 lines to your pre- mises are run from this central office and may be routed underground or overhead on telephone poles. If you are in a high- rise building, the local telephone company may also own the riser cable that runs vertically from the basement and drops off tele- phone lines on each floor. Long Distance Telephone Calls and Point-to-Point Circuits Long distance companies, also known as long distance carri- ers or IXCs (inter-exchange carriers) sell long distance telephone calls. When you pick up the telephone in your office and place a long distance call it may be sent over an outside line connect- ing you directly to your long distance company. The call may 276 4 The Telecom Handbook CHAPTER 13 also be sent over the outside lines connecting you to your local telephone company, who then passes the call along to the long distance company you have told them to use on your behalf. This is called your carrier 'pic'. The way you have your telephone system set up will control which of those two routes your call takes. This routing is controlled by the Automatic Route Selec- tion capability of your PBX. Long distance companies also rent circuits that permanently connect two or more offices of a large organization. These cir- cuits may carry voice, data or video signals. The circuits are sometimes called leased lines or dedicated lines. There are some large long distance companies and many smaller ones that cover the entire United States or a specific geographic area. Most handle international calls as well. U.S. companies may have relationships with carriers for local and long distance calls in other countries, since a call may be carried on circuits of several different companies before reaching its final destination. Even in the U.S., a long distance telephone call is most likely to use the circuits of the traditional local telephone companies at both ends of the call. The long distance companies pay the local companies for the use of these circuits. If you're renting a circuit from a long distance carrier co