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2: ZigBee Topologies > Tree Topology

Tree Topology

A Tree topology consists of a Co-ordinator, to which other nodes are connected as follows:

  • The Co-ordinator is linked to a set of Routers and End Devices - its children.
  • A Router may then be linked to more Routers and End Devices - its children. This can continue to a number of levels.

This hierarchy can be visualised as a tree structure with the Co-ordinator at the top, as illustrated in the diagram below.


A Router can be used in place of an End Device in a Tree network, but the message relay functionality of the Router will not be used -only its applications will be relevant.

Tree topology

Structural Rules

The structural rules and terminology of the Tree topology are as follows:

  • The Co-ordinator and Routers can have children, and can therefore be parents.
  • End Devices cannot have children, and therefore cannot be parents.

Communication Rules

The communication rules in a Tree topology are as follows:

  • A child can only directly communicate with its parent (and with no other node).
  • A parent can only directly communicate with its children and with its own parent.
  • In sending a message from one node to another, the message must travel from the source node up the tree to the nearest common ancestor and then down the tree to the destination node.

This is illustrated in the animation below.

A disadvantage of this topology is that there is no alternative route if a necessary link fails.


Note that message propagation is handled by the stack software (and is transparent to the application programs).

 

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