essed. A list of all classes of service in use in the system and what they mean. A list of how each extension is programmed to forward calls under a variety of conditions, including when the extension is busy and when it is not answered. Information on how each of the slots and ports is used in the PBX control cabinet. Identification of spare slots and ports available for expansion. The Telecom Handbook CHAPTER 2 Typical Differences Between Key Systems and PBXs No analog telephones: Most key systems do not provide the capability for an analog telephone. The proprietary telephone that works with the system is the only one that can be con- nected to it. Thus an analog extension on a jack to be used for a fax machine, a separate computer modem or a single line telephone can typically not be provided through a key system. No Automatic Route Selection for Routing of Calls to the Outside Line with the lowest cost for placing calls. Wireless Telephones with a PBX Wireless telephones working with a PBX are based upon ad- junct (separate but connected) controllers that may use analog links to interface to the main PBX. In the future, this will prob- ably not be necessary as distributed base stations that transmit and receive wireless signals will be supported by separate circuit boards which will reside on a shelf in the PBX cabinet. Alloca- tion of the frequency spectrum and standards must still be resolved before the use of wireless PBX extensions becomes widespread in the United States. This is one area where European and Asian organizations may move more quickly since the U.S. regulatory issues do not exist there. Some cellular telephone service providers enable the cell phone to be used as an extension of the PBX while in the office. PBX Disaster Recovery Planning It is also important to plan what to do when things go wrong. Disaster Recovery Planning is the term often used for this activity. A newer term is COB which stands for Continuation of Business. The Telecom Handbook & 55 THE PBX What if the power fails? Many