Zigbee mesh routing

Table routing uses Ad Hoc On-Demand Distance Vector Routing (AODV) and the Cluster Tree Algorithm. AODV is a pure on-demand routing system. In this model, nodes don't have to discover one another until there is some association between the two (for example, two nodes need to communicate). AODV also doesn't require nodes that aren't in the routing path to maintain routing information. If a source node needs to communicate to a destination and a path doesn't exist, then a path discovery process starts. AODV provides both unicast and multicast support. It is a reactive protocol; that is, it only provides a route to a destination on demand and not proactively. The entire network is silent until a connection is needed. 

The cluster tree algorithm forms a self-organizing network capable of self-repair and redundancy. Nodes in the mesh select a cluster head and create clusters around a head node. These self-forming clusters then connect to each other through a designated device. 

Zigbee has the ability to route packets in multiple manners:

• Broadcasting: Transmit packet to all other nodes in the fabric.
• Mesh routing (table routing): If a routing table for the destination exists, the route will follow the table rules accordingly. Very efficient. Zigbee will allow a mesh and table to route up to 30 hops away.
• Tree routing: Unicast messaging from one node to another. Tree routing is purely optional and can be disallowed from the entire network. It provides better memory efficiency than mesh routing since a large routing table doesn't exist. Tree routing does not have the same connection redundancy as a mesh, however. Zigbee supports tree routing hops up to 10 nodes away.
• Source routing: Used primarily when a data concentrator is present. This is how Z-Wave provides mesh routing.

Route discovery or path discovery is the process of discovering a new route or repairing a broken route. A device will issue a route request command frame to the entire network. If and when the destination receives the command frame, it will respond with at least one route reply command frame. All the potential routes returned are inspected and evaluated to find the optimal route.