What is PSTN and ISDN?

If you’ve owned a business for a while, you may have heard the terms ‘PSTN’ and ‘ISDN’ floating around. But what do these terms actually mean? And how do they affect the day-to-day running of your company? 

Well, we’ve got all the answers right here. In this article, we’ll explore what the PSTN and ISDN networks mean, how they work and what will happen when they get switched off by BT in 2025.

What is PSTN?

PSTN stands for Public Switched Telephone Network and is the phone system that has been used since the late 1800s. You may have heard of this network also referred to as landlines, fixed lines or plain old telephone service (POTS). Whichever you decide to call it, this system uses underground copper wires to connect these types of phones and is still widely used in both homes and businesses. 

How Does PSTN Work?

PSTN phone lines work by using circuit switching to connect two phones through telephone poles and lines. Essentially, when you dial a number from one landline to another landline, the phone will convert this into electrical signals which travel to a terminal. The terminal then transfers these signals to a central office and routes the call through a fibre optic cable to other offices until it finds the right one. Once the right office is found, the signal is then routed to the right terminal and telephone number you’re trying to reach.

While it certainly sounds like a long and complicated process, the reality is it takes just a few seconds for your phone to connect to another. 

What Will the PSTN Switch Off Mean?

In December 2025, this traditional PSTN system will be switched off for everyone and obsolete. This is because PSTN is simply outdated and is becoming more costly to run and maintain. With most people switching to mobile and internet-based phone networks, the demand for PSTN is no longer there. 

So, if your business is still running technology and equipment on a PSTN system, such as phone networks, broadband, door entry systems, alarms, EPOS machines, CCTV and more, you’ll need to switch over to digital voice services or voice-over-internet protocol (VoIP) technology. Ideally, you should switch as soon as possible to save yourself time, money and stress. 

What is ISDN?

ISDN stands for Integrated Services Digital Network, which is a system that uses digital transmissions to make standard phone calls, as well as video calls, and transmit data to other networks. This system was created by BT in 1986 as a way to update and replace traditional landline phones and outdated copper lines (PSTN) with digital phones. Typically, ISDN lines offer faster speeds, higher quality and better connections than PSTN lines, and are often used by those who need a high-speed internet connection, such as businesses. 

How Does ISDN Work?

For an ISDN system to work, you’ll need to have a current POTS line that it can be plugged into, and assigned phone numbers. Once the system is set up and ready to go, it works by splitting the traditional copper line into numerous digital channels. This means that several phones can make and receive phone calls at the same time on the same line.

There are 2 different types of ISDN lines, and the one you choose will depend on your needs and situation. BRI (Basic Rate Interface) is better suited to homes and small businesses as it is mainly used purely for voice telephone services. PRI (Primary Rate Interface) is more suitable for larger companies as it can carry multiple digital services and data.

What Will the ISDN Switch Off Mean?

While ISDN is more modern than the PSTN network and offers good internet speeds and connections, there are still certain aspects that have made it outdated. For example, with ISDN, you are still tied to a physical location, whereas services such as VoIP are cloud-based and much more flexible. 

The ISDN system hasn’t changed or been updated in several years and can now no longer compete with the ultra-fast broadband and connection speeds and quality that’s now available, which is why it’ll be getting switched off along with PSTN.

Since ISDN was created by BT, who, in recent years, have invested a lot of time and money into VoIP services, the system hasn’t changed or been updated. Financially and strategically, it doesn’t make sense for BT to keep both networks, and so ISDN will be getting switched off along with PSTN, allowing them to put all their energy and focus into building networks for the future.

Just like with the PSTN switch-off, this means any technology or equipment you have in the office that runs through ISDN will need to be updated and replaced before 2025 with digital voice services to ensure your business can continue running smoothly. 

If you need help switching services or are looking for some advice, take a look at our telephony and business phone system solutions, as well as our business broadband solutions and contact our team to discuss your needs.

Make sure you also read our blogs to find out more about what the analogue phone line switch will mean for your business and why you should switch to a VoIP system as soon as possible.

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