The actual frame transmissions are the time periods shown in green on the slide (radio frame transmission and radio ACK reception phase). Keeping in mind the microcontroller is now sleeping, the RF transceiver will autonomously execute the following tasks: Carrier Sense Multiple Access With Collision Avoidance (CSMA-CA) and Clear Channel Assessment (CCA) retries (checking that the RF channel is free from other traffic), Frame Check Sequence (FCS) generation, Frame transmission, Automatic retry (if needed), and acknowledgement of reception. Once these tasks have been completed the MCU is brought back to active state, reading the transceiver status. If there is more data to be transmitted, the sequence starts all over again. If there is no more data to be transferred, both the microcontroller and the RF transceiver can be brought back to sleep mode.