dialplan

Dialplan is the set of rules that govern how a telephony system handles calls. It defines how incoming and outgoing numbers are interpreted and what actions to take in response to different dial patterns. Dialplans are a core component of private branch exchange (PBX) and IP-PBX systems, and are implemented in software such as Asterisk, FreeSWITCH, and other telephony platforms.

In many systems, the dialplan is organized into contexts (scoped groups), extensions (call routes), and priorities (the order of actions). Each extension includes one or more steps, called applications, which perform operations such as answering a call, playing a prompt, dialing another endpoint, transferring to voicemail, or recording the call. Patterns with wildcards let the system match multiple numbers, enabling features like IVR menus and time-based routing.

Common features implemented via dialplans include call routing to internal extensions, IVR prompts, call queues, conferencing, voicemail, call forwarding, time-of-day routing, and integration with external databases for dynamic routing.

Dialplans are often written in a domain-specific language provided by the platform. For example, Asterisk uses extensions.conf syntax with lines like exten => 100,1,Dial(SIP/alice), while other systems use different formats but share the same purpose of mapping dialed digits to actions.

Design considerations include readability and maintainability, version control, and security. A well-designed dialplan minimizes hard-coded numbers, uses variables and contexts to limit scope, and includes error handling and timeouts to avoid loops or unintended routes. In distributed systems, dialplans may be complemented by external routing engines or databases.

See also: PBX, IVR, VoIP, Asterisk, FreeSWITCH.