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Caller ID is a telephone feature that displays a caller’s phone number on the recipient's phone device before the call is answered. The phone number, location and associated billing or subscriber name is shown on the handset’s display or a separate caller ID box attached to the phone.
The CLID feature is particularly useful when screening known, unknown, or unwanted calls. Unwanted calls are effectively deterred with the use of caller ID, including obscene, harassing and threatening phone calls.
Caller ID service, also known as caller identification (CID), calling line identification (CLID), and calling number identification (CNID), is provided by phone companies for analog and digital phone systems, as well as Voice over Internet Protocol (VoIP) applications.
To enable caller ID, the phone company equips a phone with a caller ID box. This usually includes a modem to decode data bits, a tiny circuit to detect a ring signal and a simple processor to drive the display. Caller ID data is transmitted between the first and second rings. When a call is answered immediately after the first ring, caller ID may not be available.
Caller ID is one of two types as follows: