What is mesh networking?

A network that uses mesh networking is capable of supporting multiple paths to a destination.

For example, in the network above a message is being sent from A to F. In this case, the message is being routed through intermediate devices B and C.

A mesh network is therefore more robust in the case of ad-hoc (unplanned) deployments, interference, and removal, movement, or addition of devices in the network.

If, as in the example above, device B were to fail, the message would automatically be routed through device D instead. This self-healing behavior is a basic capability of the ZigBee protocol.

For device-to-device networks this behavior is crucial because device placement cannot always be preplanned and in many cases devices cannot be relocated if they happen to be in a poorly placed — contrast this to your cellphone or WiFi laptop where you may move around to find a better radio signal and you can see why having multiple redundant routes becomes very important!

Network device types in ZigBee

ZigBee supports three network devices types: the coordinator, the router, and the end device. From now on, we will refer to these as ZC (ZigBee Coordinator), ZR (ZigBee Router), and ZED (ZigBee End Device). Each device has different network level responsibilities.

Note! the application level behavior does not need to be related to the ZigBee device type. This will become clear as we explore the design of an application, but for now consider the ZigBee device type to be operating only at the network level.

In this guide we will use the following icons to indicate the ZigBee device type in network diagrams:

ZR
ZED
ZC

Because a ZC is just a ZR that has some additional basic functionality, we do not have a special icon for it. In network discussions where the ZC functionality is relevant, we will add the (*) graphic tag to the device acting as the ZC.

Each of these devices is explained in more detail in the following section.

Message routing

Routing in ZigBee is automatically handled by the networking layer — the application commands the networking stack to send a message, and specifies the destination, and the route discovery or repair is automatically managed by the network.

Note that this behavior will depend on the proper configuration of the stack which may vary among vendors. The application developer usually does not need to be concerned with its behavior. However, it is useful to have a feel for how the network behaves when a route needs to be discovered or repaired.

More information on message routing, discovery of routes, and repair of routes is contained later in this section.