The basis of the Bell System and Regional Bell Operating Companies (RBOC) were the central offices located across the country. These Central Offices were as small as shacks and as big as skyscrapers. They served as the backbone of the entire public switched telephone network. Telephone lines from local subscribers traversed the town and cities via cables that were connected in the central office. Central offices were connected with one another to allow for great and great calling distance.
Telephone Vault