At the beginning of its life cycle, a new Thread or Zigbee Sleepy End Device needs to securely obtain network credentials, which allow it to communicate with other devices in the network. This process is called commissioning and is performed only once per device factory reset.
Once the device starts up, it sends a message indicating that it is looking for a router to attach to. It then gains security information from the network, which allows it to join the network as a child device. This works the same for Thread and Zigbee SEDs. The impact commissioning has on the battery life is very small and will not be analyzed in this document.
After the device is commissioned, it attaches to the mesh network by establishing communication with the neighboring router. It then starts acting as an end node. This process is repeated usually once per device power cycle.