Priorities: A priority is a step in an extension.You could have an extension called "mainIVR" if you wanted. Unlike many traditional phone systems, extensions don’t have to be numerical and they aren’t tied to a single device. Extensions: An extension is simply a grouping of steps used to handle a particular call.Contexts: A context is a logical section in the dialplan.According to Asterisk the Definitive Guide, there are four fundamental components to the Asterisk dialplan: While there are other programming interfaces for interacting with Asterisk, the dialplan is the most basic, and understanding it is fundamental to understanding how Asterisk handles calls. When the employee receives the customer’s call, the system provides them with all of the customer’s details and saves the caller some time. Optionally, the user can be routed to a queue of available customer service representatives.The IVR looks up their account and presents them with information (e.g., information about outstanding invoices). An Interactive Voice Response (IVR) system might ask the user to enter basic information, such as their account number.An external call comes into Asterisk from a standard telephone number.For example, you could create the following call flow for a small business: With the dialplan, you can design rich, voice-driven applications. You might think of phone systems as simply accepting and connecting calls, but Asterisk is capable of much more. The dialplan is written in a special scripting language, and it is extremely powerful.
The Asterisk dialplan is responsible for routing calls, so it is often referred to as the heart of an Asterisk system. Network diagram credit: Dialplan fundamentals