A protocol to coordinate multipoint groupwork in the IP-multicast framework. Called Aggregated Coordination Protocol (ACP), the protocol operates on a shared multicast tree, benefiting from the underlying tree structure to store and forward coordination primitives between hosts in different multicast groups on the tree. ACP coordinates distributed activities via message passing, and manifests control by ephemeral permissions rather than actual locks, allowing control over continuous media flows as well as discrete data. The protocol supports Internet-wide coordination for large and highly interactive groupwork, relying on transmission of coordination directives between group members across a shared end-to-end multicast tree.