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New technology is constantly emerging in the telephone world. In the past a small business might utilize a Key Telephone System or '''Key System''' to provide multiple phones for an office. Key Systems are POTS based. The key is the name for the line selector push button. Every phone set has two to six line keys along with a dial pad and other buttons. As a business grows the Key System might have to be replaced with a '''PBX''' System. PBX stands for Private Branch Exchange, which gives a business an entire telephone network. A PBX system connects the telephones within a company to one another and also connects them to the public switched telephone POTS. A PBX shares several outside lines (often referred to as trunk lines) to make and receive calls. A PBX system has more capabilities than a Key System. A PBX system can scale upward to accommodate hundreds of phone lines. A telephone '''Trunk''' is a phone line that carries multiple telephone conversations. A traditional analog trunk line carries a single channel of voice call per line. You might have a single trunk line into your phone for your POTS family phone. In a business when a trunk is terminated into a PBX special analog trunk cards (12 ports, 24 ports, etc) are used.