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A wireless LAN or WLAN is a wireless local area network, which is the linking of two or more computers with-out using wires. It is the same as LAN, but has a wireless interface. 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).

History

WLAN is expected to continue to be an important form of connection in many business areas. The market is expected to grow as the benefits of WLAN are recognized. Frost & Sullivan estimate the WLAN market to have been 0.3 billion US dollars in 1998 and 1.6 billion dollars in 2005. So far WLANs have been installed in universities, airports, and other major public places. Decreasing costs of WLAN equipment has also brought it to many homes. However, in the UK the exorbitant cost of using such connections in public has so far limited use to airports' Business Class lounges, etc. Large future markets are estimated to be in health care, corporate offices and the downtown area of major cities. New York City has even begun a pilot program to cover all five boroughs of the city with wireless internet.

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. Such places could be old protected buildings or classrooms, although the restricted range of the 802.11b (typically 30 ft.) limits its use to smaller buildings. WLAN components are now cheap enough to be used in the home, with many being set-up so that one PC (a parent's PC, for example) can be used to share an internet connection with the whole family (whilst retaining access control at the parents' PC).

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) (see separate articles) and HomeRF (2 Mbit/s, intended for home use, unknown in the UK). 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.

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:

  1. CAMP: Convenience, Affordability, Mobility, Productivity
  2. Deployment advantages: Installation flexibility, speed and scalability
  3. Regions without or with limited wired infrastructure can easily establish wireless communication
  4. Wireless networks have a better chance of surviving disasters
  5. 802.11 wireless LANs, WiMAX and 3G+ cellular networks promise high bandwidths, global mobility, quality of service and seamless integration with one another.

Source: Sampalli, Srinivas,"Module 4: Wireless LANs", page 1, October 25, 2005.

Architecture of a Wireless LAN

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.

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.

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.

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.

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

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.

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).

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.

Types of Wireless Local Area Networks

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 you have a strength meter for the signal coming from all the other ad-hoc devices the meter will not read the strength accurately, and can be misleading, because it is registering the strength of the strongest signal, such as the closest computer.

Access Point or Infrastructure Wireless LAN

The most common type of wireless LAN when a wireless enabled client connects to an access point in order to connect to the network.

An access point is often a hub or router that has an antenna built in to transmit and receive the radio frequency and bridges a wireless network to a wired Ethernet network. The network administer can configure the access point through a web interface or telnet.

Home networks typically have one access point that is directly connected to the internet to provide the network with internet access. Larger networks often found who provide wireless access to entire buildings usually have multiple access points placed at strategic locations.

Wireless distribution system

When it's difficult to get all the Access Points wired up, it's also possible to put up access points as repeaters.

Monitoring station

Some wireless network cards can be set up to monitor a network without connecting to an access point or revealing itself. This can be used to sniff clear-text activity, or to crack encryption.

Method of Communication

A Wireless LAN is a local area network that uses radio frequencies to communicate between wireless enabled devices. The transmission frequency of a Wireless LAN depends on the protocol being used and the channel.

Protocols

IEEE 802.11 (Wi-Fi)
In 1990, the IEEE (Institute of Electrical and Electronic Engineers) formed a group to develop a standard for wireless equipment. On June 26, 1997, a standard was finally developed called 802.11. The standard specified that the upper layers of the OSI model can not be modified, and WLANs must be implemented on the physical and data link layers. This provided the ability to run any operating system or LAN application on a WLAN without any modification. They accomplished this by doing upper layer features on the data link layer.

Protocol Release Date Frequency Bandwidth
IEEE 802.11 1997 2.4 GHz 1, 2 Mbps
IEEE 802.11a 1999 5 GHz 6, 9, 12, 18, 24, 36, 48, 54 Mbps
IEEE 802.11b 1999 2.4 GHz 5.5, 11 Mbps
IEEE 802.11g 2003 2.4 GHz 6, 9, 12, 18, 24, 36, 48, 54 Mbps
IEEE 802.11n ? 2.4 GHz ?
Source: Sampalli, Srinivas,"Module 4: Wireless LANs", page 8, October 25, 2005.

IEEE 802.15 (Bluetooth)

Protocol Release Date Frequency Bandwidth
IEEE 802.15 1999 2.4 GHz 1 Mbps
Source: Sampalli, Srinivas,"Module 4: Wireless LANs", page 8, October 25, 2005.

IEEE 802.16 (WiMAX)

Protocol Release Date Frequency Bandwidth
IEEE 802.16 2006 6 - 66 GHz up to 75 Mbps
Source: Sampalli, Srinivas,"Module 4: Wireless LANs", page 8, October 25, 2005.

HomeRF

Protocol Release Date Frequency Bandwidth
HomeRF ? < 5 GHz 10 Mbps
Source: Sampalli, Srinivas,"Module 4: Wireless LANs", page 8, October 25, 2005.

Components of a Wireless LAN

Access Point(AP)

Access points are two-way transceivers that broadcast data into the surrounding environment. Access points act as a mediator between wired and wireless network.

Wireless Capture Device

Wireless devices are peripherals designed for personal computers. Their purpose is to allow the computer - and therefore its user - to connect to a network through radio waves. These peripherals can be found as PCI cards, or portable USB devices. When activated, they scan their environment for signals from a wireless access point. If one is found, they allow the user to connect to the access point. The wireless capture card can determine if the access point is secured with an encryption method (usually WEP or WPA) and can still allow the user to connect to it assuming the key or passcode is available.

Concerns

Health

Because wireless LAN uses microwaves similar to those in mobile phones, any health concerns would be similar. However, the transmission power of typical wireless access point is less than 100 mW. In comparison, the radio waves emitted by a GSM handset, for example, can have a power of up to 2 watts, and it is typically used at a much shorter distance from the body.

Security

At a wired network, one can often, to some degree, restrict the access to the network by physical means. The geographical range of a wireless network will more often than not be significantly greater than the office or home it's meant to cover; any neighbour or arbitrary trespasser may be able to sniff on all the traffic and gain unauthorized access to internal network resources as well as to the Internet, possibly sending spam or doing illegal actions using the owner's IP address, if the security isn't taken seriously. Most equipment is Wi-Fi-certified, IEEE 802.11b or IEEE 802.11g compliant and offers some level of security like Wired Equivalent Privacy (WEP) and/or Wi-Fi Protected Access (WPA).

Some advocates would like to see all access points openly available for the public, with the rationale being that everyone would benefit from being able to get online when on the road. There are works in progress for maintaining a List over open wireless networks

Other

The frequency which 802.11b operates at is 2.4 GHz, which can lead to interference with cordless phones in the super high frequency range. If one wants to use a cordless telephone on the same premises, one should ensure that the cordless set uses a different frequency, such as 900 MHz or 5.8 GHz. However, any wireless router has the ability to operate in different channels. Using channel 11 is most often the best situation for a wireless access point.

See also

External links

References

Books

  • Computer Networking: A top down approach featuring the Internet by J.F. Kurose and K.W. Ross, Addison Wesley, Second Edition, 2003
  • Data Communications and Networking by B.A. Forouzan, McGraw Hill Publishers, Thrid Edition, 2004
  • Computer Networks: A Systems Approach by L. Peterson and B. Davie, Morgan-Kauffman Publishers, Second Edition
  • Data and Computer Communications by W. Stallings, Prentice Hall, Sixth Edition, 2003

Webpages

  • http://www.pdamd.com/vertical/features/wireless_3.xml
  • http://www.pc.ibm.com/ww/healthycomputing/lan.html
  • http://www.doc.ic.ac.uk/~nd/surprise_95/journal/vol2/mjf/article2.html

Other

  • Sampalli, Srinivas,"Module 4: Wireless LANs", October 25, 2005.

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This article is licensed under the GNU Free Documentation License. It uses material from the "Wireless LAN".

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