malls have begun to offer wireless access to their customers, sometimes for free. Large wireless network projects are being put up in many major cities: New York City New York is the most populous city in the United States, and the center of the New York metropolitan area, which is one of the most populous metropolitan areas in the world. A leading global city, New York exerts a powerful influence over global commerce, finance, media, culture, art, fashion, research, education, and entertainment. As host of the, for instance, has begun a pilot program to cover all five boroughs A borough is an administrative division in various countries. In principle, the term borough designates a self-governing township although, in practice, official use of the term varies widely of the city with wireless Internet The Internet is a global system of interconnected computer networks that use the standard Internet Protocol Suite to serve billions of users worldwide. It is a network of networks that consists of millions of private, public, academic, business, and government networks of local to global scope that are linked by a broad array of electronic and access.[citation needed]

Contents

History

An embedded An embedded system is a computer system designed to perform one or a few dedicated functions often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal computer , is designed to be flexible and to meet a wide RouterBoard 112 with U.FL U.FL, is a miniature coaxial RF connector for high-frequency signals up to 6 GHz manufactured by Hirose Electric Group in Japan. U.FL connectors are commonly used inside laptops and embedded systems to connect the Wi-Fi antenna to a Mini PCI card. Female U.FL connectors are not designed with reconnection in mind, and they are only rated for a few-RSMA SMA connectors are coaxial RF connectors developed in the 1960s as a minimal connector interface for coaxial cable with a screw type coupling mechanism. The connector has a 50 Ω impedance. It offers excellent electrical performance from DC to 18 GHz pigtail and R52 mini PCI Conventional PCI is a computer bus for attaching hardware devices in a computer. These devices can take either the form of an integrated circuit fitted onto the motherboard itself, called a planar device in the PCI specification, or an expansion card that fits into a slot. The name PCI is an initialism formed from Peripheral Component Interconnect Wi-Fi Wi-Fi is a trademark of the Wi-Fi Alliance that manufacturers may use to brand certified products that belong to a class of wireless local area network (WLAN) devices based on the IEEE 802.11 standards, which is by far the most widespread WLAN class today. Because of the close relationship with its underlying standards, the term Wi-Fi is often card widely used by wireless Wireless communication is the transfer of information over a distance without the use of enhanced electrical conductors or "wires". The distances involved may be short or long (thousands or millions of kilometers for radio communications). When the context is clear, the term is often shortened to "wireless". Wireless Internet The Internet is a global system of interconnected computer networks that use the standard Internet Protocol Suite to serve billions of users worldwide. It is a network of networks that consists of millions of private, public, academic, business, and government networks of local to global scope that are linked by a broad array of electronic and service providers (WISPs Wireless Internet Service Providers are Internet service providers with networks built around wireless networking. Technology may include commonplace Wi-Fi wireless mesh networking, or proprietary equipment designed to operate over open 900MHz, 2.4GHz, 4.9, 5.2, 5.4, and 5.8GHz bands or licensed frequencies in the UHF or MMDS bands) in the Czech Republic The Czech Republic (pronounced /ˈtʃɛk/ chek; Czech: Česká republika, pronounced [ˈtʃɛskaː ˈrɛpuˌblɪka] ( listen), short form Česko [ˈtʃɛskɔ]) is a country in Central Europe. The country borders Poland to the northeast, Germany to the west and northwest, Austria to the south and Slovakia to the east. The Czech Republic has been a.

In 1970, Norman Abramson, a professor at the University of Hawaii The University of Hawaiʻi System, formally the University of Hawaiʻi and popularly known as UH, is a public, co-educational college and university system that confers associate, bachelor, master, doctoral and post-doctoral degrees through three university campuses, seven community college campuses, an employment training center, three university, developed the world’s first computer communication network, ALOHAnet ALOHAnet, also known as ALOHA, was a pioneering computer networking system developed at the University of Hawaii. It was first deployed in 1970 by Bruce Rights, and while the network itself is no longer used, one of the core concepts in the network is the basis for the widely used Ethernet, using low-cost ham-like Amateur radio operators enjoy personal wireless communications with each other and are able to support their communities with emergency and disaster communications if necessary, while increasing their personal knowledge of electronics and radio theory. An estimated six million people throughout the world are regularly involved with amateur radio radios. With a bi-directional star topology, the system connected seven computers deployed over four islands to communicate with the central computer on the Oahu Island without using phone lines.[1]

"In 1979, F.R. Gfeller and U. Bapst published a paper in the IEEE The Institute of Electrical and Electronics Engineers or IEEE is an international non-profit, professional organization for the advancement of technology related to electricity. It has the most members of any technical professional organization in the world, with more than 395,000 members in around 150 countries Proceedings reporting an experimental wireless local area network using diffused infrared Infrared light is electromagnetic radiation with a wavelength between 0.7 and 300 micrometres, which equates to a frequency range between approximately 1 and 430 THz communications. Shortly thereafter, in 1980, P. Ferrert reported on an experimental application of a single code spread spectrum Spread-spectrum techniques are methods by which a signal generated in a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth. These techniques are used for a variety of reasons, including the establishment of secure communications, increasing resistance to natural interference and radio 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. In May 1985, the efforts of Marcus led the FCC to announce experimental ISM bands The industrial, scientific and medical radio bands were originally reserved internationally for the use of RF electromagnetic fields for industrial, scientific and medical purposes other than communications. In general, communications equipment must accept any interference generated by ISM equipment for commercial application of spread spectrum technology. Later on, M. Kavehrad reported on an experimental wireless PBX system using code division multiple access. 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 Packet radio is a form of packet switching technology used to transmit digital data via radio or wireless communications links. It uses the same concepts of data transmission via Datagram that are fundamental to communications via the Internet, as opposed to the older techniques used by dedicated or switched circuits. 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. 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."[2]

54 Mbit/s WLAN PCI Card (802.11g)

"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 IEEE 802.11 is a set of standards carrying out wireless local area network computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee (IEEE 802). The base current version of the standard is IEEE 802.11-2007 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. 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. 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 A wireless ad hoc network is a decentralized wireless network. The network is ad hoc because it does not rely on a preexisting infrastructure, such as routers in wired networks or access points in managed wireless networks. Instead, each node participates in routing by forwarding data for other nodes, and so the determination of which nodes, and even larger applications through internetworking. The IEEE 802.11 standard and variants and alternatives, 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 The Unlicensed National Information Infrastructure radio band is part of the radio frequency spectrum used by IEEE-802.11a devices and by many wireless ISPs. It operates over three ranges:, bands also presented new opportunities."[3]

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, primarily the various versions of IEEE 802.11 (Wi-Fi Wi-Fi is a trademark of the Wi-Fi Alliance that manufacturers may use to brand certified products that belong to a class of wireless local area network (WLAN) devices based on the IEEE 802.11 standards, which is by far the most widespread WLAN class today. Because of the close relationship with its underlying standards, the term Wi-Fi is often). An alternative ATM Asynchronous Transfer Mode is a standardized digital data transmission technology. ATM is implemented as a network protocol and was first developed in the mid 1980s. The goal was to design a single networking strategy that could transport real-time video conference and audio as well as image files, text and email. The International-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 IEEE 802.11a-1999 or 802.11a is an amendment to the IEEE 802.11 specification that added a higher throughput of up to 54 Mbit/s and uses the 5 GHz band. It has seen widespread worldwide implementation, particularly within the corporate workspace. The amendment has been incorporated into the published IEEE 802.11-2007 standard (5 GHz) and 802.11g IEEE 802.11g-2003 or 802.11g, is an amendment to the IEEE 802.11 specification that extended throughput to up to 54 Mbit/s using the same 2.4 GHz band as 802.11b. This specification under the marketing name of Wi-Fi has been implemented all over the world. The 802.11g protocol is now Clause 19 of the published IEEE 802.11-2007 standard (2.4 GHz) standards, almost certainly never will.

Architecture

Wireless Networking in the Developing World (PDF book)

Stations

All components that can connect into a wireless medium in a network Computer networking is the engineering discipline concerned with the communication between computer systems or devices. A computer network is any set of computers or devices connected to each other with the ability to exchange data. Computer networking is sometimes considered a sub-discipline of telecommunications, computer science, information are referred to as stations.

All stations are equipped with wireless network interface cards A wireless network interface controller is a network card which connects to a radio-based computer network, unlike a regular network interface controller (NIC) which connects to a wire-based network such as token ring or ethernet. A WNIC, just like a NIC, works on the Layer 1 and Layer 2 of the OSI Model. A WNIC is an essential component for (WNICs).

Wireless stations fall into one of two categories: access points In computer networking, a wireless access point is a device that allows wireless communication devices to connect to a wireless network using Wi-Fi, Bluetooth or related standards. The WAP usually connects to a router, and can relay data between the wireless devices (such as computers or printers) and wired devices on the network and clients.

Access points (APs), normally routers A router is a device that interconnects two or more computer networks, and selectively interchanges packets of data between them. Each data packet contains address information that a router can use to determine if the source and destination are on the same network, or if the data packet must be transferred from one network to another. Where, 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 The term PDA was first used on January 7, 1992, by Apple Computer CEO John Sculley at the Consumer Electronics Show in Las Vegas, Nevada, referring to the Apple Newton. In 1996, Nokia introduced the first mobile phone with full PDA functionality, the 9000 Communicator, which has since grown to become the world's best-selling PDA and which spawned, IP phones Voice over Internet Protocol is a general term for a family of transmission technologies for delivery of voice communications over IP networks such as the Internet or other packet-switched networks. Other terms frequently encountered and synonymous with VOIP are IP telephony, Internet telephony, voice over broadband (VoBB), broadband telephony,, or fixed devices such as desktops A desktop computer is a personal computer in a form intended for regular use at a single location, as opposed to a mobile laptop or portable computer. Prior to the widespread use of microprocessors, a computer that could fit on a desk was considered remarkably small. Desktop computers come in a variety of types ranging from large vertical tower, laptops, and workstations A workstation is a high-end microcomputer designed for technical or scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area network and run multi-user operating systems. The term workstation has also been used to refer to a mainframe computer terminal or a PC connected to a that are equipped with a wireless network interface.

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.

Every BSS has an identification (ID) called the BSSID, which is the MAC address In computer networking, a Media Access Control address is a unique identifier assigned to most network adapters or network interface cards (NICs) by the manufacturer for identification, and used in the Media Access Control protocol sub-layer. If assigned by the manufacturer, a MAC address usually encodes the manufacturer's registered of the access point servicing the BSS.

An independent BSS (IBSS) is an ad-hoc network A wireless ad hoc network is a decentralized wireless network. The network is ad hoc because it does not rely on a preexisting infrastructure, such as routers in wired networks or access points in managed wireless networks. Instead, each node participates in routing by forwarding data for other nodes, and so the determination of which nodes that contains no access points, which means they can not connect to any other basic service set.

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 one or more interconnected 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.

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.

Types of wireless LANs

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). 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 A peer-to-peer, commonly abbreviated to P2P, is any distributed network architecture composed of participants that make a portion of their resources directly available to other network participants, without the need for central coordination instances (such as servers or stable hosts). Peers are both suppliers and consumers of resources, in (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. 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.

Hidden node problem: Devices A and C are both communicating with B, but are unaware of each other

IEEE 802.11 IEEE 802.11 is a set of standards carrying out wireless local area network computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee (IEEE 802). The base current version of the standard is IEEE 802.11-2007 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.

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. 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 Wired Equivalent Privacy is a deprecated algorithm to secure IEEE 802.11 wireless networks. Wireless networks broadcast messages using radio and are thus more susceptible to eavesdropping than wired networks. When introduced in 1997, WEP was intended to provide confidentiality comparable to that of a traditional wired network (WEP) and Wi-Fi Protected Access Wi-Fi Protected Access is a certification program created by the Wi-Fi Alliance to indicate compliance with the security protocol created by the Wi-Fi Alliance to secure wireless computer networks. This protocol was created in response to several serious weaknesses researchers had found in the previous system, Wired Equivalent Privacy (WEP) (WPA, WPA2) to secure wireless computer networks.

Bridge

A bridge can be used to connect networks, typically of different types. A wireless Ethernet Ethernet is a family of frame-based computer networking technologies for local area networks . The name came from the physical concept of the ether. It defines a number of wiring and signaling standards for the Physical Layer of the OSI networking model as well as a common addressing format and Media Access Control at the Data Link Layer 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.

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. The notable advantage of WDS over other solutions is that it preserves the MAC addresses of client packets across links between access points.[4]

An access point can be either a main, relay or remote base station. A main base station is typically connected to the wired Ethernet. 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.

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.

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.

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

Roaming between Wireless Local Area Networks

There are 2 definitions for wireless LAN roaming:

See also

References

  1. ^ "History of Wireless". Johns Hopkins Bloomberg School of Public Health. http://www.jhsph.edu/wireless/history.html. Retrieved 2007-02-17.
  2. ^ "The First IEEE Workshop on Wireless LANS: Preface". Worcester Polytechnic Institute. http://www.cwins.wpi.edu/wlans91/scripts/preface.html. Retrieved 2008-03-16.
  3. ^ "The Second IEEE Workshop on Wireless LANS: Summary". Worcester Polytechnic Institute. http://www.cwins.wpi.edu/wlans96/scripts/summary.html. Retrieved 2008-03-16.
  4. ^ Wireless Distribution System Linked Router Network DD-WRT Wiki. Retrieved December 31, 2006.
  5. ^ "How Wi-Fi Roaming Really Works". http://www.wireless-nets.com/resources/tutorials/how_roaming_works.html. Retrieved 2008-10-09.
  6. ^ Pommer, Hermann: Roaming zwischen Wireless Local Area Networks. VDM Verlag, Saarbrücken 2008, ISBN 978-3-8364-8708-5.

Further reading

Categories: Local area networks | Wireless networking

 

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