Simple definition
A DID (Direct Inward Dialing) is a public telephone number that a carrier can route to a specific destination in a phone system.
Technical definition
The DID, also called a direct number in some environments, is delivered to the PBX through the carrier trunk. The PBX interprets the called number and applies an inbound rule to route the call to an extension, group, queue, or IVR.
How it works / role
When a call arrives, the carrier includes the called number in signaling. The PBX normalizes it to the expected format and searches for the matching inbound route, allowing the internal destination to be reached without a general receptionist number.
What is it used for?
Assign direct public numbers to users or services and build precise inbound call-routing rules.
Practical example
The carrier presents a public number on the SIP trunk; the PBX matches it against an inbound rule and sends the call directly to extension 142.
Common issues
- The received E.164 format or prefix differs from the configured value
- The DID is not provisioned or mapped correctly by the carrier
- The inbound rule is missing or too broad
- Several routes conflict over the same called number
Key takeaway: When troubleshooting a DID, compare the number actually delivered by the carrier with the exact format expected by the inbound rule.