As more businesses shift to cloud-based communications and remote workforces become the norm, ensuring consistent performance across dispersed sites has become a top priority for telecom and UC providers. For installers and resellers tasked with deploying reliable real-time communications services like VoIP and UC, the choice of underlying network transport can make or break performance.
Multiprotocol Label Switching (MPLS) is not new, but it continues to play a critical role in meeting the low latency, high reliability, and QoS demands of these modern deployments. In this article, we examine the performance of MPLS in supporting real-time communications and why it remains a go-to solution for interconnecting geographically distributed infrastructure.
Reliance on cloud infrastructure
Many UC and VoIP services today rely on the cloud as a fundamental part of their deployment. Mobile apps, softphone applications, and even physical desktop VoIP phones are often deployed with a cloud-based infrastructure at their core. A low-latency, scalable, and high-quality networking solution is required to ensure the resilience of such real-time cloud services.
Choosing MPLS as the preferred technology for interconnecting remote sites and communicating with cloud infrastructure is an excellent way to deliver high-quality, real-time applications across any environment.
How MPLS works
MPLS technology enables efficient packet forwarding across large, shared network infrastructures. Unlike traditional IP routing, which relies on routing table lookups at each hop, MPLS uses short path identifiers called labels to make forwarding decisions. These labels are inserted between the Layer 2 (Data Link) and Layer 3 (Network) headers, allowing MPLS routers, referred to as label switch routers (LSRs), to forward packets based on pre-established paths rather than on destination IP addresses alone.
As you can see in the diagram, any data that enters the MPLS network will have an MPLS header added between the IP header (layer 3) and the frame header (layer 2). For this reason, MPLS is often referred to as a "layer 2.5” protocol. This MPLS header contains, among other things, the label that corresponds to the specific path the packet is assigned through the MPLS core network. Each label switch router that the packet encounters along its journey uses this label to perform a label lookup and determine the next hop in the path.
The “multiprotocol” part of its name indicates that MPLS can encapsulate multiple data types. MPLS is designed to be protocol-agnostic, meaning that it can encapsulate a wide variety of protocols, including IPv4, IPv6, Ethernet, ATM, Frame Relay, PPP, TDM, and others.
The nature of MPLS
It's important to note that MPLS is not a protocol in and of itself but more of a technique. It leverages a whole series of other protocols that can be deployed in various combinations to deliver multiple implementation scenarios. Some of the “companion” protocols that are typically used with MPLS include the Label Distribution Protocol (LDP), Multiprotocol Border Gateway Protocol (MP-BGP), Virtual Routing and Forwarding (VRF), underlying routing protocols such as OSPF and IS-IS, and the Resource Reservation Protocol (RSVP).
Although MPLS can be used to connect an organization’s premises to the internet, its true strength lies in its ability to interconnect multiple remote sites. It excels in this role, serving as an effective WAN technology that links geographically dispersed locations. Its ability to finely control and prioritize traffic further enhances its value, particularly for real-time services, as we will see later in this article.
Key benefits of MPLS
MPLS's primary benefit is efficiency, especially for vast networks. At scale, IP routing can become highly resource-intensive: large ISP networks with hundreds or even thousands of routers and thousands or tens of thousands of customers eventually accumulate huge routing tables within each core network router. A routing-table lookup must occur every time a packet arrives at a router, and each lookup may go through several thousand routing entries to find the next hop. With trillions of packets traversing such networks, you can imagine how quickly this consumes resources!
Label switching is a much more efficient method for determining the path a packet must take at these scales and packet volumes. MPLS forwarding tables, which are MPLS’s routing table counterparts, can be looked up in a fraction of the time and with far fewer resources than conventional IP routing table lookups.
And there are more benefits than just efficiency. These include:
- Predictable performance: Ensures consistent latency and throughput.
- Predefined paths: Uses fixed label-switched paths (LSPs) for better traffic control.
- Advanced quality of service: Highly configurable prioritization of mission-critical traffic.
- Traffic engineering: Advanced policy-based optimization of traffic flows.
- VPN capabilities: Separates and secures customer or department traffic.
- Extreme scalability: Handles a vast number of routes and VPNs efficiently.
- Resiliency: Rapid traffic rerouting capabilities during failures.
- Security: Limits exposure and keeps traffic isolated.
How MPLS affects real-time services like VoIP and UC
Latency, jitter, and packet loss are the primary challenges associated with real-time services such as VoIP and UC, all of which can be considered “killers” for such time-sensitive services. These services require consistent traffic flow rates, robust QoS policies, and low delays under normal operating conditions and in the event of network failures or rerouting.
MPLS addresses all these issues in the following ways:
- Traffic engineering: Among the most critical features of MPLS, traffic engineering can be employed to optimize the network for latency-sensitive flows
- QoS enforcement: Voice, video, and collaboration traffic can be prioritized appropriately.
- Separation of services: Real-time apps can ride over dedicated paths.
- Reliability: Rerouting around faults can be done in under 50 ms with minimal interruption.
- Integrated voice, video, and messaging: Support can be provided across the enterprise WAN.
- Enhanced user experience: Fewer dropped calls/glitches.
- Unified communications as a service (UCaaS) deployment: Enables seamless management with predictable performance.
ISPs that deploy MPLS will typically work closely with the enterprises they support to deliver the required network capabilities for the networks and applications they serve.
Conclusion
Even though it's been around for more than two decades, MPLS remains a highly relevant technology capable of supporting today's real-time, performance-sensitive applications. It is a key component in multi-site enterprise networks and in interconnecting the enterprise with cloud infrastructure. With its robust and granular traffic engineering capabilities, advanced QoS, and resilient backup controls, MPLS is perfect for services where quality, reliability, and low latency are non-negotiable. Understanding MPLS is essential for anyone building or maintaining networks supporting critical business communications.
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