This article describes the architecture and the network communication of a large-scale, networked virtual environment, which is designed to specifically support closely-coupled collaboration in highly interactive scenarios. Its main goals are the maintenance of low latency during user interaction and fast multicasting of messages in order to fulfill consistency requirements. This is achieved by sophisticated message distribution techniques, peer-to-peer connections between interacting clients and a global hierarchical communication topology. Scalability is realised through partitioning the virtual world.