al sensors, and medical devices. It is meant to offer short-distance, low-speed transmissions that require little power. As a result, the battery life of ZigBee devices can range from six months to two years or longer, using only a single alkaline battery. There are three types of ZigBee devices: Reduced-function device (RFD)-The simplest ZigBee device is the RFD, also referred to as the end device. It is smart enough to talk to the network but has no routing abilities; in other words, it cannot relay data from other devices. End devices are often battery powered. Typical end devices func- tion as thermostats, humidistats, light switches, smoke detectors, and vari- ous other sensors. These devices are often built as peel-and-stick products, where installation is intended to be simple and product placement is either aesthetic, functional, or according to some governmental requirement. These end devices do not form a mesh by themselves; instead, they are usu- ally asleep in order to conserve their batteries. Full-function device (FFD)-The next level up the network from the RFD is called the FFD, or router. It is fully mesh capable and mains powered (i.e., powered from some other permanent source). FFDs can establish multiple peer-to-peer links with other routing nodes, and they accept connections from RFD devices, performing the role of intermediate routers, passing data from other devices. An FFD may also serve as a gateway to the Internet or Chapter 15 WMANs, WLANs, and WPANs other networks. Packets generated by RFD devices may pass through multi- ple FFDs to travel from the source to a destination, which is generally a load-controlling function (e.g., HVAC motor, lighting load control, damper actuator, siren). However, the destination may also be a data-collecting device (e.g., a computer or security console) or even a gateway to the Inter- net or other non-ZigBee network. ZigBee coordinator-The mains-powered coordinator assumes the most important role in a ZigBee network, acting as the root of the network tree 