DNIS explained: which number the caller dialled.
DNIS — Dialed Number Identification Service — tells the system answering a call which of its numbers the caller dialled. ANI is the other half: the caller’s own number. Here is what each one carries, how it arrives and what a business uses it for.
- DNIS = the number dialled
- ANI = the number calling
- Sent while the call is set up
What DNIS is
A business publishes three numbers — one for sales, one for support, one for a Spanish-language line — and points all three at the same phone system. The calls arrive over the same lines, so something has to say which number each caller dialled. That is DNIS: during call setup the carrier sends the dialled digits, typically four to ten of them, and the receiving system reads them before the call is answered.
It is old, unglamorous plumbing, and it is everywhere. In the United States it has long been provided as standard on toll-free and 900 numbers, and direct inward dialing (DID) delivers it too — which is how a system with hundreds of DIDs knows which extension to ring.
What a business uses it for
- 01RoutingSend each number to its own destination — a queue, a team, one person — even though every call arrives over the same lines.
- 02The right greetingAnswer the sales line as sales and the support line as support, or start a different IVR menu, before anyone picks up.
- 03Reporting by numberCount calls, answer rates and outcomes per number. A number printed on one advert or one product line becomes a report of its own.
- 04Language and region linesPublish a separate number for Spanish-speaking callers or for one region, and let the number dialled decide who answers.
How the dialled number arrives
DNIS is a function, not a single signal. How the digits travel depends on the kind of line the call comes in on.
- Older digital trunksThe digits are sent as tones over the trunk while the call is being set up, before it is answered.
- ISDN PRIThe dialled number travels as the called-party number in the call’s setup message.
- SIP trunksThe dialled number is in the INVITE that starts the call, normally in its Request-URI and To header. When a call has been forwarded, the number originally dialled can arrive in a separate Diversion or History-Info header.
Three numbers that travel with a call
The terms get mixed up because all three are phone numbers attached to the same call. They answer different questions.
- 01DNIS — the number dialledWhich of your numbers the caller dialled. It answers “what is this call about?”
- 02ANI — the number callingAutomatic Number Identification: the calling party’s billing number, captured by the network. Built for long-distance billing, it also carries two information digits (ANI II) that say what kind of line the call came from.
- 03Caller ID — the number displayedWhat the person answering sees. It is a separate service from ANI: a caller can block caller ID, but the network still captures the number and line type through ANI.
The difference matters most on toll-free lines. Toll-free numbers depend on ANI to track inbound calls, and ANI is captured even when the caller has blocked caller ID — so a toll-free line can record numbers that a caller-ID display would have hidden.
Where this matters when you set up numbers
If several of your numbers ring the same team — a main line, a support line, a number printed on one campaign — the number dialled is the most reliable way to tell those calls apart, because it comes from the call itself rather than from anything the caller says. Decide what each number is for before it is printed anywhere: which team answers it, what greeting it gets and how its calls are reported.
Routing, queues and IVR on DialPhone are covered on the contact center page, and pricing lists which plan includes what. For the structure of the number itself — area code, exchange and line — see NPA-NXX explained. For how the outcome of each call is recorded once it ends, see call dispositions.
DNIS and ANI FAQ
What does DNIS stand for?
Dialed Number Identification Service. It is the information the telephone network passes to the receiving system about which number the caller dialled.
What is DNIS used for?
Telling apart calls that arrive on the same lines but were dialled to different numbers: routing each number to the right team, playing the right greeting or IVR menu, and reporting on calls number by number.
What is the difference between DNIS and ANI?
DNIS is the number that was dialled — one of yours. ANI is the number the call came from — the caller’s. A contact center typically uses DNIS to decide where a call goes and ANI to look up who is calling.
Is ANI the same as caller ID?
No. ANI is captured by the network and is technically separate from the caller ID shown on a handset. A caller’s number and line type are captured by ANI even when caller ID blocking is switched on.
How many digits does DNIS send?
Typically between four and ten, depending on how the carrier and the receiving system are set up. A system that only needs to tell a few numbers apart may take the last four; others take the full number.
Is DNIS the same as a DID number?
They are related, not the same. A DID (direct inward dialing) number rings straight through to a line or extension; DNIS is the information about which number was dialled. DID service delivers DNIS, which is how the system knows which extension to ring.
What are ANI II digits?
Two information digits sent with ANI that identify the class of service of the calling line — for example a payphone, a hotel or a prison line. NANPA administers the assignments.
How does DNIS work on a SIP trunk?
The dialled number is part of the INVITE message that sets up the call, normally in the Request-URI and the To header. There is no separate DNIS signal; the receiving system reads the number from the call itself.
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