Ah, good old Quality of Service. How often have we spent our time as networking professionals trying to discern the archaic texts of Szigeti to learn how to make you work? QoS is something that seemed so necessary to our networks years ago that we would spend hours upon hours trying to learn the best way to implement it for voice or bulk data traffic or some other reason. That was, until a funny thing happened. Until QoS was useless to us.

Rest In Peace and Queues

QoS didn’t die overnight. It didn’t wake up one morning without a home to go to. Instead, we slowly devalued and destroyed it over a period of years. We did it be focusing on the things that QoS was made for and then marginalizing them. Remember voice traffic?

We spent years installing voice over IP (VoIP) systems in our networks. And each of those systems needed QoS to function. We took our expertise in the arcane arts of queuing and applied it to the most finicky protocols we could find. And it worked. Our mystic knowledge made voice better! Our calls wouldn’t drop. Our packets arrived when they should. And the world was a happy place.

That is, until voice became pointless. When people started using mobile devices more and more instead of their desk phones, QoS wasn’t as important. When the steady generation of delay-sensitive packets instead moved back to LTE instead of IP it wasn’t as critical to ensure that FTP and other protocols in the LAN interfered with it. Even when people started using QoS on their mobile devices the marking was totally inconsistent. George Stefanick (@WirelesssGuru) found that Wi-Fi calling was doing some weird packet marking anyway:

So, without a huge packet generation issue, QoS was relegated to some weird traffic shaping roles. Maybe it was video prioritization in places where people cared about video? Or perhaps it was creating a scavenger class for traffic in order to get rid of unwanted applications like BitTorrent. But overall QoS languished as an oddity as more and more enterprises saw their collaboration traffic moving to be dominated by mobile devices that didn’t need the old dark magic of QoS.

QoupS de Gras

The real end of QoS came about thanks to the cloud. While we spent all of our time trying to find ways to optimize applications running on our local enterprise networks, developers were busy optimizing applications to run somewhere else. The ideas were sound enough in principle. By moving applications to the cloud we could continually improve them and push features faster. By having all the bit off the local network we could scale massively. We could even collaborate together in real time from anywhere in the world!

But applications that live in the cloud live outside our control. QoS was always bounded by the borders of our own networks. Once a packet was launched into the great beyond of the Internet we couldn’t control what happened to it. ISPs weren’t bound to honor our packet markings without an SLA. In fact, in most cases the ISP would remark all our packets anyway just to ensure they didn’t mess with the ISP’s ideas of traffic shaping. And even those were rudimentary at best given how well QoS plays with MPLS in the real world.

But cloud-based applications don’t worry about quality of service. They scale as large as you want. And nothing short of a massive cloud outage will make them unavailable. Sure, there may be some slowness here and there but that’s nothing less than you’d expect to receive running a heavy application over your local LAN. The real genius of the cloud shift is that it forced developers to slim down applications and make them more responsive in places where they could be made to be more interactive. Now, applications felt snappier when they ran in remote locations. And if you’ve every tried to use old versions of Outlook across slow links you now how critical that responsiveness can be.

The End is The Beginning

So, with cloud-based applications here to stay and collaboration all about mobile apps now, we can finally carve the tombstone for QoS right? Well, not quite.

As it turns out, we are still using lots and lots of QoS today in SD-WAN networks. We’re just not calling it that. Instead, we’ve upgraded the term to something more snappy, like “Application Visibility”. Under the hood, it’s not much different than the QoS that we’ve done for years. We’re still picking out the applications and figuring out how to optimize their traffic patterns to make them more responsive.

The key with the new wave of SD-WAN is that we’re marrying QoS to conditional routing. Now, instead of being at the mercy of the ISP link to the Internet we can do something else. We can push bulk traffic across slow cheap links and ensure that our critical business applications have all the space they want on the fast expensive ones instead. We can push our out-of-band traffic out of an attached 4G/LTE modem. We can even push our traffic across the Internet to a gateway closer to the SaaS provider with better performance. That last bit is an especially delicious piece of irony, since it basically serves the same purpose as Tail-end Hop Off did back in the voice days.

And how does all this magical new QoS work on the Internet outside our control? That’s the real magic. It’s all tunnels! Yes, in order to make sure that we get our traffic where it needs to be in SD-WAN we simply prioritize it going out of the router and wrap it all in a tunnel to the next device. Everything moves along the Internet and the hop-by-hop treatment really doesn’t care in the long run. We’re instead optimizing transit through our network based on other factors besides DSCP markings. Sure, when the traffic arrives on the other side it can be optimized based on those values. However, in the real world the only thing that most users really care about is how fast they can get their application to perform on their local machine. And if SD-WAN can point them to the fastest SaaS gateway, they’ll be happy people.

Tom’s Take

QoS suffered the same fate as Ska music and NCIS. It never really went away even when people stopped caring about it as much as they did when it was the hot new thing on the block. Instead, the need for QoS disappeared when our traffic usage moved away from the usage it was designed to augment. Sure, SD-WAN has brought it back in a new form, QoS 2.0 if you will, but the need for what we used to spend hours of time doing with ancient tomes on knowledge is long gone. We should have a quiet service for QoS and acknowledge all that it has done for us. And then get ready to invite it back to the party in the form that it will take in the cloud future of tomorrow.