your conversation with the new caller. 48 - The Telecom Handbook CHAPTER 2 All of the previous capabilities are features of the PBX ac- cessible from the desktop telephone, usually accessed by pressing a specifically programmed button on the telephone, but some- times requiring the dialing of a numeric access code as well. There are also features that have to do with the physical makeup of the telephone itself such as the display and the speak- erphone. See the chapter on The Telephone for a description of these physical characteristics. Expense Control Function of the PBXs Every time a telephone call is made, money is being spent. Many of the PBX functions help an organization to control this expense. Toll Restriction Toll restriction enables you to program the telephone system SO that each extension has what is called a class of service. Each class of service designation enables the extension to call certain areas and restricts it from calling others. The most sophisticated systems can be programmed to restrict the dialing of specific telephone numbers. Others can restrict by area code or by area code and exchange. Figure 2.6 shows a typical scenario. You may also use class of service to give each extension ac- cess to certain system functions and restrict it from using others. You may hear the term six digit toll restriction, meaning that the first six digits dialed (the area code and exchange) can be restricted through programming. Ten digit toll restriction enables you to restrict dialing to a specific telephone number. Automatic Route Selection Most PBXs and some key systems have the capability for ARS (Automatic Route Selection) or LCR (Least Cost Routing), which are essentially the same thing. Many larger telephone The Telecom Handbook 49 THE PBX Figure 2.6 Classes of Service for Toll Restriction (Example) CLASS 0 = Internal Calls Only CLASS 1 = Local Calls Only to 212, 646 and 917 CLASS 2 = Local Calls to 212, 646, 917, 718, and 914 CLASS 3 = Local and Long Distance Calls Within NY Metropolitan Area 212,