From its beginnings as an extension technology for conventional wired local-area networks (LANs), IEEE Standard 802.11 has grown into something much more capable, complex, and confusing. When it first came out in 1997, the wireless LAN standard specified operation at 1 and 2 Mb/s in the license-exempt 2.4-GHz industrial, scientific, and medical (ISM) frequency band and also in the infrared. An IEEE 802.11 network in the early days was envisioned as a few PCs with wireless capability connected to an Ethernet LAN through a single network access point.

Since the IEEE 802.11 standards committee was established in 1990 and set up task groups to design specifications for systems operating in the 2.4-GHz and 5-GHz bands, the systems now known as (b) and (a), the (b) variant has taken off to a degree surpassing the expectations of those who conceived it. As a result, the IEEE's 802.11 committee has had to create still more extensions, adding to the alphabet soup, to address issues like interference, security, roaming, and even quality of service.

IEEE 802.11b defines operation in the ISM band at 5.5 Mb/s and 11 Mb/s. It was finalized in 1997 and was trademarked commercially by the Wireless Ethernet Compatibility Alliance (WECA) as Wi-Fi. (WECA certifies interoperability among Wi-Fi products from diverse manufacturers.) The physical layer combines complementary code keying (CCK) and packet binary convolutional coding (PBCC).

IEEE 802.11a, the fastest flavor of the standard, operates at data rates ranging from 6 Mb/s to 54 Mb/s. It was also finalized in 1997 and was devised in parallel with the (b) variant, partly because (b) shares spectrum with applications like cordless phones, microwave ovens, and Bluetooth, which could cause problems. IEEE 802.11a operates in the 5-GHz band (known in the United States as the Unlicensed National Information Infrastructure band). The physical layer uses orthogonal frequency-division multiplexing (OFDM) and is similar to that for HiperLAN II, the wireless standard of the European Telecommunications Standards Institute in France.

The IEEE 802.11g task group is attempting to provide the high speed of IEEE 802.11a in the 2.4-GHz ISM band—in essence, to raise the speed of Wi-Fi. The current draft of IEEE 802.11g adopts OFDM from the (a) variant as well as two additional modulation schemes: PBCC and CCK-OFDM. This draft enables data rates as high as those of IEEE 802.11a (54 Mb/s). Development of this extension involved a great deal of contention in 2000 and 2001 over modulation schemes. A breakthrough occurred last November, and the task group has worked hard this year to finalize its draft. Although final ratification is not expected until 2003, some manufacturers have already announced (g) products.

Other task groups—c, d, and h—were established to address special regulatory and networking issues. IEEE 802.11e deals with requirements of time-sensitive applications such as voice and video, IEEE 802.11f with communication among access points to support roaming, and IEEE 802.11i with advanced encryption standards to support stronger privacy.

—Michael J. Riezenman

For a more detailed version of this story, crossing all the t's: http://www.spectrum.ieee.org/WEBONLY/resource/sep02/802ABCs.html.