This read-write enumeration sets the ringing frequency in hertz, such as 17, 20, or 25 Hz, generated on locally attached telephone equipment by the unit. An administrator matches this to the ringer requirements of the specific phones or equipment connected, since different countries and devices expect different ring frequencies. For example, setting this to hz-25(3) would be appropriate for equipment designed for a 25 Hz ringing standard rather than the North American 20 Hz norm.