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What is SD-WAN (Software-Defined Wide Area Network) Technology?


In an increasingly interconnected world, organizations are looking to deliver mission-critical IT with the best application experience to all their locations. Software-defined wide area networks, or SD-WAN for short, have gained popularity as a result. IT teams are adopting these solutions for their flexibility and cost-effectiveness compared to legacy networking infrastructure solutions.

But what is SD-WAN? How does SD-WAN work, and what advantages does it have over other network solutions? This blog dives into the meaning behind SD-WAN technology and will help answer these questions.

SD-WAN Meaning Explained

SD-WAN is an automated overlay technology that uses encrypted, application-aware dynamic tunnels to provide the best user and application experience from the network infrastructure that it runs over.

SD-WAN technology enables companies to augment or replace traditional WAN traffic services such as multiprotocol label switching (MPLS). It does so by leveraging cheaper Internet access services to extend WAN connectivity with Quality of Service (QoS) cost-effectively to small sites. SD-WAN also effectively allows companies to decouple the user and application experience from the last mile network connectivity technology and provider. This gives the appearance of a cohesive network experience regardless of underlying technologies in use.

What is SD-WAN Software Defined Wide Area Network

Why Use SD-WAN?

In the past, organizations had to build their own private network or rely on traditional carrier WAN services. These solutions were not always agile enough to adapt to changing needs such as hybrid cloud adoption or mission-critical applications at small locations. These customer networks are harder to manage at scale, slower to deploy, and have limited QoS granularity. Legacy solutions also provide less visibility and bespoke handling of traffic at an application level.

But it’s not just the pitfalls of traditional WAN models that have driven the adoption of SD-WAN. Frustrations with the telecommunications buying process have also driven increased SD-WAN adoption. Customers wanted to separate the purchase of connectivity, deployment of networks, and the management of networks from one vendor. SD-WAN makes this possible, breaking them free from the telecoms buying process and providing extended flexibility.

How Does SD-WAN Work?

In essence, SD-WAN technology separates the control plane from the data plane.

The SD-WAN controller, where the control plane sits, acts as the centralized brain of the solution. The controller is typically hosted on the cloud. It provides the instructions and rules edge devices need to forward packets effectively.

The controller also gathers real-time feedback from the SD-WAN appliances about traffic coming from the connected LANs and connected circuit performance. This enables the controller to direct traffic in real time to shape applications for better performance outcomes.

The data plane exists within the SD-WAN edge appliances, which sit at each customer site. These appliances are connected to customer LANs and network access circuits. Whereas the control plane can be thought of as the brain, the data plane carries out the actions given to them by the controller.

This architecture allows for faster, more informed, and effective data transmission, leading to a better and more consistent overall end-user experience.


Although often seen as alternatives for one another, SD-WAN and MPLS are not mutually exclusive. However, there are some important differences between the two.

First and perhaps most importantly, carrier MPLS WAN solutions are run over a pre-installed shared services private network architecture. SD-WAN, on the other hand, is a virtual, software-based solution that is fairly agnostic of the underlying transport architecture. This is why it is often associated with running over the Internet, the cheapest transmission medium.

This is an important distinction because, with a traditional carrier MPLS WAN, you are restricted by the access technologies that can be used. Whereas with SD-WAN you can mix and match IP access solutions from multiple vendors, including MPLS, with the SD-WAN technology blending them into one manageable network.

Secondly, an MPLS solution is often more expensive than SD-WAN because it is designed for high-performance, high-availability networking. It’s a good solution for medium to large important sites and data centers. As a virtualized infrastructure solution, SD-WAN can allow each site to have its own access solution.

For example, SD-WAN can allow for a custom amount of resilience and bandwidth, leading to a more tailored, cost-effective solution. It also means that SD-WAN can include sites with just mobile broadband access if required. For example, scaling down to pop-up sites or remote non-staffed locations.

As mentioned above, SD-WAN enables multiple transport options – including MPLS. MPLS is considered the best transport network solution because it can guarantee bandwidth and quality for a given amount of traffic. SD-WAN, on the other hand, can shape traffic and choose the best performing circuit to meet the quality of service parameters. However, it can’t make the Internet go faster.

That’s where MPLS comes in. A high-performing, high-speed MPLS link to critical locations can help ensure traffic takes short, reliable hops from source to destination through an understood number of peering points.

SD-WAN Benefits Explained

Now that you understand how SD-WAN works and why you should use it, here are some additional benefits of an SD-WAN solution:

  • Cost-effective network. SD-WAN provides organizations the flexibility to use a multitude of transport options for resilience, scaling bandwidth as needed on a site-by-site basis.
  • Every site can be connected.  Organizations can use any carrier to cost-effectively connect every site they want on the network.
  • Increased site uptime. If there is more than one access circuit at a given site, SD-WAN automatically prioritizes and re-routes applications to use the remaining bandwidth if network issues are detected.
  • WAN Optimization. Application performance is enhanced across the network using application aware routing and targeted forward error correction negates traditional experience degradation caused by packet loss.
  • Network security over public Internet. Because SD-WAN utilizes encrypted tunnels, it enables safe use of public Internet transport which is often the cheapest access technology.
  • Short lead times for new site additions. New sites can be added to the network quickly and simply as a pre-configured SD-WAN appliance can make use of any Internet connection to bring the site online.
  • Increased Quality of Experience for end users.  Applications can be assigned their own performance requirements and automated use of forwarding error correction, route selection, and traffic prioritization results in the best quality of experience for targeted applications.
  • Centralized control and visibility. The centralized control plane allows for end-to-end performance management and visibility via a customer portal.

SD-WAN by Zayo

At Zayo, we love SD-WAN technology but recognize that today’s customers need more.

We enable our customers to scale digital transformation, enhance business productivity, accelerate change, and achieve growth by leveraging cloud services and AI.

But to do that, they need managed services from the edge through to the Cloud. Inevitably this requires complex multi-vendor equipment and services to deploy effectively and manage efficiently, especially to get the insight required to drive your business forward.

Zayo solves for this complexity using AI and automation, enabling simple consumption with deep insight analytics while we do end-to-end design and management.

As part of our SD-WAN proposition we offer:

  • Multi-vendor support. Zayo supports multiple SD-WAN vendors and will help select and deploy the right one for you.
  • Management beyond SD-WAN appliances. We go beyond the SD-WAN appliances and manage and deploy all aspects of your edge solution. This includes switches, WLANs, and cellular modems.
  • SASE services. Our networking solution is augmented with SASE services including cloud-based firewalls and zero trust network access-based secure remote worker solutions.
  • Edge-to-cloud management. We manage your network from edge to cloud, leveraging our low latency access to over 375 cloud on-ramps. This is combined with our tier-1 backbone, fiber access, and connectivity partners for a complete solution. We are also happy to co-manage the solution with our customers.
  • White glove implementation. Our experts work with you to ensure your edge equipment and SD-WAN are configured to their full potential.
  • Automated deployment.  Our automation and warehousing process enables us to truly enable zero-touch provisioning, deploying sites quickly and at scale, without human configuration errors.
  • AIOps. We use AIOps to enable fast, automated root cause analysis and proactive fixes for maximum availability, as well as to provide meaningful insight into network performance.
  • Multi-vendor customer portal, giving you a full end-to-end view of network performance and ticket visibility across all the hardware we managed for you. Plus, it can be integrated into your existing ITSM. This provides an even greater two-way exchange of inventory, network status, and ticket information
  • 24/7/365 monitoring and support. Our network operations center monitors all solution components and works with partners to resolve any faults.
  • A wide range of deployment experience. Our team of SD-WAN experts has deployed over 45,000 sites in 55 countries. We are proud to have a rolling six-month average NPS score of above 60. We are truly the market leader in SD-WAN design, deployment, and management.