In multicast communication systems, a single perturbed recipient can drastically aect the performance of a complete group of processes. This problem can be alleviated by allowing some messages to be omitted. We propose a multicast service that exploits semantic knowledge to select which messages can be omitted without compromising the application's correctness. Besides summarizing initial research results [8], this text addresses the implementation of high throughput fault-tolerant services by combining virtually synchronous and totally ordered reliable multicast with semantic reliability.