Abstract: A network comprises a set of nodes, each comprising a computer workstation in a computer network and including means responsive to messages from other computers in the network to join or leave a call. Each node maintains a list of calls in which that node is participating, an entry in the list for a call including the identities of all the other nodes in that call. In order to split a single call one node sends messages to a subset of nodes to join a second call, and leave the original call. The remaining parties in the original call then continue in a call of reduced scope. In order to merge two calls together, a node that is common to both calls sends messages to all the nodes in both calls, instructing them to leave the existing call and join a new call.