atcomsystems.ca/forum Forums General General Telephone & Systems Information DID and DNIS

Pardon my ignorance, but what exactly is the difference between DID and DNIS? I've programmed many PRI's and used DID info, but I notice many systems (like Toshiba) are looking for DNIS information or ask you to choose between the two. Thanks in advance.

Purpose is the same, but DID is actually digits number sent by provider to switch and DNIS is a Digital Number Identification Servises that comes in special format that has to be recognized by switch and translated to your numbering plan. Exapmple is Mitel: At the begining of the T1 capability it recognized services only from AT&T and MCI nobody else. DID was available only on DID Trunk card not T1. And some system still gives you a choice what kind of T1 card to use: DS1 or PRI. DS1 works only with DNIS but PRI uses DID.

I believe in Mitel, you can use DID or DNIS on T1. That's what I was taught in Light 15/16 class 11 years or so ago!
DNIS was thought to be more useful in an inbound marketing situation, while DID was more useful when many people in an organization needed their own phone number. Only real difference I can see is DNIS gives you the WHOLE dialed number, while DID gives you 3-7 digits, digits normally specified when DID is ordered. John C.

My dear John,
You are right in Lightware 15/16 was a PRI ISDN capability but not from 1001 -1004. It was only T1 DS1. But it was discriptor T1/DID available for DNIS service and T1/E&M for matching numbering plan.

Where's our switch guys? From my NODAL days. DNIS is where you dial a number and the desired digits are sent to the PBX and ring the extension. DID the trunk is dedicate to a certain extension/group. On a DNIS trunk I could access the trunk (from a test position) and dial any extension in the PBX, if I wanted. On a DID I would put ringing voltage on the trunk and it went to the specific station/group assigned to that trunk.

Hi justbill,
I remember testing DID on Merlin Legend by clipping my buttset on the DTMF DID Trunk T&R and dial digits and dedicated Extension was ringing. Yes, there is DID trunk and DID number which can be any number of didgits sent to dedicated point. As far as my knowlage goes DNIS is a string send by provider which includes some codes together with numbers that supposed to mean something to switch for proper interpretings and pointing like, for example, *4*3333# that can be like pause, 3 gitits ext# follow by actual number. 333.

Sorry Bill...busy day..but you guys got it covered

Set us straight Anthony. vad60, there are no special codes in DNIS digits that I know for sure. I'm pretty sure I'm right on the DID too. Trunks with DNIS were set up like any trunk, wink, immediate, DT, whatever the customer wanted, you got your signal from the customer switch and dumped your digits, usually 3 or 4, but whatever the customer ordered. DID trunks we didn't dump digits, just rang out on the trunk.

DIDs are a dedicated range of digits..for example you can buy a block of 200 from the carrier. Example 210-555-2000 through 210-555-2199. Any analog or digital DID trunk that is seized inbound that pulses the prescribed amount of digits (3-7 digits) will be presented to the PBX in a manner to be interpreted by the customer premise equipment. If they are sending 4 digits in the previous example and the first number was dialed the PBX would see 2000. A DID routing table would tell the system where to route the call to internally. A DNIS number would be outside the DID range. Say for instance the customer had the previous mention DID block but was porting a number that was 210-555-9933. The DNIS would probably be 9933. Still presented and routed as a DID but outside the range. No special codes.

Thanks for the explanation RBF.

Edit: A little brain work would have told me that on the DID=direct inward dialing..some days. :scratch:

So what were the ones called we just rang out on and it went to a preset extension or group?