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What are ISDN Services: All Business Enterprises Need to Know About

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ISDN stands for Integrated Services Digital Network. Being a circuit-switched telephone network system, it transmits voice and data over a digital line. It is also a set of communication standards for transmitting voice, data, and signaling. ISDN connections provide higher quality and better speeds and let data transmissions travel reliably. ISDN includes data transport and digital telephony services offered by regional telephone carriers. 

It involves the telephone network digitization to transmit voice, video, data, text, or music material over existing telephone wires. Business enterprises can make the most of ISDN services to make business communication smooth and hassle-free. Get updated information on ISDN networking and services concerning ISDN in the computer network, architecture, connection, types, applications, benefits, and services. 


ISDN stands for Integrated Services Digital Network. It bridges the premise connection (home) and the Central Office’s local loop. It is a digital service for restoring the analog plain old telephone set and uses the existing wiring. ISDN network has digital switching connections to transmit digital signals. Integrated services deliver two simultaneous connections over an individual line by merging data, fax, voice, and video. The ISDN network provides end-toned digital connectivity for voice and non-voice services. ISDN devices include the following:

  • Exchange-termination equipment 
  • Line-termination equipment 
  • Network-termination devices – Network termination type 1 (NT1) or network termination type 2 (NT2)
  • Terminal adapters (TAs) – Specialized ISDN terminals or terminal equipment type 1 (TE1) and non-ISDN terminals or terminal equipment type 2 (TE2)

When we talk about the advantages of ISDN, its channels are well-known for a reliable connection. ISDN has a faster data transfer rate, and business enterprises use it to facilitate users with multiple digital media. Conversely, there are also some disadvantages of ISDN. ISDN lines are costlier compared to other telephone systems due to the need for specialized digital devices. Moreover, it is less flexible. Business enterprises looking for better communication solutions can make a difference with ISDN. The ISDN specifications offer protocol sets to enable call setup, maintenance, and completion. The circuit-switched telephone network carries packet data and enables existing landline technology to have digital services.

What is ISDN?

What is the full form of ISDN? ISDN’s full form is related to the telephone networking system. ISDN stands for Integrated Services Digital Network. It is an abbreviation that provides high-speed, and high-bandwidth channels to subscribers activated on the public switched telephone network. It is a phone network for sending voice and computer messages. Governed by a worldwide set of standards, ISDN is a mature technology with symmetrical and consistent transfer rates. Compared to other technologies, ISDN is available at competitive prices.

ISDN is an original high-speed internet service known for revolutionizing internet use by sparking high-speed internet development during the 1990s. Like the dial-up internet service, ISDN also uses a phone line. Actually, ISDN sets the telephone data service standards and precedes ADSL (Asynchronous Digital Subscriber Line). ISDN comprises the digitization of the telephone network for transmitting voice, data, text, or video over existing telephone wires. It offers two types of channels

  • A 64-Kb/s Bearer (B) channel for data
  • A 64-Kb/s (maximum) Delta (D) channel for control over the OSI model’s layers 1, 2, and 3 

ISDN also offers two types of channel-based services: 

  • The 192-Kb/s Basic Rate Interface service offers one D channel (2B+D) and two B channels 
  • The 1.544/2.048-Mb/s Primary Rate Interface service offers one D channel and 23 to 31 B channels 

ISDN In Computer Network

When discussing ISDN architecture and connection, people generally ask: What is ISDN in a computer network? So, ISDN in networking is a set of protocols based on high-speed, fully digitized telephone service. Its’ aim is to offer a fully integrated digital service to the end users. Generally, ISDN is seen as an alternative to T1 wide area telephone service (WATS) and frame relay. ISDN applications include 

  • high-speed image applications 
  • high-speed file transfer
  • videoconferencing

Offering access to all digital facilities, faster call setup, and faster data transmission rate are some prime benefits of using digital connectivity. Following are some unique ISDN principles. 

  • ISDN supports packet and circuit switching with connections at 64 kbps.
  • Layered protocol architecture is used in ISDN for specification.
  • ISDN services cover network management functions and provide maintenance.
  • Several configurations are possible in ISDN networking when it comes to implementation.

ISDN Architecture

Being a general-purpose digital network, ISDN supports voice, data, text, and image services with the help of a set of standard multipurpose user-network interfaces. ISDN connection helps offer valuable frameworks for developing and establishing upcoming telecommunications services and networks. Formerly Integrated Digital Network (IDN), ISDN is a standardized digital technique for transmission and switching. It also supports switching operations such as packet-switched and circuit-switched operations, and ISDN protocol architecture controls switching operations. Circuit Switching is available at the very nominal bit rate of 64 kbps. On the other hand, packet switching is available for an extensive assortment of bit rates up to 64 kbps.

Channels and Layers in ISDN Architecture

ISDN commonly comprises three types of channels: H-channel (Hybrid Channel), B-channel (Bearer channel), and D-channel (Data Channel). Like three channels, there are also two types of layering mechanisms: one for the D Channel and the other for B/H Channels. ISDN contains three-layered protocol architecture for D-channel, whereas ISDN contains only one protocol layer for B-channel. This protocol layer has three different layers: Physical, data link, and network layer. 

Physical Layer

Both B and D channels are the same at this layer and use either BRI or PRI Interface. The physical layer defines primary aspects, including electrical and mechanical specifications of R, S, T, and U interface, power supply, or encoding. This layer relates to X.21 for public circuit switching network interaction through an 8-pin connector.

Data Link Layer

The data link layer covers the B or D Channel that uses the Link Access Procedure Balanced (LAPB) or Link Access Protocol D-channel (LAPD). Both B and D channels use many data link protocols.

Network Layer

At the network layer, B-channel covers many options for connecting to packet-switched, circuit-switched, frame relay, and ATM networks.

Types of ISDN

Basic Rate Interface and Primary Rate Interface are two types of ISDN networks. The prime difference between PRI and BRI is the reliability and level of service. PRI is the leading ISDN service, offering faster speed, better connection, and more reliable service, and BRI is the lower service tier and offers basic needs at a lower cost. Both ISDN types use B and D channels for sending data and other forms of communication, respectively.


The ISDN basic rate interface (BRI) service type offers two B channels and one D channel called 2B+D. BRI B-channel operates at 64 kbps to carry user data, and BRI D-channel operates at 16 kbps to carry information. Note that BRI can back user data transmission under certain circumstances.


ISDN primary rate interface (PRI) service type offers 23 B channels and 1 D channel called 23B+D. It produces a total bit rate of 1.544 Mbps and runs at 64 kbps). ISDN PRI in Europe, Australia, and other parts of the world provides

30 B channels + one 64-kbps D channel = A total interface rate of 2.048 Mbps.

Applications of ISDN

There is a long list of ISDN applications that make the networking solution a significant fit for all business types and sizes.

Video Conferencing

ISDN circuits have been around us for a decade and are very useful for video conferencing. Establishing a video conferencing session using a set-top video conferencing Codec (at both ends) and a single ISDN line (128 Kbps) is easy. You can do video conferencing at a much lower bandwidth than a packet-switched network because ISDN is a circuit-switched network. Consequently, ISDN gives equal throughput for upstream and downstream transmissions with no packet loss. ISDN can still be a good choice for your company if you don’t conduct video conferencing sessions regularly. It keeps you free from paying rent as you pay only for usage, and it carries data without congestion.

ISDN Video Phones

Many video phones connected to the ISDN network can also make a video call to other similar ISDN phones using the ISDN network. The video phones with bigger screens and built-in-camera show the output video and video capturing.

Broadcasting Industry

Radio broadcasting stations in the broadcasting industry use the ISDN network for transferring the audio signals from the covering point to the broadcasting point or radio station. The internal protocol (IP) network is also famous for this application.

Making a Couple of Telephone Calls Concurrently

Connecting two analog phones to the adapter helps you dial out two telephone calls. That is why ISDN networking matters the most. ISDN architecture enables you to browse the Internet at a speed of 128 Kbps, get a call during browsing by connecting the call in one channel (64 Kbps), and stay in other channels at a lower speed of 64 Kbps using internet connectivity. ISDN is equally beneficial in sending fax in one channel and talking to someone in the other channel simultaneously. Some countries use ISDN connections for essential voice communications.

Digital PBX/ IP PBX

ISDN interface cards allow ISDN lines that terminate on a corporate PBX, including Digital-Mixed PBX and IP PBX. So, ISDN lines can be used to remove the PBX, make outgoing calls, and receive incoming calls from phones within the business organization. Digital PBX is useful for companies interested in using ISDN for video conferencing, and ISDN lines are useful for normal voice communications and video conferencing.

Back-up Internet Connectivity

Businesses can terminate the ISDN networks directly on certain enterprise routers. These routers offer an automatic fail-over to the network for internet access when the primary broadband, lease lines, or Internet Line are down. Small companies in remote locations can use ISDN as the primary source of Internet connectivity, whereas ADSL broadband networks offer no support.

Bank ATM/ Point of Sale Locations

ISDN networks are also a good choice for connecting to low bandwidth-consuming apps, including automated teller machines and point-of-sale businesses needing network access to accept payment through credit cards.

Benefits of ISDN Lines

Business enterprises get lots of advantages when they use ISDN lines. The primary benefit of the ISDN line (Digital Line) is better voice quality (audio fidelity) than analog circuits. ISDN lines can carry data (Internet), video (video conferencing), voice (calls), and fax information simultaneously on the same line.

Each ISDN line can offer a bandwidth of 128 Kbps in the downstream and upstream directions. This feature empowers carrying video communications in real-time, and it is little or no data loss in ISDN circuit-switched networks while transmitting data in packet-switched networks. 

Troubleshooting digital networks quickly troubleshoot analog circuits. ISDN lines can rectify faults faster and make the network performance reliable and predictable. ISDN BRI can travel more than ADSL for longer distances, and that is why it is appropriate for remote Internet access. The call setup and tear-down are faster than analog circuits with ISDN. The latency is very less in digital circuits. So, ISDN is suitable for transmitting latency-sensitive apps. The channel bonding technique gives ISDN circuits a higher throughput and combines multiple lines.

ISDN Service

ISDN architecture offers a fully-integrated digital service to end users. ISDN digital services come under three categories: Bearer services, teleservices, and supplementary services. 

Bearer Service 

Users can transfer voice, data, and video information without using the bearer network. Here, ISDN needs no network for information processing. Bearer service relates to the OSI model’s first three layers which are well-defined in the ISDN standard. Business enterprises can have bearer services using packet-switched, circuit-switched, frame-switched, or cell-switched networks. 


The network may process or change data contents through teleservices. Teleservices relate to layers 4-7 of the OSI model. These services accommodate complex user needs and depend on bearer service facilities. Users needn’t go into the details of the process. Teleservices comprise

  • Teleconferencing
  • Telefax
  • Telephony
  • Teletex
  • Telex
  • Videotext

Supplementary Service 

Regarding knowing more about additional functionality to teleservices and the bearer services, supplementary services matter the most. This service type includes  

Modern telephone company services are the best supplementary service examples in the contemporary digital world.


As a network technology, Integrated Services Digital Network (ISDN) digitally supports voice and data transfer over the public switched telephone network. During the 1990s, ISDN gained popularity at the global level. It is still prevalent in all parts of the world and solves common business communication issues through modern long-distance networking technologies. Business enterprises must look beyond the ISDN full form and take quality ISDN networking solutions effectively. Many communication service-providing companies in India ( offer ISDN bearer service, teleservice, and supplementary services and solutions. 

For more information on ISDN networking services and solutions for your business, call 1800 137 3839 or email

Frequently Asked Questions

What is The Difference Between SDL and ISDN?

ISDN stands for Integrated Services Digital Network, and DSL stands for Digital Subscriber Line. ISDN is a digital transmission or circuit-switched data transmission system that transmits data and voice through copper telephone wires. DSL is a digital transmission system that uses already-installed copper wires for sending data and voice packets. Compared to an ISDN line, DSL transmits data faster. Both SDL and ISDN differ from each other in terms of speed, technology, and price.

What is The Difference Between the Internet and ISDN?

The Internet is a universal data communications system and information. It is a software and hardware infrastructure for offering connectivity between computers. ISDN is a circuit-switched data transmission system for transmitting data and voice.

What Are The Advantages of ISDN?

Faster transmissions, better quality signals, multipurpose cables, and various call management functions are some unique advantages of ISDN that businesses can ensure with ISDN services. 

What are Two Types of ISDN Services?

ISDN services are of two types: Basic Rate Interface (BRI) and Primary Rate Interface (PRI). BRI is the lower tier of service that offers basic needs only at a lower cost, and PRI is the leading service that provides better connections with faster speed and reliable services.

What is The Use of ISDN?

Both individuals and enterprises use ISDN for high-speed Internet when DSL options and cable modem connections don’t work.