one over another is most often the decid- ing factor in a new telephone system purchase decision. 20 The Telecom Handbook CHAPTER 2 Your Business Telephone System - The PBX What is a PBX? PBX is the term used for most business telephone systems. The letters stand for Private Branch Exchange. Private means that the system is on your premises as opposed to public mean- ing a similar system used by a telephone company. Branch refers to the fact that the cables connected to the PBX branch out to each office desktop, connecting the telephones to the PBX. Ex- change refers to the activity going on within the PBX known as switching (or exchanging) connections between telephones and outside lines that connect your PBX to the outside world and your calls to telephones at the other end of the call. The PBX is also called a switch which is short for switching system. When a call comes in for you, it may arrive on one of many outside lines connected to your organization's PBX. The switch- ing function in the PBX is what enables any of these outside lines to be connected to your particular telephone. Conversely, when you dial "9" to place an outgoing call, your telephone can be connected to any one of many outside lines, also through switching. If it were not for switching, every single telephone would have to have its own separate outside line which would be costly and inefficient. Switching enables a greater number of tele- phones to share a smaller number of outside lines since not everyone will be using those lines at the same time. Switching is also used by the telephone companies who do not expect every single one of their subscribers to use the tele- phone at the same time. The Telecom Handbook 85 21 THE PBX Understanding Your Own System In terms of thinking about what a PBX can do, it is important to remember that each manufacturer's PBX is different and has its strengths and weaknesses. One PBX may be outstanding in some areas but not in others. When working with a particular PBX, the more you understand it, the bett