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802.11b Tips, Tricks, and Facts

by Rob Flickenger

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There's much more to 802.11b spec than that teeny little "b" indicates. 802.11b is not just the downstairs apartment of 802.11; it's a whole new world of wireless possibilities.

Before we examine what makes that little "b" so special, let's take a look at the original 802.11:

But 802.11 isn't perfect. For example, how do you detect collisions with a device that can transmit or receive at any given moment, but can't do both at the same time?

What happens when packets you've sent bounce off of a distant wall and come right back at you microseconds later?

Another major problem with 802.11 equipment was its relatively low speed compared to wired networking -- only up to 2 Mbps -- and the fundamental incompatibility (and confusion) between FHSS and DSSS equipment. But because they were incompatible, a choice had to be made. And that choice led to the 802.11b spec.

The move to DSSS and 802.11b

The FHSS frequency-hopping cards were the first to hit the marketplace, as they were cheaper to produce and easier to implement than DSSS. As time marched on (and with Moore's Law in effect), the processing power needed to cheaply implement DSSS soon became available. As it turned out, given the FCC's broadcasting constraints and some terribly clever engineering, DSSS began to prove itself as the more reliable solution.

In September of 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 Mbps (up to 11 Mbps). While breaking compatibility with FHSS schemes, the new extensions made it possible for new equipment to continue to interoperate with older 802.11 DSSS hardware.

With the ever-present need for speed temporarily quenched, everyone who is anyone started jumping on the wireless roller coaster. While Lucent and Cisco are the major producers, Apple, Xircom, Linksys, IBM, and others have all come out with OEM equipment.

Now that the spec is set (for the moment), let's review a few tips to make your wireless networking experience as solid as possible.

Wireless networking tips

Here are some practical 802.11 facts that any self-respecting wireless hacker should be aware of:

So in short, while they're billed for 11 Mbps, your mileage will most certainly vary. The most I've been able to squeeze through a card doing WEP was about 6.5 Mbps sustained (roughly 8 Mbps without WEP), and even that was downhill with a good, stiff tailwind.

Searching for a good signal

Rob using a parabolic dish in search of the strongest signal

Antenna tips and tricks

Antenna selection has a tremendous impact on the range of your wireless network. Here a few things I've learned:

Finally, here's a real gem: Lay your antennas in the spring. Trust me.

Why, you ask?

Well, your worst natural enemy is water. Low-power microwaves will bounce off leaves like a mirror. If you set up a well-placed antenna in the winter, you will be horribly disappointed in April when the trees are blooming and your signal is dropping.

Disruptive technology?

To sum up: 802.11b has brought speed and cheap, reliable hardware to the networking world. For the first time, people can bring up high-speed, encrypted communication lines for only the cost of hardware. As disruptive technologies go, this one has its disrupter set on "obliterate."

Rob Flickenger is a long time supporter of FreeNetworks and DIY networking. Rob is the author of three O'Reilly books: Building Wireless Community Networks, Linux Server Hacks, and Wireless Hacks.

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