Caller ID

Also called: Calling Line Identification(CLI) or caller ID

Caller ID or Calling Line Identification (CLI) are official names for the system better known as caller ID. Caller ID allows the recipient of a phone call to see who is calling. At least, it makes it clear from which number is dialing.

By linking Caller ID information to a contact list, if the number is known, a telephone device or telephony software can also display the caller's name. Using the related standard Caller ID Name (CNAM), calls can include a name or description in addition to a number. The display of this is not supported by all telephones and PBXs.

The part of the standard that ensures that the caller's phone number is sent along with the call and can be displayed on the recipient's device is called Calling Line Identification Presentation (CLIP). The Calling Line Identification Restriction (CLIR) section provides the ability to suppress Calling Line Identification Presentation and thus "callanonymously.

When CLIR is activated, the caller's number is not visible to the recipient of the call. This is used by call centers and larger organizations, among others, that do not want the recipient to be able to see what number is being called from. One reason may be to prevent the recipient of the call from calling back to a direct number.

For security reasons, Caller ID suppression does not work when calling emergency numbers. For calls to the emergency number 112, the sender of the call is therefore always visible to the control room.