Types of Wireless Access

Wireless access comes in a variety of shapes and sizes. Options range from global voice and data networksthe kind usually associated with big telecommunications providers such as Sprint and T-Mobileto infrared connections, which is essentially the same technology you use in TV remote controls. However, the most common wireless access today comes in the form of IEEE 802.11 technologies. This kind of wireless access uses radio frequency technology and is meant for short-range connections (no more than about 300 feet or so without signal amplifiers) between wireless clients using 802.11 network cards and a wireless access point (WAP). Wireless access points are then connected to hard-wired methods of Internet access like cable modems, or to existing private LANs, such as might exist in any office building.

This common configuration of wireless connectivity is also known as a wireless LAN, or WLAN. The placement of WLAN components is depicted in Figure 10-1.

Figure 10-1. Common wireless LAN infrastructure.

Because of their widespread availability (chain coffee shops and bookstores notwithstanding), this chapter focuses on 802.11 network connections. This standard for wireless LANs was first approved by the Institute of Electrical and Electronics Engineers (IEEE) in 1997. The protocol known as 802.11b is currently the most common standard, transferring data at a maximum rate of 11 Mbps. However, you'd be hard pressed to find an 802.11b device on store shelves today. The prevailing standard now is 802.11g, which allows for data transfer at 54 Mbps using the 2.4 GHz frequency band. (In my experience, the 802.11g wireless cards also seem to have a greater range and more reliable connectivity than 802.11b devices.) It's only a matter of time before 802.11g overtakes 802.11b in terms of implementation; it's possible that the day will have come by the time you pick up this book.

What's the Frequency?

Wireless LANs send data packets through the air using the radio wavesthe same electromagnetic waves that carry music, cell phone conversations, garage door opening instructions, and even microwave heat. The reason you don't hear conservative talk radio every time you're making popcorn is because all these different radio devices transmit on different frequencies.

FM radio, for example, uses the 88 to 108 Mhz frequency bands, which is why you'll never tune to 109.3 or 87.1 to hear campus rock. It's also why the FM radios and wireless LANs don't interfere with each other: they transmit using different frequency bands. The same can't always be said of some cordless phones. If you put a phone base stationwhich might also use the 2.4 GHz frequency bandtoo close to a wireless access point, you're likely to experience the occasional connectivity loss. Figure 10-2 helps you see how devices might sometimes compete for the same frequency.

Figure 10-2. Lots of devices use the 2.4 GHz frequency.