Before the advent of intercoms, old mansions had a sash in e…

Before the advent of intercoms, old mansions had a sash in each room. Each sash was connected to a bell on a master board in the servants’ office. When someone pulled a sash in a particular room, a bell corresponding to the room would ring on the master board, informing a servant where to go to provide assistance. This system is similar to which of the following types of coding?