Neighbor discovery (ND) in thread decides which 802.15.4 network to join. The process is as follows:

1. Joining device contacts router for commissioning.
2. Joining device scans all channels and issues a beacon request on each channel. Waits for beacon response.
3. If a beacon containing the payload with the network Service Set Identifier (SSID) and permit-joining message is seen, the device will now join the Thread network.
4. Once a device is discovered, MLE messages will be broadcast to identify a neighbor router to the device. That router will perform commissioning. There are two commissioning modes:
   • Configuring: Uses an out-of-band method to commission a device. Allows for a device to attach to the Thread network as soon as it is introduced to the network.
   • Establishing: Creates a commissioning session between the device and a commission application running on a Smartphone, tablet, or web-based.
5. The device that is joining contacts the parent router and attaches to the network via MLE exchange. 

The device will exist as either a REED or an end device and is allocated a 16-bit short address by the parent.