5 minute read |

What is SD-WAN and How is it Linked to VoIP?

VoIP phone service background

VoIP phone systems have become a common sight in enterprises for a while now. Compared to the legacy PSTN, VoIP offers many advantages in terms of delivering phone services. VoIP vendors offer an incredible breadth of features for business users, easy service management, high-quality audio, and low prices for long-distance calls.

In spite of all these benefits, some businesses still hesitate to make the switch. Part of the issue is that many organizations are concerned about performance and reliability. Since VoIP routes voice packets over the Internet, calls have to compete with other traffic on the same circuit. A phone call between the customer and a manager will travel over the same network as email or other data. So how can you guarantee the performance of a VoIP system?

SD-WAN May be the Answer

If you’re familiar with software Defined networking or SDN, SD-WAN is a similar concept applied to enterprise Wide Area Networks. Software Defined networking is an architecture that is widely used by companies to manage internal data centers at a single location. SD-WAN, by contrast, is a technology that organizations can purchase to improve VoIP performance.

One of the biggest advantages of this technology is that it can manage multiple types of connections. A company might be using MPLS at one site, broadband connections at branch offices, and LTE for mobile devices. SD-WAN can manage all of them together, simplifying system management. Public perception is that the technology is useless for organizations with a single office or one type of Internet connection. However, it is still useful for optimizing VoIP quality even in those situations.

SD-WAN and VoIP Design

The magic of SD-WAN can change a VoIP call on a choppy connection into one with reasonable quality that allows conversation. The technology can do this because of a few reasons.


Prioritization is not a new concept for VoIP system designers. It’s part of most QoS methods and tags voice packets with a higher priority. SD-WAN extends the concept even further. One of the things you can configure on your SD-WAN device is to assign priorities to all the applications on your network. You can assign VoIP (along with other crucial apps) to a high priority group while other systems like email get lower priority. This is not new ground.

But what happens next certainly is. SD-WAN monitors network traffic in real time and makes changes to packet flows on the fly. In conjunction with QoS, this alone can boost audio quality. Voice calls no longer compete with other types of traffic, with the device changing things around as needed.

Forward Error correction

This technique is commonly used to reduce errors on noisy channels such as a congested data connection for VoIP calls. It’s also called channel coding. FEC reduces errors by adding redundancy, through the use of error correcting code to messages. What this means is that each voice data packet gets another shot at success.

What happens if the network is too slow for FEC to work? Don’t worry, SD-WAN can detect it and adapt. It may throttle other applications that have lower priority or stop forward error correction altogether to compensate. FEC can dramatically reduce packet errors and loss, the bane of most VoIP networks.

Jitter Buffering

If you are even slightly familiar with VoIP, you’ll know about jitter. It’s the bane of anyone working with VoIP system or designing networks. During a VoIP call, the voice packets travel by different routes even if the source and destination are the same. As a consequence, it means packets often arrive at different times, resulting in out of order packets at the destination.

Many QoS options use jitter buffering which is a technique to collect packets at a specific point in the network. The packets are put in order and then delivered together to ensure quality. SD-WAN, yet again, takes the concept to the next level. It monitors network quality and applies jitter buffering, only if needed.

There are a variety of different SD-WAN solutions on the market, ranging from those that focus on WAN layers to ones that replace WAN hardware completely. When you purchase an SD-WAN device, you’ll most likely get a bare-bones router. It’s up to you to configure it to suit your network design and needs. Unfortunately, most SD-WANs are not compatible with each other and changing the one you use in the future isn’t going to be cheap.

Quite a few organizations are switching to SD-WAN and cutting out the MPLS costs (regular broadband connections work fine with SD-WAN) entirely. However, switching may not be possible if you’re stuck with a multi-year contract with your provider. But if the ROI calculations give you a good number, then SD-WAN might be the way to go for VoIP.

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Start a free 30 day trial now, no credit card details are needed!