In this contribution we analyze communication requirements of multi-agent simulation systems using ITSimBw – developed at Fraunhofer IAIS – as an example. A focus is put on issues concerning inter-agent communication but complementary aspects of user interaction and coupling with C2 systems are also discussed. We propose an augmented version of the battle management language BML as a communication protocol that perfectly matches our communication requirements both syntactically as well as on the semantic level. We furthermore explain how such BML messages are processed by our system.