The parent-child relationship is directly used in tree topology to build a ZigBee network. Such tree topology is based on top of IEEE 802.15.4 peer-to-peer data transfer model and has following properties: routers are able to have child nodes, direct communication is possible only in terms of parent-child relations, and hierarchical routing without alternative paths. In tree topology if a link fails, i.e. data cannot be transmitted along a certain branch, there is no alternative link available without changing the network structure.