Multiprotocol Label Switching (MPLS), is not a service, but rather a data-carrying technique used to label packets that enter a network and assign them a specific MPLS header, which allows those same packets to be prioritized.
Since MPLS is a part of packet-switched network design, which is used to optimize the network capacity and minimize latency, it can be compared to Asynchronous Transfer Mode (ATM) or the Frame Relay, but also bring certain improvements for modern type networks.
The MPLS header contains one or more labels, called label stacks, with each label stack containing four specific fields; a 20-bit label value, a 3-bit Traffic Class field for QoS, a 1-bit bottom of stack flag, and an 8-bit TTL (time to live) field.
MPLS does not depend on a specific OSI layer service and is often described as a „layer 2.5 protocol“.
Unlike ATM or Frame Relay, which are OSI Layer 2 technologies, MPLS supports different type of traffic, including standard IP packets, native ATM, SONET, and Ethernet frames.
This also allowed it to effectively replace ATM or Frame Relay in modern networks and allowed it to get seamlessly integrated over any existing infrastructure. It is also can be used in both IPv4 and IPv6 environments and is most commonly usually used for Layer 2 and Layer 3 VPNs, offering not only highly efficient but also scalable and secure networks.
All of these features and advantages made MPLS a go-to technology for running real-time apps over the WAN, including voice, video conferencing or remote desktop usage.
The most common benefits of MPLS networks are an improved uptime, an ability to create scalable IP VPNs, hide network complexity, improve both bandwidth utilization by putting multiple types of traffic on the same link or separate settings for different types of traffic, and most importantly, reduce network congestion by reducing latency and picking the best possible paths for a specific traffic.
MPLS and its future
While MPLS is a well-proven technique, and although usually described as expensive, it still offers low latency, jitter and packet loss. This is why it has been a choice for most enterprise WANs.
A recent introduction of software-defined WAN, also known as SD-WAN, which promises reliability of an MPLS network design with an ability to dynamically share and aggregate multiple ISP Internet and WAN connections at a single site as well as bring better performance for small, remote or international sites, has somewhat shaken the MPLS, but it is still far from replacing it.
Plenty of big enterprises are still committed to an MPLS network design even if they are deploying SD-WAN and using both in a so-called „Hybrid WAN“ network design.