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Building Wireless Community Networks by Rob Flickenger

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Chapter 1.  Wireless Community Networks

In recent times, the velocity of technology development has exceeded “blur” and is now moving at speeds that defy description. Internet technology in particular has made astounding strides in the last few years. Where only a few short years ago 56Kb modems were all the rage, many tech heads now find themselves complaining about how slow their company’s T1 connection seems compared to their 6Mb DSL connection at home.

Never before have so many had free and fast access to so much information. As more people get a taste of millisecond response times and megabit download speeds, they seem only to hunger for more. In most places, the service everyone is itching for is DSL , or Digital Subscriber Line service. It provides high bandwidth (typically, anywhere from 384Kbps to 6Mbps) over standard copper telephone lines, if your installation is within about three miles of the telephone company’s CO, or central office (this is a technical constraint of the technology). DSL is generally preferred over cable modems, because a DSL connection provides guaranteed bandwidth (at least to the telephone company) and thus is not directly affected by the traffic habits of everyone else in your neighborhood. It isn’t cheap, ranging anywhere from $50 to $300 per month, plus ISP and equipment charges, but that doesn’t seem to be discouraging demand.

Telephone companies, of course, are completely enamored with this state of affairs. In fact, the intense demand for high-bandwidth network access has led to so much business that enormous lead times for DSL installations are now the rule in many parts of the country. In many areas, if you live outside the perceived “market” just beyond range of the CO, lead times are sometimes quoted at two to three years (marketing jargon for “never, but we’ll take your money anyway, if you like”). Worse than that, in the wake of widespread market consolidation, some customers who were quite happy with their DSL service are finding themselves stranded when their local ISP goes out of business.[1]

What are the alternatives for people who want high-speed Internet access but aren’t willing to wait for companies to package a solution for them? The telephone companies own the copper, and the cable companies own the coax.

Wireless networking now provides easy, inexpensive, high-bandwidth network services for anyone who cares to set it up.

Approved in 1997 by the IEEE Standards Committee, the 802.11 specification detailed the framework necessary for a standard method of wireless networked communications. It uses the 2.4GHz microwave band designated for low-power, unlicensed use by the FCC in the U.S. in 1985. 802.11 provided for network speeds of one or two megabits, using either of two incompatible encoding schemes: Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS).

In September, 1999, the 802 committee extended the specification, deciding to standardize on DSSS. This extension, 802.11b, allowed for new, more exotic encoding techniques. This pushed up the throughput to a much more respectable 5.5 or 11Mbps. While breaking compatibility with FHSS schemes, the extensions made it possible for new equipment to continue to interoperate with older 802.11 DSSS hardware. The technology was intended to provide “campus” access to network services, offering typical usable ranges of about 1500 feet.

It didn’t take long for some sharp hacker types (and, indeed, a few CEO and FCC types) to realize that by using 802.11b client gear in conjunction with standard radio equipment, effective range can extend to more than twenty miles and potentially provide thousands of people with bandwidth reaching DSL speeds, for minimal hardware cost. Connectivity that previously had to creep up monopoly-held wires can now fly in through the walls with significantly higher performance. And since 802.11b uses unlicensed radio spectrum, full-time connections can be set up without paying a dime in airtime or licensing fees.

While trumping the telco and cable companies with off-the-shelf magical hardware may be an entertaining fantasy, how well does 802.11b equipment actually perform in the real world? How can it be applied effectively to provide access to the Internet?

The Problem

An obvious application for 802.11b is to provide the infamous “last mile” network service. This term refers to the stretch that sits between those who have good access to the Internet (ISPs, telcos, and cable companies) and those who want it (consumers). This sort of arrangement requires 802.11b equipment at both ends of the stretch (for example, at an ISP’s site and at a consumer’s home).

Unfortunately, the nature of radio communications at microwave frequencies requires line of sight for optimal performance. This means that there should be an unobstructed view between the two antennas, preferably with nothing but a valley between them. This is absolutely critical in long distance, low power applications. Radio waves penetrate many common materials, but range is significantly reduced when going through anything but air. Although increasing transmission power can help get through trees and other obstructions, simply adding amplifiers isn’t always an option, as the FCC imposes strict limits on power. (See Appendix A for a copy of the FCC Part 15 rules that pertain to 2.4GHz emissions. We will return to this subject in detail in Chapter 7.)

Speaking of amplifiers, a related technical obstacle to wireless nirvana is how to deal with noise in the band. The 2.4GHz band isn’t reserved for use solely by 802.11b gear. It has to share the band with many other devices, including cordless phones, wireless X-10 cameras, Bluetooth equipment, burglar alarms, and even microwave ovens! Using amplifiers to try to “blast” one’s way through intervening obstacles and above the background noise is the social equivalent of turning your television up to full volume so you can hear it in your front yard (maybe also to hear it above your ringing telephone and barking dog, or even your neighbor’s loud television...).

If data is going to flow freely over the air, there has to be a high degree of coordination among those who set it up. As the airwaves are a public resource, the wireless infrastructure should be built in a way that benefits the most people possible, for the lowest cost. How can 802.11b effectively connect people to each other?



[1] One currently circulating meme for this phenomenon deems a stranded DSL customer “Northpointed,” in honor of the ISP NorthPoint.net, which went out of business last March, leaving thousands without access.

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