802.11 Wireless Networks: The Definitive Guide

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Our reviewer says this is the best 802.11 reference he's read, even though it omits some key points.

Title: 802.11 Wireless Networks: The Definitive GuideAuthor: Matthew S. GastPublisher: O'Reilly & Associates Inc.ISBN: 0-596-00183-5

When its time to microwave your house, neighbors or office, this is the book you need. (Microwave as in wireless Ethernet, that is.) With some minor exceptions, this book is a great reference for all things WiFi. If you plan on deploying a wireless network or are having trouble with an existing one, most of this book is required reading--just don't read it in chapter order (more about that later). This is just the book I wished for while thumping my forehead against the wall trying to inject the same material directly from the IEEE 802.11 docs. Thank you, Mr. Gast, for saving my house while giving me a better understanding of low level 802.11.

Now, with that glowing overview fresh in your mind it seems only fair to talk about what is wrong with the book first. Don't worry, I'll get the good parts soon enough.

First off, some topics related to wireless Ethernet are not covered in this book that should be.

Antenna Building

If you are looking for a reference to build a Pringles can/yagi, a coffee can/circular wave guide, a homemade DSS parabolic dish or other high performance, homemade antenna, you'll have to look elsewhere (like The ARRL Antenna Book 19th Edition, ISBN 0-87259-804-7). But don't look here because you won't find it.

FCC Regulations Title 47 Part 15

Part 15 describes what is legal and illegal in terms of these unlicensed radio devices. This book barely mentions these regulations and incorrectly interprets some of their meaning. I'd expect "The Definitive Guide" to include part 15 in an appendix along with some helpful interpretive commentary. In particular, information on calculating ERP for directional antennas and point to point applications, where the FCC regulations make special allowances, would be helpful. Commentary on FCC certification for radio systems would be useful as well. It seems that the common practice of adding antennas that are within the gain allowed for ERP, but not specifically certified with the radio, is done often done but technically not allowed. The missing part 15 reference is a large oversight.

Long Distance Links and Bridges

Virtually no coverage is given to creating "long distance" links with 802.11b. The ability to dump leased data lines with high monthly fees is an exciting and profitable application of this technology. 802.11b equipment can replace T-1 lines in some instances with virtually no recurring cost and with greater throughput (nearly 6Mbs for 802.11b versus 1.54 Mbs for T-1.) Such point-to-point links and wireless Ethernet bridging certainly should receive more coverage. The few sentences about long distance links suggest using a compass and topo map to point directional antennas across long distances; no mention is made of using a GPS to calculate bearings (to use with the compass) and a handheld mirror.

The boy scout trick of flashing a mirror to locate someone too far away to easily see really works; I've used it for long links. There was also no mention of calculating the signal loss of microwave radiation over distance, fade margins, Fresnel zones or signal polarization. All these items would be useful, particularly for long distance links. Antenna diversity was mentioned, but not the fact that both antennas should cover the same basic domain for proper operation, effectively disallowing the use of one high gain and one omni directional antenna with the thought of covering stations both close and far away. In addition, practical advice on selecting equipment housing for outdoor installations is missing. Also interesting would be information on using solar cells to power wireless relay nodes in places where AC power isn't easily available.

IP Addresses and Routing

IP address allocation (unrouted IP space) and IP routing are not covered. For folks who aren't already accustomed to unrouted IP ranges, NAT and IP routing can become hairy when deploying networks of any size. Although not just a WiFi issue, they deserve more coverage. (Gast does get brownie points for his mention of mobile IP, though.)

A few errors, misrepresentations, type-setting problems and contradictions are present, but they are relatively scarce amongst the volumes of accurate and useful info. But in case I've piqued your interest, I'll list a few. The most notable are his recommendations concerning WEP, which are frequent and contradictory.

In the typesetting department "Re-addressing" becomes "read-dressing", which confused me for a few seconds (poor hyphenation algorithm I suppose). For the minor error department: in the WEP key length sidebar talking about the 128-bit WEP, Gast says, "After subtracting 104 bits for the shared secret component of the RC4 key, only 104 bits are secret", when he means something like "after subtracting the 24 bit Initialization Vector component of the RC4 key, only 104 bits are secret."

A little more perplexing is the nice sidebar on page 154 about "the nonexistent Microwave Absorption Peak of Water", a point he seems to ignore on page four when he says the 2.4GHz frequency was chosen for microwave ovens "because electromagnetic radiation at that frequency is particularly effective for heating water." And finally, of greater concern, he also ignores FCC part 15 regulations concerning certification when talking about the use of amplifies and specialized antennas for covering large areas--a much more serious omission.

While reading the book I sometimes found myself asking "didn't you just tell me that?" because of the redundancy, though no doubt some will find the repetition more useful than annoying.

O'Reilly maintains a web site to list book corrections, a useful service. Hopefully corrections will appear shortly on the errata site for this book.

Okay, that's most of the bad stuff. So what was good? Plenty!

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Thanks.

Jnanesh's picture

Thanks for such an elaborate review.

Re: 802.11 Wireless Networks: The Definitive Guide

Anonymous's picture

About the microwave absorption at 2.45Ghz, the short answer is that water absorbs different frequencies differently at different temperatures, and you don't want the frequency with the most absorption, or else the thin outside layer of the food gets boiled off while the inside remains cold.

The 2.45Ghz frequency is the best balance of absorption between 0C and 100C for cooking food. Details can be found at this link:

http://www.sbu.ac.uk/water/microwave.html

Re: 802.11 Wireless Networks: The Definitive Guide

Anonymous's picture

it's just OR-IH-NO-CO

Re: 802.11 Wireless Networks: The Definitive Guide

Anonymous's picture

Obviously not an Enya fan. :)