In a communication network with separate data planes including a control plane and a user plane, an application function is provided as a combination of an application function control plane (AF-CP) part operating in the network's control plane and an application function user plane (AF-UP) part operating in the network's user plane. The application function user plane part may be configured for the application-specific processing of user data, and instanced multiple times. The application function control plane part may be configured to support selecting an optimal instance of the application function user plane part for a particular UE.