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The Institute of Electrical and Electronics Engineers (IEEE) committee 802 defines physical and data link technologies. The IEEE decomposes the OSI link layer into two sublayers:r The media-access control (MAC) layer, sits immediately on top of the physical layer (PHY), and implements the methods used to access the network, typically the carriersense multiple access with collision detection (CSMA/CD) used by Ethernet and the carrier-sense multiple access with collision avoidance (CSMA/CA) used by IEEE wireless protocols.r The logical link control layer (LLC), which formats the data frames sent over the communication channel through the MAC and PHY layers. IEEE 802.2 defines a frame format that is independent of the underlying MAC and PHY layers, and presents a uniform interface to the upper layers.Since 1980, IEEE has defined many popular MAC and PHY standards (Figure 1.1 shows only the wireless standards), which all use 802.2 as the LLC layer. 802.15.4 was defined by IEEE 802.15 task group 4/4b (http://ieee802.org/15/pub/ TG4b.html). The standard was first published in 2003, then revised in 2006. The 2006 version introduces improved data rates for the 868 and 900 MHz physical layers (250 kbps, up from 20 and 40 kbps, respectively), and can be downloaded at no charge from the IEEE at http://standards.ieee.org/getieee802/download/802.15.4-2006.pdf The Physical LayerThe design of 802.15.4 takes into account the spectrum allocation rules of the United States (FCC CFR 47), Canada (GL 36), Europe (ETSI EN 300 328-1, 328-2, 220-1) and

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