This sets the frequency, in Hz, of the first tone the gateway transmits during a CAS continuity test, a check that the voice path between the originating and terminating gateways is actually passing audio before a call is connected. If this frequency is mismatched against the far end's expected continuity-tone setting, the test can falsely fail and the gateway will report continuity failures or refuse to complete calls even though the trunk is otherwise healthy. A common continuity test pairing might set this object to 1780 Hz as the first tone, verified against a specific return tone at the far end before the call is allowed through.