Which regions in output characteristics are used to switching action of transistor in CE configuration?

In a common emitter (CE) configuration, the output characteristics used for switching action are primarily the active region and the saturation region. When the transistor is in the active region, it can amplify signals, while in the saturation region, it acts as a closed switch, allowing maximum current to flow. The transition between these two regions is crucial for effective switching, where the transistor is turned on (saturation) or off (cut-off) to control the output.