When it Comes to User Experience, Not All SD-WAN QoS Is the Same

Ricardo Belmar
Jul. 8 2019

Most software-defined wide-area network (SD-WAN) solutions offer quality-of-service (QoS) features to improve application performance. In many cases though, those features don’t actually translate to better user experiences. Or, they improve things for some users, in some locations, but not others. What’s going on?

Core capabilities that impact user experience:

  • End-to-end QoS
  • Dynamic QoS queue
  • Per-session traffic handling

Vendors aren’t lying about SD-WAN QoS, but they’re not telling the whole story either. If you want to ensure a great experience for every user, every time, you’ll need to look deeper.

What does SD-WAN QoS mean anyway?

When it comes to application performance, consistency is key. Your WAN should deliver the same experience for every user, all day, across every site on your network, all the time. But if you’re using Internet links to carry more WAN traffic (a big reason to deploy SD-WAN), consistency can be a big problem.

When WANs use only MPLS circuits, you can use built-in class of service-based QoS traffic prioritization to boost app performance (for example, sending traffic from critical business apps over a high-priority queue, while treating Web traffic as low-priority). But Internet links don’t support QoS, so you’ll need your SD-WAN to provide that intelligence. And some solutions are smarter than others.

For example, some advertise “QoS” but really just offer forward error correction (FEC). FEC works by re-sending packets multiple times to make sure none get missed. This can improve performance—if your problems are caused by unreliable links dropping packets because of high bit error rates. In some parts of the developing world, that’s a big deal. But in most modern markets, it’s not really an issue. And FEC can actually cause new problems, because you’re now transmitting up to 3x the traffic, using up lots of capacity to do it. It’s essentially a 20th century technique trying to solve a 21st century performance problem.

Building Better SD-WAN QoS

If you’re banking on your SD-WAN to improve application user experiences, look for solutions that feature these three core capabilities:

  • End-to-end QoS: Your SD-WAN overlay should apply QoS prioritization consistently across all links at all sites on all network links. If it doesn’t, it can still move users experiencing poor performance from one link to another. But you’ll have no way to guarantee the new link actually delivers a better experience.

  • Dynamic QoS queues: Your SD-WAN should be able to adjust the size of prioritization queues in response to changing network traffic. For example, if you suddenly have twice as many users than normal using a high-priority app at a given site, the SD-WAN should dynamically add capacity to that queue to keep the experience consistent for all users.

  • Per-session traffic handling: Many SD-WAN QoS solutions can only classify traffic on a per-application basis. If you want to ensure good performance for every actual user, you need QoS intelligence applied to each and every session.

Plenty of SD-WAN solutions offer some of these capabilities. But for consistently great app experiences, you need all three. For example, say your SD-WAN features end-to-end QoS and adjustable queues, but only applies them at the application-level. You can easily end up with a scenario where some users at a site get a great experience with a business-critical app, while others don’t. Without per-session QoS, there’s no way to know.  

Or, say your SD-WAN applies end-to-end QoS at the session-level but uses only fixed queues. Now, you have more control over each user’s experience, but you’re not using your capacity very efficiently. Businesses using adjustable QoS queues can achieve a 95% utilization rate of network links. Those without typically never do better than 80%.

Learn More

Want to know more about the factors that matter most in improving application experiences over SD-WAN? Download the eBook, Top SD-WAN Myths – BUSTED!

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