Q. Explain about Register marker?

Register marker: Stronger selectors perform searching and counting . Though, the crossbar switch has no ‘intelligence'. Something external to switch should decide which magnets to operate. This is known as a Register Marker. As it takes less than a second to operate the switch, a marker can control many switches as well as serve many registers. So even a large exchange needs few markers. This is further stage of common control, which we willcall centralized control.