05-03-2013, 12:06 PM
WLAN-Wireless LAN
WLAN.doc (Size: 238 KB / Downloads: 23)
ABSTRACT
The term “Computer Network” to mean a collection of autonomous computers interconnected by a single technology .By this interconnection they are able to exchange information. Local Area Networks are privately owned networks within a single building or campus of few kilometers in size. In a traditional LAN we are connecting computers to the network through cables. But the wireless local area network (WLAN) is a flexible data communications system that can use either infrared or radio frequency technology to transmit and receive information over the air. Here each computer has a radio Modem and Antenna with which it can communicate with other systems. One important advantage of WLAN is the simplicity of its installation. Installing a wireless LAN system is easy and can eliminate the needs to pull cable through walls and ceilings. WLANs allow greater flexibility and portability than do traditional wired local area networks (LAN). 802.11 was implemented as the first WLAN standard. It is based on radio technology operating in the 2.4 GHz frequency and has a maximum throughput of 1 to 2 Mbps.
Unfortunately, wireless networking is a double-edged sword. WLANs use electromagnetic waves to transmit information, the radio waves can easily penetrate outside the building, it’s a risk that the network can be hacked from the parking lot or the street. So it’s very important to put enough attention on the WLANs security aspects. With wireless networking, there is no physical security. The radio waves that make wireless networking possible are also what make wireless networking so dangerous. An attacker can be anywhere nearby listening to all the traffic from the network. By properly engineering and using your wireless network, we can keep attackers at bay.
INTRODUCTION
As we know “Computer Net work” is the linking of two or more computers within a well defined area. Of the common networks used today Local area networks(LAN) serve to provide solutions of the most general interest .A wireless Local area network (WLAN ) is a flexible data communication system implemented as an extension to ,or as an alternative for a wired LAN. As the name suggests a wireless LAN is one that makes use of wireless transmission medium, i.e. wireless LAN transmits and receives data over air, and minimizing the need for the wired connection. Thus wireless LAN combines data connectivity with user mobility. WLANs also allow greater flexibility and portability than traditional wired LAN which requires a wire to connect a user computer to the network. The initial cost for WLAN hardware can be higher than the cost of wired LAN hardware. But the overall installation expenses and lifecycle cost can be significantly lower. With WLAN users can access shared information without looking for a place to plug in, and network managers can setup or argument networks without installing or moving wires. There are many reasons people choose to deploy a wireless LAN, Increase the productivity due to increase mobility, Lower infrastructure cost compared to wired networks, Rapid deployment schedules
WHAT IS WIRELESS
The term “wireless “reflects any means of communication that occurs without wires. The wireless is also called unguided media, i.e. wireless provide a means for transmitting electromagnetic waves but not guided them. Wireless technology in simplest sense enables one or more devices to communicate with out any physical connection, without requiring network of peripheral cabling.
WIRELESS LAN REQUIREMENTS
A wireless LAN must meet some sort of requirements typical of any LAN
• High capability
• Ability to cover short distances
• Full connectivity among attached stations.
• Broadcast Capability
In addition there are no of requirement specific to wireless LAN environment.
WIRELESS STATION
A wireless station or client is typically a laptop or notebook personal computer (PC) with Wireless Network Interface Card (NIC). A WLAN client may also be a desktop or handheld device within publicly addressed area. Wireless laptops and notebooks-“Wireless enabled”-are identical to laptops and notebooks except that they use Wireless NIC to connect to the access point (AP) in the network.
NETWWORK INTERFACE CARD (NIC)
The wireless (NICs) is commonly inserted in the clients Personal Computer Memory Card International Association (PCMCIA) slot or Universal Serial Bus (USB) port. The NIC use radio signals to establish connection to the WLAN. It is also called wireless adapter or WLAN cards. It consists of the radio transceiver and the logic to interact with the client machine and software. WLAN adapters provide an interface between client network operating system (NOS) and wireless via antenna. The nature of the wireless connection is transparent to the NOS.
NARROWBAND TECHNOLOGY
A narrowband radio system transmits and receives user information on a specific radio frequency. Narrowband radio keeps the radio signal frequency as narrow as possible just to pass the information. Undesirable crosstalk between communications channels is avoided by carefully coordinating different Users on different channel frequencies. A private telephone line is much like a radio frequency. When each home in a neighborhood has its own private telephone line, people in one home cannot listen to calls made to other homes. In a radio system, privacy and non interference are accomplished by the use of separate radio frequencies. The radio receiver filters out all radio signals except the ones on its designated Frequency.
SPREAD SPECTRUM
Spread Spectrum is a modulation technique that spreads the data transmission across the entire available frequency band. By spreading the signal across the entire band, the signal becomes less vulnerable to noise or interference. Because the signal is less vulnerable, it can be used in most environments. Spread spectrum also permits many users to share the same frequency band with Minimal interference from other users or from devices (such as microwave ovens).Spread spectrum first was developed for use by the military because it uses Wideband signals that are difficult to detect and that resist attempts at jamming. In Recent years, researchers have turned their attention to applying spread spectrum Processes for commercial purposes, especially in local area wireless networks.
Direct Sequence Spread Spectrum
Under DSSS the information to be transmitted is divided into small pieces. These small pieces are spread across the entire available frequency band. The pieces of information are encoded by using a redundant pattern, called a chip. This chip is only known by the transmitting and receiving device. This makes it difficult for an intruder to intercept and decipher wireless data endoed in this manner. The redundant pattern also makes it possible to recover data without retransmitting it if one or more bits are damaged. This means that the signal is less susceptible for interference.
SUMMARY
Wireless technologies have become increasingly popular in our every day business and personal lives. The wired world of copper and fibre-based networks will continue to be the basics fabric of networks, but WI-FI is a rapidly growing niche. Wireless communication is a great attraction to users who are constantly on the move. Wireless network cards are seen installed on laptop computers rather than on desktop systems because of the inherent mobility that laptops offer. Wireless connectivity in PDA’s and other handheld computing device is also getting popular. In a nutshell wireless technologies are our call to liberation and will undoubtedly continue to grow in popularity and increase performance capabilities .Over the past several years the price of wireless LAN equipments has dropped significantly. Wireless NIC’s are nearing the price of their wired counterparts. At the same time performance increased dramatically. In 1998 WLAN topped out at 2 Mbps, now WLAN has reached speed up to 100Mbps. This high performance wireless solutions can greatly increased the productivity by providing real time access to e–business applications and valuable network data. Infrastructure maturity may be an initial reason for replacing the traditional wired LAN with a wireless LAN. But increasingly the simplicity and flexibility and the ease of deploying WLAN s is appearing to enterprises.