In telecommunications, a plant test number is a telephone number reserved for use by telephone installers or other workers to test an individual telephone line. Test number are typically unlisted.
The
North American Numbering Plan
The North American Numbering Plan (NANP) is a telephone numbering plan for twenty-five regions in twenty countries, primarily in North America and the Caribbean. This group is historically known as World Zone 1 and has the international calling ...
(NANP) reserves the exchange (''central office'') prefixes ''958'' and ''959'' for plant testing.
[''Telcordia Notes on the Network'', Telcordia Technologies, Special Report SR-2275 Issue 4 (October 2000), Section 8.2.5, p.8-8]
Central office code 958 is intended for communications between switching centers. Central office code 959 with three or four additional digits is dedicated for access to office test lines in local exchange carrier (LEC) and interoffice carrier (IC) central offices. The specifications define several test features for line conditions, such as quiet line and busy line, and test tones transmitted to callers.
The tests available for plant testing include
*
Automatic number announcement circuit, a machine which announces the caller's number
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Loop around, a primitive conference call bridge
*
Milliwatt test, a standardized 1004 Hz, zero
dBm sinusoidal test tone used to measure line quality and
transmission loss
Transmission loss (TL) in general describes the accumulated decrease in intensity of a waveform energy as a wave propagates outwards from a source, or as it propagates through a certain area or through a certain type of structure.
It is a termino ...
between stations.
*
Ringback number, which causes the calling telephone to ring to verify an installation is working and the phone number routing properly.
Some localities reserve 959 only.
Each country uses different codes.
BT Linetest Facilities (for example) are available by ringing 17070 and a self-service test facility for subscribers is no longer available.
References
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Telephone numbers
Communication circuits