DID (Direct Inward Dialing)
A DID is a public phone number that routes directly to a specific extension or destination on a PBX, without going through an operator or auto attendant.
Published 8 November 2026 · 1 min read · By SpaGreen Creative
Short answer
A DID is a public telephone number delivered over a trunk that the PBX routes directly to a particular extension, queue or other destination.
DID stands for Direct Inward Dialing. In some regions the same concept is called DDI, for Direct Dial-In. It refers to a public phone number that reaches a specific person or service inside an organisation directly, instead of a main number answered by a receptionist or a menu.
With a SIP trunk, the carrier assigns a block of numbers to the trunk. When someone dials one of them, the carrier sends an INVITE to the PBX with that number in the Request-URI or the To header. The PBX looks the number up in its inbound routes and sends the call to the configured destination, which might be an extension, a ring group, a queue, voicemail or a time-based condition. Asterisk-based systems configure this under inbound routes in FreePBX and Issabel, keyed on the DID number.
One trunk can carry many DIDs, and a single DID can be re-pointed to a different destination at any time without involving the carrier. DIDs also determine the caller ID shown on outbound calls: the PBX sets the From header to the DID associated with the calling extension so that return calls arrive at the right place.
Softphone users do not configure DIDs; they receive calls to a DID through their extension.
Sources and further reading
- Asterisk documentationdocs.asterisk.org
- RFC 3261: SIP: Session Initiation Protocolwww.rfc-editor.org
This article is published by SpaGreen Creative, the maker of SIPdia. Product names mentioned belong to their owners. Where it describes other software, treat the steps as general guidance and check the official documentation linked above.
