Functions a COR like a control in Repeater Push To Talk. The difference between COR with COS only on the voltage output. COR like a Contact Point – Relay .
Now a days the radio is well known as the Solid State Cos the resulting change in value is a voltage, where the Signal received by the receiver unit at the point open squelch status will change from to Logic Low Logic High (+5 V / 0V-Ground) or vice versa.
The most easy to see from the changes in the Indicator is "Channel Busy" is usually in the form LED. Logic is what's used to drive relay, transistor or optoisolator used as PTT.
In the bottom pictures below are from the COR (cos buffer - Delay - Relay Driver) and Audio Buffer Block diagram snd repeater.