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 vary between telephone administrations in different countries. Some systems employ alternating current pulses superimposed on the direct current (battery) levels of the local loop, whereas others may utilize a reversal of tip-ring polarity of the wire pair.