MPLS Leased Line Primer – A Short Guide

An MPLS Leased line is a leased line that uses a technology called Multi-Protocol Label Switching.

MPLS enables traffic to be split into multiple classes of service, which can then be treated differently as they travel across the WAN, so that time-sensitive traffic, such as VoIP phone calls, can be prioritised over less time-sensitive traffic such as general web traffic.

For key sites, you can get multiple MPLS leased lines and configure the network to use MPLS Fast ReRoute. If one of your leased lines goes down, your data can be rerouted over an alternative path, automatically, in a fraction of the time it takes to blink an eye.

As higher-bandwidth leased lines have become cheaper, businesses have moved towards 'converged solutions', where Internet access, phone calls and corporate VPN traffic share a common connection. While this is very cost-effective, it's important to remember that there's more to a good connection than high bandwidth. Delay (latency), variations in delay (jitter) and data loss (packet loss) also matter. And they impact some types of traffic more than others. MPLS enables you to ensure that traffic is treated appropriately, so as to minimise the effects of latency, jitter and packet loss on the user experience.

In the perfect world, all traffic would suffer little delay, almost no jitter, and no packets would be lost. In reality, that's not always practical. Sometimes a branch offices can't get plentiful bandwidth, because its in a poorly connected location. Or to be more precise,  the branch office can't get plentiful bandwidth at sensible prices.

Sometimes the demands on your network will suddenly peak, for example, as staff work from home using their VPN software when there are transport strikes or heavy snow. You can't always afford to buy network capacity based on rare incidents of peak usage.

MPLS enables you to buy more conservatively and prioritise traffic to reduce the impact of occasional congestion on your user-experience. MPLS leased lines can be configured to ensure that important traffic does not suffer unnecessarily. In the event of network congestion, time-sensitive traffic should take priority over delay-tolerant traffic, and important traffic can be prioritised over less important traffic.

MPLS can ensure time-sensitive traffic ALWAYS gets treated appropriately. So too can traditional approaches. However, those traditional approaches are often wasteful. For example, an organisation might ring-fence 2Mbit/s of connectivity just for VoIP phone calls. This delivers quality-of-service, but has the disadvantage of wasting bandwidth  when there are few concurrent calls. MPLS frees this bandwidth, so that the voice calls have priority and can use it when needed, but other traffic is able to use it when few calls are being made.  By making greater use of the existing bandwidth, MPLS may be able to improve your user-experience without requiring you to buy higher-bandwidth connections than you already have.

Companies are making greater use of VoIP, to take advantage of the cost-savings that can come from ditching expensive ISDN30 circuits in favour of SIP Trunks.  The cost savings have fuelled a demand for low-latency low-jitter low-packet-loss connections, such as those provided by MPLS leased line.