A service offered by PSTN carriers that passes the dialed digits to the destination PBX in advance of connecting the call. DNIS operates much like direct inward dial (DID) service, but over toll-free lines, enabling the PBX to determine which toll-free number was dialed and to route the call to the proper agent or agent group. DNIS is heavily used in call centers that service multiple clients or client groups, each of which has one or more unique toll-free numbers. See also call center, DID, and toll free.