nation of Outgoing and Incoming Toll-Free Calls) Dial "9" to Place an Outgoing Long Distance Call. PBX Routes the Call to the T- 1 to Your Long Distance Carrier. OUTSIDE LINES number assignment or line assignment, provided by the local tele- phone company. This is a seven digit number preceded by the three-digit area code. The first three digits of the seven numbers are called the exchange, the central office, or the NNX. In the case of a dial tone line, the telephone number assignment is also the circuit number. Other types of circuits have different types of circuit numbers usually including letters and not in the seven- digit format (for example 96OSNA111222). More On Loop Start vs. Ground Start A dial tone line may be a loop start or ground start line. When ordering an outside telephone line, you will be asked if the line is to be ground start or loop start. Dial tone lines coming into most key telephone systems or, directly to a telephone, fax or modem, are loop start. This means that when you access the line, the physical "loop" connecting you to the local telephone company central office becomes a complete circuit for sending and receiv- ing calls. (Tip and ring, a term used by telephone installers, refers to the two wires that complete the talk path.) You hear the dial tone immediately and can place your call. PBXs work better with ground start lines where the cen- tral office switch is looking for a signal from the PBX before the circuit is completed and dial tone is delivered. When you are at a PBX telephone, you may lift the receiver and hear a dial tone. This is not the dial tone being sent from the local telephone company, but rather the dial tone sent from the PBX on premises. To place a call to the outside world, you typically dial 9 and hear a second dial tone that will be the one from the local tele- phone company. You may then dial the outside telephone number you are calling. 226 * The Telecom Handbook CHAPTER 10 Point-To-Point (Dedicated) Voice Communications Lines MANUAL AND AUTOMATIC RINGDOW