ANI (Automatic Number Identification) is a system utilized by telephone companies to identify the DN (Directory Number) of a calling subscriber.
ANI serves a function similar to Caller-ID, but utilizes different underlying technology. In addition, although Caller-ID can be blocked by prefixing a call with *67, ANI is (usually) impossible to block.
ANI was originally developed for telephone company billing purposes. ANI technology is also now offered to commercial customers who may benefit from knowing who is calling them. In addition, ANI is one of the core technologies behind the 911 emergency service.
ANI data is usually transmitted in-band using multi-frequency (MF) signaling. However, ANI data can also be transmitted separately if you have an ISDN PRI.
ANI (Automatic Number Identification Messages)
The format for an ANI message is:
- KP (Key Pulse)
- I (Information Digit)
- 7-10 digits (Directory Number)
- ST (Start Signal)
These messages are sent using multi-frequency (MF) signaling as shown below.
SignalFrequency #1Frequency #2
KP 1100 1700 KP2 1300 1700 1 700 900 2 700 1100 3 900 1100 4 700 1300 5 900 1300 6 100 1300 7 700 1500 8 900 1500 9 1100 1500 10 1300 1500 ST 1500 1700
The possible values of the Information Digit under ANI I are:
0 Automatic Identification (normal) 1 Operator Identification (ONI) 2 Identification Failure (ANI Failure)
ANI II adds many more options for the Information Digits. These are documented at NANPA.
