Abstract: The proliferation of QoS? -aware group applications over the Internet has accelerated the need for scalable and efficient multicast support. We present a multicast "life cycle" model that identifies the various issues involved in a typical multicast session. During the life cycle of a multicast session, three important events can occur: group dynamics, network dynamics, and traffic dynamics. The first two aspects are concerned with maintaining a good-quality (e.g., cost) multicast tree taking into account member join/leave and changes in the network topology due to link/node failures/additions, respectively. The third aspect is concerned with flow, congestion, and error control. We examine various issues and solutions for managing group dynamics and failure handling in QoS? multicasting, and outline several future research directions