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The pulse code modulation (PCM) technology was patented and developed in France in 1938, but could not be used because suitable technology was not available until World War II. This came about with the arrival of digital systems in the 1960s, when improving the performance of communications networks became a real possibility. However, this technology was not completely adopted until the mid-1970s, due to the large amount of analog systems already in place and the high cost of digital systems, as semiconductors were very expensive. PCM’s initial goal was that of converting an analog voice telephone channel into a digital one based on the sampling theorem. PCM30 describes an application of pulse-code modulation (PCM) in which 30 telephony analog signals are binary coded into a digital signal stream. The term is used today mostly as a synonym for the encoding of 30 channels each with a signalling rate of 64-kbit/s. This rate is also used in the first stage of European PDH technique, so PCM30 is also known as E1. Originally it described a device in communications technology which converted the 30 analog telephone signals into a digital bit stream of 2048 kbit/s . ==PDH and T-carrier== At the beginning of the 1960s, the proliferation of analog telephone lines, based on copper wires, together with the lack of space for new installations, led the transmission experts to look at the real application of PCM digitalization techniques and TDM multiplexing. The first digital communications system was set up by Bell Labs in 1962, and consisted of 24 digital channels running at what is known as T1. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「PCM30」の詳細全文を読む スポンサード リンク
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