Wireless LAN
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The notebook is connected to the wireless access point using a PCMCIA wireless card. |
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54 MBit WLAN PCI Card (802.11g) |
A
wireless LAN or
WLAN is a
wireless local area network, which is the linking of two or more computers without using wires. It uses radio communication to accomplish the same functionality that a wired
LAN has. 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).
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) (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.
Wireless LANs offer users an array of benefits ranging from cost efficiency to seamless integration with other networks.
The benefits Wireless LANs include:
#CAMP: Convenience, Affordability, Mobility, Productivity#Deployment advantages: Installation flexibility, speed and scalability#Regions without or with limited wired infrastructure can easily establish wireless communication#Wireless networks have a better chance of surviving disasters#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. |
Wireless Local Area Network Architecture using an Infrastructure BSS |
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 but can be a
wireless LAN.
|
Peer-to-Peer or ad-hoc Wireless LAN |
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
|
Infrastructure Wireless Local Area Network |
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
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, diagnostics and troubleshooting. Or more malevolently, to sniff clear-text activity, or crack encryption.
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 | expected mid-2007 | 2.4 GHz | 540 Mbps |
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 | December 2005 | 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 | ?IEEE 802.16 December 2005 6 - 66 GHz up to 75 Mbps | < 5 GHz | 10 Mbps |
Source: Sampalli, Srinivas,"Module 4: Wireless LANs", page 8, October 25, 2005.IEEE 802.16 December 2005 6 - 66 GHz up to 75 Mbps
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 Network Interface Cards
Wireless NICs 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.
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 networksOther
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.
*
Comparing WLAN and LAN*
Wireless LAN client comparison*
MANETs
*
Microconnect Distributed Antennae*
SSID or
service set identifier*
Wardriving*
Wireless community networks
*
Wireless MANs
*
Wireless PANs
*
Ambient networks
*
Magoo's Ultimate Guide to wireless networking*
How to Build a Wireless Home Network (Tutorial)*
freewlan.org A WIKI for listing intentionally free and open WLANs
*
20 Things Not to Do When Setting Up a Wireless NetworkBooks
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
*http://blogs.chron.com/techblog/archives/2005/07/wifi_scarfing_i.html
*http://www.techdirt.com/articles/20060320/1636238.shtml
Other
*Sampalli, Srinivas,"Module 4: Wireless LANs", October 25, 2005.
