What iss Wireless LAN??

Wireless LAN:-

Wireless LANs are more commonly referred to by their trade name Wi-Fi. The terms Wi-Fi, WLAN, and 802.11 are used interchangeability in this text. Local-area networks (LANs) within a company, government agency, hospital, or other organization typically use CAT5 or CAT6 unshielded twisted pair as the transport medium. However, more and more, wireless extensions to these LANs are becoming popular as are entirely 

wireless LANs. Low-cost wireless modems installed in personal computers and laptops make this possible. Three common coni gurations are shown in Fig. 21-2. Fig. 21-2(a) shows a wireless access point (AP) is connected to an existing wired LAN, usually through an Ethernet switch. This AP contains a transceiver that can cover a specii c geographic area, usually inside a building. This area usually extends out to no more than about 100 m, but generally the range is less due to the great signal attenuation of the walls, ceilings, l oors, and other obstructions. PCs or laptops within that range and 

containing a radio modem can link up with the AP, which in turn connects the PC or 

laptop to the main LAN and any services generally available via that LAN such as email and Internet access.

 Another popular coni guration is shown in Fig. 21-2(b). Here the AP is connected 

to the main LAN or more commonly to an Internet service provider (ISP) by way of a 

long-range interconnection such as a hardwired T1 or T3 line, i ber connection, or a microwave relay link such as WiMAX, as described later in this chapter. The AP is usually installed in a restaurant, coffee shop, airport, hotel, convention center, or other public place. It is more commonly known as a “hot spot.” Some cities are also installing municipal hot spots. Anyone with a laptop equipped with a LAN modem interface can link up to the AP and access his or her e-mail or the Internet. There are hundreds of thousands of hot spots around the world.

 What makes the wireless LAN so appealing is that it offers l exibility, convenience, and lower costs. To add a node to an existing wired LAN, the main problem is the new wiring. If such wiring is not in place already, it is time-consuming and expensive to pull cables through walls and ceilings and to install connectors. Moving computers within a building because of ofi ce reconi guration is a huge problem and expense unless existing 

wiring can be reused. By using a wireless extension such problems essentially disappear.

Any computer can be located at any new point quickly and easily at no additional cost. 

As long as the computer is within the range of the AP, the connection is automatic. Wireless is a great way to expand an existing network.

 Wireless LANs also serve our continuing need to be more mobile in our jobs and 

activities. The cell phone has given us freedom to maintain communications anywhere, at any time, and virtually in any place. The wireless LAN also gives us that same portability for our computers, mainly laptops, which have essentially become the de facto PC form factor. Within an organization, a user can take her or his laptop to the conference room for a meeting, to a colleague’s ofi ce, or to the cafeteria for lunch. And with all the available hot spots, we can use our laptops almost anywhere, especially while we are traveling.

 Another growing use of wireless LANs is in the implementation of home 

 networks. See Fig. 21-2(c). As more and more families become users of multiple PCs, tablets, and smart phones, there is a need to interconnect each device to a broadband Internet connection such as a DSL or cable TV line. It allows each user to access e-mail or the Internet or to share a common peripheral such as a printer. Most homeowners do not want to wire their homes with CAT5/6 cable at great expense. Installing a wireless LAN is fast, easy, and very inexpensive these days. A special box called a residential gateway or wireless router connects to the cable TV or DSL and serves as the access point. This gateway or router uses a software approach called network address translation (NAT) to make it appear as if each networked PC has its own Internet address, when in reality only the one associated with the incoming 

broadband line is used.