The two final interconnection networks introduced in this section are examples of multistage networks. Systems built with these topologies have processors on one edge of the network, memories or processors on another edge, and a series of switching elements at the interior nodes. In order to send information from one edge to another, the interior switches are configured to form a path that connects nodes on the edges. The information then goes from the sending node, through one or more switches, and out to the receiving node. The size and number of interior nodes contributes to the path length for each communication, and there is often a ``setup time'' involved when a message arrives at an interior node and the switch decides how to configure itself in order to pass the message through.
Figure 14: Crossbar Switch.