Some types of antenna focus the signal in a particular direction and are referred to as directional antennas. In special applications where you want an AP to send its signal only in a specific direction, you could replace the omnidirectional antenna with a directional antenna. In a home, omnidirectional is usually the best choice, but that also depends on the shape of the home; some antennas are better for brownstones and multifloor buildings because they have a more spherical signal footprint rather than the standard flat-ish one.

Receive sensitivity: The receive sensitivity of an AP or other wireless networking device is a measurement of how strong a signal is required from another radio before the device can make a reliable connection and receive data.

Signal attenuation: A radio signal can get weaker as a result of interference caused by other radio signals because of objects that lie in the radio wave path between radios and because of the distance between the radios. The reduction in signal is attenuation. Read through Chapter 6 for a discussion of how to plan the installation of your wireless network to deal with signal attenuation.

In order to replace or add an antenna to an AP or other wireless device, you need to have a place to plug it in — as obvious a statement as that is, many antennas are not detachable, and you can’t add another antenna. Some access points use reverse TNC connectors that let optional antennas be used in 802.11b/g products, but there’s a minor trend away from using detachable antennas in 802.11a products because of potential conflict in the frequency channels allocated to 802.11a. This potentially thwarts misuse, but also robs those deploying access points of their ability to choose optimal antennas.

Industry Standards

One of the most significant factors that has led to the explosive growth of personal computers and their impact on our daily lives has been the emergence of industry standards. Although many millions of personal computers are in use today around the world, only three families of operating system software run virtually all these computers: Windows, Mac OS, and Unix (including Linux). Most personal computers that are used in the home employ one of the Microsoft Windows operating systems or one of the Apple Macintosh operating systems. The existence of this huge installed base of potential customers has enabled hundreds of hardware and software companies to thrive by producing products that interoperate with one or more of these industry standard operating systems.

Computer hardware manufacturers recognize the benefits of building their products to industry standards. To encourage the adoption and growth of wireless networking, many companies that are otherwise competitors have worked together to develop a family of wireless networking industry standards that build on and interoperate with existing networking standards. As a result, reasonably priced wireless networking equipment is widely available from many manufacturers. Feel safe buying equipment from any of these manufacturers because they’re all designed to work together, with one important caveat. The current three major flavors of this wireless networking technology for LAN applications are IEEE 802.11a, 802.11b, and 802.11g. You just have to pick the flavor that best fits your needs and budget. (Note: There are other wireless standards for other applications in the home, like Bluetooth for short range communications. We talk about these in Chapter 3 and elsewhere where their discussion is appropriate.)

The Institute for Electrical and Electronics Engineers

The Institute for Electrical and Electronics Engineers (IEEE) is a standardsmaking industry group that has for many years been developing industry standards that affect the electrical products that we use in our homes and businesses every day. At present, the IEEE 802.11b standard is the overwhelming market leader in terms of deployed wireless networking products. Products that comply with this standard weren’t the first wireless networking technology on the market . . . but they are now, by far, the dominant market installed base. As you will soon see, the 802.11a and g products are coming on strong.

TX power output and antenna gain

The Wi-Fi Alliance

In 1999, several leading wireless networking companies formed the Wireless Ethernet Compatibility Alliance (WECA), a nonprofit organization (www.weca. net). This group has recently renamed itself the Wi-Fi Alliance and is now a voluntary organization of over 200 companies that make or support wireless networking products. The Wi-Fi Alliances’ primary purpose is to certify that IEEE 802.11 products from different vendors will interoperate (work together). These companies recognize the value of building a high level of consumer confidence in the interoperability of wireless networking products.

The Wi-Fi Alliance organization has established a test suite that defines how member products will be tested by an independent test lab. Products that pass these tests are entitled to display the Wi-Fi trademark, which is a seal of interoperability. Although there is no technical requirement in the IEEE specifications stating that a product must pass these tests, Wi-Fi certification encourages consumer confidence that products from different vendors will work together.

The Wi-Fi interoperability tests are designed to ensure that hardware from different vendors can successfully establish a communication session with an acceptable level of functionality. The test plan includes a list of necessary features. The features themselves are defined in detail in the IEEE 802.11 standards, but the test plan specifies an expected implementation.

IEEE 802.11b: The defending champ

In 1990, the IEEE adopted a document entitled “IEEE Standards for Local and Metropolitan Area Networks” that provided an overview of the networking technology standards used in virtually all computer networks in prevalent use today. The great majority of computer networks use one or more of the standards included in IEEE 802; the most widely adopted is IEEE 802.3, which covers Ethernet.

IEEE 802.11 is the section that defines wireless networking standards and is often called wireless Ethernet. The first edition of the IEEE 802.11 standard, adopted in 1997, specified two wireless networking protocols that can transmit at either one or two megabits per second (Mbps) using the 2.4 GHz radio frequency band, broken into 14 5-MHz channels (11 in the United States). IEEE 802.11b-1999 was a supplement to IEEE 802.11 that added subsections to IEEE 802.11 that specify the protocol used by Wi-Fi-certified wireless networking devices.

The IEEE 802.11b protocol is backward compatible with the IEEE 802.11 protocols adopted in 1997, using the same 2.4 GHz band and channels as the slower protocol. The primary improvement of the IEEE 802.11b protocol is a technique that enables data transmission at either 5.5 Mbps or 11 Mbps.

When does a + b = g?

The last of the IEEE standards-based products to hit the street is 802.11g, and these products are selling like hotcakes. Although the g standard is still being finalized as we write — it’s expected to be final in mid-2003 and will enter interoperability testing soon thereafter — the appeal of 802.11g is so great that many vendors aren’t waiting for the final standard to be adopted before they release their first products based on this technology. Instead, they will offer upgrades via firmware downloads when the final software is complete.

IEEE 802.11g is intended to be backward compatible with 802.11b wireless networking technology but still delivers the same transmission speeds as 802.11a — up to 54 Mbps — thus, effectively combining the best of both worlds. The 802.11g products are expected to outsell a and b products in the next few years.

IEEE 802.11g equipment offers a nice upgrade path to people who have already invested in IEEE 802.11b equipment. The first products released carry prices that are only marginally more expensive than plain-old IEEE 802.11b. Tests of these products have uncovered some interoperability problems with IEEE 802.11b equipment, but these problems are certain to be ironed out by the time products are released on the final standard.

If you plan to do streaming video over your network, you should seriously consider purchasing IEEE 802.11a equipment or IEEE 802.11g equipment. Otherwise, IEEE 802.11b products should be more than adequate for your wireless home network and are probably available at bargain prices. However, if you’re one to hedge your bets, consider purchasing an access point that supports multiple standards — dual-mode, tri-standard a/b/g products are available. Only time and the marketplace will determine whether IEEE 802.11a will survive or be pushed out by IEEE 802.11g. We think that they’ll coexist. It is a virtual certainty that IEEE 802.11b’s current position as the dominant standard will give way to one or both of the faster standards. We predict that IEEE 802.11g will represent the majority of all wireless shipments within the next few years.

The ISM bands

Here we talk about frequency bands used by the various standards in detail. In 1985, the Federal Communication Commission (FCC) made changes to the radio spectrum regulation and assigned three bands designated as the industrial, scientific, and medical (ISM) bands. These frequency bands are

902 MHz–928 MHz: a 26 MHz bandwidth

2.4 GHz–2.4835 GHz: an 83.5 MHz bandwidth

5.15–5.35 GHz and 5.725 GHz–5.825 GHz: a 300 MHz bandwidth

Gauging your network’s throughput

The FCC also opened up some additional frequencies known as Unlicensed National Information Infrastructure (U-NII), in the lower reaches of the five GHz frequencies.

The purpose of the FCC change was to encourage the development and use of wireless networking technology. The new regulation permits a user to operate radio equipment that transmits a signal within each of these three ISM bands without obtaining an FCC license, within certain guidelines.

Wireless networks use radio waves to send data around the network. IEEE 802.11a uses part of the U-NII frequencies, and IEEE 802.11b and g use the ISM 2.4 GHz band.

An important concept when talking about frequencies is the idea of overlapping and non-overlapping channels. As we discuss in Chapter 18, signals from other APs can cause interference and poor performance of your wireless network. This specifically happens when the APs’ signals are transmitting on the same (or sometimes nearby) channels. Recall that the standards call for a number of channels within a specified frequency range.

Take 802.11b, for example: Its frequency range is between 2.4 GHz and 2.4835 GHz, and it’s broken up into 14 equally sized channels (although only 11 can be used in the United States — any equipment sold for use here will only allow you to access these 11 channels). The problem is that these are defined in a way such that many of the channels overlap with one another — and with 802.11b, there are only three non-overlapping channels. Thus, you wouldn’t

want to have channels 10 and 11 operating side by side because you’d get signal degradation. You want non-interfering, non-overlapping channels. So you find that people tend to use Channels 1, 6, and 11, or something similar. 802.11a doesn’t have this problem because its eight channels, in the 5 GHz frequency band, don’t overlap; therefore, you can use contiguous channels. As with 802.11b and g, however, you don’t want to be on the same channel.