Integrated Services Digital Network
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Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Work on the standard began in 1980 at
Bell Labs Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial Research and development, research and scientific developm ...
and was formally standardized in 1988 in the CCITT "Red Book". By the time the standard was released, newer networking systems with much greater speeds were available, and ISDN saw relatively little uptake in the wider market. One estimate suggests ISDN use peaked at a worldwide total of 25 million subscribers at a time when 1.3 billion analog lines were in use. ISDN has largely been replaced with digital subscriber line (DSL) systems of much higher performance. Prior to ISDN, the telephone system consisted of digital links like T1/ E1 on the long-distance lines between telephone company offices and analog signals on copper telephone wires to the customers, the " last mile". At the time, the network was viewed as a way to transport voice, with some special services available for data using additional equipment like
modem A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by Modulation#Digital modulati ...
s or by providing a T1 on the customer's location. What became ISDN started as an effort to digitize the last mile, originally under the name "Public Switched Digital Capacity" (PSDC). This would allow call routing to be completed in an all-digital system, while also offering a separate data line. The
Basic Rate Interface Basic Rate Interface (BRI, 2B+D, 2B1D) or Basic Rate Access is an Integrated Services Digital Network (ISDN) configuration intended primarily for use in subscriber lines similar to those that have long been used for voice-grade telephone servi ...
, or BRI, is the standard last-mile connection in the ISDN system, offering two 64 kbit/s "bearer" lines and a single 16 kbit/s "delta" channel for commands and data. Although ISDN found a number of niche roles and some wider uptake in specific locales, the system was largely ignored and garnered the industry nickname "innovation subscribers didn't need." It found a use for a time for small-office digital connection, using the voice lines for data at 64 kbit/s, sometimes "bonded" to 128 kbit/s, but the introduction of 56 kbit/s modems undercut its value in many roles. It also found use in
videoconference Videotelephony, also known as videoconferencing and video teleconferencing, is the two-way or multipoint reception and transmission of audio signal, audio and video signals by people in different locations for Real-time, real time communication. ...
systems, where the direct end-to-end connection was desirable. The
H.320 H.320 or Narrow-band visual telephone systems and terminal equipment is an ''umbrella Recommendation'' by the ITU-T for running Multimedia (Audio/Video/Data) over ISDN based networks. The main protocols in this suite are H.221, H.230, H.242, au ...
standard was designed around its 64 kbit/s data rate. 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 Twisted pair cabling is a type of wiring used for communications in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility. Compared to a single conductor or an untwisted ba ...
copper line has been installed for telephone use worldwide, with well over a billion individual connections installed by 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.
Bell Labs Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial Research and development, research and scientific developm ...
' seminal work on digital encoding of voice led to the use of 64 kbit/s as a standard for voice lines (or 56 kbit/s in some systems). 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. This was used in the Bell network to carry traffic between local switch offices, with 24 voice lines at 64 kbit/s and a separate 8 kbit/s line for signaling commands like connecting or hanging up a call. This could be extended over long distances using repeaters in the lines. T1 used a very simple encoding scheme,
alternate mark inversion In telecommunication, bipolar encoding is a type of return-to-zero (RZ) line code, where two nonzero values are used, so that the three values are +, −, and zero. Such a signal is called a duobinary signal. Standard bipolar encodings are designed ...
(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. Digitizing this " last mile" was increasingly seen as the next problem that needed to be solved. However, these connections now represented over 99% of the total telephony network, as the upstream links had increasingly been aggregated into a smaller number of much higher performance systems, especially after the introduction of
fiber optic An optical fiber, or optical fibre in Commonwealth English, is a flexible, transparent fiber made by drawing glass (silica) or plastic to a diameter slightly thicker than that of a human hair. Optical fibers are used most often as a means t ...
lines. 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.


Standardization

Around 1978, Ralph Wyndrum, Barry Bossick and Joe Lechleider of
Bell Labs Nokia Bell Labs, originally named Bell Telephone Laboratories (1925–1984), then AT&T Bell Laboratories (1984–1996) and Bell Labs Innovations (1996–2007), is an American industrial Research and development, research and scientific developm ...
began one such effort to develop a last-mile solution. They studied a number of derivatives of the T1's AMI concept and concluded that a customer-side line could reliably carry about 160 kbit/s of data over a distance of . That would be enough to carry two voice-quality lines at 64 kbit/s as well as a separate 16 kbit/s line for data. At the time,
modem A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by Modulation#Digital modulati ...
s 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. In this market, 16 kbit/s represented a significant advance in performance in addition to being a separate channel and thus allowing voice and data at the same time. A key problem was that the customer might only have a single twisted pair line to the location of the handset, so the solution used in T1 with separate upstream and downstream connections was not universally available. With analog connections, the solution was to use
echo cancellation Echo suppression and echo cancellation are methods used in telephony to improve voice quality by preventing echo from being created or removing it after it is already present. In addition to improving subjective audio quality, echo suppression ...
, but at the much higher bandwidth of the new concept, this would not be so simple. A debate broke out between teams worldwide about the best solution to this problem; some promoted newer versions of echo cancellation, while others preferred the "ping pong" concept where the direction of data would rapidly switch the line from send to receive at such a high rate it would not be noticeable to the user. John Cioffi had recently demonstrated echo cancellation would work at these speeds, and further suggested that they should consider moving directly to 1.5 Mbit/s performance using this concept. The suggestion was literally laughed off the table (His boss told him to "sit down and shut up") but the echo cancellation concept was taken up by Joe Lechleider eventually came to win the debate. Meanwhile, the debate over the encoding scheme itself was also ongoing. 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 them was not going to be easy. 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. Thomas Starr of the newly formed
Ameritech AT&T Teleholdings, Inc., formerly known as Ameritech Corporation (and before that American Information Technologies Corporation), is an American telecommunications company that arose out of the 1984 AT&T divestiture. Ameritech was one of the sev ...
led this effort and eventually convinced the ANSI group to select the 2B1Q standard proposed by Peter Adams of British Telecom. This standard used an 80 kHz base frequency and encoded two bits per baud to produce the 160 kbit/s base rate. Ultimately Japan selected a different standard, and Germany selected one with three levels instead of four, but all of these could interchange with the ANSI standard. From an economic perspective, the
European Commission The European Commission (EC) is the executive of the European Union (EU). It operates as a cabinet government, with 27 members of the Commission (informally known as "Commissioners") headed by a President. It includes an administrative body ...
sought to liberalize and regulate ISDN across the European Economic Community. The
Council of the European Communities The Council of the European Union, often referred to in the treaties and other official documents simply as the Council, and informally known as the Council of Ministers, is the third of the seven Institutions of the European Union (EU) as ...
adopted Council Recommendatio
86/659/EEC
in December 1986 for its coordinated introduction within the framework of CEPT. ETSI (the European Telecommunications Standards Institute) was created by CEPT in 1988 and would develop the framework.


Rollout

With ISDN allowing digital-quality voice, two separate lines and all-the-time data, the telephony world was convinced there would be high customer demand for such systems in both the home and office. This proved not to be the case. During the lengthy standardization process, new concepts rendered the system largely superfluous. In the office, multi-line digital switches like the
Meridian Norstar The Nortel Norstar, previously the Meridian Norstar, was a small and medium-sized business digital key telephone system introduced by Nortel (formerly Northern Telecom) and later sold to Avaya. It featured automatic call distribution, and supp ...
took over telephone lines while
local area network A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building. By contrast, a wide area network (WAN) not only covers a larger ...
s like
Ethernet Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 1 ...
provided performance around 10 Mbit/s which had become the baseline for inter-computer connections in offices. ISDN offered no real advantages in the voice role and was far from competitive in data. 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. A similar standard emerged in Europe to replace their E1 lines, increasing the sampling range from 80 to 100 kHz to allow 2.048 Mbit/s. By the mid-1990s, these Primary Rate Interface (PRI) lines had largely replaced T1 and E1 between telephone company offices.


ISDN becomes ADSL

Lechleider also believed this higher-speed standard would be much more attractive to customers than ISDN had proven. Unfortunately, at these speeds, the systems suffered from a type of crosstalk known as "NEXT", for "near-end crosstalk". This made longer connections on customer lines difficult. Lechleider noted that NEXT only occurred when similar frequencies were being used, and could be diminished if one of the directions used a different carrier rate, but doing so would reduce the potential bandwidth of that channel. 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 Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. ...
concept, which emerged in 1995. An early supporter of the concept was
Alcatel Alcatel may refer to: * Alcatel, a former French telecommunications equipment company, which became Alcatel-Lucent and is now part of Nokia * Alcatel Mobile, a brand of mobile phones, tablets and wearables, formerly a joint venture between Alcatel ...
, who jumped on ADSL while many other companies were still devoted to ISDN. Krish Prabu stated that "Alcatel will have to invest one billion dollars in ADSL before it makes a profit, but it is worth it." They introduced the first DSL Access Multiplexers (DSLAM), the large multi-modem systems used at the telephony offices, and later introduced customer ADSL modems under the Thomson brand. Alcatel remained the primary vendor of ADSL systems for well over a decade. ADSL quickly replaced ISDN as the customer-facing solution for last-mile connectivity. ISDN has largely disappeared on the customer side, remaining in use only in niche roles like dedicated teleconferencing systems and similar legacy systems.


Design

''Integrated services'' refers to ISDN's ability to deliver at minimum two simultaneous connections, in any combination of data, voice,
video Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media. Video was first developed for mechanical television systems, which were quickly replaced by cathode-ray tube (CRT) syst ...
, and
fax Fax (short for facsimile), sometimes called telecopying or telefax (the latter short for telefacsimile), is the telephonic transmission of scanned printed material (both text and images), normally to a telephone number connected to a printer o ...
, over a single line. Multiple devices can be attached to the line, and used as needed. That means an ISDN line can take care of what were expected to be most people's complete communications needs (apart from broadband Internet access and entertainment
television Television, sometimes shortened to TV, is a telecommunication medium for transmitting moving images and sound. The term can refer to a television set, or the medium of television transmission. Television is a mass medium for advertisin ...
) at a much higher transmission rate, without forcing the purchase of multiple analog phone lines. It also refers to integrated switching and transmission in that
telephone switch telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syste ...
ing and
carrier wave In telecommunications, a carrier wave, carrier signal, or just carrier, is a waveform (usually sinusoidal) that is modulated (modified) with an information-bearing signal for the purpose of conveying information. This carrier wave usually has ...
transmission are integrated rather than separate as in earlier technology.


Configurations

In ISDN, there are two types of channels, ''B'' (for "bearer") and ''D'' (for "data"). ''B channels'' are used for data (which may include voice), and ''D channels'' are intended for signaling and control (but can also be used for data). There are two ISDN implementations. Basic Rate Interface (BRI), also called basic rate access (BRA) — consists of two B channels, each with bandwidth of 64
kbit/s In telecommunications, data-transfer rate is the average number of bits (bitrate), characters or symbols (baudrate), or data blocks per unit time passing through a communication link in a data-transmission system. Common data rate units are multi ...
, and one D channel with a bandwidth of 16 kbit/s. Together these three channels can be designated as 2B+D. Primary Rate Interface (PRI), also called primary rate access (PRA) in Europe — contains a greater number of B channels and a D channel with a bandwidth of 64 kbit/s. The number of B channels for PRI varies according to the nation: in North America and Japan it is 23B+1D, with an aggregate bit rate of 1.544
Mbit/s In telecommunications, data-transfer rate is the average number of bits ( bitrate), characters or symbols ( baudrate), or data blocks per unit time passing through a communication link in a data-transmission system. Common data rate units are mu ...
( T1); in Europe, India and Australia it is 30B+2D, with an aggregate bit rate of 2.048 Mbit/s ( E1).
Broadband Integrated Services Digital Network In the 1980s, the telecommunications industry expected that digital services would follow much the same pattern as voice services did on the public switched telephone network, and conceived an end-to-end circuit switched service, known as Broadband ...
(BISDN) is another ISDN implementation and it is able to manage different types of services at the same time. It is primarily used within
network backbone A backbone or core network is a part of a computer network which interconnects networks, providing a path for the exchange of information between different LANs or subnetworks. A backbone can tie together diverse networks in the same building, ...
s and employs ATM. Another alternative ISDN configuration can be used in which the B channels of an ISDN BRI line are bonded to provide a total duplex bandwidth of 128 kbit/s. This precludes use of the line for voice calls while the internet connection is in use. The B channels of several BRIs can be bonded, a typical use is a 384K videoconferencing channel. Using bipolar with eight-zero substitution encoding technique, call data is transmitted over the data (B) channels, with the signaling (D) channels used for call setup and management. Once a call is set up, there is a simple 64 kbit/s synchronous bidirectional data channel (actually implemented as two simplex channels, one in each direction) between the end parties, lasting until the call is terminated. There can be as many calls as there are bearer channels, to the same or different end-points. Bearer channels may also be
multiplexed In telecommunications and computer networking, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource - a ...
into what may be considered single, higher-bandwidth channels via a process called B channel BONDING, or via use of Multi-Link PPP "bundling" or by using an H0, H11, or H12 channel on a PRI. The D channel can also be used for sending and receiving
X.25 X.25 is an ITU-T standard protocol suite for packet-switched data communication in wide area networks (WAN). It was originally defined by the International Telegraph and Telephone Consultative Committee (CCITT, now ITU-T) in a series of drafts ...
data packets, and connection to X.25 packet network, this is specified in X.31. In practice, X.31 was only commercially implemented in the UK, France, Japan and Germany.


Reference points

A set of ''reference points'' are defined in the
ISDN Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Work ...
standard Standard may refer to: Symbols * Colours, standards and guidons, kinds of military signs * Standard (emblem), a type of a large symbol or emblem used for identification Norms, conventions or requirements * Standard (metrology), an object th ...
to refer to certain points between the telco and the end user ISDN equipment. * R – defines the point between a non-ISDN terminal equipment 2 (TE2) device and a ''
terminal adapter A terminal adapter or TA is a device that connects a terminal device – a computer, a mobile communications device, or other – to a communications network. ISDN In ISDN terminology, the ''terminal adapter'' connects a ''terminal'' (computer) ...
'' (TA) which provides translation to and from such a device * S – defines the point between the ISDN terminal equipment 1 (TE1) or TA and a ''Network Termination Type 2'' ( NT2) device * T – defines the point between the NT2 and network termination 1 (NT1) devices. Most NT-1 devices can perform the functions of the NT2 as well, and so the S and T reference points are generally collapsed into the S/T reference point. In North America, the NT1 device is considered
customer premises equipment In telecommunications, a customer-premises equipment or customer-provided equipment (CPE) is any terminal and associated equipment located at a subscriber's premises and connected with a carrier's telecommunication circuit at the demarcation po ...
(CPE) and must be maintained by the customer, thus, the U interface is provided to the customer. In other locations, the NT1 device is maintained by the telco, and the S/T interface is provided to the customer. In India, service providers provide U interface and an NT1 may be supplied by Service provider as part of service offering.


Basic Rate Interface

The entry level interface to ISDN is the
Basic Rate Interface Basic Rate Interface (BRI, 2B+D, 2B1D) or Basic Rate Access is an Integrated Services Digital Network (ISDN) configuration intended primarily for use in subscriber lines similar to those that have long been used for voice-grade telephone servi ...
(BRI), a 128
kbit/s In telecommunications, data-transfer rate is the average number of bits (bitrate), characters or symbols (baudrate), or data blocks per unit time passing through a communication link in a data-transmission system. Common data rate units are multi ...
service delivered over a pair of standard telephone copper wires. The 144 kbit/s overall payload rate is divided into two 64 kbit/s
bearer channel A bearer channel is a DS-0 that carries call content i.e. one that does not carry signaling. In the common-channel signaling scheme for telecommunications, signaling is sent out-of-band, while all other traffic rides bearer channels. When a call ...
s ( 'B' channels) and one 16 kbit/s signaling channel ( 'D' channel or data channel). This is sometimes referred to as 2B+D. The interface specifies the following network interfaces: * The ''
U interface U or u, is the twenty-first and sixth-to-last letter and fifth vowel letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''u'' (pr ...
'' is a two-wire interface between the exchange and a ''network terminating unit'', which is usually the
demarcation point In telephony, the demarcation point is the point at which the public switched telephone network ends and connects with the customer's on-premises wiring. It is the dividing line which determines who is responsible for installation and maint ...
in non-North American networks. * The ''
T interface A T-interface or T reference point is used for basic rate access in an Integrated Services Digital Network (ISDN) environment. It is a User–network interface reference point that is characterized by a four-wire, 144 kbit/s (2B+D) user rate. ...
'' is a serial interface between a computing device and a ''
terminal adapter A terminal adapter or TA is a device that connects a terminal device – a computer, a mobile communications device, or other – to a communications network. ISDN In ISDN terminology, the ''terminal adapter'' connects a ''terminal'' (computer) ...
'', which is the digital equivalent of a modem. * The '' S interface'' is a four-wire bus that ISDN consumer devices plug into; the S & T reference points are commonly implemented as a single interface labeled 'S/T' on a Network termination 1 (NT1). * The '' R interface'' defines the point between a non-ISDN device and a terminal adapter (TA) which provides translation to and from such a device. BRI-ISDN is very popular in Europe but is much less common in North America. It is also common in Japan — where it is known as INS64.


Primary Rate Interface

The other ISDN access available is the Primary Rate Interface (PRI), which is carried over
T-carrier The T-carrier is a member of the series of carrier systems developed by AT&T Bell Laboratories for digital transmission of multiplexed telephone calls. The first version, the Transmission System 1 (T1), was introduced in 1962 in the Bell Syste ...
(T1) with 24 time slots (channels) in North America, and over
E-carrier The E-carrier is a member of the series of carrier systems developed for digital transmission of many simultaneous telephone calls by time-division multiplexing. The European Conference of Postal and Telecommunications Administrations (CEPT) ori ...
(E1) with 32 channels in most other countries. Each channel provides transmission at a 64 kbit/s data rate. With the E1 carrier, the available channels are divided into 30 bearer (''B'') channels, one data (''D'') channel, and one timing and alarm channel. This scheme is often referred to as 30B+2D. In North America, PRI service is delivered via T1 carriers with only one data channel, often referred to as 23B+D, and a total data rate of 1544 kbit/s.
Non-Facility Associated Signalling {{Unreferenced, date=September 2015 Non-Facility Associated Signaling or NFAS is a Primary Rate Interface configuration whereby multiple T1 carriers share a signaling channel (or D channel). A T1 circuit typically carries 24 individual timeslot ...
(NFAS) allows two or more PRI circuits to be controlled by a single
D channel D channel (delta channel) is a telecommunications term which refers to the ISDN channel in which the control and signalling information is carried. The bit rate of the D channel of a basic rate interface is 16 kbit/s, whereas it amounts to 64 kb ...
, which is sometimes called ''23B+D + n*24B''. D-channel backup allows for a second D channel in case the primary fails. NFAS is commonly used on a
Digital Signal 3 A Digital Signal 3 (DS3) is a digital signal level 3 T-carrier. It may also be referred to as a T3 line. *The data rate for this type of signal is 44.736 Mbit/s (45 Mb). *DS3 uses 75ohm coaxial cable and BNC connectors. *This level of carrier ca ...
(DS3/T3). PRI-ISDN is popular throughout the world, especially for connecting
private branch exchange A business telephone system is a multiline telephone system typically used in business environments, encompassing systems ranging in technology from the key telephone system (KTS) to the private branch exchange (PBX). A business telephone syst ...
s to the public switched telephone network (PSTN). Even though many network professionals use the term ''ISDN'' to refer to the lower-bandwidth BRI circuit, in North America BRI is relatively uncommon whilst PRI circuits serving PBXs are commonplace.


Bearer channel

The bearer channel (B) is a standard 64 kbit/s voice channel of 8 bits sampled at 8 kHz with
G.711 G.711 is a narrowband audio codec originally designed for use in telephony that provides toll-quality audio at 64 kbit/s. G.711 passes audio signals in the range of 300–3400 Hz and samples them at the rate of 8,000 samples per second ...
encoding. B-channels can also be used to carry data, since they are nothing more than digital channels. Each one of these channels is known as a
DS0 Digital Signal 0 (DS0) is a basic digital signaling rate of 64 kilobits per second (kbit/s), corresponding to the capacity of one analog voice-frequency-equivalent communication channel. The DS0 rate, and its equivalents E0 in the E-carrier system ...
. Most B channels can carry a 64kbit/s signal, but some were limited to 56K because they traveled over
RBS RBS may refer to: Organisations Banking * The Royal Bank of Scotland, a retail banking subsidiary of NatWest Group ** RBS International, the offshore banking arm of NatWest Group Education * Regent's Business School * Rotterdam Business School ...
lines. This was commonplace in the 20th century, but has since become less so.


X.25

X.25 X.25 is an ITU-T standard protocol suite for packet-switched data communication in wide area networks (WAN). It was originally defined by the International Telegraph and Telephone Consultative Committee (CCITT, now ITU-T) in a series of drafts ...
can be carried over the B or D channels of a BRI line, and over the B channels of a PRI line. X.25 over the D channel is used at many point-of-sale (credit card) terminals because it eliminates the modem setup, and because it connects to the central system over a B channel, thereby eliminating the need for modems and making much better use of the central system's telephone lines.
X.25 X.25 is an ITU-T standard protocol suite for packet-switched data communication in wide area networks (WAN). It was originally defined by the International Telegraph and Telephone Consultative Committee (CCITT, now ITU-T) in a series of drafts ...
was also part of an ISDN protocol called "Always On/Dynamic ISDN", or AO/DI. This allowed a user to have a constant multi-link PPP connection to the internet over X.25 on the D channel, and brought up one or two B channels as needed.


Frame Relay

In theory,
Frame Relay Frame Relay is a standardized wide area network (WAN) technology that specifies the physical and data link layers of digital telecommunications channels using a packet switching methodology. Originally designed for transport across Integrated Se ...
can operate over the D channel of BRIs and PRIs, but it is seldom, if ever, used.


Uses


Telephone industry

ISDN is a core technology in the telephone industry. A
telephone network A telephone network is a telecommunications network that connects telephones, which allows telephone calls between two or more parties, as well as newer features such as fax and internet. The idea was revolutionized in the 1920s, as more and more ...
can be thought of as a collection of wires strung between switching systems. The common electrical specification for the signals on these wires is T1 or E1. Between telephone company switches, the signaling is performed via SS7. Normally, a PBX is connected via a T1 with
robbed bit signaling In communications systems, robbed-bit signaling (RBS) is a scheme to provide maintenance and line signaling services on many T1 digital carrier circuits using channel-associated signaling (CAS). The T1 carrier circuit is a type of dedicated circuit ...
to indicate on-hook or off-hook conditions and MF and
DTMF Dual-tone multi-frequency signaling (DTMF) is a telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers. DTMF was first developed ...
tones to encode the destination number. ISDN is much better because messages can be sent much more quickly than by trying to encode numbers as long (100 ms per digit) tone sequences. This results in faster call setup times. Also, a greater number of features are available and fraud is reduced. In common use, ISDN is often limited to usage to
Q.931 ITU-T Recommendation Q.931 is the ITU standard ISDN connection control signalling protocol, forming part of ''Digital Subscriber Signalling System No. 1''. Unlike connectionless systems like UDP, ISDN is connection oriented and uses explicit sign ...
and related protocols, which are a set of
signaling protocol A signaling protocol is a type of communications protocol for encapsulating the signaling between communication endpoints and switching systems to establish or terminate a connection and to identify the state of connection. The following is a list ...
s establishing and breaking circuit-switched connections, and for advanced
calling feature A vertical service code (VSC) is a sequence of digits and the signals star (*) and number sign (#) dialed on a telephone keypad or rotary dial to enable or disable certain telephone service features. Some vertical service codes require dialing of ...
s for the user. Another usage was the deployment of
videoconference Videotelephony, also known as videoconferencing and video teleconferencing, is the two-way or multipoint reception and transmission of audio signal, audio and video signals by people in different locations for Real-time, real time communication. ...
systems, where a direct end-to-end connection is desirable. ISDN uses the
H.320 H.320 or Narrow-band visual telephone systems and terminal equipment is an ''umbrella Recommendation'' by the ITU-T for running Multimedia (Audio/Video/Data) over ISDN based networks. The main protocols in this suite are H.221, H.230, H.242, au ...
standard for
audio coding An audio coding format (or sometimes audio compression format) is a content representation format for storage or transmission of digital audio (such as in digital television, digital radio and in audio and video files). Examples of audio coding f ...
and
video coding A video coding format (or sometimes video compression format) is a content representation format for storage or transmission of digital video content (such as in a data file or bitstream). It typically uses a standardized video compression algori ...
. ISDN is also used as a smart-network technology intended to add new services to the public switched telephone network (PSTN) by giving users direct access to end-to-end circuit-switched digital services and as a backup or failsafe circuit solution for critical use data circuits.


Video conferencing

One of ISDNs successful use-cases was in the
videoconference Videotelephony, also known as videoconferencing and video teleconferencing, is the two-way or multipoint reception and transmission of audio signal, audio and video signals by people in different locations for Real-time, real time communication. ...
field, where even small improvements in data rates are useful, but more importantly, its direct end-to-end connection offers lower latency and better reliability than packet-switched networks of the 1990s. The
H.320 H.320 or Narrow-band visual telephone systems and terminal equipment is an ''umbrella Recommendation'' by the ITU-T for running Multimedia (Audio/Video/Data) over ISDN based networks. The main protocols in this suite are H.221, H.230, H.242, au ...
standard for
audio coding An audio coding format (or sometimes audio compression format) is a content representation format for storage or transmission of digital audio (such as in digital television, digital radio and in audio and video files). Examples of audio coding f ...
and
video coding A video coding format (or sometimes video compression format) is a content representation format for storage or transmission of digital video content (such as in a data file or bitstream). It typically uses a standardized video compression algori ...
was designed with ISDN in mind, and more specifically its 64 kbit/s basic data rate. including
audio codecs An audio codec is a device or computer program capable of encoding or decoding a digital data stream (a codec) that encodes or decodes audio. In software, an audio codec is a computer program implementing an algorithm that compresses and decompres ...
such as
G.711 G.711 is a narrowband audio codec originally designed for use in telephony that provides toll-quality audio at 64 kbit/s. G.711 passes audio signals in the range of 300–3400 Hz and samples them at the rate of 8,000 samples per second ...
( PCM) and G.728 (
CELP Code-excited linear prediction (CELP) is a linear predictive speech coding algorithm originally proposed by Manfred R. Schroeder and Bishnu S. Atal in 1985. At the time, it provided significantly better quality than existing low bit-rate algori ...
), and discrete cosine transform (DCT)
video codecs The following is a list of compression formats and related codecs. Audio compression formats Non-compression * Linear pulse-code modulation (LPCM, generally only described as PCM) is the format for uncompressed audio in media files and it is al ...
such as
H.261 H.261 is an ITU-T video compression standard, first ratified in November 1988. It is the first member of the H.26x family of video coding standards in the domain of the ITU-T Study Group 16 Video Coding Experts Group (VCEG, then Specialists Gro ...
and H.263.


Broadcast industry

ISDN is used heavily by the broadcast industry as a reliable way of switching low-latency, high-quality, long-distance audio circuits. In conjunction with an appropriate
codec A codec is a device or computer program that encodes or decodes a data stream or signal. ''Codec'' is a portmanteau of coder/decoder. In electronic communications, an endec is a device that acts as both an encoder and a decoder on a signal or da ...
using MPEG or various manufacturers' proprietary algorithms, an ISDN BRI can be used to send stereo bi-directional audio coded at 128 kbit/s with 20 Hz – 20 kHz audio bandwidth, although commonly the
G.722 G.722 is an ITU-T standard 7 kHz wideband audio codec operating at 48, 56 and 64 kbit/s. It was approved by ITU-T in November 1988. Technology of the codec is based on sub-band ADPCM (SB-ADPCM). The corresponding narrow-band codec based on ...
algorithm is used with a single 64 kbit/s B channel to send much lower latency mono audio at the expense of audio quality. Where very high quality audio is required multiple ISDN BRIs can be used in parallel to provide a higher bandwidth circuit switched connection.
BBC Radio 3 BBC Radio 3 is a British national radio station owned and operated by the BBC. It replaced the BBC Third Programme in 1967 and broadcasts classical music and opera, with jazz, world music, Radio drama, drama, High culture, culture and the arts ...
commonly makes use of three ISDN BRIs to carry 320 kbit/s audio stream for live outside broadcasts. ISDN BRI services are used to link remote studios, sports grounds and outside broadcasts into the main broadcast studio. ISDN via satellite is used by field reporters around the world. It is also common to use ISDN for the return audio links to remote satellite broadcast vehicles. In many countries, such as the UK and Australia, ISDN has displaced the older technology of equalised analogue landlines, with these circuits being phased out by telecommunications providers. Use of IP-based streaming codecs such as
Comrex Comrex is an American corporation that designs and manufactures equipment for radio and television broadcasting. Beginnings Comrex was founded in 1961 by John Cheney, a broadcast engineer. His mission, as outlined in Comrex's inaugural press ...
ACCESS and
ipDTL ipDTL is an IP codec which runs in a web browser, used for remote broadcasts in television, radio, and voice-over. It serves as a replacement for and is compatible with older ISDN audio codecs. Developed by former BBC sound engineer Kevin Leach, i ...
is becoming more widespread in the broadcast sector, using broadband internet to connect remote studios.


Backup lines

Providing a backup line for business's inter-office and internet connectivity was a popular use of the technology.


International deployment

A study of the German Department of Science shows the following spread of ISDN-channels per 1,000 inhabitants in 2005: *
Norway Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...
401 *
Denmark ) , song = ( en, "King Christian stood by the lofty mast") , song_type = National and royal anthem , image_map = EU-Denmark.svg , map_caption = , subdivision_type = Sovereign state , subdivision_name = Danish Realm, Kingdom of Denmark ...
339 *
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
333 *
Switzerland ). Swiss law does not designate a ''capital'' as such, but the federal parliament and government are installed in Bern, while other federal institutions, such as the federal courts, are in other cities (Bellinzona, Lausanne, Luzern, Neuchâtel ...
331 *
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...
240 *
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
160 *
Finland Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of B ...
160 *
Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...
135 *
Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical re ...
105 *
France France (), officially the French Republic ( ), is a country primarily located in Western Europe. It also comprises of Overseas France, overseas regions and territories in the Americas and the Atlantic Ocean, Atlantic, Pacific Ocean, Pac ...
85 *
Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = ''Plus ultra'' (Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , i ...
58 *
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
47


Australia

Telstra Telstra Group Limited is an Australian telecommunications company that builds and operates telecommunications networks and markets voice, mobile, internet access, pay television and other products and services. It is a member of the S&P/ASX 20 ...
provides the business customer with the ISDN services. There are five types of ISDN services which are ISDN2, ISDN2 Enhanced, ISDN10, ISDN20 and ISDN30. Telstra changed the minimum monthly charge for voice and data calls. In general, there are two group of ISDN service types; The Basic Rate services – ISDN 2 or ISDN 2 Enhanced. Another group of types are the Primary Rate services, ISDN 10/20/30. Telstra announced that the new sales of ISDN product would be unavailable as of 31 January 2018. The final exit date of ISDN service and migration to the new service would be confirmed by 2022.


France

France Telecom Orange S.A. (), formerly France Télécom S.A. (stylized as france telecom) is a French multinational telecommunications corporation. It has 266 million customers worldwide and employs 89,000 people in France, and 59,000 elsewhere. In 2015, ...
offers ISDN services under their product name Numeris (2 B+D), of which a professional Duo and home Itoo version is available. ISDN is generally known as RNIS in France and has widespread availability. 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 Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
, 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). Due to the success of ISDN, the number of installed analog lines was decreasing.
Deutsche Telekom Deutsche Telekom AG (; short form often just Telekom, DTAG or DT; stylised as ·T·) is a German telecommunications company that is headquartered in Bonn and is the largest telecommunications provider in Europe by revenue. Deutsche Telekom was ...
(DTAG) offered both BRI and PRI. Competing phone companies often offered ISDN only and no analog lines. However, these operators generally offered free hardware that also allows the use of POTS equipment, such as NTBAs (" Network Termination for ISDN Basic rate Access": small devices that bridge the two-wire UK0 line to the four-wire S0 bus) with integrated
terminal adapter A terminal adapter or TA is a device that connects a terminal device – a computer, a mobile communications device, or other – to a communications network. ISDN In ISDN terminology, the ''terminal adapter'' connects a ''terminal'' (computer) ...
s. Because of the widespread availability of ADSL services, ISDN was primarily used for voice and fax traffic. Until 2007 ISDN (BRI) and
ADSL Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. ...
/
VDSL Very high-speed digital subscriber line (VDSL) and very high-speed digital subscriber line 2 (VDSL2) are digital subscriber line (DSL) technologies providing data transmission faster than the earlier standards of asymmetric digital subscriber li ...
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. This practice turned into an issue for the operators when vendors of ISDN technology stopped manufacturing it and spare parts became hard to come by. Since then phone companies started introducing cheaper xDSL-only products using
VoIP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet t ...
for telephony, also in an effort to reduce their costs by operating separate data & voice networks. Since approximately 2010, most German operators have offered more and more VoIP on top of DSL lines and ceased offering ISDN lines. New ISDN lines have been no longer available in Germany since 2018, existing ISDN lines were phased out from 2016 onwards and existing customers were encouraged to move to DSL-based VoIP products. Deutsche Telekom intended to 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 OTE is the national telecommunications provider of Greece. OTE may also refer to: * Ocean thermal energy conversion, a renewable energy source * Oda of Haldensleben (978–1023), daughter of the Margrave of the North March, Theoderich * On-ta ...
, the incumbent telecommunications operator, offers ISDN BRI (BRA) services in
Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders with ...
. Following the launch of ADSL in 2003, the importance of ISDN for data transfer began to decrease and is today limited to niche business applications with point-to-point requirements.


India

Bharat Sanchar Nigam Limited Bharat, or Bharath, may refer to: * Bharat (term), the name for India in various Indian languages ** Bharata Khanda, the Sanskrit name for the Indian subcontinent (or South Asia) * Bharata, the name of several legendary figures or groups: ** Bhar ...
,
Reliance Communications Reliance Communications Limited (RCOM) was an Indian mobile network provider headquartered in Navi Mumbai that offered voice and 2G and 3G and 4G data services. In February 2019, the company filed for bankruptcy as it was unable to sell asse ...
and
Bharti Airtel Bharti Airtel Limited, commonly known as (d/b/a) Airtel, is an Indian multinational telecommunications services company based in New Delhi. It operates in 18 countries across South Asia and Africa, as well as the Channel Islands. Currently, ...
are the largest communication service providers, and offer both ISDN BRI and PRI services across the country. Reliance Communications and Bharti Airtel uses the DLC technology for providing these services. With the introduction of broadband technology, the load on bandwidth is being absorbed by ADSL. ISDN continues to be an important backup network for point-to-point leased line customers such as banks, Eseva Centers,
Life Insurance Corporation of India Life Insurance Corporation of India (LIC) is an Indian central public sector undertaking headquartered in Mumbai, Maharashtra, India. It is under the ownership of Ministry of Finance, Government of India. The Life Insurance Corporation of ...
, and SBI ATMs.


Japan

On April 19, 1988, Japanese telecommunications company NTT began offering nationwide ISDN services trademarked INS Net 64, and INS Net 1500, a fruition of NTT's independent research and trial from the 1970s of what it referred to the INS (Information Network System). Previously, in April 1985, Japanese digital telephone exchange hardware made by Fujitsu was used to experimentally deploy the world's first I interface ISDN. 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 Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. ...
,
cable Internet access In telecommunications, cable Internet access, shortened to cable Internet, is a form of broadband Internet access which uses the same infrastructure as a cable television. Like digital subscriber line and fiber to the premises services, cable In ...
, and
fiber to the home Fiber to the ''x'' (FTTX; also spelled "fibre") or fiber in the loop is a generic term for any broadband network architecture using optical fiber to provide all or part of the local loop used for last mile telecommunications. As fiber opt ...
gained greater popularity. On November 2, 2010, NTT announced plans to migrate their backend from
PSTN The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local teleph ...
to the
IP network The Internet protocol suite, commonly known as TCP/IP, is a framework for organizing the set of communication protocols used in the Internet and similar computer networks according to functional criteria. The foundational protocols in the suit ...
from around 2020 to around 2025. For this migration, ISDN services will be retired, and fiber optic services are recommended as an alternative.


Norway

On April 19, 1988, Norwegian telecommunications company
Telenor Telenor ASA ( or ) is a Norwegian majority state-owned multinational telecommunications company headquartered at Fornebu in Bærum, close to Oslo. It is one of the world's largest mobile telecommunications companies with operations worldwide, ...
began offering nationwide ISDN services trademarked INS Net 64, and INS Net 1500, a fruition of NTT's independent research and trial from the 1970s of what it referred to the INS (Information Network System).


United Kingdom

In the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
,
British Telecom BT Group plc (trade name, trading as BT and formerly British Telecom) is a British Multinational corporation, multinational telecommunications holding company headquartered in London, England. It has operations in around 180 countries and is th ...
(BT) provides ISDN2e (BRI) as well as ISDN30 (PRI). 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. Later versions of the Highway products also included built-in
USB Universal Serial Bus (USB) is an industry standard that establishes specifications for cables, connectors and protocols for connection, communication and power supply (interfacing) between computers, peripherals and other computers. A broad ...
sockets for direct computer access. 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.


United States and Canada

ISDN-BRI never gained popularity as a general use telephone access technology in Canada and the US, and remains a niche product. The service was seen as "a solution in search of a problem", and the extensive array of options and features were difficult for customers to understand and use. ISDN has long been known by derogatory
backronym A backronym is an acronym formed from an already existing word by expanding its letters into the words of a phrase. Backronyms may be invented with either serious or humorous intent, or they may be a type of false etymology or folk etymology. The ...
s highlighting these issues, such as ''It Still Does Nothing'', ''Innovations Subscribers Don't Need'', and ''I Still Don't kNow'', or, from the supposed standpoint of telephone companies, ''I Smell Dollars Now''. Although various minimum bandwidths have been used in definitions of Broadband Internet access, ranging up from 64 kbit/s up to 1.0 Mbit/s, the 2006 OECD report is typical by defining broadband as having download data transfer rates equal to or faster than 256 kbit/s, while the United States FCC, as of 2008, defines broadband as anything above 768 kbit/s.. Once the term "broadband" came to be associated with data rates incoming to the customer at 256 kbit/s or more, and alternatives like
ADSL Asymmetric digital subscriber line (ADSL) is a type of digital subscriber line (DSL) technology, a data communications technology that enables faster data transmission over copper telephone lines than a conventional voiceband modem can provide. ...
grew in popularity, the consumer market for BRI did not develop. Its only remaining advantage is that, while ADSL has a functional distance limitation and can use ADSL loop extenders, BRI has a greater limit and can use repeaters. As such, BRI may be acceptable for customers who are too remote for ADSL. Widespread use of BRI is further stymied by some small North American CLECs such as
CenturyTel Lumen Technologies, Inc. (formerly CenturyLink) is an American telecommunications company headquartered in Monroe, Louisiana, that offers communications, network services, security, cloud solutions, voice, and managed services. The company is a ...
having given up on it and not providing Internet access using it.. However, AT&T in most states (especially the former SBC/SWB territory) will still install an ISDN BRI line anywhere a normal analog line can be placed and the monthly charge is roughly $55. ISDN-BRI is currently primarily used in industries with specialized and very specific needs. High-end
videoconferencing Videotelephony, also known as videoconferencing and video teleconferencing, is the two-way or multipoint reception and transmission of audio signal, audio and video signals by people in different locations for Real-time, real time communication. ...
hardware can bond up to 8 B-channels together (using a BRI circuit for every 2 channels) to provide digital, circuit-switched video connections to almost anywhere in the world. This is very expensive, and is being replaced by IP-based conferencing, but where cost concern is less of an issue than predictable quality and where a QoS-enabled IP does not exist, BRI is the preferred choice. Most modern non-
VoIP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet t ...
PBXs use ISDN-PRI circuits. These are connected via T1 lines with the central office switch, replacing older analog two-way and
direct inward dialing Direct inward dialing (DID), also called direct dial-in (DDI) in Europe and Oceania, is a telecommunication service offered by telephone companies to subscribers who operate a private branch exchange (PBX) system. The feature provides service for ...
(DID) trunks. PRI is capable of delivering
Calling Line Identification Caller identification (Caller ID) is a telephone service, available in analog and digital telephone systems, including voice over IP (VoIP), that transmits a caller's telephone number to the called party's telephone equipment when the call is ...
(CLID) in both directions so that the telephone number of an extension, rather than a company's main number, can be sent. It is still commonly used in
recording studio A recording studio is a specialized facility for sound recording, mixing, and audio production of instrumental or vocal musical performances, spoken words, and other sounds. They range in size from a small in-home project studio large enoug ...
s and some
radio program A radio program, radio programme, or radio show is a segment of content intended for broadcast on radio. It may be a one-time production or part of a periodically recurring series. A single program in a series is called an episode. Radio networ ...
s, when a
voice-over Voice-over (also known as off-camera or off-stage commentary) is a production technique where a voice—that is not part of the narrative (non- diegetic)—is used in a radio, television production, filmmaking, theatre, or other presentation ...
actor or host is in one studio conducting remote work, but the director and producer are in a studio at another location. The ISDN protocol delivers channelized, not-over-the-Internet service, powerful call setup and routing features, faster setup and tear down, superior audio fidelity as compared to
plain old telephone service Plain old telephone service (POTS), or plain ordinary telephone system, is a retronym for voice-grade telephone service employing analog signal transmission over copper loops. POTS was the standard service offering from telephone companies from 1 ...
(POTS), lower delay and, at higher densities, lower cost. In 2013,
Verizon Verizon Communications Inc., commonly known as Verizon, is an American multinational telecommunications conglomerate and a corporate component of the Dow Jones Industrial Average. The company is headquartered at 1095 Avenue of the Americas ...
announced it would no longer take orders for ISDN service in the
Northeastern United States The Northeastern United States, also referred to as the Northeast, the East Coast, or the American Northeast, is a geographic region of the United States. It is located on the Atlantic coast of North America, with Canada to its north, the Southe ...
.


See also

*
ISDN User Part The ISDN (Integrated Services Digital Network) User Part or ISUP is part of Signaling System No. 7 (SS7), which is used to set up telephone calls in the public switched telephone network (PSTN). It is specified by the ITU-T as part of the Q.76x se ...
*
DSS1 Digital Subscriber Signalling System No. 1 (DSS1) is a digital signalling protocol (D channel protocol) used for the ISDN. It is defined by ITU-T I.411 (ETS 300 102). It supports Bearer Capability, Low Level Compatibility and High Level Compat ...
*
DSS2 Digital Subscriber Signalling System No. 2 (DSS2), as the successor to DSS1, is also a digital signalling protocol (D channel protocol) used for the B-ISDN In the 1980s, the telecommunications industry expected that digital services would f ...
* 4ESS * Digital Access Carrier System *
QSIG QSIG is an ISDN based signaling protocol for signaling between private branch exchanges (PBXs) in a private integrated services network (PISN). It makes use of the connection-level Q.931 protocol and the application-level ROSE protocol. ISDN "prop ...
*
Remote Operations Service Element protocol The Remote Operations Service Element (ROSE) is the OSI service interface, specified iITU-T Recommendation X.219, ISO/IEC International Standard 9072-1 that (a) provides remote operation capabilities, (b) allows interaction between entities in a di ...
*
Q.931 ITU-T Recommendation Q.931 is the ITU standard ISDN connection control signalling protocol, forming part of ''Digital Subscriber Signalling System No. 1''. Unlike connectionless systems like UDP, ISDN is connection oriented and uses explicit sign ...
*
FTZ 1 TR 6 FTZ 1 TR 6 (or 1 TR 6) is the standard for the obsolete German national digital signalling protocol (D channel protocol) used for the ISDN. It has been superseded by DSS1 but is still in use on some lines and private exchanges. 1  ...
* I.430 * I.431 *
Common ISDN Application Programming Interface The Common ISDN Application Programming Interface (short CAPI) is an ISDN-conformant standardized software interface. With the help of CAPI, computer software intended for the use with ISDN can be provided, without knowledge of the deployed, propr ...
*
Asynchronous Transfer Mode Asynchronous Transfer Mode (ATM) is a telecommunications standard defined by American National Standards Institute (ANSI) and ITU-T (formerly CCITT) for digital transmission of multiple types of traffic. ATM was developed to meet the needs of ...
*
B-ISDN In the 1980s, the telecommunications industry expected that digital services would follow much the same pattern as voice services did on the public switched telephone network, and conceived an end-to-end circuit switched service, known as Broadba ...
*
IpDTL ipDTL is an IP codec which runs in a web browser, used for remote broadcasts in television, radio, and voice-over. It serves as a replacement for and is compatible with older ISDN audio codecs. Developed by former BBC sound engineer Kevin Leach, i ...
*
H.320 H.320 or Narrow-band visual telephone systems and terminal equipment is an ''umbrella Recommendation'' by the ITU-T for running Multimedia (Audio/Video/Data) over ISDN based networks. The main protocols in this suite are H.221, H.230, H.242, au ...
* ETSI * List of device bandwidths


References


External links

* * * * * {{DEFAULTSORT:Integrated Services Digital Network 1986 introductions Audio network protocols ITU-T recommendations Network access Telephony Videotelephony Wide area networks