Many engineers are still reluctant to adopt advanced object-oriented technologies (such as high modularity, dynamic binding, automatic garbage collection, etc.) for embedded systems with real-time constraints, because of their supposed inefficiency. We set ourselves into the context of building telecommunication systems with a standard object-oriented analysis and design approach. We describe how we use relevant design patterns, followed with an implementation in a pure object-oriented language (Eiffel) to conciliate the needed efficiency with the benefits of the object-oriented approach —flexibility, dynamic configurability, maintenability, portability, etc. We discuss a case study based on the implementation of SMDS (Switched Multi-megabits Data Service) servers featuring high-throughput and low-delay transmissions and respecting the real-time constraints of SMDS.