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Today's vocabulary wireless it often means connection without wires or cables. This is different to remote control. Wireless Local Area Network (WLAN) is the use of wireless devices in a local area network (LAN). LAN is any group of computers connected to each other interchanging data in a building or campus lab. To achieve this cables are connected from computer to routers or switches all through the LAN. With wireless, the needs for cables are eliminated because electromagnetic waves are used to send and receive data from computers in the network. Also the 802.11 modem (term used to refer to WLAN) is still in its infancy, high demand, great security risk, very few experts in the field and may dominate the landscape of Network in the future. Wireless Technology may just render RJ45 cables obsolete.
Wireless LAN - WLAN history
This technology has existed since the seventies. According to Wikipedia.Org"In1970 University of Hawaii, under the leadership of Norman Abramson, developed the world's first computer communication network using low-cost ham-like radios, named ALOHAnet"(wiki)
In 1979, F.R. Gfeller and U. Bapst published a paper about an experimental wireless local area network using diffused infrared communications. Then in 1980, P. Ferrert reported on an experimental application of a single code spread spectrum radio for wireless terminal communications in the IEEE National Telecommunications Conference.
In 1984, Kaveh Pahlavan published a paper in the IEEE Computer Networking Symposium and Communication Society Magazine comparing Infrared and CDMA spread spectrum communications for wireless office information
In 1980 amateur groups developed the first generation wireless data modems. This was achieved by adding voice-band data to communication modem and connecting it to distance radio system such as a walkie-talkie.
Today WLANs are found installed in campuses, airports, public places and coffee shops. The low costs of WLAN equipment has made it affordable for home use. New York City has even begun to cover the entire city with wireless internet. (wikipedia)
Both Japan and Korea are starting to roll out speedy WiMAX data networks that can deliver wireless broadband access to entire cities (www.businessweek.com)
54 MBit/s WLAN PCI Card (802.11g)
WLAN hardware were expensive in the early days that it was only used in places where cabling was difficult or impossible to connect.
Distance records (using non-standard devices) include 382 km (237 mi) in June 2007, held by Ermanno Pietrosemoli and EsLaRed of Venezuela, transferring about 3 MB of data between the mountain-tops of El Águila and Platillon. [Wikipedia] The Swedish Space Agency transferred data 420 km (260 mi), using 6 watt amplifiers to reach an overhead stratospheric balloon. [wikipedia.org/wiki/Wi-Fi]
The picture show OSI reference model for 802.11. The data link layer, lower layers of the OSI reference model is what differentiates it from conventional cable networks OSI models.
WI-FI is a trademark name to brand devices compliant to IEEE 802.11 standards. Devices in a WLAN essentially use WI-FI branded products. A WI-FI ready device simply means that it is ready for network operation within a WLAN.(Wikipedia)
Wireless LAN Requirements:
A basic for WLAN:
Ability to cover short distances.
Full connectivity among attached stations(NIC)
The 2 main components are
Wireless station refers to laptops or computers with Network Interface Card (NIC). NIC uses radio signals to communicate, sometimes called wireless adapters. It contains radio transceivers and logic interacts with client machine and software.
A.P a stationary device which is a part of wired LAN. Acts as a bridge between wired networks. Its bridging function is able to connect 2 or more networks.
Wireless Networking is accomplished by Sending and receiving radio waves between transmitter and receiver.
Common terms in radio transmission:
Data Rate: Measured in HZ. Faster frequency means more information can be transmitted
Signal Strength: Measured in Watt. WLAN devices generally transmit 30milliwatts
Antenna: Turns the electrical impulses to radio waves.
Range in office space: 29 METRES-11Mbps.
Open Area: 485 METRES-1Mbps.
See picture below:
Picture shows range of signal 
There are 2 technologies mainly used:
Narrow band technology uses radio system to transmit and receives user information on a specific radio frequency. Narrowband keeps radio signal frequency as narrow as possible to pass signals. This is to avoid undesirable crosstalk. This is achieved by carefully coordinating different users on different channel frequencies.
Spread spectrum is a modulation technique which spreads data transmission along the frequency band. This enables users to share the same frequency band with little interference from other users. Spread spectrum was used by the military because the wideband signals are hard to detect and be jammed by enemies. Transmission is more secure, reliable and detectable.
The 2 architecture types for WLAN:
Â Ad hoc mode:
Ad-hoc refers to network that connects devices directly with each other. There is no central A.P. It won't communicate with Infrastructure devices or any other devices connected to a wired network. Ad-hoc mode security is less secured than Infrastructure mode network.
Â It is used to connect devices which are in the same area. All client stations are grouped together in a single geographic area.
Infrastructure mode requires an Access Point like 802.11 WLAN routers. Benefit of Infrastructure mode is increased levels of security, potentially faster data transmission speeds and integration with a wired network providing wireless coverage to buildings or university area. Each client stations or computer must have NIC installed to connect to the network.
IEEE Wireless Networking Specifications
The IEEE refers to Institute of Electrical and Electronic Engineers which provides a global standard for the 802.11. This is to enable WLAN devices of different manufacturers to be able to connect and have the same specification and work together interchangeably. It first released the 802.11 specifications in June 1999. The first specification for 802.11 had 2.4 GHz frequency with 1 Mbps. The latest specification is the 802.11g which supports 54 Mbps and 60 Mbps
802.11 operated in the 2.4 GHz range and was the original specification of the 802.11 IEEE standards. This specification delivered 1 to 2 Mbps using a technology known as phase-shift keying (PSK) modulation. This specification is no longer used and has largely been replaced by other forms of the 802.11 standard. 
802.11a operates in the 5 - 6 GHz range with data rates commonly in the 6 Mbps, 12 Mbps, or 24 Mbps range. Because 802.11a uses the orthogonal frequency division multiplexing
(OFDM) standard, data transfer rates can be as high as 54 Mbps. OFDM breaks up fast serial information signals into several slower sub-signals that are transferred at the same time via different frequencies, providing more resistance to radio frequency interference. The
802.11a specification is also known as Wi-Fi5, and though regionally deployed, it is not a global standard like 802.11b.
2.4 GHz range with up to 600 Mbps data set to release in 2012.
WLAN has a weak security policy. It basically uses 3 basic security services:
Authentication :Checking the identity
Integrity: Ensures the message that it is not modified.
Privacy: Preventing passive attacks.
According to website wikipedia"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 networks'.
Piggybacking refers to access to a wireless Internet connection by bringing one's own computer within the range of another's wireless connection, and using that service without the subscriber's explicit permission or knowledge.
'Sniff' or 'spoofing' as its sometimes called, session hijacking is accomplished by monitoring a valid wireless station successfully complete authenticating to the network with a protocol l analyser. The attacker will send a spoofed disassociate message from the AP causing the wireless station to disconnect.
When WEP (Wired Equivalent Privacy) is not activated by home or office user, the attacker has use of the connection until the next time out. The wireless station and AP are not synchronized allowing the attacker to disassociate the wireless station while the AP is unaware that the original wireless station is not connected.
The increasing use of Wireless LANs has created over looked vulnerabilities that allow hacking. Strategies that have worked on securing wired networks should be implemented on WLAN and its vulnerabilities.
Benefits of WLAN:
The general benefits of WLAN are: Mobility :
Information can be accessed from any where in the campus
installing a Wireless LAN is quick and easy.
No wiring except in Access Point Installlation
Easily upgradeable and low cost to owner
installation cost is less compared to Wired LAN
Scalability, Can connect over 1000 users
Classrooms\office and other can have flexible access to the network, more space
Warehouse workers can exchange information with central databases and increase their productivity
11 Mbps for 802.11b
54 Mbps for 802.11a/g (GSM:9.6Kbps, HCSCD:~40Kbps, GPRS:~160Kbps, WCDMA:up to 2Mbps)
Long-term cost savings
O & M cheaper that for wired nets
Comes from easy maintenance, cabling cost, working efficiency and accuracy
Network can be established in a new location just by moving the PCs!
Because WLAN is still generally new in comparison to wired LAN, there has not been much attention given to improving overall quality and tweaking its bugs. Range and coverage depends on the transmission power and receiving capabilities of the transceiver. Radio interference can cause degradation in output. Any interference caused by lakes or walls. If the number of clients increased for a particular access point, performance will decrease and cause internet lag.
Wireless technologies will become a permanent fixture business and homes throughout the world. WLAN outperforms conventional LAN, also physically easy to upgrade. Initially WLAN was outputting at 2 Mbps then WLAN has reached speed up to 100Mbps and soon Wi-Fi in Korea will exceed 1Gbps by 2012on the new 802.11n.  Any conceivable notion that WLAN will replace conventional LAN is highly unlikely, overall. Long distance communication still needs cables so do telephone lines. But for small areas, like classroom, office and homes WLAN proves to be the best violable option both in practicality and comfort.