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Published on The O'Reilly Network (http://www.oreillynet.com/) http://www.oreillynet.com/pub/a/wireless/2001/03/02/802.11b_facts.html See this if you're having trouble printing code examples 802.11b Tips, Tricks, and Facts by Rob Flickenger 03/02/2001 Related Articles 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: Approved in 1997 by the IEEE 802 committee, 802.11 details the framework necessary for a standard method of wireless networked communications. It uses the 2.4-GHz microwave band designated for low-power unlicensed use by the FCC in the USA in 1985. It allows for two different (and incompatible) methods of encoding, FHSS and DSSS. FHSS (Frequency Hopping Spread Spectrum) spreads the conversation across 75 one-MHz subchannels, continually skipping between them. DSSS (Direct Sequence Spread Spectrum) breaks the band into 14 overlapping 22-MHz channels and uses one at a time. Two operating modes are defined: infrastructure and ad hoc. Most dedicated hardware (the "access point") provides a basic or extended service set that builds the wireless "infrastructure." It goes a bit beyond basic bridging, allowing clients to roam from access point to access point (provided they all exist on the same physical Ethernet segment; roaming across routers isn't allowed -- at least, not yet). The ad hoc (IBSS, or Independent Basic Service Set) mode allows individual nodes to participate in a peer-to-peer network without an access point. The 802.11 spec also allows for Wired Equivalent Privacy encryption at the MAC (Media Access Control) layer. 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 a