 you, buy in your neighborhood telephone store. Digital vs. Analog Telephones Some telephones are digital and others are analog. The dis- tinction has to do with how the speech is processed in the telephone before it is sent over the line back to the business tele- phone system or the local telephone company central office. Voice starts as analog, represented by a sine wave (Figure 1.6). In many systems, the voice is transmitted in the analog form. In systems that convert the voice to a digital signal, the voice signal is sampled 8,000 times per second. Each sample is assigned a numerical equivalent, some combination of zeroes and ones. The binary numbering system uses only zeroes and ones to rep- resent all numbers. Each sample is a voltage reading, which is given a numeric value and changed into binary form Figure 1.7). When the signal reaches its destination, it is converted back to analog SO that the human ear can hear it. Figure 1.6 - Compliments of Siemens Digital Telphony provide by Clem Napolitano The Telecom Handbook $8 19 THE TELEPHONE Figure 1.7 SAMPLINGS CONVERTED TO BINARY NUMBERS REPRESENTING THE AMPLITUDE AT EACH SAMPLING POINT - Compliments of Siemens Digital Telphony provide by Clem Napolitano The telephone systems themselves are also either analog or digital, but this has to do with how the signals are moved around within the system control cabinet. The systems manufactured in recent years are digital although some analog systems remain in operation. It is possible for a digital telephone system to have analog telephones. Analog telephones may be similar in func- tion and appearance to the digital telephones. The Continued Importance of the Telephone on Your Desk Despite the increasing ubiquity of desktop computers and e-mail, it can be argued that the telephone is still the most important communications device. It is telling that the movers and shakers of industry often relegate computer functions to their assistants, and do business solely with the telephone. Also, the preference of one teleph