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IS-54 and IS-136 are second-generation (2G) mobile phone systems, known as Digital AMPS (D-AMPS), and a further development of the north-american 1G mobile system AMPS. It was once prevalent throughout the Americas, particularly in the United States and Canada since the first commercial network was deployed in 1993.〔Anton A. Huurdeman, (The Worldwide History of Telecommunications ), John Wiley & Sons, 31 juli 2003, page 533〕 D-AMPS is considered end-of-life, and existing networks have mostly been replaced by GSM/GPRS or CDMA2000 technologies. This system is most often referred to as TDMA. That name is based on the abbreviation for time division multiple access, a common multiple access technique which is used in most 2G standards, including GSM, as well as in IS-54 and IS-136. However, D-AMPS has been competing against GSM and systems based on code division multiple access (CDMA) for adoption by the network carriers, although it is now being phased out in favor of GSM/GPRS and CDMA2000 technology. D-AMPS uses existing AMPS channels and allows for smooth transition between digital and analog systems in the same area. Capacity was increased over the preceding analog design by dividing each 30 kHz channel pair into three time slots (hence ''time division'') and digitally compressing the voice data, yielding three times the call capacity in a single cell. A digital system also made calls more secure because analog scanners could not access digital signals. Calls were encrypted, although the algorithm used (CMEA) was later found to be weak.〔()〕 IS-136 added a number of features to the original IS-54 specification, including text messaging, circuit switched data (CSD), and an improved compression protocol. SMS and CSD were both available as part of the GSM protocol, and IS-136 implemented them in a nearly identical fashion. Former large IS-136 networks included AT&T in the United States, and Rogers Wireless in Canada. AT&T and Rogers Wireless have upgraded their existing IS-136 networks to GSM/GPRS. Rogers Wireless removed all 1900 MHz IS-136 in 2003, and has done the same with its 800 MHz spectrum as the equipment failed. Rogers deactivated its IS-136 network (along with AMPS) on May 31, 2007. AT&T soon followed in February 2008, shutting down both TDMA and AMPS. Alltel, who primarily uses CDMA2000 technology but acquired a TDMA network from Western Wireless, shut down its TDMA and AMPS networks in September 2008. US Cellular, which now also primarily uses CDMA2000 technology, shut down its TDMA network in February 2009. IS-54 is the first mobile communication system which had provision for security, and the first to employ TDMA technology.〔()〕 ==Introduction== IS-54 stands for Interim Standard-54, which is a mobile communication standard employing digital technology. It was standardized by Electronic Industries Alliance (EIA) and Telecommunications Industry Association (TIA) together. It later became an American National Standard when it got approved by the American National Standards Institute (ANSI). When an interim standard becomes an American National Standard, the IS designator is dropped. The ANSI designation of IS-54 is ANSI/TIA/EIA-627, but this standard is still popularly referred to as IS-54. IS-54 maintains compatibility with Advanced Mobile Phone System (AMPS) in many ways. It is a digital extension of AMPS and so it is also quite widely known as Digital AMPS (D-AMPS). Another name for IS-54 is United States Digital Cellular (USDC). But sometimes D-AMPS and USDC also refers to the other prominent interim standard IS-136. 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「Digital AMPS」の詳細全文を読む スポンサード リンク
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