What is Channel Integration Framework(CIF):
Channel Integration Framework(CIF) is to integrate third-party channel providers with Dynamics 365 Unified Interface Application using browser-based JavaScript API library with cloud-to-cloud extensibility.
With CIF we can integrate any third-party channel provider into a model-driven app, where the CIF acts as an interface between the providers and model-driven applications.
Technically CIF is a set of APIs (methods, events and protocols) that enables developers and partners to build diving communication experiences such that third party communication widgets running on channel provider/partner cloud can interact with Dynamics 365.