The ZigBee Alliance is an association of industry companies with the target of WSN technology standardization and adaptation for real-life applications. For more information on the ZigBee Alliance visit www.zigbee.org. The ZigBee specification was ratified in 2004 with enhancements following in 2006 and 2007 and covers all OSI layers. The two lowest layers (PHY and MAC) in ZigBee standard are the same as those in IEEE 802.15.4. Higher layers in ZigBee stack are specified to allow efficient communication within the entire network and on the application level. Routing mechanisms on the network layer allow multi-hop data transmissions, and selection of the best suitable path and mesh routing. The application framework provides an interface that enables simultaneous execution of several applications within a network and on a single device.