The device’s radio transceiver is disabled while the device is sleeping. In order to communicate, it must be in an active state.
A SED can transmit at any time, as its parent keeps the transceiver permanently on. However, to receive data, the SED must initiate the process by using a data polling mechanism.
A data poll mechanism is initiated periodically through a data request frame, asking the parent
if there is any data to receive. The parent replies with an ACK packet, including a frame pending
bit set to 1 if there are pending frames to receive. Depending on the reply, a
SED can stay in the reception state and get data, or go to sleep state to save energy, as shown
in the following figure. The parent buffers the data meant for a SED and sends it as a response
to the data request message.
The interval between when the SED sends data request packets is known as the poll period. You can adjust its value according to your application needs. This feature enables a poll period suited to its role, creating an energy efficient device.
