802.11d

802.11b

The vast majority of wireless network activity happening around the world today operates under the 802.11b standard, which many now prefer to call Wi-Fi. (Two syllables rather than eleven-no contest!) The original 1997 802.11 standard called for two data rates-1 and 2 Mbps. This was par for that time (pre-802.11 wireless products like the original WaveLAN operated at similar speeds) but far below the 10 or increasingly 100 Mbps that wired Ethernet networks were achieving.

The IEEE created the 802.11b task group to develop a faster but still backwardscompatible enhancement to 802.11. The final standard was approved and published in 1999, and the first products appeared on the market soon after. The IEEE simultaneously created a separate task group to develop a much faster wireless system that was not required to be backwards compatible. This was 802.11a, and because both the standards work and creation of actual products took longer than 802.11b, 'a' trailed 'b' by almost two years. (I discuss the differences between 802.11a and 802.11b at greater length in the 802.11a topic.)

802.11b added two additional data rates of 5.5 and 11 Mbps. At its best, 802.11b was thus on par with the common and inexpensive 10-Base-T Ethernet system. 802.11b hardware could still communicate with most older 802.11 hardware, though at the slower 802.11 data rates.

When implementing the original 802.11 standard, manufacturers could choose either of two frequency management schemes: Frequency Hopping Spread Spectrum (FHSS) or Direct Sequence Spread Spectrum (DSSS). The two schemes are similar, and both grew out of original ideas patented in the 1940s by (of all people) actress Hedy Lamarr and a composer and player piano hobbyist named George Antheil. FHSS was cheaper to implement, but DSSS allowed higher data rates, so DSSS quickly pushed FHSS into the status of a historical footnote. The 802.11b spec calls for the use of DSSS alone, except at the lowest bit rates-and that's simply an option; modern Wi-Fi gear neither generates nor understands FHSS, even at the lower bit rates. DSSS does it all for 802.11b. This means that 802.11b gear is for the most part not backward compatible with 1997-vintage 802.11 equipment running FHSS.

802.11b networks, like the original 802.11 networks, operate in the unlicensed 2.4 GHz Industrial Scientific and Medical (ISM) band. As the name of the band implies, 802.11b networks must share spectrum space in the band with all manner of gadgetry including microwave ovens, industrial heating machines, medical monitoring equipment, cordless telephones, and (more recently) Bluetooth-equipped computers and peripherals. Spread spectrum techniques reduce the effects of interference, but it's possible that running the microwave oven will cause your Wi-Fi network to drop packets. Reports from my contacts indicate that interference is rarely a problem, and defining when it becomes a problem is a fluky business. I have both a microwave oven and a 2.4 GHz cordless phone system in my home, and it has never become an issue in over three years of Wi-Fi experience. (The problems I have had have all been due to the geometry of my house, which is an odd-shape two-story sprawling ranch. See Chapter 15 for details on the consequences of having my kitchen between my access point and my living room coffee table.)

Compared to the newer and faster 802.11a hardware, 802.11b equipment is dirtcheap. As of late 2002/early 2003 you can get started for under $200 if you shop aggressively. For this we must thank the people at Apple Computer, who brought Wi-Fi prices down into consumer territory with their AirPort system, based on Agere's Orinoco PCMCIA cards. (The AirPort access points I have seen are miniature 486-based embedded computers with an Orinoco Silver card to handle the radio part of the connection. Yes, a client card can act as an access point. It's all in the firmware.)

For the next couple of years, I feel that 802.11b is definitely the technology to reckon with. Eventually, I feel that 802.11a and especially 'dual-mode' 80211a+b hardware will replace it for new networks, and 802.11g hardware will be used to upgrade existing 802.11b networks to higher data rates. Technology does not stand still. Monitor Web sites like 802.11 Planet ( http://www.80211-planet.com/) to stay ahead of what's up in the Wi-Fi world.



Jeff Duntemann's Drive-By Wi-Fi Guide
Jeff Duntemanns Drive-By Wi-Fi Guide
ISBN: 1932111743
EAN: 2147483647
Year: 2005
Pages: 181

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