DID (Direct Inward Dial) and DDI (Direct Dial-In) are two different names for the same telephonic functionality. DID is the term most often used in the US, while the use of DDI is more common in Europe.
This function allows individual extensions on a private phone network (traditionally administered by a PBX) to receive direct incoming calls, despite the fact that they don’t each have their own separate line to the outside world.
What is direct inward dialing used for?
Calling an Office Without Direct Inward Dialing
PBXs allow multiple extensions to share the same trunks for incoming and outgoing calls based on an extension system – incoming calls to the main number go to the PBX, which either routes them to an operator or activates an automated attendant. The caller then selects the department or employee they want to speak with and are transferred to their extension.
Calling With Direct Inward Dialing
DID/DDI numbers allow outside callers to avoid the operator/automated attendant and ring direct to the desk of the person they’re trying to reach. The PBX is still involved in routing in the call, but it does so in the background – the process is seamless from the caller’s perspective.
Why do you need direct inward dialing numbers?
Being able to directly call the person they’re trying to reach can reduce callers’ frustration and add a more personal touch to organizations’ interactions with the public.
On the other hand, not using (or publicizing) DID numbers to route calls to the operator and auto-attendant can also provide valuable screening steps to prevent unnecessary work disruptions.
How does direct inward dialing work?
When an organization is setting up their trunk connections to the outside world, they also license a set of numbers from the phone company (likely more than the number of trunks). The service provider sets all of those numbers to call into the organization’s main number, where the PBX (or software equivalent) will answer.
While calls to the main number will then get sent to an operator or auto-attendant, calls to these secondary numbers pass along what number was dialed via DNIS signaling (Dialed Number Identification Service). The PBX/software will then take that information, check it against an internal database, and route the number to the correct extension without interrupting the call.
It is also possible to set up the system to transfer different DID numbers to the same device. This can be useful for situations such as:
- When multiple people in the office need their own fax numbers, but sharing a fax machine/MFD is ok.
- When the same call center is servicing multiple support lines. The system can be set up to route calls into specific sections of the center with populated information based on the number dialed.
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