Automatic number announcement circuit

An automatic number announcement circuit (ANAC) is a component of a central office of a telephone company that provides a service to installation and service technicians to determine the telephone number of a line. The facility has a telephone number that may be called to listen to an automatic announcement that includes the caller's telephone number.

The ANAC number is useful primarily during the installation of landline telephones to quickly identify one of multiple lines.

A technician calls the local telephone number of the automatic number announcement service. This call is connected to equipment at a local central office that uses a voice synthesizer or digital samples to announce the telephone number of the line calling in. The main purpose of this system is to allow telephone company technicians to identify the telephone line they are connected to.

Automatic number announcement systems are based on automatic number identification, and meant for phone company technicians, the ANAC system works with unlisted numbers, numbers with caller ID blocking, and numbers with no outgoing calls allowed. Installers of multi-line business services where outgoing calls from all lines display the company's main number on call display can use ANAC to identify a specific line in the system, even if CID displays every line as "line one".

Some ANACs are very regional or local in scope, while others are state-/province- or area-code-wide: there appears to be no consistent national system for them. Most are provider-specific. Every telephone company, whether large or small, determines its own ANAC for each individual central office, which tends to perpetuate the current situation of a mess of overlapping and/or spotty areas of coverage. No official lists of ANAC numbers are published as telephone companies believe overuse of these numbers could make them more likely to be busy when needed by installers.

Under the North American Numbering Plan, almost all North American area codes reserve telephone numbers beginning with 958 and 959 for internal local and long distance testing (respectively), sometimes called plant testing. (One exception is Winnipeg, which reserves 959 only). Numbers within this block are used for various test utilities such as a ringback number (to test the ringer when installing telephone sets), milliwatt tone (a number simply answers with a continuous test tone) and a loop around (which connects a call to another inbound call to the same or another test number). ANAC numbers can also appear in the 958 range, but there is no requirement that they reside there.

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