QoS & SD-WAN: Why You Should Care

SD-WAN solutions are nothing if not feature-rich. There may be so many features that you can’t keep them all straight – but all features are not equally important to your business environment. Quality-of-Service or QoS is arguably one of the most important. (You may also know it as Quality-of-Experience or QoE – same thing, different name.)

It is QoS that, ultimately, is responsible for making your WAN users happy. QoS is in charge of dividing up available bandwidth and making sure that applications that are important to your business get the quality treatment that they deserve.

It is QoS that moves traffic – transparently one hopes – to backup links in the event of main link failure.

It is QoS that – in some solutions at least – is smart enough to migrate traffic even in “brown out” conditions. That is, when the link is still “up” but not performing up to your application’s needs.

It is QoS that should be smart enough to know which of your multiple links makes the most economic sense to be using. For example, an LTE link might be great to have as a backup link but too expensive to use for traffic on a regular basis.

And, since QoS is, by nature, a proprietary function of these various SD-WAN systems, the only way for you to really know how it will work in your environment is to benchmark it.

Those are just a few reasons why you should care – why you should REALLY care!

The Tolly Group SD-WAN Benchmarking Best Practices for QoS report will help you in your efforts.

QoS is Standard – Why Should I Test It?

If you believe that QoS is “standard” – you should read on – because although you are technically “right,” you are fundamentally wrong.

So, let’s start with what IS “standard” about QoS and that is “tagging.” By tagging, we mean bits that are set in a frame or packet header that indicates what level of priority that a session is requesting. It is only a request – something like writing “urgent” on a package. It is only an indicator of the processing that you want, not what you will get.

At Layer 2, the IEEE 802.1p standard defines priority bits – usually referred to as “p-bits.”  At Layer 3, the less-simply-named “differentiated services code points” or DSCP do the same thing.

But, that is where the standards end. There is no standard for implementing the queues and other traffic management logic that make up the core of any QoS solution. All QoS solutions are the same in that they all will use some form of queuing but differ in how many queues are used (often up to eight) and how they are managed.

The only way that you can determine how an SD-WAN solution will handle YOUR traffic is to benchmark it – to test it.

Unfortunately, there are no test tools that will magically do this testing for you.  You will need to understand the nature of your traffic and craft a microcosm of that traffic to run through the SD-WAN to determine just how the QoS mechanism will handle your traffic.

The Tolly Group SD-WAN Benchmarking Best Practices for QoS report will help you in your efforts.