The underlying ISDN concepts found wider use as a replacement for the T1/E1 lines it was originally intended to extend, roughly doubling the performance of those lines. ==History== ===Digital lines=== Since its introduction in 1881, the twisted pair copper line has been installed for telephone use worldwide, with well over a billion individual connections installed by the year 2000.
Over the first half of the 20th century, the connection of these lines to form calls was increasingly automated, culminating in the crossbar switches that had largely replaced earlier concepts by the 1950s. As telephone use surged in the post-WWII era, the problem of connecting the massive number of lines became an area of significant study.
T1 used a very simple encoding scheme, alternate mark inversion (AMI), which reached only a few percent of the theoretical capacity of the line but was appropriate for 1960s electronics. By the late 1970s, T1 lines and their faster counterparts, along with all-digital switching systems, had replaced the earlier analog systems for most of the western world, leaving only the customer's equipment and their local end office using analog systems.
As the new standard was to be international, this was even more contentious as several regional digital standards had emerged in the 1960s and 70s and merging these back together was not going to be easy.
In 1962, Robert Aaron of Bell introduced the T1 system, which allowed a pair of twisted pair lines to carry 1.544 Mbit/s of data over a distance of about one mile.
T1 used a very simple encoding scheme, alternate mark inversion (AMI), which reached only a few percent of the theoretical capacity of the line but was appropriate for 1960s electronics. By the late 1970s, T1 lines and their faster counterparts, along with all-digital switching systems, had replaced the earlier analog systems for most of the western world, leaving only the customer's equipment and their local end office using analog systems.
If the system was to become all-digital, a new standard would be needed that was appropriate for the existing customer lines, which might be miles long and of widely varying quality. ===ISDN standardization=== Around 1978, Ralph Wyndrum, Barry Bossick and Joe Lechleider of Bell Labs began one such effort to develop a last-mile solution.
Work on the standard began in 1980 at Bell Labs and was formally standardized in 1988 in the CCITT "Red Book".
At the time, modems were normally 300 bps and 1200 bit/s would not become common until the early 1980s and the 2400 bit/s standard would not be completed until 1984.
Additionally, modems had continued improving, introducing 9600 bit/s systems in the late 1980s and 14.4 kbit/s in 1991, which significantly eroded ISDN's value proposition for the home customer. Meanwhile, Lechleider had proposed using ISDN's echo cancellation and 2B1Q encoding on existing T1 connections, allowing the distance between repeaters to be doubled to about .
At the time, modems were normally 300 bps and 1200 bit/s would not become common until the early 1980s and the 2400 bit/s standard would not be completed until 1984.
To further confuse issues, in 1984 the Bell System was broken up and the US center for development moved to the American National Standards Institute (ANSI) T1D1.3 committee.
Work on the standard began in 1980 at Bell Labs and was formally standardized in 1988 in the CCITT "Red Book".
Lechleider suggested that most consumer use would be asymmetric anyway, and that providing a high-speed channel towards the user and a lower speed return would be suitable for many uses. This work in the early 1990s eventually led to the ADSL concept, which emerged in 1995.
Additionally, modems had continued improving, introducing 9600 bit/s systems in the late 1980s and 14.4 kbit/s in 1991, which significantly eroded ISDN's value proposition for the home customer. Meanwhile, Lechleider had proposed using ISDN's echo cancellation and 2B1Q encoding on existing T1 connections, allowing the distance between repeaters to be doubled to about .
Another standards war broke out, but in 1991 Lechleider's 1.6 Mbit/s "High-Speed Digital Subscriber Line" eventually won this process as well, after Starr drove it through the ANSI T1E1.4 group.
Lechleider suggested that most consumer use would be asymmetric anyway, and that providing a high-speed channel towards the user and a lower speed return would be suitable for many uses. This work in the early 1990s eventually led to the ADSL concept, which emerged in 1995.
The underlying ISDN concepts found wider use as a replacement for the T1/E1 lines it was originally intended to extend, roughly doubling the performance of those lines. ==History== ===Digital lines=== Since its introduction in 1881, the twisted pair copper line has been installed for telephone use worldwide, with well over a billion individual connections installed by the year 2000.
The I interface, unlike the older and incompatible Y interface, is what modern ISDN services use today. Since 2000, NTT's ISDN offering have been known as FLET's ISDN, incorporating the "FLET's" brand that NTT uses for all of its ISP offerings. In Japan, the number of ISDN subscribers dwindled as alternative technologies such as ADSL, cable Internet access, and fiber to the home gained greater popularity.
The introduction of ADSL is reducing ISDN use for data transfer and Internet access, although it is still common in more rural and outlying areas, and for applications such as business voice and point-of-sale terminals. ====Germany==== In Germany, ISDN was very popular with an installed base of 25 million channels (29% of all subscriber lines in Germany as of 2003 and 20% of all ISDN channels worldwide).
Until April 2006, they also offered services named Home Highway and Business Highway, which were BRI ISDN-based services that offered integrated analogue connectivity as well as ISDN.
Because of the widespread availability of ADSL services, ISDN was primarily used for voice and fax traffic. Until 2007 ISDN (BRI) and ADSL/VDSL were often bundled on the same line, mainly because the combination of DSL with an analog line had no cost advantage over a combined ISDN-DSL line.
On November 2, 2010, NTT announced plans to migrate their backend from PSTN to the IP network from around 2020 to around 2025.
Since then phone companies started introducing cheaper xDSL-only products using VoIP for telephony, also in an effort to reduce their costs by operating separate data & voice networks. Since approximately 2010, most German operators are offering more and more VoIP on top of DSL lines and ceased offering ISDN lines.
Home Highway was bought by many home users, usually for Internet connection, although not as fast as ADSL, because it was available before ADSL and in places where ADSL does not reach. In early 2015, BT announced their intention to retire the UK's ISDN infrastructure by 2025. ====France==== France Telecom offers ISDN services under their product name Numeris (2 B+D), of which a professional Duo and home Itoo version is available.
As from 2018 on, new ISDN lines are not available anymore in Germany, existing ISDN lines are phased out from 2016 onwards and existing customers are encouraged to move to DSL-based VoIP products. Deutsche Telekom expected to complete this phase-out by 2018 but postponed the date to 2020, other providers like Vodafone estimate to have their phase-out completed by 2022. ====Greece==== OTE, the incumbent telecommunications operator, offers ISDN BRI (BRA) services in Greece.
Telstra announced that the new sales of ISDN product would be unavailable as of 31 January 2018.
As from 2018 on, new ISDN lines are not available anymore in Germany, existing ISDN lines are phased out from 2016 onwards and existing customers are encouraged to move to DSL-based VoIP products. Deutsche Telekom expected to complete this phase-out by 2018 but postponed the date to 2020, other providers like Vodafone estimate to have their phase-out completed by 2022. ====Greece==== OTE, the incumbent telecommunications operator, offers ISDN BRI (BRA) services in Greece.
On November 2, 2010, NTT announced plans to migrate their backend from PSTN to the IP network from around 2020 to around 2025.
As from 2018 on, new ISDN lines are not available anymore in Germany, existing ISDN lines are phased out from 2016 onwards and existing customers are encouraged to move to DSL-based VoIP products. Deutsche Telekom expected to complete this phase-out by 2018 but postponed the date to 2020, other providers like Vodafone estimate to have their phase-out completed by 2022. ====Greece==== OTE, the incumbent telecommunications operator, offers ISDN BRI (BRA) services in Greece.
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