Binary--base two--uses a single digit to represent zero or one. With only 2 states, machines can differentiate between the two; if there is voltage it’s a one and if there is no voltage it’s a zero. Since digital computers communicate using binary numbers, network engineers need to have an in depth understanding of binary.
Cox, Clyde, "Binary the Digital Language" (2012). Computer and Internetworking Technologies (CIT) Scholarship. Paper 1.