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Leased line vs dark fibre

The advancement of technology and the introduction of fibre has resulted in the rapid evolution of internet connectivity, the amount of available bandwidth and the download and upload speeds we receive.

We often hear the term ‘fibre’ bandied about, but it covers such a broad range of products that very few people actually know what it actually is, let alone what leased lines and dark fibre are. 

In this article we will look specifically at these two types of connectivity, compare them in key areas and finally state which one we would recommend you choose and why.

leased line vs dark fibre

What is a leased line?

A leased line is a full fibre connection straight into your premises. Leased lines are uncontended which means the connection is only used by you and cannot be accessed by others, so you will receive the full capacity of your connection at all times.

What is dark fibre?

Dark fibre is an ultrafast, reliable and flexible internet connection. It is a cable that is already installed but currently unused or unlit – hence the name ‘dark fibre’. 

Dark fibre allows you to build a dedicated, private, 1:1 connection with your ISP. Dark fibre doesn’t utilise shared infrastructure and isn’t a contended service therefore you will always receive the guaranteed speeds you pay for right from day one.

Leased line vs dark fibre:

Speeds you will receive

We already know that leased lines and dark fibre both provide ultrafast connectivity. They’re also synchronous services so the upload and download speeds you receive will be the same – great news for those carrying out large backups. Even better, they are both uncontended services and provide you with the option to increase the available bandwidth. Which must leave you wondering what the difference actually is between them. Let us explain.

Leased line speeds range from 10Mbps up to 10Gbps, which coincidentally is very similar to dark fibre. Where leased lines differ is they have a bearer which provides a maximum capacity of data transfer for the line. There are usually two bearer options to choose from – 1Gb or 10Gb. If you choose the former and in the future require speeds above 1Gb then the bearer will need to be upgraded and therefore cannot be scaled quickly. You can check your current speed here.

In contrast, dark fibre has unrivalled flexibility and when it comes to speeds the sky is literally the limit (well almost). Speeds range from 300Mbps up to 10Gbps – which is more than most would currently need – but faster options are available if you require. The biggest benefit of dark fibre is that bandwidth is scalable virtually instantaneously. This means if you work at a venue and have a large conference taking place for two days, you can speak to your ISP and temporarily upgrade your connection for those two days and reduce it again after with no additional construction work required, ensuring you will only ever pay for what you use.

Service Level Agreements

Both leased lines and dark fibre have strict SLAs attached. Each connection comes complete with a full 99.9% SLA, ensuring completely reliable performance throughout the year.


Whether you’re part of a business or school, the reliability of your internet connection is absolutely vital, with outages posing major problems. Thankfully both these connections are the most robust on the market, ensuring that downtime is kept to an absolute minimum. 

In the unlikely event there is an issue the fix times are impressive, with leased lines around five hours, but dark fibre just comes out on top with four hours.


Leased lines are available everywhere however installation can be costly. Often the fibre cabling will need to be installed which requires a physical dig and can result in road closures and excess construction charges. 

Dark fibre isn’t currently available to everyone as it is reliant on your ISP having a point of presence (PoP) in the area. However, if it is available then installation is less costly because the fibre is already in place and just requires your ISP to light it up with an active connection.

Which should I get?

When you look at leased line vs dark fibre, how do you decide? Whilst leased lines can be more expensive to install, dark fibre isn’t available everywhere which you will need to bear in mind. 

Dark fibre’s ability to increase and reduce bandwidth quickly and easily is certainly an attractive proposition. For leased lines a distinct advantage is the potential to install anywhere – even in the most remote areas.

If we were to nail our colours to the mast, personally our connection of choice, if it’s available to you, would be dark fibre. This technology is completely future-proofed and unparalleled in terms of capability. 

Regardless of which you choose, leased lines and dark fibre are both resilient and reliable services that will provide you with ultrafast speeds and minimal downtime.

Here at Exa we have our own dark fibre product called DarkLight which is available in towns and cities including Bradford; Leeds, Sheffield, Wakefield, Doncaster, Halifax and Northampton. We genuinely believe DarkLight is the last internet connection you’ll ever need to install for your premises. It’s really that simple. To find out more about how DarkLight can transform your organisation contact us.

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Is DarkLight connectivity best suited to you?

Dark fibre is perfect if you are looking for a potentially limitless, ultrafast connection with complete flexibility and control.

If you fully rely on the internet, a dark fibre connection could be the best option for you.

Is Leased Line connectivity best suited to you?

Leased Lines are best suited to you if you have high bandwidth requirements and need a reliable, uncontended service.

It is ideal for you if you regularly carry out large uploads and downloads, use cloud based services and a VoIP telephone system as well as video conferencing, for everyday communication.

Is GPON connectivity best suited to you?

GPON is a great choice for you if you need gigabit speeds but don’t need them to be symmetrical. It is becoming more widely available across the UK but may not be immediately available to you yet.

Is Rural Fibre connectivity best suited to you?

If you want to make the move to full fibre, but are based in a rural area, this option is for you.

Is FTTP connectivity best suited to you?

If you have a number of users who use cloud-based applications to upload and download data on a daily basis, but don’t transfer large amounts of data, FTTP might be your best option.

Is Gfast connectivity best suited to you?

If your line cannot support a minimum of 100Mbps, this connection is not for you. Gfast must meet the speed as a minimum. 

If your line meets this need, and you’re looking for an ultrafast, consistent and reliable connection without the hassle and upheaval of construction work – this could be a good fit.

It’s worth noting that Gfast is a stop gap to FTTP, and is not a technology that is likely to be around for a long time.

Is FTTC connectivity best suited to you?

If you need more bandwidth but don’t really need a guaranteed speed, FTTC could be for you. It is widely available throughout the UK, making it suitable as a main connection. As this connection provides higher speeds than ADSL, it is also a good option for a back up to a leased line.

As with ADSL, once the PSTN is turned off in 2025/26, FTTC will become virtually obsolete and at the very least you will require FTTP to remain connected.



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Is DSL connectivity best suited to you?

DSL connections offer very limited bandwidth so it might be right for you if you typically use the internet for less data-intensive tasks. If you’re sending emails, browsing the web, downloading very small files and working with small amounts of data – you should be fine with DSL.

It is worth noting connections based on copper wire, like DSL, will be switched off in the UK by Openreach, with a phased approach due to begin at the end of 2025. If you don’t have a fibre connection at the moment, you’ll need to upgrade this as well as move to a VoIP telephone system.

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