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March 17, 2003 The primary IEEE 802.11 standards in use today are 802.11a and 802.11b, which both use radio waves for transferring information wirelessly over a network. Few people realize, however, that the 802.11 standard also includes the 802.11 Infrared (IR) Physical Layer. 802.11 IR defines 1Mbps and 2Mbps operation by bouncing light off ceilings and walls to provide connectivity within a room or small office. This infrared version of the standard has been available since the initial release of the 802.11 standard in 1997. The reason that 802.11 IR is unheard of is that there are no known vendors that sell products compliant with 802.11 IR. Some offer infrared-based wireless LANs that come close to the standard. For example Spectrix, once the chair of the 802.11 IR group, offers wireless LAN products that implement diffused optical technologies very similar to 802.11 IR. There have not been any updates to the 802.11 IR standard in order to successfully compete with the higher performing 802.11a and 802.11b. With only 2Mbps data rates, most IT organizations opt for radio-based solutions instead. As a result, 802.11 is known primarily as a radio-based technology. The primary difference between infrared and radio wireless LANs is the frequency of the transmitted signal. 802.11a and 802.11b operate in the 2.4 and 5GHz bands respectively, but infrared systems use frequencies in the terahertz range. This places infrared signals in the light region invisible to the human eye and beyond the control of the Federal Communications Commission (FCC). Because of the extremely high frequency, infrared light is highly reflective, which makes it behave like an incandescent light bulb. Each client station (e.g., laptop or PC) is equipped with an infrared transducer that can both transmit and receive light signals. The transducer diffuses the light, which makes the signal available from anywhere within a typical room. Infrared-based wireless LANs pulse a light on and off to represent the transmission of data bits with a carrier sensing mechanisms that are similar to what the 802.11 Medium Access Control (MAC) Layer provides. Stations take turns sending light signals addressed to another station that's capable of receiving the light. Attributes Worth ConsideringBefore assuming that a radio-based solution is best for meeting wireless LAN requirements, think about the following attributes that infrared wireless LANs provide:
Even though the traditional technology for wireless LANs is radio waves, at least ponder the idea of using infrared as an alternative. In almost all cases, the use of radio waves will prevail, but you may have a unique application that an infrared wireless LAN will satisfy the best. Jim Geier provides independent consulting services to companies developing and deploying wireless network solutions. He is the author of the book, Wireless LANs and offers workshops on deploying wireless LANs. Join Jim for discussions as he answers questions in the 802.11 Planet Forums. |