Joining a network (Routers and End Devices)

Routers and End Devices can join an existing network already created by a Coordinator. The Coordinator and Routers have the capability to allow other nodes to join the network through them. The join process is as follows:

Search for network

The new node first scans the channels of the relevant RF band to find a network. Multiple networks may operate, even in the same channel, and the selection of a network is the responsibility of the application (for example, this decision could be based on a pre-defined Extended PAN ID).

Parent topic:Joining a network (Routers and End Devices)

Select parent

The node now selects a parent node within the chosen network by listening to network activity. The node may be able to ‘hear’ multiple Routers and the Co- ordinator from the network. Given a choice of parents, the node chooses the parent with the smallest depth in the network - that is, the parent closest to the Coordinator (which is at depth zero).

Parent topic:Joining a network (Routers and End Devices)

Request joining

The node sends a message to the desired parent, asking to join the network.

Parent topic:Joining a network (Routers and End Devices)

Receive response

The node now waits for a response from the potential parent, which determines whether the node is a permitted device and whether the parent is currently allowing devices to join. To determine whether the joining node is a permitted device, the parent consults the Trust Centre (if it is not the Trust Centre itseIf). If these criteria are satisfied, the parent will then allow the node to join the network as its child. In its acceptance response to its new child, the parent will include the 16-bit network address that it has randomly allocated to the child (see Section 3.2.4).

If the potential parent is unable to accept the node as a child, a rejection response is sent. to the node, which must then try another potential parent (or another network).

Parent topic:Joining a network (Routers and End Devices)

Learn network IDs

The new node learns the PAN ID and Extended PAN ID of the network, as well as the network address that it has been assigned. It will need the PAN ID for communications with the network and will need the Extended PAN ID if, at some point in the future, it needs to rejoin the network (it will also be able to re- use its network address if it later rejoins the network).

A Router or Coordinator can be configured to have a time-period during which joins are allowed, controlled by its ‘permit joining’ status. The join period may be initiated by a user action, such as pressing a button. An infinite join period can also be set, so that child nodes can join the parent node at any time.

Note: When an orphaned node attempts to rejoin the network, the ‘permit joining’ status of a potential parent is ignored. Thus, the node is able to rejoin the network through a parent on which ‘permit joining’ is disabled.

Parent topic:Joining a network (Routers and End Devices)

Parent topic:Network creation