We built a system that allows musical performers (and listeners) who wish to play together to organize into multiple session groups. The users interact in real time over the network, and may dynamically join or leave a session group. The players contribute to the session by playing on their MIDI controllers, using General MIDI protocol. We assume a totally asynchronous environment in which failures of both end systems and communication links are possible. TransMIDI was implemented using the Transis group communication system for fault tolerance and coordination. Transis is a transport layer that supports efficient and reliable multicast and membership services. The advanced Transis group services allow for different forms of cooperation among performers, so that many different kinds of musical ensembles can be easily established. Moreover, TransMIDI provides its users with means for exploring novel ways of musical interaction. 1 Introduction Increasing improvement in communication tec...