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What is the difference between P.S.T.N and I.S.D.N?


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PSTN stands for Public Switched Telephone Network. ISDN stands for Integrated Services Digital Network.

These are two distinct networks that work to transfer voice and data over the phone lines.

Public Switched Telephone Network

The public switched telephone network is a traditional circuit-switched telephone network. It has been around for a very long time, even before the commercialization of the telephone network around 1874.

It consists of the complex interconnection of switching centers and end-users that offers a voice connection between any two valid subscribers.

A successful connection to the public switched telephone network needs an operator and a pair of wires, typically overheadRunning from each subscriber to the exchange where these are terminated at a switchboard. It also needs a telephone exchangeAutomatic exchange basically composed of switches.

As the number of subscribers increases, the demand for physical space to house the switchboards and operators also increases. This led to massive exchange buildings and a large staff required to operate the PSTN system when it came into existence.

PSTN is analog in nature.

An illustration of PSTN

Integrated Services Digital Network

The integrated services digital network provides end-to-end digital connectivity to support a wide range of services, including voice and non-voice services.

Users have access to these services via a limited set of standard multi-purpose customer interfaces.

ISDN came to light around 1960, when the analog system was unable to provide long-distance connection.

The innovation of ISDN eased the transition of networking and improved the quality of the communication network with its packet-based digital system.

ISDN works on a high-speed internet option with the requirements of a plain old telephone services (POTS) line, including an accessible telephone number.

An illustration of ISDN

Differences between PSTN and ISDN


  1. It is analog in nature and came to light before ISDN.
  2. It functions basically for small franchises or companies.
  3. Transfer speed is very slow and only voice transmission is allowed.
  4. It does allow simultaneous line connections, so just a single line can be used here.
  5. End-to-end connection is not possible here. It’s impossible to make fast calls with PSTN.


  1. Digital in nature and came into the communication scene around 1960.
  2. It is used mainly for big companies.
  3. The data speed here is very fast. Circuit-switching operation makes data and voice transmission possible.
  4. Allows simultaneous line connection and can run 10-30 line connections at a time.
  5. End-to-end connection is possible here, so this makes phone calls a possibility.


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