Explain All Types Of Leased Lines

Leased lines are widely recognised as offering superior speed, reliability, and resiliency compared to ADSL business connections in the UK. However, when discussing the benefits of these connections, it’s common to lump all types of leased lines together. It’s important to understand that a leased line is a dedicated internet connection for a business, but there are different types of leased lines available.

In the UK, leased lines are commonly recognised for their advantages over ADSL business connections, such as improved speed, dependability, and robustness. Despite this, when the benefits of these connections are discussed, all types of leased lines are often grouped. It’s important to differentiate the various types of leased lines available, as each one constitutes a dedicated internet connection for a business.

When talking about types of leased lines, reference is likely being made to site-to-site or site-to-network data connectivity.

Here we will describe types of leased lines so you can choose which is right for you.

MPLS Leased Lines

Leased lines of these types are becoming increasingly popular. Multi-Protocol Label Switching (MPLS) is a technology used to transfer data from one point to another by encapsulating the data, attaching one or more labels, and determining its destination based on these labels. The significance of this technology becomes clear when considering the potential congestion issues in a corporate WAN network. For example, consider a WAN network with 12 sites, 11 regional sites, each with 2Mbps connections, and a head office with a 10Mbps connection (including 4Mbps of Internet access). In theory, there could be 22Mbps of traffic from regional sites to the head office and an additional 4Mbps from the Internet to the head office, making a total of 26Mbps, which is significantly more than a 10Mbps connection at the head office could handle.

It’s unlikely that the links would be utilised to their fullest capacity. However, even at 50% utilisation, there would still be 13Mbps of data attempting to travel over a 10Mbps connection, resulting in 25% of the packets being discarded. The challenge lies in deciding which packets to discard and ensuring that time-sensitive applications, such as VoIP telephony, are not affected by network congestion. The network must be designed to prioritise which packets to keep and prevent degradation of service for important applications.

MPLS enables you to categorise different types of data on your WAN and prioritise time-sensitive data over data that can tolerate delays. It enables you to apply different “Classes of Service” to different types of traffic, ensuring that each type of traffic experiences appropriate levels of latency, jitter, and packet loss. In more technical terms, MPLS allows you to prioritise network traffic according to different levels of service.

MPLS is a service that is built on top of a leased line circuit. In other words, you can obtain an MPLS leased line that is based on cable leased lines, DSL leased lines or a combination of both.

DSL Leased Lines

DSL is utilised to provide other forms of low-speed leased lines. In contrast to most DSL connections which are shared and asymmetrical, leased lines are dedicated and symmetrical. However, it’s possible to use a symmetrical alternative to ADSL, known as SDSL, that provides a faster upload speed and establishes a symmetrical connection.

There’s also a newer version of ADSL called ADSL2+ Annex M, which provides a faster upload speed compared to regular ADSL. However, it is not symmetrical. By intentionally restricting the downstream connection, it’s possible to offer symmetrical connections of up to 3.5 Mbps or lower.

The speed of an ADSL or SDSL connection decreases as the distance from the telephone exchange increases, which may limit the desired speed that can be achieved through a DSL leased line. DSL leased lines are typically only utilised in instances where a fibre-leased line is not readily available.

ADSL2+ Annex M has a limited download speed compared to its capacity. Most DSL services share bandwidth with other customers’ traffic during transmission between the local exchange and the ISP network. It is a cost-saving business strategy aimed at reducing backhaul and IP transit costs. Dedicated DSL connections can also be obtained.

The performance of DSL decreases as the distance from the local telephone exchange increases. To address this issue, multiple DSL connections can be combined to increase the available maximum speeds.

Fibre Leased Lines

Fibre leased lines are a type of dedicated, symmetrical data connection that utilise fibre optic cables to transmit data. Although most leased lines use fibre for a significant portion of the route, some are entirely fibre-based. When choosing between fibre and DSL leased lines, fibre-based options offer the highest speeds and should be considered.


In conclusion, leased lines are dedicated internet connections for businesses that offer speed, reliability, and robustness over ADSL connections. When choosing a leased line, it’s important to understand the available types. MPLS leased lines are becoming increasingly popular for their ability to transfer data from one point to another and categorise different data types for prioritisation. On the other hand, DSL leased lines provide low-speed connections and can be combined to increase the available maximum speeds. Finally, fibre-leased lines are dedicated, symmetrical connections that use fibre optic cables for data transmission and offer the highest speeds of all leased lines.

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