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Leased Lines vs Dark Fibre: A Comprehensive Comparison

With the evolution of new technologies and the introduction of fibre, internet connectivity has significantly transformed. Now we can get better connectivity, increased bandwidth and faster upload and download speed with advanced internet connections such as leased line, ethernet first mile or fibre to the cabinet.

You may often hear the term ‘fibre’ providing high-quality internet connection at domestic and commercial levels. But it covers a wide range of products; only a few people know what it is.

In this article, we will describe two types of fibre internet: leased line and dark fibre. Stay with us till the end of this article to compare key areas of these connectivity solutions and find which one is best for your business.

What Is A Leased Line?

A leased line is a deducted, full-fibre internet connection with a fixed bandwidth and symmetrical speed. It can be a perfect solution for data-hungry businesses that need a high-quality and reliable internet connection to complete their day-to-day operations.

It is an uncontested connection, meaning it is solely dedicated to your business, and you do not need to share it with neighboring businesses.


Leased lines use fibre optic cable for data transmission, and even at peak usage hours speed of your connection does not slow down. With such a connection, you can complete your business operations efficiently.

What Is Dark Fibre?

Dark fibre is a reliable, high speed and flexible internet connection. It is a fibre optic cable installed but not transferring data because it is unlit. That is why it is named dark fibre.

Internet providers lay down unused fibre because the cost for providers is associated with physical installation. So, if they are already installing fibre optic cables for a customer, putting more than one cable makes sense. In the future, they do not need to install a cable; instead, they can simply ‘light’ the dark fibre to provide an internet connection to a new customer.

Dark fibre lets you get a private, dedicated, and 1:1 connection. It is a connection that does not use a shared infrastructure, and it is an uncontended service. Therefore, you will always receive a guaranteed speed for which you pay.

Now that you know what leased line and dark fibre are, let’s move to the next part and compare leased line and dark fibre.

Difference Between Leased Line And Dark Fibre

Many people think that leased lines and dark fibre are the same, but you must consider the differences between these two connectivity solutions.

Here we describe some factors that differentiate leased lines from dark fibre.

1. Speed

We already described above that leased lines and dark fibre comes with ultrafast speed. They also provide symmetrical speed, meaning the upload and download speeds you get will be the same.

It is highly beneficial for those who have to carry out larger backups. Furthermore, they both are uncontended services providing a fixed bandwidth you do not need to share with anyone.

Now you may wonder if both connections are the same, what makes them different.

Lets Explain It

Leased lines offer a speed of 10Mbps to 10Gbps, similar to dark fibre. What makes the leased lines different is that they have a bearer that provides your connection with a full data transfer capacity.

Most leased line providers offer two bearer options, 1 GB or 10 Gb, and you can choose one according to your business needs. If you choose a 1Gb bearer and need a speed of more than 1GB in the future, you have to upgrade your barrier, which will take some time.

On the other hand, dark fibre has unbeatable flexibility, and when it comes to the speed of dark fibre, the sky’s the limit. Its speed ranges from 300Mbps to 10Gbps. The biggest advantage of dark fibre is that it has virtually scalable bandwidth.

For example, if you have a conference at your workplace for two days, you can ask your Internet Service Provider (ISP) and temporarily upgrade your connection and reduce it again. With dark fibre, you do not need to pay any extra construction costs; you will only pay for what you use.

2. Service Level Agreement

Leased lines and dark fibre have a guaranteed Service Level Agreement (SLA). It means if there is any issue with your internet line, it will be fixed within the shortest possible time.

Each connection offers a 99.9% SLA, ensuring reliable performance throughout the year.

3. Availability

Leased lines are now available almost everywhere in the Uk. However, the installation of dedicated internet lines can be costly. Often it needs physical digging to install fibre optic cables that result in road closure and additional construction charges.

In contrast, dark fibre is not currently available to everyone because it depends on whether your service provider has a point of presence in your area. However, suppose it is available in your area.

In that case, its installation is less costly because fibre optic cable is already present, and your ISP only needs to light it up with an active connection.

4. Reliability

Whether you are running a school or need an internet connection for your business, reliability is an essential factor because outages can cause major problems.

Thankfully, both these connections are reliable and robust compared to other internet connections in the market, ensuring keeping downtime to a minimum.

If there is any unlikely event, it will be fixed in an impressive time. In the case of leased lines, it typically takes five hours to fix a problem, and dark fibre only takes four hours.

Final Words - Leased Line vs Dark Fibre

Leased lines and dark fibre are high-speed, reliable, and uncontended internet connections, providing symmetrical upload and download speeds. Leased lines are dedicated, full-fibre connections with fixed bandwidth and offer a choice of bearers, typically 1Gb or 10Gb. Dark fibre is an unused fibre optic cable installed and unlit, providing a virtually scalable bandwidth without construction costs. Leased lines are available almost everywhere in the UK but can be costly to install, while dark fibre availability depends on the point of presence in the area. Both connections have guaranteed Service Level Agreements and offer high reliability with minimal downtime. The choice between leased lines and dark fibre will depend on the specific needs and budget of the business.

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