IEEE 802.15.4 start-up sequence

IEEE 802.15.4 maintains a process for startup, network configuration, and joining of existing networks. The process is as follows:

1. Device initializes its stack (PHY and MAC layers).
2. PAN coordinator is created. Each network has only one PAN coordinator. The PAN coordinator must be assigned at this phase before proceeding.

1. The PAN coordinator will listen to other networks it has access to and derives a PAN ID that is unique to the PAN it will administer. It can do this over multiple frequency channels. 
2. The PAN coordinator will choose a specific radio frequency to use for the network. It will do this using an energy detection scan where it scans the frequencies the PHY can support and listens to find a quiescent channel. 
3. The network will be started by configuring the PAN coordinator and then starting the device in coordinator mode. At this point, the PAN coordinator can accept requests.
4. Nodes can join the network by finding the PAN coordinator using an active channel scan where it broadcasts a beacon request across all its frequency channels. When the PAN coordinator detects the beacon, it will respond back to the requesting device. Alternatively, in a beacon-based network (detailed earlier), the PAN coordinator will routinely send out a beacon and the device can perform a passive channel scan and listen for the beacon. The device will then send an association request. 
5. The PAN coordinator will determine if the device should or can join the network. This could be based on access control rules, or even if the PAN coordinator has enough resources to manage another device. If accepted, the PAN coordinator will assign a 16-bit short address to the device.