Dialed Number Identification Service (DNIS)
Dialed Number Identification Service (DNIS) is a service offered by PSTN carriers that passes the dialed digits to the destination PBX in advance of connecting the call. This tells the receiving PBX which number was called.
DNIS operates much like direct inward dial (DID) or direct inward dialing service, and when used with toll-free lines, it enables the PBX to determine which toll-free number was dialed and to route the call to the proper agent or agent group.