The standard dictates that all addresses are based on unique 64-bit values (IEEE address or MAC address). However, to conserve bandwidth and reduce the energy of transmitting such large addresses, 802.15.4 allows a device joining a network to "trade-in" their unique 64-bit address for a short 16-bit local address, allowing for more efficient transmission and lower energy.
This "trade-in" process is the responsibility of the PAN coordinator. We call this 16-bit local address the PAN ID. The whole PAN network itself has a PAN identifier, as multiple PANs can exist. The following figure is a diagram of the 802.15.4 packet structure.
Frames are the basic unit of data transport, and there are four fundamental types (some of the underlying concepts were covered in the last section):
- Data frame: Application data transport
- Acknowledgement frame: Confirmation of reception
- Beacon frame: Sent by PAN coordinator to set up a SuperFrame structure
- MAC command frame: MAC layer management (associate, disassociate, beacon request, GTS request)