A system utilized by telephone companies to identify the directory number of a calling subscriber. Similar to Caller-ID service, it utilizes different underlying technology and is (usually) impossible to block. ANI is offered to commercial customers who may benefit from knowing who is calling them and is one of the core technologies behind the 911 emergency service. It uses either in-band multi-frequency (MF) or ISDN PRI signaling.

More: Automatic Number Identification