Although most SOHO (Small Office/Home Office) Wi-Fi network users incorporate only one wireless access point (AP) in their networks, it’s possible to create a network with multiple access points, each access point serving a zone within an area too large for a single AP to serve. Such a network, incorporating multiple access points, is called an extended service set (ESS.) In an ESS, users with laptops and PDAs are able to roam about the entire area covered by the ESS and not lose their connections to the network. The several access points seamlessly ‘hand off ‘ users who ‘roam’ from place to place, just as the cells in mobile telephone network do.

At least that’s how it should work in theory.

The problem is that this is one of the several ’soft spots’ in the 802.11b Wi-Fi wireless networking specification. 802.11 dictates that roaming is permitted, and explains what should happen when clients roam from the influence of one AP into the influence of another. Unfortunately, the specification doesn’t say how this roaming should be accomplished. Roaming isn’t trivial, and requires some pretty detailed communication among the various access points within the ESS. The numerous manufacturers of access points have all implemented the details of roaming in different ways, most of which are incompatible with all the others.

What this means is that for an ESS to implement roaming correctly, all the access points in the ESS must be from the same manufacturer -and, ideally, of the same model. In general, access points designed for corporate rather than residential service work best in roaming installations. Some of the lower-end residential access points and wireless residential gateways don’t implement roaming at all.
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For years, getting onto the Internet meant plugging into it that is, literally connecting a wire to your computer that, if you could crawl inside and follow it through all the walls, ceilings, pipes, and relay stations of the world, would eventually lead you to the Internet.

Nowadays, however, an increasing number of people get online without connecting any wires at all. Wireless hot spots, also known as WiFi or Hotspot networks, are invisible pools of Internet signal, 300 feet across, that let wireless-equipped computers get onto the Internet at high speed. Travelers with wireless-ready laptops connect to the Internet via these wireless hot spots in airports, coffee shops, hotel lobbies, and just about anywhere else they have work to do or time to kill.

Usually, you have to pay a fee to use one of these public hot spots. But if you live in an apartment building or other tightly spaced housing, an even better option may await you. You may be able to hop onto the Internet using someone else’s wireless signal. Sometimes the signal bleeds into your home without the owner’s knowledge, in which case you very lucky person you may be able to get online free, at least until the owner catches on. More often, though, someone in the building makes his signal available deliberately, collecting, say, $5 a month from each person who shares it.

If you’re such a lucky neighbor, then it’s not true that you need an ISP to get onto the Internet. Your neighbor has an ISP account, which he’s sharing with you. In that case, you’re getting online not via an ISP, but through a Very Shrewd Neighbor.

Maybe you know there’s a wireless network in the air, but no message is popping up on your screen. Or maybe the message does pop up, but it won’t let you by without a password. Or maybe no password’s necessary, but you still can’t actually do anything on the Internet.

Here’s your guidebook to the obstacles that may stand between you and wireless Internet heaven.

Possibility 1
Sometimes the dialog box just doesn’t pop up, even though the hot spot is otherwise perfectly available.

In Windows XP, choose Start, Connect To. If you don’t see any networks listed, right-click the Wireless Connection icon in the Network Connections window and choose View Available Wireless Networks from the shortcut menu.

On a Mac, click the AirPort icon on the Mac’s menu bar to see a list of wireless networks in the area.

Possibility 2
At many conferences, libraries, hotel lobbies, and schools, just clicking Connect or OK in the “a wireless network is available” dialog box is all it takes to get online.

At commercial hot spots, though the ones you have to pay for you can’t just open your email program to start communicating. Instead, you must first open your Web browser and log in at the welcome page.

At Starbucks, restaurant, and many airports, that welcome page bears the Free Hospot logo; at many hotels and other airports, it’s a welcome page. Either way, this is where you’re supposed to plug in your credit card number (or, if you have an existing account, sign in).

Only then can you use your Web browser, email program, chat software, and other functions that require your laptop to be online

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Continue from Discover Potential of Network Coding.

The hypothetical six-node digital network depicted can help clarify those options. Recall that in computers, all messages take the form of a string of binary code. Imagine that each link, or road, in this network can carry one bit—be it a 0 or a 1—per second and only in the direction designated by the corresponding arrow. Amy, a network user at node A, hopes to send information at one bit per second to Dana at node D. Meanwhile Ben at node B hopes to send, at exactly the same time and rate, information to Carl at node C. Can both Amy’s and Ben’s demands be satisfied simultaneously without exceeding any of the links’ capacities?

In a router system, the outlook seems bleak. Both paths, from Amy to Dana and from Ben to Carl, require traversing link 5. This link becomes the equivalent of a narrow, one-lane bridge. The router at node E, where link 5 starts, receives a total of two bits per second (one from link 2 and one from link 3), but because link 5’s capacity is one, the router can send only one bit per second along it. In the transportation model, such bottlenecks cause nightmare traffic jams, with more and more bits piling up over time, waiting their turn.

In the new approach, though, the plain router would be replaced by a coder, which would have more options than would be open to a traffic cop. Instead of relaying the actual bit streams collected at the bottleneck, the coder could send quite different information. It could, for example, add up the number of 1s that arrive during any given second and transmit a 0 if that sum is even. If the sum is odd, the device could transmit a 1. So, if link 5 simultaneously receives a 1 and a 0 from links 2 and 3, it carries a 1. If either two 0s or two 1s are received from links 2 and 3, link 5 carries a 0. The result then gets sent by router F down links 6 and 7 to Carl and Dana, respectively.

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An approach called network coding could dramatically enhance the efficiency and reliability of communications networks. At its core is the strange notion that transmitting evidence about messages can be more useful than conveying the messages themselves.

Claude E. Shannon, mathematician and engineer, launched one such revolution almost 60 years ago by laying the foundation of a new mathematical theory of communications, now known as information theory. Practical outgrowths of his work, which dealt with the compression and reliable transmission of data, can be seen today in the Internet, in land line and wireless telephone systems, and in storage devices, from hard drives to CDs, DVDs and fl ash memory sticks.

Shannon tackled communications over phone lines dedicated to individual calls. These days, information increasingly travels over shared networks (such as the Internet), in which multiple users simultaneously communicate through the same medium, be it a cable, an optical fiber or, in a wireless system, air. Shared networks can potentially improve the usefulness and efficiency of communications systems, but they also create competition for communal resources. Many people must vie for access to, say, a server offering downloadable songs or to a wireless hot spot.

The challenge, then, is to find ways to make the sharing go smoothly; parents of toddlers will recognize the problem. Network operators frequently try to solve the challenge by increasing resources, but that strategy is often insufficient. Copper wires, cables or fiber optics, for instance, can now provide high bandwidth for commercial and residential users yet are expensive to lay and difficult to modify and expand. Ultrawideband and multiple-antenna transmission systems can expand the number of customers served by wireless networks but may still fail to meet ever increasing demand.

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Many corporations and industries are jumping into the wireless arena.Two of the industries most committed to deploying wireless technologies are airports and hotels, for business travelers’ communications needs. If they are traveling in a car, they use their wireless phones. When they are at work or home, they are able to use their computers and resources to again be productive. But when staying in a hotel for the night or even a week, there are few choices, a business traveler can look for the RJ-11 jack and connect to the Internet via 56-kilobit modem, not connect at all, or connect wirelessly. When
a hotel provides the correct configuration information based on the provider, and a software configuration, a business traveler with wireless capabilities
can connect to their network without worrying about connection speed or out-of-date modems.

Airports offer such services to increase travelers’ productivity at a time when they would otherwise be isolated from business resources.The same configuration applies: set the configuration in the wireless client software and, voilà, you are connected. This wireless technology allows users to get access to the Internet, e-mail, and even the corporate intranet sites utilizing a virtual private network (VPN) solution. Now, the work (or in some cases, gaming) can be done during what used to be known as idle time.This increase in productivity is very attractive to corporations

Using Wireless in the Retail World
Wireless point-of-sale (POS) applications are extremely useful for both merchant and customer, and will revolutionize the way retail business transactions occur. Registers and printers are no longer fixed in place and can be used at remote locations. Wireless scanners can further assist checkout systems.Wireless technology is used for connecting multiple cash registers through an access point to a host computer that is connected to the WAN.This WAN link is used to send real-time data back to a corporate headquarters for accounting information.

Another type of wireless point-of-sale application is inventory control. A handheld scanner is used for multiple purposes.The operator can check inventory on a given product throughout the day and wirelessly transfer the data back to the main computer system.This increases efficiency in that the device is mobile and small, and the data is recorded without manually having to enter the information.

Using Wireless in Monitoring Applications
We have been using wireless technologies for monitoring for years.There are typically two types of monitoring: passive and active. Active monitoring is conducted by use of radio signals being transmitted, and any of a number of expected signals received. An example of this implementation is the use of radar guns in traffic control. In this case, the patrolman points the gun and pulls the trigger, and a specific reading of a specific target is displayed on the radar unit. Passive monitoring is a long-term implementation whereby a device listens to a transmitter and records the data. An example of this is when an animal is tagged with a transmitter and the signal is collected and data is gathered over a period of time to be interpreted at a later date.

Monitoring applications in use today include NASA listening to space for radio signals, and receiving pictures and data relayed from probes; weather satellites monitoring the weather patterns; and geologists using radio waves to gather information on earthquakes.

Applying Wireless Technology to Horizontal Applications
Along with the many vertical markets and applications, you can apply wireless technologies to horizontal applications, meaning that delivery services, public safety, finance, retail, and monitoring can all use and benefit from them.Next post gives an overview of some of the more popular horizontal trends in wireless technology.

Internet connection sharing is probably the biggest single part of Wi-Fi’s attraction for small office and home office users, but sharing printers can also be extremely useful. Not everyone in the house needs his or her own laser printer! You can buy a small device called a wireless print server, which connects to a printer via a parallel port usually and has a built-in Wi-Fi client adapter, complete with antenna. The popular Linksys WPS-11 supports only one printer, but other similar devices like D-Link’s DP-313 have additional parallel ports for supporting more than one printer on the same wireless link.

With its data cable connected to a wireless print server, your printer can be anywhere in your home or office where it’s within range of a wireless access point. You don’t need a computer nearby at all-whatever computing power is needed for the print server function is built into the wireless print server itself. Linksys has recently released a new print server, the Linksys PPS1UW EtherFast Wireless-Ready USB PrintServer, with support for USB-interface printers. Interestingly, the Linksys PPS1UW has both a wired and wireless interface, making it compatible with almost any type of home office network.

Game consoles that allow Ethernet connections for multi-player gaming can be connected to your Wi-Fi network through an Ethernet wireless bridge like the Linksys WET-11 or the D-Link DWL-810+ Ethernet to Wireless Bridge. An Ethernet wireless bridge allows any Ethernet device to connect wirelessly to a Wi-Fi access point or gateway. Game consoles are the #1 use of such bridges, but they can also be used with Ethernet-equipped printers, scanners, and anything else that communicates through a standard Ethernet port.

Other Wi-Fi gadgetry continues to show up on a regular basis, and some of it is very cool. One of my favorite recent entries is the D-Link DCS-1000W wireless network camera. It can take both snapshot images and streaming video and send them over your Wi-Fi network. When used as a security camera, it has a motion detector feature that triggers transmission of images when something moves in its field of view. (It can actually email you when it ’sees’ something-with a snapshot attached!) It can stream video to hard disk, or act as a Webcam with its integrated Web server. Unlike a lot of inexpensive wireless video baby monitors, it incorporates data encryption using Wired Equivalent Privacy so that people outside your home can’t use your own cameras to spy on you.