Since DTMF, MF, and R2 MF tone signals can provide the telephone number of the called subscriber's line, these signals may be used by applications providing Direct Dialing In (DDI) service, also called dialed number identification service (DNIS) and analog DNIS for direct inward dialing (DID).
DDI service allows an outside caller to dial an extension within a company without requiring an operator's assistance to transfer the call. The CO passes the last 2, 3, or 4 digits of the dialed number to the CPE, and the CPE completes the call.
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