The platform can broadly be divided into three key components as shown in the figure.
There is a need for considering external applications, because most internal applications that one can think of will be some sort of services provided to say, a downloader (internal) that lets user to download files through an android app or a website(external).
The Routing platform block model can be thought of as depicted in the picture. The most basic feature is the Network core and Router/Network API upon which a permission and user service can regulate applications, managed by application manager.