An input-queued switch is the piece of silicon in the heart of
high-end Internet routers. It is an example of a switched network.
This diagram shows an input-queued switch with three inputs and three outputs.
At each clock tick, the switch chooses which inputs to connect to which
outputs, and it sends packets along the connections. The two diagrams here
show two different sets of connections.
The switch chooses the connections based on how much work there is
at each input for each output. In the left-hand diagram the switch has
chosen badly, since it connects the bottom input to the middle output—but there are no packets waiting here to be sent.