TC systems, or telecommunications systems, are switching systems that connect several telecommunications devices, such as phones, fax machines or answering machines, to each other and to the public telephone network. Other names for TC systems include telephone systems, private branch exchanges or switchboards. In international parlance, the term PBX (Private Branch Exchange) is most often used. Thanks to TC systems, connected phones can make internal calls free of charge, or be connected to the public telephone network by means of an exchange line. Outside lines, which usually come with a fee, can be used more efficiently, since not every end device requires its own exchange line. Depending on the total number of exchange lines that are available, a certain number of public phone calls can be made at the same time. Incoming calls can be forwarded automatically, depending on the system and configuration, either by means of a direct dial number to the appropriate extension, or manually by means of an attendant console.