Plant test number
In landline telephony, a plant test number or exchange is a number or group of numbers reserved for use by telephone installers to perform routine tests on an individual telephone line.
These include, but are not limited to:
- Automatic number announcement circuit, a machine which announces the caller's own number
- Loop around, a primitive conference call bridge
- Milliwatt test, a standardised 1004 Hz, zero dBm sinusoidal test tone used to measure line quality and transmission loss between stations.
- Ringback number, which causes the calling telephone to ring to verify an installation is working and the phone number routing properly.
This disambiguation page lists articles associated with the title Plant test number.
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