For continued and consistent success, your business needs a reliable phone system. For years, ISDN phone systems have fulfilled this role and met the communications needs of many businesses.

However, the time has come for you to replace these systems. In this post, we’ll look at ISDN phone systems in more detail and show you why VoIP is the best alternative.

What is ISDN?

ISDN is the acronym for Integrated Systems Digital Network. Introduced in 1986, ISDN is a further development of POTS or Plain Old Telephone Service and upgraded traditional landlines to digital lines.

It’s a set of communication standards that allows you to make phone calls, video calls, transmit data, and use data by using digital transmission through the Public Switched Telephone Network (PSTN).

With the increased adoption of VoIP systems, the VoIP market is expected to reach $102.5 billion by 2026.

How Does ISDN Work?

Like traditional phone lines, an ISDN line is plugged through a POTS line. However, in contrast to traditional phone lines that provided a single line, ISDN splits the copper line into several digital channels. This then allows you to make and receive calls or transmit data using a single physical line.

What Are the Types of ISDN?

Now that we’ve seen what ISDN is and how it works, let’s look at the different types of ISDN in more detail. Here, it’s important to note that the two main types are Basic Rate Interface and Primary Rate Interface, while Broadband ISDN was never widely adopted.

Basic Rate Interface (BRI)

Basic Rate Interface or BRI is the basic or entry-level ISDN option as is suited to voice-grade telephone services or standard internet connectivity. As such, it offers ISDN services at a lower cost and is regarded as the best option for small businesses or home use.

BRI carries data over two 64 Kbps B or Bearer channels, and it handles control information and protocol negotiation with a 16 Kbps D or Data channel. Although this gives BRI transmission speeds of up to 128 Kbps, copper wires hardly ever allow it to reach these speeds.

Primary Rate Interface (PRI)

Primary Rate Interface or PRI offers higher speeds than BRI and, as such, is mostly intended for larger companies and enterprise use. In contrast to BRI, which uses two B channels, PRI uses 23 parallel B channels. As a result, PRI can offer speeds of between 1.544 Mbps and 2.94 Mbps, depending on the carrier system used.

Broadband ISDN (B-ISDN)

Broadband ISDN or B-ISDN is an advanced variation of ISDN and was designed to improve the capabilities of PRI. It aims to do this by using fiber-optic cables and using ATM switching to enable both uploads and downloads of vast amounts of data.

However, before ISDN could be widely adopted, the technology was overtaken by ADSL, which offered far more advanced capabilities.

What are the Advantages and Disadvantages of ISDN?

Compared to traditional phone lines, ISDN offers several advantages. For one, one of the main benefits of ISDN is that it allows both voice and data communication through the same cable, while traditional phone lines require multiple lines to offer the same capabilities. Also, it offers much faster data transmission speeds. As mentioned earlier, the most basic type of ISDN is capable of carrying data at speeds of up to 128 Kbps.

Another advantage of ISDN compared to traditional phone lines is that it offers a better quality signal. As a result, it offers a more stable internet connection and higher voice quality telephone calls. Finally, in addition to these advantages, ISDN also offers more advanced features like call forwarding, messages, and more.

Although ISDN offers all these advantages, there are, however, several significant disadvantages when using ISDN. One of the main disadvantages is that ISDN still requires physical lines to operate. This not only results in its installation being challenging and time-consuming, but also limits its flexibility. As such, it limits the possibilities of expansions, relocation, and remote work.

Moreover, installing and operating an ISDN system is costly because installation is expensive, and it comes with costs such as line leasing, service costs, and more. Finally, and maybe more significantly, ISDN is an aging technology that can’t compete with newer, more advanced technologies. As such, ISDN is being phased out and an end-of-life date has been confirmed for 2025.

What’s the Difference Between ISDN, DSL, and ADSL?

Now that we’ve seen some of the disadvantages of ISDN, let’s consider one of the alternatives – DSL. Like ISDN, DSL, or Digital Subscriber Line also uses copper wiring to send and receive data. However, unlike ISDN, DSL uses existing telephone lines and a modem. Also, unlike ISDN, DSL lines don’t need to dial a number, so they’re often referred to as “always-on” connections.

Considering the above, there are two main differences between ISDN and DSL. For one, DSL connections are far faster than ISDN lines. While, as mentioned, ISDN can transmit data at speeds of up to 2.94 Mbps, DSL’s data transmission speeds start at 128 Kbps and go up to 100 Mbps in the case of Asymmetric DSL or ADSL.

Another significant difference between ISDN and DSL is that DSL is more affordable. This is simply because it uses existing telephone lines that are already installed at a home or business. In contrast, ISDN lines need to be installed and, in addition, you’ll need to pay connection and service charges. This is even more so if you want an “always-on” connection similar to DSL connections, as ISDN is typically charged on a per-minute basis.

What’s the Best Alternative to ISDN?

We’ve now seen that DSL can be an alternative to ISDN. But there are some disadvantages to DSL, including that it’s still dependent on physical cables, which limits its flexibility. So, the question is: What is the best alternative to ISDN? And here the answer is most definitely VoIP or Voice over Internet Protocol.

One of the main advantages of VoIP over ISDN is that it foregoes the need for any physical lines and allows you to make calls and transmit data over the internet. In addition to this, VoIP offers several other benefits.


A significant benefit of VoIP compared to ISDN is the cost savings it brings about. This is because, as mentioned, it doesn’t require any physical phone lines and relies on a reliable internet connection to provide voice and data services. Because of this, there’s no need for any expert installation and there’s no equipment to buy or maintain.

Compared to traditional phone and ISDN lines which could cost, on average, $50 per line, VoIP results in savings of as much as 60% on communication costs.


The fact that VoIP doesn’t rely on any physical phone lines, brings about another benefit. Due to this, VoIP phone systems are easy to move, and you can use them from anywhere. As such, they don’t cause any challenges when you want to relocate offices or when your employees need to work from home or remotely.

This capability gives you the ultimate flexibility and allows you and your team to use the VoIP almost from anywhere.


Another major benefit of VoIP compared to ISDN is that it’s inherently scalable. As such, the system can grow as your business grows and keep meeting all your communication needs, no matter the size of your business.

Let’s consider a simple example. Let’s assume you have a team of 10 employees who all require a separate phone line. With an ISDN system, you’ll need to install a line for every employee and if you hire more employees, you’ll need to add more lines. In contrast, with VoIP, it’s as simple as going online and adding new lines.


With today’s VoIP system, you’ll get voice quality similar to or even better than ISDN systems, depending on your internet connection. In addition, with VoIP, your communication services will likely be more reliable with lower call failures. In fact, the only time when you’ll experience challenges with VoIP phone systems is when you have internet connection issues.


With VoIP phone systems, you have far more control over your business’s communication systems. For example, with VoIP systems, you can choose a number suitable to your business, set up auto attendants, and easily set up new numbers when you need them.

As a result, this helps you build your reputation and allows your customers to always get hold of your business when they need to.

Advanced Features

In addition to all the advantages mentioned above, VoIP also gives you access to more advanced features. These include features like call forwarding and waiting, voicemail, caller ID, and more.

CostsISDN relies on physical phone lines, installation, and connection and service charges, which makes it costly.VoIP relies solely on a reliable internet connection and doesn’t require physical installation or specialized equipment. As such, it’s more affordable than ISDN.
FlexibilityPhysical phone lines limit ISDN’s flexibility.Relying on the internet, VoIP can be used almost anywhere.
ScalabilityAs a business grows, the installation of additional ISDN lines would be required.VoIP makes it easy to set up new lines with just a few clicks.
QualityISDN offers good voice quality.VoIP offers voice quality similar to ISDN and far higher data transmission speeds.
ControlWith ISDN, businesses have little to no control over the service.VoIP offers more control and allows users to customize the offering to their specific needs.
FeaturesISDN offers only basic features.VoIP offers more advanced features.
Did you know that small businesses can save an average of 32 minutes per day when using VoIP? Click To Tweet

Frequently Asked Questions

We’ve now looked at ISDN in more detail and why VoIP is the best alternative to ISDN. Let’s now answer some frequently asked questions users often have in respect of ISDN.

Why is ISDN being switched off?

ISDN, as a technology, has become obsolete and can no longer compete with VoIP and cloud-based systems. As a result, it’s being switched off.

Is ISDN still available?

Although ISDN still works, as of 2020, it’s no longer possible to order any new ISDN lines. From 2023, there will be no new line installations and from 2025, ISDN will be switched off and no one will be able to use it anymore. As a result, it’s important for businesses to find viable alternatives now. As mentioned earlier, VoIP is the best alternative for ISDN systems.

What is an example of ISDN?

A perfect example of ISDN would be the traditional dial-up lines businesses used to make phone calls, video calls, and transmit data over the internet.

Is ISDN high-speed?

Although ISDN was regarded as a high-speed service at the peak of its adoption, it can no longer compete with VoIP and cloud-based systems when it comes to data transfer speeds.


Hopefully, this post helped illustrate what ISDN is, why you need to consider replacing ISDN systems, and why VoIP or cloud-based phone systems are the best alternatives.

If you need to learn more about VoIP and cloud-based phone systems and how they can help your business, get in touch with ULTATEL. Our fast and reliable cloud phone systems can unify the way you and your customers communicate.