ZigBee is a short-distance, low-power, low-data-transmission-rate wireless network technology. It is a technical solution between wireless tag technology and Bluetooth technology.

The reason why ZigBee can be widely used in sensor network and other fields is due to its powerful networking capabilities. It can form three types of ZigBee networks, such as star network, tree network and mesh network. You can choose the appropriate ZigBee network structure for networking according to the actual development project needs. These three ZigBee network structures also have their own advantages.

Star topology

The star topology is the simplest of the three topological structures. It contains a Co-ordinator (central coordinator) node and multiple End Device (terminal) nodes. Each End Device (terminal) node can only communicate with the Co-ordinator (coordinator) node, and cannot connect to other End Device (terminal) nodes. If you need to communicate between two End Device (terminal) nodes, you must connect to the Co-ordinator (coordinator) node to receive and forward information.

This topology has a disadvantage: there is only one unique route for data transmission between nodes. The state of the Co-ordinator node may become the influencing point of the entire network.

The networking implemented by the star network topology does not need to use the ZigBee network layer protocol, because the IEEE 802.15.4 protocol layer itself is already implemented on the basis of the star topology, but this adds more work for developers at the application layer, including the need to process the reception and forwarding of information by themselves.

Tree topology

The tree topology includes a Co-ordinator node and multiple Routers and End Devices. The Co-ordinator connects multiple Routers and End Devices, and its child Routers can also connect multiple Routers and End Devices. By repeatedly stacking multiple levels, a tree network is formed. The tree topology is as shown in the 

It should be noted that:

Co-ordinator nodes and Router nodes can have multiple connected child nodes. However, End Device nodes cannot be connected to other child nodes. Nodes with the same parent node (coordinator or router) can be called brother nodes. Nodes with the same grandparent node (coordinator or router) can be called cousin nodes.

Communication rules in tree topology

Each routing node can only communicate with its parent node and child nodes.

If data needs to be sent from node to node, the information will be passed up along the tree route to the nearest ancestor node, and then passed down to the target node.

Disadvantages of tree topology: Information has only one routing channel. Moreover, the transmission route of information is processed through the protocol stack layer, and the entire communication routing process is relatively completely transparent to the application layer.

Mesh topology

Mesh topology contains a Co-ordinator node and multiple Router nodes and End Device nodes. The mesh network topology is roughly the same as the tree topology; however, based on the tree structure, the mesh network topology is a topology with more flexible communication routing rules. When possible, routing nodes can communicate directly.

This routing mechanism makes information communication between nodes more efficient, and it also means that when a problem occurs in a routing path during communication, the information can also be automatically transmitted along other routes. The schematic diagram of the mesh topology is as follows:

The network with a mesh network topology has very powerful functions. The network can communicate through a "multi-hop" method; and the mesh network topology can also form a very complex network; the network it forms also has the functions of self-organization and self-healing.

Both star and tree networks are more suitable for point-to-multipoint applications with short transmission distances.