a Reseller. The telephone installation and maintenance company is not the place to call for problems with telephone bills or for help in deciding the types of local and long distance telephone services you need. Some companies can provide service nationally in the U.S., but most serve smaller areas. When evaluating a company, it is important to focus on the support available in the local area where the telephone system will be installed. Some smaller telephone systems (for less than 20 people) can be purchased in telephone stores or through catalogs. It's a good idea to have an experienced telephone installer put the sys- tem in for you rather than doing it yourself, unless you want to learn by doing. Business Telephone System Manufacturers There are approximately ten major manufacturers of telephone systems for large organizations and perhaps another twenty to thirty that make smaller size systems. Two of the manufactures (Avaya and Northern Telecom) evenly share approximately 50% of the business telephone system marketplace worldwide. Avaya was formerly Lucent and before that it was AT&T. These companies manufacture the control equipment (PBX cabinet, circuit boards, processors, etc.) and the telephones them- selves that work only with the system from that particular manufacturer. Local or Long Distance Company Switching Manufacturers The major companies that manufacture telephone systems (called PBXs or switches) for large businesses also manufacture The Telecom Handbook to 285 UNDERSTANDING THE INDUSTRY switches for use by either a local telephone company or a long distance company to connect the many calls from all sources to destinations passing through their network. These are often called central office switches and are said to be part of the public switched telephone network or PSTN. PSTN is often used to re- fer to the separate network other than the Internet. The network consists not only of these switches but also of the connections between them, most often made via copper or fiber optic cable. Manufa