r Security and access control, lighting, heating, ventilation building automation and air conditioning (HVAC), irrigation Healthcare Patient monitoring, fitness monitoring Industrial control Asset management, industrial process control, energy management. Wireless PAN Standards Although a ZigBee network may be competing for access to the 2.4 GHz ISM band with Wi-Fi and Bluetooth networks, as well as a range of other control and communication devices, ZigBee is likely to be very robust to potential interference since the duty cycle of a ZigBee device will generally be very low. The CSMA/CA mechanism, together with backoff and retry if no acknowledgement is received, means that if there is interference, ZigBee devices can simply wait for an opening and keep trying until packet reception is confirmed. The low duty cycle and low data volumes also mean that ZigBee devices are unlikely to cause significant interference to overlapping Wi-Fi or Bluetooth networks. Mesh Implementation Considerations A number of special considerations arise in order to ensure the successful implementation of a functional, robust and reliable ZigBee mesh network, for example in an extensive building or industrial automation application. Mesh functionality requires that every device is able to communicate with at least one, and preferably several other devices, providing one or more paths to the central controller or point of exit from the mesh. Clearly this is also the case for WLAN installations, but in a ZigBee mesh, where devices may be installed in or concealed by machinery or pipework, special attention to signal strength site surveying will be required. Weak or broken links in the mesh can result in the separation from the main mesh of one (orphan) or a group of devices (split mesh). The robustness of a mesh will also be adversely affected by any susceptibility to single link failures. During planning, the mesh topology should be carefully reviewed for single point vulnerability and after installation the signal strength of each link 