Operation
A technician will call a local ANAC's phone number. This number connects to a computer at a local central office, which uses a voice synthesizer or digital samples to "speak" the phone number of the line calling in. The main purpose of this system is to allow phone company technicians to identify which telephone line they are connected to.
Because this system is based on automatic number identification (not caller ID) 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. 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.
Read more about this topic: Automatic Number Announcement Circuit
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