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What is MPLS (Multiprotocol Label Switching)?

MPLS – short for Multiprotocol Label Switching – is a now-aging network routing system that transfers data between nodes using labels that denote predetermined pathways instead of network addresses that refer to the nodes themselves. This article explains how MPLS works, its types, and the core architecture. 

What is MPLS (Multiprotocol Label Switching)?

Multiprotocol label switching (MPLS) is a technique for speeding up network connections that was first developed in the 1990s. The public Internet functions by forwarding packets from one router to the next until the packets reach their destination. MLPS, on the other hand, sends packets along predetermined network paths. Ideally, the result is that routers spend less time deciding where to forward each packet, and packets take the same path every time.

Consider the process of planning a long drive. Instead of identifying which towns and cities one must drive through to reach the destination, it is usually more efficient to identify the roads that go in the correct direction. Similarly, MPLS identifies paths — network “roads” — rather than a series of intermediary destinations.

MPLS is considered to operate at OSI layer “2.5”, below the network layer (layer 3) and above the data link layer (layer 2).

multiprotocol label switching

How does MPLS work?

Multiprotocol Label Switching is not a product or a service, and this distinction is key to understanding how MPLS works. Rather, it is a technique that designates paths to send data between nodes instead of endpoints. As a packet first enters the network, it gets assigned to a forwarding equivalence class (FEC), which dictates how the data packet is forwarded. This is done by appending a bit sequence label to the packet.

In MPLS, the bit sequence label acts like an address on an envelope that tells the data packet where to go. Packets with the same characteristics are associated with the same label and thus get forwarded using the same rules. As the data packet is forwarded from one router to the next, each router contains a table that tells it how to handle those specific types of packets.

In this way, data skips along short path labels instead of long network addresses. This can be done regardless of the underlying network protocols because MPLS is not limited to only handling one specific protocol. It supports whichever access technology is used—T1/E1, frame relay, digital subscriber line (DSL), or asynchronous transfer mode (ATM).

Because each data packet has specific directions as to where it should go, MPLS can allow for lower latency and better quality of service for the end-user.

Traditional IP routing can be compared to the current international airline system. If you want to fly from Belize to Boston, you may have to take one flight from Belize to Houston, Texas, another one to Newark, New Jersey, and yet another flight to Boston. Due to all of the transfers, the total trip can easily take over 24 hours.

With Multiprotocol Label Switching — and SD-WAN — it is like you are put on a private jet that follows its own, more efficient path. Likely, the jet could go straight from Belize to Boston. If the plane had to stop in the States, it would choose a spot along the way, such as North Carolina, not Houston which is hundreds of miles off course.

When millions of packets of data travel all over the country, some are bound to suffer delays, resulting in latency and poor quality. When data comes with specific directions that send it along a more efficient path, the end-user gets better quality video and audio, as well as faster overall transmissions.

MPLS vs. SD-WAN

SD-WAN is a solution that enables end-to-end enterprise connectivity over large geographical distances. It provides the flexibility and economics of multiple WAN links such as Multiprotocol Label Switching, wireless, broadband, virtual private networks (VPNs), and the internet to give users in remote offices access to corporate applications, cloud services, and workloads, allowing them to work regardless of location. SD-WAN monitors the performance of WAN connections and manages traffic intelligently based on these measurements to maintain high speeds and optimize connectivity. SD-WANs offer organizations agility and cost savings compared to an MPLS infrastructure which is costly and not easy to make changes to. With centralized management that is often cloud-managed, it simplifies configuring and provisioning networks at scale and speed, greatly reducing operational complexity. The argument for SD-WAN vs. MPLS is never-ending, and organizations may end up choosing a hybrid of both to fit their needs.

 Pros and Cons of Multiprotocol Label Switching

The benefits of MPLS are scalability, performance, better bandwidth utilization, reduced network congestion, and a better end-user experience.

MPLS itself does not provide encryption, but it is a virtual private network and, as such, is partitioned off from the public internet. Therefore, MPLS is considered a secure transport mode. And it is not vulnerable to denial-of-service attacks, which might impact pure-IP-based networks.

On the negative side, an MPLS connection is much more expensive than a standard internet connection. In addition, MPLS was designed for organizations that have multiple remote branch offices that are geographically dispersed across the country or the world where the majority of traffic is backhauled to enterprise data centers. Today, businesses have re-directed much of their traffic so it’s going to and from cloud providers instead, making MPLS suboptimal.

multiprotocol label switching

How is MPLS used in organizations?

Service providers and organizations use MPLS to implement network connectivity with predictable QoS. They do this by defining LSPs (predetermined network paths) that meet the required levels of traffic delay, jitter, packet loss, and downtime.

For example, an MPLS network can have three service levels that prioritize different types of traffic: level 1 with the highest QoS for voice or video conferencing, level 2 for time-sensitive traffic, and level 3 for  “best effort” traffic.

Multiprotocol Label Switching also supports traffic isolation and the creation of virtual private networks (VPNs), virtual private LAN (VLAN) services, and virtual leased lines.

Conclusion

While MPLS remains foundational to network infrastructure, its usage is waning. According to a 2021 study by Telegeography, implementation of MPLS decreased by 24% between 2019 and 2020. During this time, the adoption of SD-WAN increased, speaking to the growing preference for more agile and flexible software-based technologies.

On the other hand, MPLS involves expensive but highly reliable infrastructure that promises excellent performance, especially for real-time data transfers. As a result, certain enterprises may want to hold onto their MPLS investments and have them co-exist with new technologies.

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