AVOS tools are electronic with onboard sensors and power packs. Commands are sent to the tools via surface Downlinking. This is a simple sequence of RPM followed by a pumps on/off cycle. The tools read the sequence and move to the corresponding position. There are no balls, darts or any mechanical devices pumped down the drillstring.
The AVS and AVD can also be functioned when packed off by sending a sequence of pressure pulses using the mud pumps. This gives the possibility of being able to break up the pack off and get circulation back.