The DECOS architecture divides the overall system into a set of nearly-independent distributed application subsystems, which share the node computers and the physical network of a single distributed computer system. Through restricting each application subsystem's communication activities to a corresponding encapsulated virtual network realized as an overlay network on a time-triggered backbone, the DECOS architecture supports fault isolation, complexity management, and the independent development of application subsystems. This paper provides a solution to the controlled export and import of information between distributed application subsystems. We give the designer the ability to coordinate application services and exploit redundancy in the system to either improve reliability or reduce resource duplication. We introduce virtual gateways for the coupling of virtual networks by the selective redirection of messages. Virtual gateways not only resolve property mismatches between distributed application subsystems, but also preserve encapsulation.