ISDN vs PSTN: Difference and Comparison

Communication is the essential ingredient and backbone of all aspects of the world. From the stone age to the modern day, communication has gone through a sea change.

From symbols to mobile, we have come a long way. Gone are the days when we dialled manual telephones to get in touch with our loved ones.

With the evolution of networks and technology, we can now video call, send and receive messages, documents, and photographs at the click of a button. During the manual telephone age, the network was analog(continuous electrical signals).

As it moved through many switches, the quality of the voice got worse.


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In a network, the switch manages the flow of data from one device to another. ISDN(Integrated Services Digital Network) and PSTN(Public Switched Telephone Network) are networks outlined to transmit data and voice over phones.

Key Takeaways

  1. ISDN (Integrated Services Digital Network) transmits voice and data over digital lines, while PSTN (Public Switched Telephone Network) primarily carries analog voice signals.
  2. ISDN provides higher call quality, faster connection speeds, and additional features compared to PSTN.
  3. PSTN is the traditional phone system, whereas ISDN represents a more advanced, digital alternative.


ISDN stands for Integrated Services Digital Network and is a type of telecommunications network that uses digital technology to transmit voice, data, and video signals over a dedicated line. PSTN stands for Public Switched Telephone Network and is the traditional telecommunications network that uses analog technology to transmit voice signals over a dedicated line.


The ISDN design is incorporated to carry voice or any data you want to the end user. It provides a single interface(both hardware and communication)to connect to the phone, fax, computer, or video phone.

ISDN was considered the future of a fast service network. Using fibre was expensive. The usage of copper slowed the network. It depleted the quality received by the end-user.

PSTN system has been in use since the year 1800. This platform has been a reliable source of communication for ages with the help of underground copper wires.

PSTN is the worldwide assemblage of the inter-connected voice-oriented telephone network, and it consists of all the switched telephone operated locally or internationally around the world. The network provides the infrastructure for public telecommunication.

Comparison Table

Parameters of ComparisonISDNPSTN
Full-FormIntegrated Services Digital Network. It is digitalPublic Switched Telephone Network. It is analog in nature.
ConnectionISDN can run 2,10,20,30 channels in a single time.Only a single line can be used.
TransmissionIt is a circuit-switched network and transfers data and voice.It transfers only voice.
CompaniesISDN is used by big companies.PSTN is used by small companies.
SpeedWe can make faster calls.No possibility of this option.

What is ISDN?

With the failure of the analog system in providing reliable long-distance connections, there was an urgent of an alternative source. By the year 1960, there was a gradual shift to the packet-based digital system.

In 1988, the UN-based International Telecommunication Union(ITU) recommended utilizing the ISDN network system to deliver data.

The innovation improved the quality of the communication network. It was the initiative of manufacturing giants like Motorola and USRobotics to ease the transition of networking. This launched ISDN is a big picture in the US, providing consumers with better internet access and pricing.

The utilization of ISDN is for high-speed internet options. To set up an ISDN network, you must take the help of the Internet Service Provider(ISP). The ISDN requires a traditional Plain Old Telephone Service(POTS) line and an accessible telephone number.

We must ensure both the POTS and the telephone number are in working condition. Now it is all set up for voice and data communication.

There are mainly two types of ISDN. A Basic rate interface (BRI) is a type of ISDN mostly used for telephone services. It is often used in residential areas or small businesses.

Primary rate interface (PRI) is an ISDN configuration used for multiple digital zero services. PRI is often used in huge companies and enterprises.


What is PSTN?

The commercialization of the telephone began in the year 1876. The telephones had to be wired in pairs for usage as there was no network connection. It limited the utility of this marvellous invention.

There was an expansion of the network by 1900, as the number of telephone users increased. It is when PSTN gained importance using analog signals.

By 1960 manual switching was gradually being replaced by digital voice signals. It gave an advantage to the same wire shared by other phone calls.

PSTN is Public Switched Telephone Network. It is a global system that comprises public telephone networks. It is a circuit-switched network which means when we call, the communication gets established between two points.

The analog data is transferred through the copper wires for the conversation to happen.

PSTN is always associated with the usage of copper wiring, and the latest infrastructure utilizes fibre optic cables to replace the copper wiring. The PSTN phone line uses traditional dialling to get connected to the Internet on the computer.


Main Differences Between ISDN and PSTN

  1. ISDN means Integrated Services Digital Network is a digital network, and larger companies work with ISDN. PSTN means Public Switched Telephone Network is an analog network. Small companies work with PSTN.
  2. ISDN can parallelly run 2,10,20, or 30 channels in a single line. PSTN can run a single line for a firm 
  3. ISDN is a circuit-switched telephone network and it digitally transmits both voice and data. It provides better voice quality. PSTN digitally transfers voice data, and it does not exploit the advantages of broadband.
  4. ISDN is multifaceted, can choose to use two connections simultaneously, like telephone and fax. PSTN is single-faced and has only one connection.
  5. ISDN can help in making faster calls. PSTN has no such options to make faster calls. 

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