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Digital AMPS
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{{Short description|2G mobile-phone standard that uses time-division multiple access}} {{More citations needed|date=April 2011}} {{List of mobile phone generations}} '''Digital AMPS''' ('''D-AMPS'''), most often referred to as '''TDMA''', is a second-generation ([[2G]]) [[cellular phone]] system that was once prevalent throughout the [[Americas]], particularly in the [[United States]] and [[Canada]] since the first commercial network was deployed in 1993.<ref>{{cite book |last=Huurdeman |first=Anton A. |url=https://books.google.com/books?id=SnjGRDVIUL4C&q=d-amps+tia+history&pg=PA533 |title=The Worldwide History of Telecommunications |date=31 July 2003 |publisher=John Wiley & Sons |isbn=9780471205050 |page=533}}</ref> Former large D-AMPS networks included those of [[AT&T Wireless Services|AT&T]] and [[Rogers Wireless]]. The name TDMA is based on the abbreviation for [[time-division multiple access]], a common [[multiple access]] technique which is used in most 2G standards, including [[GSM]]. D-AMPS competed against GSM and systems based on [[code-division multiple access]] (CDMA). It is now considered [[end-of-life product|end-of-life]], as existing networks have shut and been replaced by GSM/[[General Packet Radio Service|GPRS]] or [[CDMA2000]] technologies. The last carrier to operate a D-AMPS network was [[U.S. Cellular]], who terminated it on February 10, 2009.<ref>{{Cite web |title=The First Digital Cellular Systems β TDMA, GSM and iDEN (2G) |url=https://telephoneworld.org/cellular-phone-history/the-first-digital-cellular-systems-tdma-gsm-and-iden-2g/ |access-date=2025-05-19 |website=telephoneworld.org}}</ref> The technical names for D-AMPS are '''IS-54''' and its successor '''IS-136.'''<ref>{{Cite web |title=Definition of IS-54 |url=https://www.pcmag.com/encyclopedia/term/is-54 |access-date=2025-05-19 |website=PCMAG |language=en}}</ref><ref>{{Cite web |title=Definition of IS-136 |url=https://www.pcmag.com/encyclopedia/term/is-136 |access-date=2025-05-19 |website=PCMAG |language=en}}</ref> IS-54 was the first mobile communication system which had provision for security, and the first to employ [[time-division multiple access]] (TDMA) technology.<ref>{{Cite web |title=Digital Wireless Basics: "1990s" |url=http://www.privateline.com/mt_digitalbasics/2006/01/1990s.html |url-status=dead |archive-url=https://web.archive.org/web/20061113074148/http://www.privateline.com/mt_digitalbasics/2006/01/1990s.html |archive-date=2006-11-13 |access-date=2007-02-02}}</ref> IS-136 added a number of features to the original IS-54 specification, including [[Short message service|text messaging]] (SMS), [[Circuit switching|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. D-AMPS was a further development of the North American [[1G]] mobile system [[Advanced Mobile Phone System]] (AMPS) and used 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 in the beginning, as analogue scanners could not access digital signals. Calls were encrypted, using [[Cellular Message Encryption Algorithm|CMEA]], which was later found to be weak.<ref>{{cite web |last1=Wagner |first1=David |author-link1=David A. Wagner |last2=Schneier |first2=Bruce |author-link2=Bruce Schneier |last3=Kelsey |first3=John |author-link3=John Kelsey (cryptanalyst) |title=Cryptanalysis of the Cellular Message Encryption Algorithm |url=http://www.schneier.com/paper-cmea.pdf |url-status=dead |archive-url=https://web.archive.org/web/20131019105727/https://www.schneier.com/paper-cmea.pdf |archive-date=2013-10-19 |access-date=2004-05-21}}</ref>
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