Caller ID and Called Number (DID)

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Caller ID, known also as Caller Identification (CID), is a telephone service, that transmits a caller's number 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. Where available, Caller ID can also provide a name associated with the calling telephone number. The information made available to the called party may be made visible on a telephone's own display or on a separate attached device. This information is sent once between the first and second ring. The modem can decode this caller information and display it on your computer monitor during the second ring period as part of the call progress ring message. Depending on the software, Caller Id can be used with various functions, such as "Black and White list".

The Called Number is a phone number of the person who (or device that) answers a telephone call. Direct inward dialing (DID) is a telecommunication service offered by telephone companies that provides service for multiple telephone numbers over one or more phone lines, and transmits the dialed telephone number to the target phone device. DID service is widely used by fax servers. A telephone line is terminated at a telephone interface (fax modem) of a computer that runs fax server software. A set of digits of the assigned phone numbers are used to identify the recipient of the fax. This allows many recipients to have an individual fax number, even though there is only one fax machine available.