wifi detailed document
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Inexpensive broadband wireless networks that can keep you connected while you move about the office or home are getting better all the time Far from what tradition might indicate, the wireless Internet isn't turning out to be one of those tech breakthroughs that arrives accompanied by a Microsoft-size marketing campaign and eight-foot-high displays in consumer-electronics stores. Instead, it's a grassroots trend that has moved from research labs, to techie circles, to hobbyists -- and that now, after five years -- is about to reach the general public.
The broadband wireless Web is being built around a technology known as Wi-Fi, or 802.11b, that's easy to underestimate. Wi-Fi stands for wireless fidelity, an increasingly popular networking standard that's used to create wireless local area networks (LANs) in homes and offices at speeds up to 11 megabits per second, far faster than the peak 144-kilobit-per-second rate so-called 3G (for third-generation) mobile-phone networks that Sprint PCS for one, plans to deliver.
For now, Wi-Fi primarily provides broadband Internet access to specially outfitted PCs and laptops within a few hundred feet of a so-called Wi-Fi base station, or transmitter. These create what in the Wi-Fi vernacular are known as "hot spots" in homes, airport lounges, or libraries. Businesses are also adding Wi-Fi networks to allow for easy Net access from conference rooms and temporary work stations -- and also to avoid the hefty costs in both time and money of wiring an office.
A BREIF HISTORY
Network technologies and radio communications were brought together for the first time in 1971 at the University of Hawaii as a research project and implimentation called ALOHANET. The ALOHANET system enabled computer sites at seven campuses spread out over four islands to communicate with the central computer on Oahu without using the existing unreliable and expensive phone lines. ALOHANET offered bidirectional communications, in a star topology, between the central computer and each of the remote stations. The remote stations had to communicate with one another via the centralized computer.
In the 1980s, amateur radio hobbyists, hams, kept radio networking alive within the United States and Canada by designing and building terminal node controllers (TNCs) to interface their computers through ham radio equipment. TNCs act much like a telephone modem, converting the computer's digital signal into one that a ham radio can modulate and send over the airwaves by using a packet-switching technique. In fact, the American Radio Relay League (ARRL) and the Canadian Radio Relay League (CRRL) have been sponsoring the Computer Networking Conference since the early 1980s to provide a forum for the development of wireless WANs. Thus, hams have been utilizing wireless networking for years, much earlier than the commercial market.
What is Wi-Fi ?
Wi-Fi is a trade-group certified wireless networking standard that relies on the IEEE 802.11a and 802.11b specifications. The 802.11b spec allows for the wireless transmission of approximately 11 Mbps of raw data at indoor distances from several dozen to several hundred feet and outdoor distances of several to tens of miles as an unlicensed use of the 2.4 GHz band. The 802.11a spec uses the 5 GHz band, and can handle 54 Mbps at typically shorter distances. The distances for both standards depends on impediments, materials, and line of sight.
The 802.11b specification started to appear in commercial form in mid-1999, with Apple Computer's introduction of its AirPort components, manufactured in conjunction with Lucent's WaveLAN division. (The division changed its named to Orinoco and was spun off to the newly formed Agree corporation with a variety of other Lucent assets in early 2001; these assets were resold to Proxim Corporation in June 2002, although Agree continues to make the chips.)
WHY WI –FI ?
Mobility enables users to physically move while using an appliance, such as a handheld PC or data collector. Many jobs require workers to be mobile, such as inventory clerks, healthcare workers, police officers, and emergency-care specialists. Of course, wireline networks require a physical tether between the user's workstation and the networks resources, which makes access to these resources impossible while roaming about the building or elsewhere.
Mobile applications requiring w-fi networking include those that depend on real-time access to data-usually stored in centralized databases. If your application requires mobile users to be immediately aware of changes made to data, or if information put into the system must immediately be available to others, you have a definite need for wireless networking. For accurate and efficient price markdowns, for example, many retail stores use wireless networks to interconnect handheld bar code scanners and printers to databases having current price information. This enables the printing of the correct price on the items, making both the customer and the business owner more satisfied.
Another example of the use of wireless networking is in auto racing. Formula-1 and Indy race cars have sophisticated data acquisition systems that monitor the various on-board systems in the car. When the cars come around the track and pass the respective teams in the pit, this information is downloaded to a central computer, thereby enabling real-time analysis of the performance of the race car.
Wi fi systems can be configured in a variety of topologies to meet the needs of specific applications and installations. Configurations are easily changed and range from peer-to-peer networks suitable for a small number of users to full infrastructure networks of thousands of users that enable roaming over a broad area.
A problem inherent to wired networks is the downtime that results from cable faults. In fact, cable faults are often the primary cause of system downtime. Moisture erodes metallic conductors via water intrusion during storms and accidental spillage or leakage of liquids. With wired networks, users may accidentally break their network connector when trying to disconnect their PCs from the network to move them to different locations. Imperfect cable splices can cause signal reflections that result in unexplainable errors. The accidental cutting of cables can bring a network down immediately. Wires and connectors can easily break through misuse and even normal use. These problems interfere with the users' ability to utilize network resources, causing havoc for network managers. An advantage of wireless networking, therefore, results from the use of less cable. This reduces the downtime of the network and the costs associated with replacing cables.
Reduced Installation Time
The installation of cabling is often a time-consuming activity. For LANs, installers must pull twisted-pair wires above the ceiling and drop cables through walls to network
outlets that they must affix to the wall. These tasks can take days or weeks, depending on the size of the installation. The installation of optical fiber between buildings within the same geographical area consists of digging trenches to lay the fiber or pulling the fiber through an existing conduit. You might need weeks or possibly months to receive right-of-way approvals and dig through ground and asphalt.
The deployment of wireless networks greatly reduces the need for cable installation, making the network available for use much sooner. Therefore, many countries lacking a network infrastructure have turned to wireless networking as a method of providing connectivity among computers without the expense and time associated with installing physical media. This is also necessary within the United States to set up temporary offices and "rewire" renovated facilities.
Wi-Fi is a no-risk financial decision especially for small businesses or companies in hard-to-wire locations, because of its low cost. Consulting firm Adventist, which spent $30,000 to wire its Boston office last year, says a similar Wi-Fi installation today would cost only $500. Gartner's Dulaney estimates that 20% of large companies currently have wireless LANs as an adjunct to their wired networks. By 2003, when the technology will provide even faster Net access -- plus tighter security and less interference -- he thinks 50% of the largest 1,000 public companies will have it.
Long-Term Cost Savings
Companies reorganize, resulting in the movement of people, new floor plans, office partitions, and other renovations. These changes often require recabling the network, incurring both labor and material costs. In some cases, the recabling costs of organizational changes are substantial, especially with large enterprise networks. A reorganization rate of 15 percent each year can result in yearly reconfiguration expenses as high as $250,000 for networks that have 6,000 interconnected devices. The advantage of wi fi is again based on the lack of cable: You can move the network connection by just relocating an employee's PC.or Aps
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