Abstract: A serial switched interconnection network comprises several stages of switching units each having a plurality of source ports and destination ports interconnected so that any source port of the first stage can be connected to any destination port of the final stage by operation of switching units in successive stages. Connections are by shared data and control paths each of which paths may comprise a single line or multiple lines and each switching unit when switched to along a path sends a request back up that path for sufficient data signals to operate the switching unit initiating the request. The setting up of a path through the network is thus stage-by-stage asynchronously.