ATM is a core protocol used over the SONET / SDH backbone of the public switched telephone network ( PSTN ) and Integrated Services Digital Network ( ISDN ), but its use is declining in favour of All IP.

The call control protocol is derived from ISDN DSS1, which is a Q. 931 derived protocol.

* Digital Subscriber System No. 1 ( DSS1 ) The ISDN PBX interface is most often used for ( new ) PRA connected PBX

Digital Access Signalling System 1 ( DASS1 ) is a proprietary protocol defined by British Telecom to provide ISDN services in the United Kingdom.

Digital Access Signalling System 2 ( DASS2 ) is an obsolescent protocol defined by British Telecom for digital links to PSTN based on ISDN.

Integrated Services Digital Network ( ISDN ) is a set of communications standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network.

The key feature of ISDN is that it integrates speech and data on the same lines, adding features that were not available in the classic telephone system.

ISDN is a circuit-switched telephone network system, which also provides access to packet switched networks, designed to allow digital transmission of voice and data over ordinary telephone copper wires, resulting in potentially better voice quality than an analog phone can provide.

A major market application for ISDN in some countries is Internet access, where ISDN typically provides a maximum of 128 kbit / s in both upstream and downstream directions.

ISDN should not be mistaken for its use with a specific protocol, such as Q. 931 whereby ISDN is employed as the network, data-link and physical layers in the context of the OSI model.

ISDN is designed to provide access to voice and data services simultaneously.

The entry level interface to ISDN is the Basic ( s ) Rate Interface ( BRI ), a 128 kbit / s service delivered over a pair of standard telephone copper wires.

* 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 an Network termination 1 ( NT1 ).

The other ISDN access available is the Primary Rate Interface ( PRI ), which is carried over an E1 ( 2048 kbit / s ) in most parts of the world.

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.

Since the principal consumer application is for Internet access, ISDN was mostly superseded by DSL in the early 21st century.

There is a second viewpoint: that of the telephone industry, where ISDN is a core technology.

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.

Personal computers have also long been able to handle incoming and outgoing faxes using analogue modems or ISDN, eliminating the need for a stand-alone fax machine.

X. 25 was also part of an ISDN protocol called " Always On / Dynamic ISDN ", or AO / DI.

It's also common to use ISDN for the return audio links to remote satellite broadcast vehicles.

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.

The terms “ customer-premises equipment ,” “ Customer-provided Equipment ,” or “ CPE ” may also refer to any devices that terminate a WAN circuit, such as an ISDN, E-carrier / T-carrier, DSL, or metro Ethernet.

S interface ( also known as S0 ): For basic rate access in an Integrated Services Digital Network ( ISDN ) environment, a User – network interface reference point that

It also supports supplementary functions, such as hold, transfer, conference, and call park found in PBX, ISDN, and other telephone systems.

The final link to the local loop remained the same with digital signalling ( ISDN ) and analogue signalling for basic telephony ( also known as POTS in the industry ).

A competing encoding technique, also used for ISDN basic rate interfaces, is 4B3T.

Besides digital audio and digital video transmission, DVB also defines data connections ( DVB-DATA-EN 301 192 ) with return channels ( DVB-RC ) for several media ( DECT, GSM, PSTN / ISDN, satellite etc.

SAGEM also introduced an ISDN adaptor for GeoPort, the " Planet-ISDN Geoport Adapter ", or SPIGA, which they now sell in a USB version.

With Ethernet and audio over IP ( live ) or FTP ( recorded ), this also allows remote access, so that DJs can do shows from a home studio via ISDN or the Internet.

ISDN dial up access, and ability to use the Internet to blink ( a term used to collect messages ) were also introduced.

Digital Subscriber Signalling System No. 1 ( DSS1 ), also known as Euro-ISDN or E-DSS1 ( European DSS1 ), is a digital signalling protocol ( D channel protocol ) used for the ISDN.

The flat-rate service was also offered to customers with ISDN connections at the same price as for analog service.

Conformance test cases of ETSI standards like ISDN, DECT, GSM, EDGE, 3G, DSRC have also been written in TTCN.

It is also possible to directly use the digital signal as an Integrated Services Digital Network ( ISDN ) data signal and feed it into the equivalent of a remote access server.

ISDN PBX systems also replaced some traditional PBXs in the 1990s, as ISDN offers features such as conference calling, call forwarding, and programmable caller ID.

G. 722 has also been widely used by radio broadcasters for sending commentary grade audio over a single 56 or 64 kbit / s ISDN B-channel ( the least significant bit is dropped on 56kb circuits ).

Newbridge also offered ( for the time ) innovative network management and ISDN, RS-232C PC and Mac networking products, including distributed star-topology routing through both proprietary hardware and telco switches.

The communications device class is used primarily for modems, but also for ISDN and fax machines and telephony applications for performing regular voice calls.

British Telecom used the term ISDN when

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 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 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.

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.

Previously, on April 1985, Japanese digital telephone exchange hardware made by Fujitsu was used to experimentally deploy the world's first I interface ISDN.

Because of the widespread availability of ADSL services, ISDN is today primarily used for voice and fax traffic, but is still very popular thanks to the pricing policy of German telecommunication providers.

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.

In North America, ISDN is now used mostly as an alternative to analog connections, most commonly for Internet access.

ISDN is commonly used in radio broadcasting.

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.

Originally designed for transport across Integrated Services Digital Network ( ISDN ) infrastructure, it may be used today in the context of many other network interfaces.

Inverse multiplexers are used, for example, to combine a number of ISDN channels together into one high rate circuit, where a higher rate connection than is available from a single ISDN connection is needed.

* 4B3T used in some ISDN basic rate interface

A T-interface is used for basic rate access in an Integrated Services Digital Network ( ISDN ) environment.

Basic Rate Interface ( BRI, 2B + D, 2B1D ) is an Integrated Services Digital Network ( ISDN ) configuration intended primarily for use in subscriber lines similar to those that have long been used for plain old telephone service.

Two-binary, one-quaternary ( 2B1Q ) is a physical layer encoding used for Integrated Services Digital Network ( ISDN ) Basic Rate Interface ( BRI ) implementations.