Association procedures
A device becomes a member of a PAN by associating with its coordinator.
Procedures.
In IEEE 802.15.4, association results are announced in an indirect fashion.
A coordinator responds to association requests by appending devices’ long addresses in beacon frames.
Devices need to send a data request to the coordinator to acquire the association result.
After associating to a coordinator, a device will be assigned a 16-bit short address.
Data transfer model
Device to Coordinator
Data is transferred from the device to the coordinator.
In a beacon-enable network, the device finds the beacon to synchronize with the superframe structure. Then using slotted CSMA/CA to transmit its data.
In a non-beacon-enable network, the device simply transmits its data using unslotted CSMA/CA.
Coordinator to Device
Data transferred from coordinator to device.
In a beacon-enable network, the coordinator indicates in the beacon that the data is pending. The device periodically listens to the beacon and transmits a MAC command request using slotted CSMA/CA if necessary.
In a non-beacon-enable network, a device transmits a MAC command request using unslotted CSMA/CA. If the coordinator has pending data, the coordinator transmits the data frame using unslotted CSMA/CA. Otherwise, the coordinator transmits a data frame with a zero-length payload.
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