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Difference Between PSTN & ISDN

Much like any other form of technology, telecommunication networks have evolved and developed over time to meet new demands, requirements and functionalities. From basic analogue technology to modern-day video conferencing and messaging, phones have changed rapidly over the past few decades in Australia. We’ve covered all you need to know about PSTN and ISDN, two of the key telecommunications technologies, below:


What is PSTN?

When you think old-school landline telephones, you’re probably thinking of the classic PSTN form of telecommunications. PSTN stands for ‘Public Switch Telephone Network’, and is the forefather of the modern technology that thousands of homes and businesses across Australia use for everyday functionality. From the commercialisation of telephones in 1876, public telephone networks with copper wire became popular. PSTN offered connectivity through analogue data, transmitted along those copper wires to enable conversation from one side of Australia to the other.

PSTN is often considered the standard telephone service compared to the shiny, additional functionality that fibre and similar systems offer. While digital integration is standard across Australia for telecommunications, analogue signals may still be used from the exchange to the end-user, making PSTN a valuable part of the overall telecoms grid.


What is ISDN?

As the shinier and newer cousin of PSTN, ISDN stands for ‘Integrated Services Digital Network’. As the name suggests, ISDN offers the digital transmission of data and choice while also having greater flexibility for fast, practical internet connectivity. The average business and household in Australia make full use of ISDN for their daily communications needs. However, more rural areas may still rely on the old-school analogue copper wire at some part in the process.

ISDN has been around since 1991 and has been utilised by many businesses to access the number of lines. Particularly for those that need multiple voice, fax, and data transmissions at once without the need to install dozens of PSTNs. The ISDN comes in two specific forms, which are as follows:


Basic Rate Interface (BRI)

The basic rate interface is the standard telecommunications service you’ll see offered to small businesses and individuals’ households, providing the capacity to meet relatively low demand. In terms of facts and figures, the includes two 64 kbit/s voice channels plus a 16 kbit/s signalling channel for up to 144 kbit/s.


Primary Rate Interface (PRI)

The primary rate interface is the big business side of ISDN telecoms, meeting the far greater remand placed on larger companies or call centres. A heavy-hitting capacity of up to 2048 kbit/s includes up to 30 individual and simultaneous channels or calls at 64 kbit/s apiece, plus signalling and timing channels on top. Depending on business needs, these larger-scale ISDN options are usually bundled in blocks of 10, 20 or 30.


What Are The Differences Between ISDN and PSTN?

With ISDN and PSTN both utilised by Australian households and businesses, there are some key differences to consider between the two. Whether you’re considering upgrading or you want to know more about the typical distinctions between each option, here are some of the differences that typify each kind of telecoms:


Analogue vs Digital

The most significant and most obvious difference between ISDN and PSTN is the method used to send data down the phone lines. PSTN has a far longer history of usage in Australia, making the most out of copper phone lines and poles to connect much of the country via analogue over the past century. On the other hand, ISDN utilises digital signals to get information from A to B, taking advantage of advancements in technology in a far more modern way.


Line Capacity

ISDN has a far larger capacity than PSTN without question. While a business ISDN may offer a bundle of anything from 2 to 30 channels in a single line, PSTN requires a new installation for every additional channel, with limited capacity that only supports a single line for each channel installed.


Voice Quality

As a digital telecommunications method, ISDN takes advantage of the digital transference of voice and data to produce excellent clarity and reliability in sound. You can quickly tell the difference between the distortion and crackle of an older PSTN connection compared to an ISDN connection, which exploits the advantage of broadband for improved voice quality.



ISDN provides multiple facets, making it easy to use two connections simultaneously, such as a fax and a telephone. PSTN provides a single connection by contrast, which means that both devices cannot be used at once as the line is occupied by one or the other.


Speed of Calls

In some cases, ISDN can be utilised to make faster and more efficient calls, reducing wait times in environments where call logs are important. On the other hand, PSTN doesn’t offer an option for faster calls, relying on a standard speed each time.



One of the critical differences between ISDN and PSTN is their target audience and the level of utilisation required. PSTNs are traditionally used in small business and households, where the demand placed on the phone channels are far lower. Larger companies and operations with extensive use of telecommunications benefit from ISDN, making it worth the higher cost in exchange for additional functionality and flexibility in the workplace.


ISDN or PSTN – Which is Better?

PSTN has long been the traditional method of communications across Australia and in other parts of the world. While ISDN has generally overtaken PSTN in recent years, both forms of technology are slowly being phased out by even newer options on the market. With the addition of both Session Initiation Protocol (SIP) and Voice Over Internet (VoIP) technology, investing in new telecommunications may involve leaving both ISDN and PSTN behind.

The best telecommunications service for your household or business will depend entirely on your demand and requirements. While extremely simple or rarely used phone lines may still be fully functional on PSTN, and more traditional offices may function on ISDN, many workplaces enjoy the added functionality that the next generation of telecoms provides.

Are you interested in upgrading your telecommunications? As leading telecoms experts on the Gold Coast, Techwell is here to bring the latest services to your business. Get in touch with us today to find out more.

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