erentiate ringing sounds in different ways. One is the "cadence". For example, a call coming in from outside may be "riiiiing - riiiiing" while an internal call may be "ring ring - ring ring" (short little bursts of ringing in the same time interval that an outside call takes to ring two long rings). Another differentiator is pitch. Some rings have a high pitch changing to a low and others start with a low and change to a high. Some actually have different sounds. Different ringing for internal and outside calls is becom- ing less important as information on the display lets you know whether the caller is internal or from the outside world. Differentiated ringing among a group of telephones all in the same area is often useful. That way if you are not sitting right at your desk, it is still possible to know that it is your telephone that is ringing. Most telephones do not enable you to have a different ringing sound for each line or extension appearing on a multi- line telephone. More detail on the functions of the telephone and more functions of business telephone systems are described in the chapter on the PBX. How Does The Telephone Work? Now, let's get to what is inside the telephone. Remember that these components described are commonly found in the older traditional telephones. We are providing this information to lend an historical perspective. Most of today's telephone systems sub- stitute electronic components to emulate these functions. 14 & The Telecom Handbook CHAPTER 1 Figure 1.4 The Transmitter DIAPHRAGM CONNECTION TO FRONT AND BACK OF CAPSULE CARBON SPEECH GRANULES PRESSURE HANDSET VARIATIONS HOUSING TRANSMITTER FLEXIBLE SUPPORT COUPLING a. The transmitter. (Figure 1.4) The transmitter is the ear of the telephone in that it "hears" the voice of the person speaking into it. The transmitter is a miniature carbon pile rheostat. A rheostat is a device that controls an electric current by vary- ing the resistance in the circuit, similar to the action of a dim- mer switch control. The variations in sound