A traditional PBX is made up of two key elements: lines and stations. The lines, sometimes called trunks, are connections to the global public switched telephony network (PSTN) by way of a telephone company. Stations are simply telephones or other endpoint devices like fax machines, modems and credit card terminals. The original mission of the PBX was to provide shared access to limited resources. Rather than having a separate phone line for each phone, a business could share a small pool of lines across a much larger pool of stations. When a call came it was answered by an operator who then connected it with the appropriate person or department. When someone inside needed to make a call, the operator connected them with an available line. Frequently these early systems were simply called switchboards.