Communication environments including network attachments as well as equipment and applications are increasingly hetreogeneous. Many upcoming multimedia applications require multicast support for group communication. Typical examples are collaboration environments. The goal of AMnet is to provide dedicated support for heterogeneous multicast communication. Therefore, active multicast nodes are implanted in the network. The talk presents a first prototype implementation based on RSVP with some measurement results. Furthermore, a collaboration environment , MACS, will be presented that can utilize this active multicast network.