Difference Between ISDN and PSTN (With Table)

Communication is the essential ingredient and backbone to 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 dialed the 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, 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 voice got worse.

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.


The difference between ISDN and PSTN is that ISDN (Integrated Services Digital Network) design handles the digital telecommunication network. PSTN (Public Switched Telephone Network) on the other hand is a traditional circuit-switched telephone network.

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 fiber was expensive. The usage of copper slowed the network. It depleted the quality received by the end-user.

PSTN system is 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 Between ISDN and PSTN

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 provided consumers 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 marvelous 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 the manual switching was gradually being replaced by digital voice signals. It gave an advantage of 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 fiber optic cables replacing the copper wiring. The PSTN phone line uses traditional dialing 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 helps in making faster calls. PSTN has no such options to make faster calls. 


ISDN introduced in the beginning did take some time for the transition to take place. The PSTN was the traditional way of communication when a voice was digitally transmitted. But it helped to transfer both data and voice at a much faster phaseThe telecommunication industry is booming with technology. Both ISDN and PSTN have withstood the ever-lasting changes in the communication world. 

The Session Initiation Protocol(SIP) and voice over Internet(VoIP) is the latest technology and the days of ISDN and PTSN are in the last years of the life cycle. Time will be the witness to the new age of communication technology.


  1. https://ieeexplore.ieee.org/abstract/document/184877/
  2. https://www.sciencedirect.com/science/article/pii/S0169755298002645
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