possible permutations of these labels. This essentially reorders the input sequence of sam- ples that may be coming in from multiplexed lines. Therefore, it effectively behaves as a switch. In space-division multiplexing, input samples follow a physically different path inside the switch core between input and output. The most rudimentary space-division switch is a crossbar such as the one shown in Figure 14.1. The principle can be extended geometrically. Signals are understood to be flowing horizontally into the switch from the ports shown on the left-hand side of the drawing, whereas ports on the right-hand side of the switch represent outputs from where signals exit the switch. At every moment and depending on which state the switch is in (among the two possible posi- tions), we distinguish the bar state and the cross state. Another basic concept is that of the crosspoint switch, which can be functionally visualized as hor- izontal bars (corresponding to inputs) physically running over a set of vertical bars (corresponding outputs). Based on an implementation-specific scheduling mechanism, connections are established at the junction points, thereby effectively connecting a horizontal bar to one or more vertical bars. Figures 14.2 and 14.3 show the core principle of each connection junction. It works very much like the cross- bar switch, but it is characterized by a slightly different topology and it can be in either the bar state or in the cross state. In the crosspoint switch, signals are propagated either in the vertical or horizon- tal direction. Input signals flow into the switch along the horizontal lines, whereas outputs are read out along the vertical bars. Active elements called crosspoints are placed between input and output lines. When a crosspoint is active, the signal flows from the corresponding input to the corresponding output. We can have the same or different number of inputs and outputs, which correspond to NXN or NXK configurations, respectively. The possibility of activating a different out