Disclosed is a communication system for effecting communication events between endpoints connected via a communication network. The communication system comprises a plurality of processing units, each having access to computer storage holding executable code modules for managing a communication event. The code modules are configured to implement a media modality controller configured to manage media modality of an established communication event and a call controller configured to establish the communication event. The communication system further comprises a resource allocator configured to allocate physical resources of the processing units and computer storage to each of the call controller and the media modality controller. A grant of physical resources to the call controller is independent and different from a grant of physical resources to the media modality controller.