Network creation
This section outlines the process of starting and forming a ZigBee PRO network:
Section 3.3.1 describes how the Coordinator starts a network.
Section 3.3.2 describes how a Router or End Device joins a network as part of the network formation process.
Note: The network formation actions described in this section are performed automatically by the ZigBee stack. The actions required at the application level are described later in Section 6.1, “Forming and Joining a Network”.
Starting a Network (Coordinator)
The Coordinator is responsible for starting a network. It must be the first node to be started and, once powered on, goes through the following network initialization steps:
Set EPID and Coordinator address
The Coordinator first sets the Extended PAN ID (EPID) for the network and the device’s own network address:
Sets the EPID to the 64-bit value specified in the Coordinator’s application (if this value is zero, the EPID will be set to the 64-bit IEEE/MAC address of the Coordinator device)
Sets the 16-bit network address of the Coordinator to 0x0000
Parent topic:Starting a Network (Coordinator)
Select radio channel
The Coordinator then selects the radio channel in which the network will operate, within the chosen RF band. The Coordinator performs an Energy Detection Scan in which it scans the RF band to find a quiet channel (the scan can be programmed to ‘listen’ to specific channels). The channel with the least detected activity is chosen.
Parent topic:Starting a Network (Coordinator)
Set the PAN ID of the network
Once the radio channel has been selected, the Coordinator chooses a 16-bit PAN ID for the network. To do this, it listens in the channel for traffic from other networks and identifies the PAN IDs of these networks (if any). To avoid conflicts, the Coordinator assigns its own network a random PAN ID that is not in use by another network.
Parent topic:Starting a Network (Coordinator)
Receive join requests from other devices
The Coordinator is now ready to receive requests from other devices (Routers and End Devices) to wirelessly connect to the network through it. For more information on joining a network, refer to Section 3.3.2.
Parent topic:Starting a Network (Coordinator)
Parent topic:Network creation
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
Parent topic:ZigBee PRO architecture and operation