Wireless LAN
From Wikipedia, the free encyclopedia
A wireless LAN or WLAN is a wireless local area network, which is the linking of two or more computers without using wires. WLAN utilizes spread-spectrum technology based on radio waves to enable communication between devices in a limited area, also known as the basic service set. This gives users the mobility to move around within a broad coverage area and still be connected to the network.
This technology is becoming more and more popular, especially with the rapid emergence of small portable devices such as PDAs (personal digital assistants). For the home user, wireless has become popular due to ease of installation, and location freedom with the gaining popularity of laptops. For the business, public businesses such as coffee shops or malls have begun to offer wireless access to their customers, some are even provided as a free service. Large wireless network projects are being put up in many major cities, Google is providing a free service to Mountain View, California[1] and has entered a bid to do the same for San Francisco[2], New York City has also begun a pilot program to cover all five boroughs of the city with wireless internet.
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[edit] History
In 1971, researchers at the University of Hawaii developed the world’s first WLAN, or wireless local area network, it was named ALOHAnet. The bi-directional star topology of the system included seven computers deployed over four islands to communicate with the central computer on the Oahu Island without using phone lines [3]
Originally WLAN hardware was 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). An alternative ATM-like 5 GHz standardized technology, HIPERLAN, 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.
The Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) claims to have first developed wireless networking, and as of 2006 they are engaged in a controversial battle with software and hardware giants looking for royalties on the alleged patents held by CSIRO reguarding these technologies.[4]
[edit] Benefits of Wireless LANs
Wireless LANs offer users an array of benefits ranging from cost efficiency to seamless integration with other networks.
The benefits Wireless LANs include:
- Convenience: Wireless freedom allows users to access network resources from any location.
- Mobility: With the emergence of public wireless networks, users can access the internet even outside their normal work environment.
- Productivity: Using a PDA or any other wireless portable device, the user can remain constantly connected with the network.
- Deployment: Initial setup of an infastructure-based wireless network requires little more than an access point, as opposed to traditional networks which need wiring to be run to all locations. Wireless networks can also be deployed to areas that would normally be prohibitive of wired networks.
- Expandability: Adding additional clients to the network requires no additional infastructure as long as they are within range.
- Cost: Wireless networking hardware is only a slight cost increase from their wired counterparts, but the cost savings in infastructure such as running cables, and expanding the network can offset this increase.
[edit] Disadvantages of Wireless LANs
Wireless LANs, despite the above mentioned advantages are still unpopular or an unconsidered option in many environments, this is due mostly to the inherant disadvantages of the technology including:
- Security: Wireless LANs have the inherant security risk that everyone in the area can receive the wireless signals, however, there are encryption methods to combat this. (See main article Wireless security)
- Range: The average range of an 802.11g network is approximately 30 meters, aditional range requires either a repeater or aditional access points. Other technologies such as WiMAX offer ranges upwards of 100km, which is far beyond that of traditional copper-based networking.
- Reliability: A wireless signal is susceptible to external interference, and thus the connection may become unstable, for this reason alone it is not recommended that important network resources such as servers be connected wirelessly.
- Speed: 802.11g, The most common wireless network operates at 54Mbps, the most common wired networks operate at 100Mbps, with 1Gbps becoming increasingly common, and 10Gbps just emerging. Future wireless technologies such as 802.11n operate at 540Mbps greatly reducing the gap between wireless and wired speed.
[edit] Architecture of a Wireless LAN
[edit] 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). Stations fall into one of two categories: Wireless Clients and Access Points.
[edit] Access Points (AP’s)
Access Points are base stations for the wireless network. They transmit and receive radio frequencies for wireless enabled devices to communicate with.
[edit] Wireless Clients
Wireless clients can be mobile devices such as laptops, personal digital assistants (PDAs), IP phones or fixed devices such as desktops and workstations that are equipped with a wireless network interface card.
[edit] 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 and Infrastructure BSS. Every BSS has an id called the BSSID, it is the MAC address of the access point servicing the BSS.
[edit] Independent Basic Service Set
Independent BSS are an ad-hoc network that contain no Access Points. Since they do not use Access Points they can not connect to any other basic service set
[edit] Infrastructure Basic Service Set
An Infrastructure BSS can communicate with other stations not in the same basic service set by communicating to each other through Access Points.
[edit] Extended Service Set
An Extended Service Set (ESS) is a set of connected BSS. Access Points in an extended service set are connected by a distribution system. Each ESS has an ID called the SSID which is a 32 byte (maximum) character string. Example: linksys (the default SSID for Linksys routers).
[edit] Distribution System
A distribution system connects Access Points in an extended service set. A distribution system is usually a wired LAN but can be a wireless LAN.
[edit] Types of Wireless Local Area Networks
[edit] Peer-to-peer or ad-hoc
This type of 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.
[edit] Wireless distribution system
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.
[edit] Monitoring station
Good wireless network cards can be set up to monitor a network without connecting to an access point or revealing itself. This can be used for NIDS (network intrusion detection systems), diagnostics, and troubleshooting, or more malevolently, to sniff clear-text activity or crack encryption.
[edit] See also
- Local area network
- IEEE 802.11
- Wireless network
- Exposed terminal problem
- Hidden terminal problemcs:WLAN
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