ZigBee network technology is used for low data rate Wireless Personal Area Networks that requires long battery life and is affordable. The ZigBee protocol refers to the entire network protocol stack. ZigBee applications run on top of ZigBee network, MAC and physical layers. A ZigBee network is capable of supporting up to 65,535 nodes. ZigBee network is used in many areas such as environmental monitoring systems, personal health care and consumer electronics. In ZigBee network the nodes can be mobile and fixed.
1.2 ZigBee Topologies
The three ZigBee network device types are end device, router and coordinator. ZigBee support three kinds of topologies. These are star, tree and mesh. In all topologies the ZigBee network must contain one coordinator. The coordinator is responsible for allowing other devices to join the network, selecting transmission channels and for starting the ...view middle of the document...
The central node is the coordinator and it handles all network traffic as well as providing ZigBee coordinator services. In the star topology all end devices send all their data through the central node. Star topology is not very good for ZigBee networks with large number of nodes because the central node need to handle all the traffic so network bottleneck and congestion can easily occur. Also the failure of central node will bring the entire network down, so it’s not very reliable.
• Tree – This topology provides hierarchical communication. The coordinator is the root node in tree topology. The coordinator provides the usual network services, but it does not handle all the network traffic. In tree topology routers and end devices can be connected to the coordinator. The routers can have end device or other routers connected to them as child nodes. The routers can route traffic so not all traffic is handled by the coordinator; therefore there is less bottleneck and congestion problems. The message will travel up the tree until it can be routed down to the destination. In tree topology the data can only travel up or down the tree, so there is only one path between all nodes. Therefore if a link or router fails all the nodes connected to the tree through that link will not be able to function.
• Mesh – The mesh topology is more reliable than the star and tree topologies because it allows multiple routes to exist on the network. The mesh topology is made of end devices, routers and a coordinator. The coordinator is the root node and the routers and end devices can be its children. In mesh topology the coordinator does not handle all traffic. The routers can be connected to other routers and end devices. Mesh topology can use route discovery process to find alternative path when a route fail or link becomes congested. In the mesh topology the data does not have to travel only up or down; it can travel side ways to allow better performance. Mesh topology is said to be the most optimal ZigBee topology.