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What is the Full Form of ISDN

ISDN: Integrated Service Digital Network

The telephone system was viewed as a means of transmitting voice before Integrated Services Digital Network (ISDN), with some special services being offered for data. Speech and data can now be integrated on the same lines using ISDN, which was not possible with the traditional telephone system.

ISDN Full Form

Although ISDN is a packet-switched network that enables digital speech and data transmission, it is also a circuit-switched telephone network system. This may lead to speech or data quality that is superior to what an analogue phone can deliver. It offers a packet-switched connection that can transfer data at a rate of sixty-four kilobits per second. It offered upstream and downstream bandwidth at a maximum rate of 128 kbit/s. Channel bonding allowed for a higher data rate. Six to eight 64 kb/s channels on ISDN B-channels with three or four BRIs are typically bonded.

The OSI model is used by ISDN as the network between the physical layer and data-link, but ISDN is often only used with Q.931 and its related protocols. These signalling protocols, which were first developed in 1986, are used to initiate and terminate circuit-switched connections as well as for advanced calling features for the user. In between single desktop videoconferencing systems and group videoconferencing systems, ISDN enables simultaneous audio, video, and text communication between them.

Interfaces for ISDN

The ISDN interfaces are as follows:

1. BRI, or Basic Rate Interface

BRI uses two data-bearing channels (referred to as "B" channels) and one signalling channel (referred to as a "D" channel) to start connections. The D channel can only go as fast as 16 Kbps, whereas the B channels can go as fast as 64 Kbps. The two channels operate separately from one another. For instance, one channel might be used to establish a TCP/IP connection to one site while the other is used to fax information to a different place. ISDN is supported through a basic rate interface in iSeries (BRl).

According to the basic rate interface (BRl), a digital pipe with two B channels running at 64 Kbps each and one D channel running at 16 Kbps is required. This translates to 144 Kbps of speed. In addition, a 48 Kbps operating overhead is needed for the BRl service itself. Consequently, a 192 Kbps digital pipe is needed.

2. Primary Rate Interface (PRI) - The Primary Rate Interface service consists of a D channel and either 23 or 30 B channels, depending on the country you are in. PRI is not supported by the iSeries. A digital pipe with 23 B channels and one 64 Kbps D channel is incorporated in the conventional Primary Rate Interface (PRI). 1.536 Mbps is equal to 23 B channels at 64 Kbps apiece and 1 D channel at 64 Kbps. Additionally, the PRI service uses 8 Kbps of overhead. As a result, PRI needs a 1.544 Mbps digital pipe.

3. Broadband-ISDN (B-ISDN): Unlike narrowband ISDN, which relies significantly on copper cable to operate over the current communications infrastructure, B-ISDN is primarily dependent on the development of fibre optics.

Services offered by ISDN

ISDN offers customers a fully integrated digital service. The bearer services, teleservices, and supplemental services are subcategories of this service.

  1. Bearer Services - The bearer network allows users to communicate with one another via voice, data, and video without the network changing the nature of the connection. The network does not have to manage the data, which prevents it from changing the information's content. Bearer services are present in the OSI model's top three levels. They have precise definitions thanks to the ISDN standard. They can be transmitted across circuit-, packet-, frame-, or cell-switched networks.
  2. Teleservices - In this case, the network has the option to modify or process the data's contents. Layers 4 through 7 of the OSI model relate to these services. Teleservices are built to manage complicated user needs and rely on the bearer services' infrastructure. The user is not required to understand every step of the procedure. Telephony, teletex, telefax, videotex, telex, and teleconferencing are all examples of teleservices. Even though these services are specifically defined by the ISDN, they have not yet been become standards.
  3. Additional Service- Supplementary services offer bearer services and teleservices more capably. Call waiting, message handling, and reverse charging are a few examples of supplemental services that are common in today's telephone company offerings.

Principle of ISDN

The ITU-T standards serve as the foundation for how ISDN operates (formerly CCITT). For the International Telecommunication Union (ITU), the Telecommunication Standardization Sector (ITU-T), with its headquarters in Geneva, Switzerland, organises telecommunications standards. According to ITU-T recommendations, ISDN's different guiding concepts include:

  • Accommodate switched and un-switched applications.
  • Accommodate both voice and non-voice applications.
  • Using 64-kbps connections only.
  • Networked intelligence.

International Development

According to a study by the German Department of Science, the number of ISDN channels per 1,000 people was as follows in 2005.:

  • Norway: 401
  • Denmark: 339
  • Germany: 333
  • Switzerland: 331
  • Japan: 240
  • United Kingdom: 160
  • Finland: 160
  • Sweden: 135
  • Italy: 105
  • France: 85
  • Spain: 58
  • United States: 47


Telstra offers ISDN services to its commercial clients. The minimum monthly fee for voice and data calls was changed by Telstra. There are two main categories of ISDN services i.e., Basic Rate services, either ISDN 2 or ISDN 2 Enhanced. The Basic Rate services, ISDN 10/20/30, are of different kind. Telstra stated that beginning from January 31, 2018, recent sales of ISDN products would cease. By 2022, it would be announced when ISDN service would officially end and transition to the new service would begin.


Under the brand name Numeris (2 B+D), a professional Duo and residential I2 version of the ISDN service is provided by France Telecom. In France, ISDN is commonly referred to as RNIS and is widely accessible. Although it is still prevalent in more remote and outlying locations and for applications like business voice and point-of-sale terminals, the use of ISDN for data transfer and Internet access is decreasing because of the arrival of ADSL.


The number of installed analogue lines was declining because of ISDN's success. BRI and PRI were both offered by Deutsche Telekom (DTAG). Competing phone providers frequently provided just ISDN and no analogue lines. Due to the ubiquitous accessibility of ADSL services, voice and fax traffic were the main uses of ISDN.

Due to the fact that the pairing of DSL with an analogue line had no cost benefit over a combined ISDN-DSL connection, ISDN (BRI) and ADSL/VDSL were frequently bundled on the same line up until 2007. When the manufacturers of the ISDN technology stopped producing it and spare parts were difficult to find, this behaviour started to cause problems for the operators. Since then, phone companies have been offering less expensive xDSL-only solutions that use VoIP for telephony to cut costs by running separate data and voice networks.

Most German operators stopped supplying ISDN lines about 2010 and started offering increased VoIP on top of DSL lines. In Germany, there are no longer any new ISDN lines available as of 2018. Existing ISDN lines have been phased out since 2016 and existing customers have been urged to switch to VoIP services based on DSL. Other carriers like Vodafone anticipate their phase-out to be complete by 2022, while Deutsche Telekom originally planned to phase out by 2018.


Greece's established telecommunications provider, OTE, provides ISDN BRI (BRA) services. After ADSL was introduced in 2003, the significance of ISDN for data transport began to wane, and it is now only used for specialised corporate applications with point-to-point requirements.


Bharat Sanchar Nigam Limited, Reliance Communications, and Bharti Airtel, the country's top three communication service providers, provide both PRI and ISDN BRI services. DLC technology is used by Bharti Airtel and Reliance Communications to deliver these services. With the advent of broadband technologies, ADSL is taking on more of the bandwidth demand. ISDN is still a vital backup network for point-to-point leased line customers such as banks, Eseva Centres, Life Insurance Corporation of India, and SBI ATMs.


NTT, a Japanese telecommunications corporation, launched its INS Net 64 and INS Net 1500 branded ISDN services on April 19, 1988. This was the result of NTT's own investigation and test of what it called the INS (Information Network System) in the 1970s.

Previously, using Japanese digital telephone exchange technology created by Fujitsu, the first I interface ISDN was experimentally implemented in April 1985. Modern ISDN services employ the I interface rather than the outdated and incompatible Y interface.

As alternative technologies like ADSL, cable Internet connection, and fibre to the home gained more traction in Japan, the number of ISDN subscribers decreased. NTT has announced their plans to switch backend from PSTN to the IP network between 2020 and 2025 on November 2, 2010. ISDN services will be phased out during this transfer, and fibre optic services are advised as a replacement.


As a result of NTT's independent investigation and testing of INS in the 1970s begun by Telenor, a Norwegian telecommunications operator, and it also started providing state-wide ISDN services on April 19, 1988, under the trademarked names INS Net 64 and INS Net 1500.

United Kingdom

In the UK, British Telecom (BT) provides both ISDN30 and ISDN2e (BRI) (PRI). Up until April 2006, Home Highway and Business Highway were BRI ISDN-based systems that offered both integrated analogue connectivity and ISDN. For direct computer access, later versions of the Highway devices also had built-in USB ports. Home Highway was purchased by many home users, typically for Internet access, even though it was slower than ADSL since it was accessible in areas where ADSL was not. BT revealed their intention to phase out the UK's ISDN infrastructure by 2025 in the early months of 2015.

United States and Canada

In Canada and the US, ISDN-BRI has never become a widely used telephone access technology; it is still a specialised offering. Customers found the service to be "a solution in search of a problem" and found it challenging to navigate and use the wide variety of options and features.

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