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| | Telephony - Encyclopedia.WorldSearch (Site not responding. Last check: 2007-10-22) |
 | | Edison discovered that carbon grains, squeezed between two metal plates had a resistance that was related to the pressure, thus, the grains could vary their resistance as the plates moved in response to sound waves, and reproduce sound with good fidelity, without the problems associated with a liquid contact. |
 | | This style of transmitter remained standard in telephony until the 1980s, and is still produced. |
 | | Newer systems include IP telephony, ISDN, DSL, cell phone (mobile) systems, digital cell phone systems, cordless telephones, and the third generation cell phone systems that promise to allow high-speed packet data transfer. |
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