caller ID

Caller ID (caller identification or CID, and more properly calling number identification - CNID) is a telephony intelligent network service that transmits the caller's telephone number and in some places the caller's name to the called party's telephone equipment during the ringing signal or when the call is being set up but before the call is answered. The CID is only the calling party number. In the United States, the calling party name is a separate piece of data and must be requested by the consumer's terminating central office if the consumer has subscribed to that service. Calling name delivery is not automatic. An SS7 (or Signaling System 7) TCAP query must be launched by the called party's central office to retrieve the information for Calling Name delivery to the Caller ID equipment at the consumer's location. Canadian systems automatically send the calling name with the call set up and routing information at the time of the call. Fully 99 per cent of the names that could be delivered are available to all central offices in the US. Most carriers, however, are now refusing to retrieve the information for delivery, since it may reside in a non-owned database and would require payment to another provider for the data. The local carrier will then claim the name is "unavailable", or "out of area", or default to a "city, state" response. China caller ID industry had great progress in recent years.