A relevant class of Distributed MultiMedia Applications (DMMAs) can be implemented to support critical activities from which either financial investments, or human lives, or both, may depend. These DMMAs can be distributed across wide geographical distances; owing to their critical nature, the principal requirements they exhibit include the need for scalable services that be both timely and highly available (i.e. responsive). In order to provide support to these DMMAs, we have designed and developed a communication software architecture that meets effectively these requirements. In this paper, we introduce that architecture, and discuss its performance as resulting from a prototype implementation we have developed.