The properties of metering signals differ between the telephone administrations in various countries. Some systems use alternating current pulses superimposed on the direct current (battery) levels of the local loop, while others may use a reversal of tip-ring polarity of the wire pair.
The characteristics of metering signals exhibit differences between telephone administrations across nations. Some systems utilize alternating current pulses on top of the direct current (battery) levels in the local loop, whereas others may involve altering the polarity of the wire pair.