FreeSWITCH proper, the core FreeSWITCH, is a switching and mixing fabric with some message queues and a lot of very abstract APIs that define concepts and actions. The only possible interaction with the core is via those APIs and message queues; there is no access whatsoever to internal data, structure, functions, and so on. Everything is completely opaque and protected; there is no way to harm the stability and performance of core. From the outside, core is a blackbox able to accept commands and return results via APIs.

All functionalities are implemented in modules.

A FreeSWITCH module is a shared library to be loaded by core. A module provides additional features, APIs, and implementations. Usually, a module is the low-level plumbing needed to interact with the real world.

In core you have the concepts of channel, session, call, message, codec, and many others. These are just concepts, well thought-out and articulated abstractions useful to describe real-time...