WiFi

1. INTRODUCTION

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.

Wi-Fi's most admirable attributes are that it's fast (to both set up and use) and cheap (under $200 for a small installation). It operates on unlicensed airwave spectrum, so no extra monthly costs on top of the charge for a broadband connection are incurred. It's also easy to install. Most high-end laptops now come ready for Wi-Fi, equipped with a special plug-in circuit card. Hotels and coffee shops are offering customers Wi-Fi access as a convenience. Starbucks has equipped 530 stores and plans eventually to enable more than 70% of its 3,200 company-owned North American outlets.

2.  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 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.

In 1985, the Federal Communications Commission (FCC) made the commercial development of radio-based LAN components possible by authorizing the public use of the Industrial, Scientific, and Medical (ISM) bands. This band of frequencies resides between 902 MHz and 5.85 GHz, just above the cellular phone operating frequencies.

The ISM band is very attractive to wireless network vendors because it provides a part of the spectrum upon which to base their products, and end users do not have to obtain FCC licenses to operate the products. The ISM band allocation has had a dramatic effect on the wireless industry, prompting the development of wireless LAN components. Without a standard, however, vendors began developing proprietary radios and access points.

In the late 1980s, the Institute for Electrical and Electronic Engineers (IEEE) 802 Working Group, responsible for the development of LAN standards, such as ethernet and token ring, began development of standards for wireless LANs. Under the chairmanship of Vic Hayes, an engineer from NCR, the IEEE 802.11 Working Group developed the Wireless LAN Medium Access Control and Physical Layer specifications.

The IEEE Standards Board approved the standard on June 26, 1997, and the IEEE published the standard on November 18, 1997. The finalizing of this standard is prompting vendors to release 802.11-compliant radio cards and access points throughout 1998. Other vendors new to the wireless market are sure to develop and release 802.11-compliant products based on the standard blueprint provided by the 802.11 standard.

Another widely accepted wireless network connection, however, has been wireless WAN services, which began surfacing in the early 1990s. Companies such as ARDIS and RAM Mobile Data were first in selling wireless connections between portable computers, corporate networks, and the Internet. Companies then began introducing Cellular Digital Packet Data (CDPD) services, which enable users to send and receive data packets via digital transmission services. These services enable employees to access email and other information services from their personal appliances without using the telephone system when meeting with customers, traveling in the car, or staying in a hotel.

 3.  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.)

Wi-FI is an extension of wired Ethernet, bringing the same principles to wireless communication, and as such is ecumenical about the kinds of data that pass over it. It's primarily used for TCP/IP, but can also handle other forms of networking traffic, such as AppleTalk or PC file sharing standards.

4.  WHY WI –FI ?

o   Mobility

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.

• Scalability:

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.

• Increased Reliabilit

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.

• Financial benefit

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.

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• 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

An oil exploration company operating in Colombia, South America, experienced high expenses when relocating its drilling rigs. The oil drilling setup requires two control rooms in portable sheds located approximately 5,000 feet from the drilling platform to provide 500 Kbps computer communication between the sheds and the drilling rig. The communication system consisted of ethernet networks at each of the three sites. Each shed had four PCs running on the network, and the drilling site had one PC for direct drilling control purposes.

Every time the oil company needed to move to a different drilling site, which occurred four or five times each year, it had to spend $50,000 to $75,000 to reinstall optical fiber over the difficult terrain between the sheds and the drilling platform. With cabling expenses reaching as high as $375,000 per year, the system engineer on site designed a wireless point-to-point system to accommodate the portability requirements and significantly reduce the cost of relocating the drilling operation. The solution includes a spread spectrum radio-based wireless system that uses point-to-point antennas to direct communication between the sheds and the drilling platform. The cost of purchasing the wireless network components was approximately $10,000. Whenever the oil company moves its operation, it saves the costs of laying new cable between the sites.

5.  Wi-fi Standard

802.11b

The most established wireless LAN technology, it's also the most affordable. Allows wireless connections up to 300 feet from an access point, and can easily be added to existing wired networks. With speeds up to 11 Mbps,performance is comparable to a standard wired Ethernet network. Industry standard 802.11b products are easy to find and compatible with each other.

802.11a
802.11a provides a bigger pipe for data and supports more simultaneous users. Ideal for deployments where speed and bandwidth are important, 802.11a networks can run at up to 54Mbps and support more users per access point than a Wi-Fi solution. wi-Fi (short for wireless fidelity) is a wireless communications specification for digital devices. Wi-Fi is often referenced by its standards numbers in the 802.11x family.

802.11b

            The popular 802.11b Wi-Fi devices broadcast in the 2.4-Ghz band also used by cordless phones; faster but shorter-range 802.11a devices use the 5-Ghz ban. Both can send signals many hundreds of feet in clear territory. (For better or worse, their range inside buildings is usually much less, absent range-enhancing antenna add-ons.) Wireless Equivalent Privacy (WEP) encryption is part of the 802.11 standard, and available in almost all compatible devices. The primary purpose of WEP is to prevent eavesdropping, but it has the important secondary benefit of preventing unauthorized use of one's wireless network.

Many analyses have documented the vulnerability of WEP to a sophisticated attack. However, the most common reason for WEP failure is that it is turned off by default in 802.11 devices, and most users never bother to turn it on.

6.     COMPONENTS OF WI-FI

          There are currently two types of Wi-Fi components you'll need to build your home or office network: Wi-Fi radio (also known as client devices) devices (desktops, laptops, PDAs, etc.), and access points or gateways that act as base stations. A third type, Wi-Fi equipped peripherals, are emerging and will soon be commonplace. This group includes printers, scanners, cameras, video monitors, set-top boxes and other peripheral equipment.

PC Card Radio

 Wi-Fi networks use a radio band to "broadcast" data to other Wi-Fi enabled equipment and the most common client device is the PC Card Wi-Fi radio. There are hundreds of variations, but most look like a standard Type II PC Card that slides into your laptop's PC Card slot

These cards used to be known as PCMCIA (Personal Computer Memory Card International Association) cards but are now simply called PC Cards.) The protruding end of most Wi-Fi PC Cards contains a built-in antenna, usually a miniature twin diversity antenna, which can sometimes spring out to improve coverage. Some of them have a tiny connector on the end to which you can attach a larger, more powerful antenna to maximize range.

On many laptop computers, the software and drivers for these PC Cards are already built in. If you are using Windows XP, you may find that when you slide in the card, the drivers and software will load automatically. The computer will then scan the area to find and log onto the closest Wi-Fi network.

You can also use Wi-Fi PC Card Radios in various cameras, audio systems, PDAs and other mobile computing devices that have a PC Card slot.

Mini-PCI Modules and Embedded Radios

Your desktop or laptop may come Wi-Fi enabled. If so, it most likely has a Mini-PCI radio installed by the manufacturer.

Many manufacturers now install an embedded Mini-PCI Wi-Fi radio in laptop computers and other mobilecomputing devices before they leave the factory. Apple Computers uses a somewhat similar Wi-Fi radio module,

Apple AirPort that can be installed by the factory, the retail outlet or the end user.If you are using a Windows-based laptop in your network and you can't use a PC Card or other Wi-Fi adapter, you'll need one with a pre-installed Mini-PCI Wi-Fi radio. You should ask the factory to install one when you order a new laptop

USB Adapters

Most desktop computers do not provide PC slots for Wi-Fi PC radios. You can solve this problem by using a PCI/ISA bus adapter (see below) or a USB adapter. For most users with desktop computers, the easiest way to add a Wi-Fi radio is to use a USB adapter, a one-piece unit that combines

a Wi-Fi radio and a USB converter circuit.

Simply plug the USB connector into one of the USB jacks on your desktop PC. Because their power is delivered through the USB cable, most USB adapters don't require a separate DC power module.

PCI and ISA Bus Adapters

Many Wi-Fi vendors provide ISA and PCI-compliant radios that fit inside a desktop computer and enable the computer to work in a Wi-Fi network(Until recently, most computersinternally contained open slots called ISA and PCI buses, but in most new computers PCI.)

These can be either one-piece ISA or PCI radios or two-piece units that comprise a PC Card reader or adapter and a separate Wi-Fi PC Card Radio that slides into the reader

Compact Flash and Other Small-Client Formats

Designed for smaller PDAs and other mobile computing devices, 802.11b/Wi-Fi radios can be built onto a Compact Flash format. Much smaller than a typical Type II PC Card, CF (Compact Flash) Wi-Fi cards have the same range and performance as their larger cousins.

Access Points and Gateways

Even though client device radios can be configured to talk to each other, a Wi-Fi network operates more effectively when using a central base station to oordinate ommunications  There are two types of Wi-Fi wireless base stations gateway and an access point. However, the distinctions between the two are

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not always clear, in prt because the functions they perform can overlap. Even more confusing, many wired devices and other home Internet appliances also call themselves gateways.

A wireless gateway is targeted toward a totally wireless home or small-office environment; an access point is targeted toward a more integrated combined Ethernet and wireless environment-usually - larger businesses, campuses, or corporations. Gateways and access points can also differ regarding their capacity to perform security functions, provide firewall protection, and manage network traffic and tasks.

Gateways often include NAT (Network Address Translation) routing and DHCP (Dynamic Host Control Protocol) services. These create and provide the individual IP addresses all the wireless (and wired) clients need to function in a network and also

enable a single Wi-Fi gateway to simultaneously provide Internet access to numerous users from a single shared Internet connection . Gateways may also include other applications and features such as encryption and security, VPN, firewall.

An access point does not usually furnish NAT routing or DHCP; the wired routers in the system provide those network functions. Access points work as merely transparent bridges between wired networks and the various wireless users throughout a facility. Even though access points generally do not provide NAT or DHCP, they usually enable roaming (the ability to move from one access point to another without losing contact with your network), higher levels of security, and a high level of network control and management. Some gateways also provide these services. In fact, by toggling certain functions on and off, many wireless base stations can operate either as a gateway or as an access point. But a gateway is usually the only wireless base station in a small office or home, whereas in a large office or campus there might be hundreds or thousands of access points forming one or multiple overlapping wireless networks.

Wi-Fi drivers

As wireless LANs grow within corporations, the desire to extend support follows naturally. Cahners estimates that the number of 802.11-based access points shipped each year will nearly triple from 1.2 million in 2001 to 3.5 million in 2005. The firm expects yearly 802.11 network interface card (NIC) shipments to jump from 6.3 million last year to 19.4 million in 2005.

In fact, most of the major notebook computer makers ship products today with embedded 802.11 NICs. Combine that with the fact that Microsoft has embedded Wi-Fi capabilities into Windows XP and it is clear that, like it or not, there is a Wi-Fi user base growing up around you.

The XP operating system automatically searches for a Wi-Fi access point and, if it finds one, asks the user if he would like to use the service. "We had users

signing up for our service before it was even announced," says Tim Barrett, vice president of AirPath.

Wi-Fi support can indeed draw business. Mark Hedley, CTO at hotelier Wyndham International, based in Dallas, says his company is "most certainly taking conference business away from other hotels" thanks to the 802.11 connectivity in 148 of its properties.

Wireless provider Wayport ate the up-front capital costs, Hedley says. "You won't likely see much more of that in the wake of the dot-com demise. At the time, everyone expected a 20% consumption rate, but it's actually been more like 2% to 4%."

1. 7.                WHAT TRANSMITION TECHNOLOGY

Manufacturers of wireless LANs have a range of technologies to choose from when designing a wireless LAN solution. Each technology comes with its own set of advantages and limitations.

7.1  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 noninterference are accomplished by the use of separate radio frequencies. The radio receiver filters out all radio signals except the ones on its designated frequency.

From a customer standpoint, one drawback of narrowband technology is that the end-user must obtain an FCC license for each site where it is employed.

7.2  Spread Spectrum Technology
Most wireless LAN systems use spread-spectrum technology, a wideband radio frequency technique developed by the military for use in reliable, secure, mission-critical communications systems. Spread-spectrum is designed to trade off bandwidth efficiency for reliability, integrity, and security. In other words, more bandwidth is consumed than in the case of narrowband transmission, but the tradeoff produces a signal that is, in effect, louder and thus easier to detect, provided that the receiver knows the parameters of the spread-spectrum signal being broadcast. If a receiver is not tuned to the right frequency, a spread-spectrum signal looks like background noise. There are two types of spread spectrum radio: frequency hopping and direct sequence.

Spread spectrum simply means that data is sent in small pieces over a number of the discrete frequencies available for use at any time in the specified range. Devices using direct-sequence spread spectrum (DSSS) communicate by splitting each byte of data into several parts and sending them concurrently on different frequencies. DSSS uses a lot of the available bandwidth, about 22 megahertz (MHz). Devices using frequency-hopping spread spectrum (FHSS) send a short burst of data, shift frequencies (hop) and then send another short burst. Since the FHSS devices that are communicating agree on which frequencies to hop to, and use each frequency for a brief period of time (less than 400 milliseconds) before moving on, several independent FHSS networks can exist in the same physical area without interfering with each other. Also, due to FCC restrictions, as well as the fact that FHSS devices generally send data on just two to four frequencies simultaneously, they only use 1 MHz or less of the available bandwidth. Because they use any given frequency for such a short time, FHSS devices are less prone to interference than DSSS devices. But DSSS is capable of much greater speed than FHSS since these devices can send a lot more data at the same time. Currently, FHSS-based devices are easier and cheaper to produce, which has led the HomeRF group to adopt FHSS as the method of communication for their products.

7.3  Frequency-hopping  Spread Spectrum Technology
Frequency-hopping spread-spectrum (FHSS) uses a narrowband carrier that changes frequency in a pattern known to both transmitter and receiver. Properly synchronized, the net effect is to maintain a single logical channel. To an unintended receiver, FHSS appears to be short-duration impulse noise.

7.4  Direct-Sequence_Spread_Spectrum_Technology
Direct-sequence spread-spectrum (DSSS) generates a redundant bit pattern for each bit to be transmitted. This bit pattern is called a chip (or chipping code). The longer the chip, the greater the probability that the original data can be recovered (and, of course, the more bandwidth required). Even if one or more bits in the chip are damaged during transmission, statistical techniques embedded in the radio can recover the original data without the need for retransmission. To an unintended receiver, DSSS appears as low-power wideband noise and is rejected (ignored) by most narrowband receivers.

1. 8.                ABOUT NETWORK

What Makes Up a Wireless Network?

Wi-Fi devices "connect" to each other by transmitting and receiving signals on a specific frequency of the radio band. Your components can connect to each other directly (this is called "peer-to-peer") or through a gateway or access point. When you create your Wi-Fi network it will consist of two basic components: Wi-Fi radios and access points or gateways.

Wi-Fi radios are embedded or attached to the desktop computers, laptops and mobile devices in your network. The access points or gateways act as "base stations" — they send and receive signals from the Wi-Fi radios to connect the

various components to each other as well as to the Internet. All computers in your Wi-Fi network can then share resources, exchange files and use a single Internet connection.

Planning for Access Points and Gateways

A Wi-Fi network operates more effectively when using a central wireless base station to coordinate communications. There are two types: a gateway and an access point.

Most home and small office networks should use a Wi-Fi gateway.

Depending on how your system is set up now, you may choose an access point rather than a gateway. For instance, if you have an existing wired network or a combined broadband modem/router, you can use just a basic access point because the existing wired network router or hub will handle network addressing NAT or DHCP. If you have a broadband modem with no router connected to a single computer, or if you don't yet have an existing wired network, then you should get a Wi-Fi gateway that provides NAT (Network Address Translation) routing and a DHCP (Dynamic Host Control Protocol) server. If your cable modem or DSL connection is providing NAT or DHCP you can disable NAT and DHCP on your gateway because the network addressing is already provided by the modem or connection and only one device on a network can provide these services.

The Wi-Fi access point or gateway functions as the base station for your network. This is the central connection among all your wireless client devices—laptop computers, PDAs, desktop computers and wireless peripherals like printers. The base station sends and receives radio signals to and from the Wi-Fi radio in your laptop or PC, enabling you to share your Internet connection with other users on the network. Access points and gateways have a wide range of features and performance capabilities, but they all provide this basic network connection service.

How Many Users Can Use a Single Access Point?

Wi-Fi networks, like wired networks, are a shared medium. An 802.11b Wi-Fi network may provide 11 Mbps of bandwidth to an individual user. Theoretically, if ten users are simultaneously using the network, each will have to share and may only get 1 Mbps or so each. However, network sharing is not quite this simple. A lot depends on the users' behaviors. Someone who is just sending and receiving e-mail just uses the wireless connection in bursts. They will probably never notice any slow down. On the other hand, a roomful of Wi-Fi users who are accessing high-resolution multimedia over a single access point may indeed notice a slowdown. In this instance, they may require additional access points or higher speed access points that use 802.11a or 802.11g that provide 54 Mbps or better of bandwidth.

Depending on how the users connect and what they do once they are on the network, you may need to use higher speed access points, as well as more of them.

You will also need a Wi-Fi access point or gateway to serve as the central base station for your network. A typical Wi-Fi access point can support some 15 to 20 users, so most homes and small offices need only a single access point. However, if you have a very large dwelling (or house) or if your office is spread out, you may need more. How far will your WLAN go? A basic rule of thumb is 100 to 300 feet indoors and 2000 feet outdoors. Your range may vary, based on the building or environment you're using it in. See Access Point Range Guide.

Of course, the number of access points depends on how the network is used and the total number of users, as well as how big a space needs to be covered. A single access point can easily handle from 10 to 30 users who only use the network to send e-mail, cruise the Internet and occasionally save and retrieve large files. Within a typical office environment, most access points can provide good wireless coverage up to 150 feet or so. For large facilities with many users, or with users who require a lot of bandwidth, you may need more than a single access point. Many access points can be connected to each other wirelessly or via Ethernet cables to create a single large network.

How to  Install Your Access Point or Gateway 

During the installation, make sure you follow the manufacturer's instructions to install an access point- or gateway-based network, not a peer-to-peer network. For most Wi-Fi systems, you must first plug in and power up the base station. Then connect the Ethernet cable from your DSL or cable modem to the base station. If your broadband connection is already connected to your computer, disconnect that cable and attach it to your base station. ]

Most cable and DSL modems use Ethernet technology (cable and built in card) to connect to computers or to networks. However, some versions of DSL or cable modems use a USB cable to connect to computers. Find out which your system uses because few if any Wi-Fi access points can use USB for their broadband connection. If your broadband modem connects using a USB cable, you then need to buy the correct RJ-45 Ethernet cable to connect your modem to your Wi-Fi gateway or access point.

Install the First Wi-Fi Radio Device

After carefully reviewing instructions, install the Wi-Fi radio device in the first computer. If you're installing devices in both desktops and laptops, start with the machine with the newest operating system. Follow the manufacturer's instructions to be sure you're configuring them to work with your base station and not as a peer-to-peer network. If all your OS's, or operating systems, are about the same, begin by installing PC Card radios in the laptops and then install in the desktops.

If you already have an embedded Wi-Fi radio in your laptop, simply initiate the appropriate program or utility software to scan and find the new access point. If your desktop has a Windows XP operating system, it should already

contain the software that will automatically scan and find your new Wi-Fi network.

How Do You Connect Your Wi-Fi Network to the Internet?

You can use a variety of high-speed Internet connections with a Wi-Fi network, including cable modems, different types of DSL, satellite broadband, ISDN, etc. Your broadband Internet connection will connect to your gateway or access point, and its Internet connection will be distributed to all the computers on your network. And don't worry about Wi-Fi slowing down your connection speed: it's at least four times faster than the fastest of any of these connections. If there's an Ethernet cable attached to your Internet device, you can connect it to your base station to distribute your Internet connection throughout your home or small office Wi-Fi network.

Take note while connect

• § Make very, very sure that your NIC (Network Interface Card) or built-in Wi-Fi adapter really, really is compatible with the Wi-Fi standard. Wi-Fi is actually a super-set of the IEEE's 802.11b standard. Consequently, you can be sold all kinds of wireless cards that are 802.11b compliant but if they don't have Wi-Fi on the box, then there's no guarantee they'll work. Here's the URL for the Wi-Fi Alliance so you can double-check compatibility before you make a purchase. http://www.wifizone.org/.

• § Next, ensure you've got the right software drivers loaded. In the case of a PCMCIA style card inserted into a standard Windows laptop, an icon of a PC surrounded by radio waves should appear in the toolbar with its screen turned green (not red) to indicate that it really is working OK.

• § You switch your portable computer on in an area where you suspect that there really is a public Wi-Fi network in operation. There is flashing green light glowing somewhere on your computer to indicate that the Wi-Fi interface really is fired up. Windows XP should automatically ask you to try to log in as soon as it detects a nearby Wi-Fi network.

• § Trying starting up your Internet browser. It should at least make some vague attempt to detect the existence of a Wi-Fi service provider. If not, then check your browser isn't set to only connect via dial-up networking instead of via a LAN connection.

• § If no automatic log-on process is triggered by firing up the browser (try firing up and closing the browser several times), then consider you might have the wrong SSID (Service Set Identification). Microsoft calls the SSID the 'network name'. In our case this had been set to the default setting, which was 'linksys' (the card supplier's name). Try changing this to the name of the Wi-Fi network you require such as eurospot or open zone. Despite advice to the contrary, I've never found that 'any' or 'default' will work.

• § To change the SSID, you’ll normally need to find the utility that comes with your Wi-Fi interface. With Linksys, it shows which Wi-Fi access points it can see. This not only gives you a clue as to which SSID to use (ie ‘public’) but you can also click on one specific detected access point and then on the button marked 'connect'. In theory this will ensure you are at least trying to the same channel (usually numbered between 1 and 13) as the access point and whether you need to activate WEP (Wired Equivalency Protocol) to encrypt your data to prevent snooping.

• § There are two ways of connecting to Wi-Fi networks. One is called 'ad hoc' or 'peer-to-peer' and is the usual way to 'roam' onto any public Wi-Fi network. Sometimes this is set to 'automatic'. What you don't want is for it to be set to 'access point' or 'infrastructure'. So ensure you Wi-Fi card hasn’t been fixed to search for infrastructure.

1. 9.     TOPOLOGY DESIGN OF AP

9.1  Design approach

In selecting AP locations. One must avoid coverage gaps, areas where no service will be available to users. On the other hand, one would like to space the Aps as far apart as possible to minimize the cost of equipment and installation. Another reasons to space the Aps far apart is that coverage overlap between Aps operating on the same radio channel (co – channel overlap) degrades performance (this is the reason one should not “overprovision” a wireless lan using Aps then necessary.) . Minimizing overlap between AP’s coverage areas when one is selecting AP locations help to minimize co-channel overlap.We have found that rules of thumb are inadequate in doing this type of design.

Rather, each building design must be based on careful signal strength measurements.  This is particularly challenging because the building is a three-dimensional space and an APs located on one floor of the building Provides signals coverage to adjacent floors of the same building and perhaps to other buildings as well[3]

After the APS have been located and their coverage areas measured, radio channels are assigned to the APs .  eleven DSSS radio channels are available in the 2.400-2.4835GHz band used in North America; of these are three that have minimal spectral overlap. These are channels 1,6,and 11[1]. Thus in North America, Aps can operate on three separate noninterfering channels. Furthermore, some NAS can switch between channels in order to talk with the AP proving the best signal strength or the one with the AP providing the best signal strength or the one with the lightest traffic load. Use of multiple channels can be very helpful in minimizing co-channels overlap, which would otherwise degrade performance.

Our approach is to assign one of these three channels to each of the Aps and to do so in a way that provides the smallest possible co-channels coverage overlap. Making these frequency assignment

Is essentially a map coloring problem, and there are various algorithms that give optimal or near –optimal assignment of the three radio channels, given a   particular set of AP placements and coverage areas. The design must also consider service to areas with high and low densities of users. If many users of wi-fi computers (mobile computers) are located in a small area (a high density area), it may be necessary to use special design techniques in these areas. We expect that most parts of a campus will be low-density areas. However, there will be some areas, particularly classrooms and lecture halls that will be high-density area, with high concentrations of users, mostly students.

Two design layout techniques that are useful in high-density situation are increasing receiver threshold settings and using multiple wi–fi  Aps. Wi-fi products some provides the controlling the size of coverage area of each Access points.

Here we will discuss on the ideal AP coverage, the coverage volume of the AP

Is shown in fig as three coaxial cylinders, the middle cylinder, representing coverage on floor on which the axis point is located, has radius R. The AP is located on the axis of this cylinder. The upper and lower cylinder, representing the coverage on the floors above and below the one on which theAP is located, have radius R’,

which is less than R. the height of each of the three cylinders can be thought ofbuilding. These three cylinders can be  thoughtof as a single object, which moves about as the location of the AP moves.

The problem of locating of APs   within a building can be viewed as a problem of locating these shapes within the building in such a way that all spaces are filled with as little overlap as possible, while coverage volumes are not actually perfect cylinders, one can find the average coverage radius inside a building and use this as the radius of an idealized cylindrical coverage volume. This can be achieved by defining an acceptable signal strength threshold and determining the average distance from AP at which signals fall below the threshold.

9.2  Design Procedure

The initial selection of  AP location begins with a complete set of signal strength measurements within the building. Signal strength measurements should be made in all areas of building, with particular attention to the building's construction so that characteristics within each part of the building are understood. These measurements have two purpose : to divide the building into spaces  that are relatively isolated from each other from a propagation perspective and to determine the typical coverage radius os AP .signal strength measurements should be taken to determine the same floor coverage radius R' and  the adjacent floor coverage age R' of AP

Access points can be placed within a building in an array that is either linear array shown in figure   each  of these shows how APs can be located in a  single floor needing Wlan coverage.it is only necessary to locates the APs in a way that provides coverage throughout the floor and also minimizes as far as possible the overlap between and among AP coverage areas .A linear array  is used when the building is narrow relative to R, and a rectangular array when the building width is large relative to R

On the hand , in a building that requires coverage on more than one floor ,adjacent floorcoverage must be considered in locating each AP.Usually , a staggered approach is used. As one moves along the length (or width ) of a building, one places APs first on one floor and then on an adjacent floor . In this case the coverage of an AP's adjacent coverage must "dovetails"with the coverage of the next AP's same floor coverage. As in a single floor building, a linear array is used when the building is narrow relative to R, and a rectangular array when the building width is large relative to R.

we illustrate by using four scenarios one will encounter when designing an indoor wireless network. Each is determined by whether the building is single -story or multi-story and by the width of the building relative to R and R' .In each case we give the appropriate out approach and list the figure that illustrates it. Solid lines show coverage on a floor; dashed lines show adjacent floor coverage.

Scenario 1  : single-floor linear array,  illustrated in fig A single story building (or a building that requires wireless coverage on only one floor)whose width (smallestouter dimension)is not large relative to R,D denotes the distance between adjacent Access points

Scenario 2 :                                                            

single floor rectangular array illustrated in fig A single story building(or a building that requires wireless coverage on only one floor)whose width(smallest outer dimension)is large relative to R D denotes the distance between two AP's

Scenario 3

: multi floor linear array illustrated in fig A multistory building whose width is not large relative to R and R' ,D' denotes the distance between adjacent APs on different floors.

Scenario 4: Multi floor rectangular array , illustrated in fig A multistory building whose width (smallest outer dimension) is large relative to R and R',D denotesthe distance between adjacent APs on the same floor , and D' denotes the distance between adjacent APs on  different floors.

10.  Wi-fi v/s bluetooth

As wi-fi continuous it’s expansion the much hyped personal area networking technology known as Bluetooth is recently enter the market. Bluetooth is designed to provide short-range connectivity for peripheral such as keyboards speakers, and headsets. it is design to support low data rate (721 kbps) and limited range (10 m)in order to achieve low coast.

When you compare Bluetooth with wi-fi you will find that Bluetooth is short wire replacement for the mask of the cable. Bluetooth also have network capabilities to max of seven users , with one machine as masters on the other hand wi-fi is “long wire” wireless network replacement technology, it is design to allow user to lock on to the office / business network .

Concerning the technical deference, wi-fi users the packet switching multi point technology as the Ethernet where as Bluetooth users a much simpler time division techniques

Some problem that Bluetooth face is the Microsoft’s most recent operating system, window-XP does not support the Bluetooth. the current price for Bluetooth chip sets is still considerly above the target price US$5. In fact still same range of wi-fi chip sets us$20 to us$30

	Wi-fi	Bluetooth	Swap	irDA	3G
Speed

Range

 10 mbps (802.11b)

54mbps (802.11a)

  300ft – 2000ft741kbps

10m2 mbps

75-125 ft4 mbps2 mbps

11.  WI-FI Security

Wi-Fi CERTIFIED = Confidence

Look for the Wi-Fi CERTIFIED logo on a product before you buy it. The Wi-Fi certified logo is your only assurance that the product has met rigorous interoperability testing requirements to assure products from different vendors will work together. The Wi-Fi CERTIFIED logo means that it's a "safe" buy.

Wi-Fi Certification comes from the Wi-Fi Alliance, a nonprofit international trade organization that tests 802.11-based wireless equipment to make sure it meets the Wi-Fi standard and works with all other manufacturers' Wi-Fi equipment on the market. Thanks to the Wi-Fi Alliance, you don't have to read the fine print or study technical journals: if it says Wi-Fi, it will work.

Wi-Fi Protected Access

Wi-Fi Protected Access had several design goals, i.e.,: be a strong, interoperable,security replacement for WEP, be software upgradeable to existing Wi-Fi CERTIFIED products, be applicable for both home and large enterprise users, and be available immediately. To meet these goals, two primary security enhancements needed to be made. Wi-Fi Protected Access was constructed to provide an improved data encryption, which was weak in WEP, and to provide user authentication, which was largely missing in WEP.

Enhanced Data Encryption through TKIP

To improve data encryption, Wi-Fi Protected Access utilizes its Temporal Key Integrity Protocol (TKIP). TKIP provides important data encryption enhancements including aper-packet key mixing function, a message integrity check (MIC) named Michael, an extended initialization vector (IV) with sequencing rules, and a re-keying mechanism.

Through these enhancements, TKIP addresses all WEP’s known vulnerabilities.

Enterprise-level User Authentication via 802.1x and EAP

WEP has almost no user authentication mechanism. To strengthen user authentication,Wi-Fi Protected Access implements 802.1x and the Extensible Authentication Protocol (EAP). Together, these implementations provide a framework for strong user authentication. This framework utilizes a central authentication server, such as RADIUS, to authenticate each user on the network before they join it, and also employs “mutual authentication” so that the wireless user doesn’t accidentally join a rogue network that might steal its network credentials.

Wi-Fi Protected Access for the Enterprise

Wi-Fi Protected Access effectively addresses the WLAN security requirements for the enterprise and provides a strong encryption and authentication solution prior to the ratification of the IEEE 802.11i standard. In an enterprise with IT resources, Wi-Fi Protected Access should be used in conjunction with an authentication server such as RADIUS to provide centralized access control and management. With this implementation in place, the need for add-on solutions such as VPNs may be eliminated,

at least for the express purpose of securing the wireless link in a network.

Wi-Fi Protected Access for Home/SOHO

In a home or Small Office/ Home Office (SOHO) environment, where there are no central authentication servers or EAP framework, Wi-Fi Protected Access runs in a special home mode. This mode, also called Pre-Shared Key (PSK), allows the use of manually-entered keys or passwords and is designed to be easy to set up for the home user. All the home user needs to do is enter a password (also called a master key) in their access point or home wireless gateway and each PC that is on the Wi-Fi wireless network. Wi-Fi Protected Access takes over automatically from that point. First, the password allows only devices with a matching password to join the network, which keeps out eavesdroppers and other unauthorized users. Second, the password automatically kicks off the TKIP encryption process.

Wi-Fi Protected Access for Public Access

The intrinsic encryption and authentication schemes defined in Wi-Fi Protected Access may also prove useful for Wireless Internet Service Providers (WISPs) offering Wi-Fi public access in “hot spots” where secure transmission and authentication is particularly important to users unknown to each other. The authentication capability defined in the specification enables a secure access control mechanism for the service providers and for mobile users not utilizing VPN connections.

12.  WI FI  APPLICATIONS

Wireless networking is applicable to all industries with a need for mobile computer usage or when the installation of physical media is not feasible. Such networking is especially useful when employees must process information on the spot, directly in front of customers, via electronic-based forms and interactive menus. Wireless networking makes it possible to place portable computers in the hands of mobile front-line workers such as doctors, nurses, warehouse clerks, inspectors, claims adjusters, real estate agents, and insurance salespeople.

The coupling of portable devices with wireless connectivity to a common database and specific applications meets mobility needs, eliminates paperwork, decreases errors, reduces process costs, and improves efficiency. The alternative to this, which many companies still employ today, is utilizing paperwork to update records, process inventories, and file claims. This manual method processes information slowly, produces  redundant data, and is subject to errors caused by illegible handwriting. The wireless computer approach using a centralized database is clearly superior.

Installation in Difficult-to-Wire Areas

The implementation of wi-fi networks offers many tangible cost savings when performing installations in difficult-to-wire areas. If rivers, freeways, or other obstacles separate buildings you want to connect, a wi-fi solution may be much more economical than installing physical cable or leasing communication circuits, such as T1 service or 56 Kbps lines. Some organizations spend thousands or even millions of dollars to install physical links with nearby facilities. If you are facing this type of installation, consider wireless networking as an alternative. The deployment of wireless networking in these situations costs thousands of dollars, but will result in a definite cost savings in the long run.

 A Wi-fi Solution in an Historic Building

An observatory in Australia has provided stargazing to astronomy enthusiasts for nearly 140 years. Built in 1858, the observatory is classified by the National Trust as one of Australia's historical buildings.

When the observatory began investigating ways to share these views of space with a much broader audience, the obvious solution was to download images to multiple PCs and large screens via a local area network. Due to the historical nature of the building, however, cabling was not an option. Very thick sandstone walls and historic plaster ceilings could not be easily drilled into, and strings of cable would have been unsightly and unsafe to the public.

The observatory installed Lucent Wi fi radio cards in each of the their eight PCs and the network server. Telescopic images are downloaded from the Internet or from electronic cameras housed in the observatory's telescopes. These images are then displayed on the various PCs for individual viewing or on larger monitors for group viewing.

 

Retail

Retail organizations need to order, price, sell, and keep inventories of merchandise. A wireless network in a retail environment enables clerks and storeroom personnel to perform their functions directly from the sales floor. Salespeople are equipped with a pen-based computer or a small computing device with bar code reading and printing capability, with the wireless link to the store's database. They are then able to complete transactions-such as pricing, bin labeling, placing special orders, and taking inventory-from anywhere within the store.

Warehouses

Warehouse staff must manage the receiving, putting away, inventory, and picking and shipping of goods. These responsibilities require the staff to be mobile. Warehouse operations have traditionally been a paper-intensive and time-consuming environment. An organization can eliminate paper, reduce errors, and decrease the time necessary to move items in and out, however, by giving each warehouse employee a handheld computing device with a bar code scanner interfaced via a wireless network to a warehouse inventory system.

Upon receiving an item for storage within the warehouse, a clerk can scan the item's bar coded item number and enter other information from a small keypad into the database via the handheld device. The system can respond with a location by printing a put-away label. A forklift operator can then move the item to a storage place and account for the procedure by scanning the item's bar code. The inventory system keeps track of all transactions, making it very easy to produce accurate inventory reports.

As shipping orders enter the warehouse, the inventory system produces a list of the items and their locations. A clerk can view this list from the database via a handheld device and locate the items needed to assemble a shipment. As the clerk removes the items from the storage bins, the database can be updated via the handheld device. All these functions depend heavily on wireless networks to maintain real-time access to data stored in a central database.

 

Healthcare

Healthcare centers, such as hospitals and doctors' offices, must maintain accurate records to ensure effective patient care. A simple mistake can cost someone's life. As a result, doctors and nurses must carefully record test results, physical data, pharmaceutical orders, and surgical procedures. This paperwork often overwhelms healthcare staff, taking 50-70 percent of their time. Doctors and nurses are also extremely mobile, going from room to room caring for patients. The use of electronic patient records, with the ability to input, view, and update patient data from anywhere in the hospital, increases the accuracy and speed of healthcare. This improvement is possible by providing each nurse and doctor with a wireless pen-based computer, coupled with a wireless network to databases that store critical medical information about the patients.

A doctor caring for someone in the hospital, for example, can place an order for a blood test by keying the request into a handheld computer. The laboratory will receive the order electronically and dispatch a lab technician to draw blood from the patient. The laboratory will run the tests requested by the doctor and enter the results into the patient's electronic medical record. The doctor can then check the results via the handheld appliance from anywhere in the hospital.

Another application for wireless networks in hospitals is the tracking of pharmaceuticals. The use of mobile handheld bar code printing and scanning devices dramatically increases the efficiency and accuracy of all drug transactions, such as receiving, picking, dispensing, inventory taking, and the tracking of drug expiration dates. Most importantly, however, it ensures that hospital staff can administer the right drug to the right person in a timely fashion. This would not be possible without the use of wireless networks to support a centralized database and mobile data collection devices.

 

Real Estate

Real estate salespeople perform a great deal of their work away from the office, usually talking with customers at the property being sold or rented. Before leaving the office, salespeople normally identify a few sites to show a customer, print the Multiple Listing

Service (MLS) information that describes the property, and then drive to each location with the potential buyer. If the customer is unhappy with that round of sites, the real estate agent must drive back to the office and run more listings. Even if the customer decides to purchase the property, they must both go back to the real estate office to finish paperwork that completes the sale.

Wireless networking makes the sale of real estate much more efficient. The real estate agent can use a computer away from the office to access a wireless MLS record. IBM's Mobile Networking Group and Software Cooperation of America, for example, make wireless MLS information available that enables real estate agents to access information about properties, such as descriptions, showing instructions, outstanding loans, and pricing. An agent can also use a portable computer and printer to produce contracts and loan applications for signing at the point of sale.

Hospitality

Hospitality establishments check customers in and out and keep track of needs, such as room-service orders and laundry requests. Restaurants need to keep track of the names and numbers of people waiting for entry, table status, and drink and food orders. Restaurant staff must perform these activities quickly and accurately to avoid making patrons unhappy. Wireless networking satisfies these needs very well.

Wireless computers are very useful in the situations where there is a large crowd, such as a restaurant. For example, someone can greet restaurant patrons at the door and enter their names, the size of the party, and smoking preferences into a common database via a wireless device. The greeter can then query the database and determine the availability of an appropriate table. Those who oversee the tables would also have a wireless device used to update the database to show whether the table is occupied, being cleaned, or available. After obtaining a table, the waiter transmits the order to the kitchen via the wireless device, eliminating the need for paper order tickets.

 

Utilities

Utility companies operate and maintain a highly distributed system that delivers power and natural gas to industries and residences. Utility companies must continually monitor the operation of the electrical distribution system and gas lines, and must check usage meters at least monthly to calculate bills. Traditionally, this means a person must travel from location to location, enter residences and company facilities, record information, and then enter the data at a service or computing center. Today, utility companies employ wireless networks to support the automation of meter reading and system monitoring, saving time and reducing overhead costs.

Kansas City Power & Light operates one of the largest wireless metering systems, serving more than 150,000 customers in eastern Kansas and western Missouri. This system employs a monitoring device at each customer site that takes periodic meter readings and sends the information back to a database that tracks usage levels and calculates bills, avoiding the need for a staff of meter readers.

13.  The Future of  Wi-Fi

Intel put aside $150 million of this fund to invest in Wi-Fi initiatives.

Intel expects to introduce its Banias processor for mobile devices during the first half of 2004, said a company spokeswoman. Banias is a low-power processor designed specifically for mobile devices that includes integrated 802.11a and 802.11b wireless capabilities.

Cometa aims to roll out a nationwide Wi-Fi network and sell exclusively through the channel, said Lawrence Brilliant, CEO of Cometa, in a recent interview with CRN.

Looking to Wi-Fi rather than 3G, BT  ( British Telco )  has installed some 80 Wi-Fi hotspots, called ‘Openzone’, in Hilton hotels, airports and motorway service stations across the UK, and has agreements to put in place another 40.

BT believes that Wi-Fi - which is expected to be half the price of 3G and three times faster - is will be the fastest growing mobile technology.

The Hilton hotel group, which was one of the first businesses to trial BT Openzone, has allowed the installation of  wi-fi hotspots in 36 of their hotels across England, Scotland and Wales. Hilton has agreed to install 15 more hotspots at further hotels in the near future.

The company hopes to have 400 hotspots by summer this year and 4,000 by June 2005. In the future it is expected that BT’s wi-fi hotspots will also reach railway stations