Respect the Tag

Where did I leave that QOS stamp?

Old guys like myself remember the red ‘AIR MAIL’ stamp that you’d sometimes see on an envelope that came from a faraway land… but more likely it was from a direct marketer that thought the stamp proudly displayed on the front of the envelope, printed in red and at a rakish angle to simulate an actual ‘stamp’, would make you feel the letter was special.  You know what they were going for here — Gee, this came from a sender who cared enough about this correspondence that they took the time to trot down to the post office, carefully placing said correspondence in one of those odd-sized envelopes with the blue and red hash marks wrapped around the edges.  Then waiting in the queue, seeing the postal official, paying a little extra, the flourish surrounding the hand stamp — ink pad, loud thump or two on the counter — and finally leaving with the assurance that the badge wielding bureaucrat would personally see to it that this most important of letters was delicately placed in the belly of the fastest plane both leaving immediately and traveling directly to its destination.

Yeah, right…

As I speak to networking people about what Quality of Service means and how QOS tagging is implemented in reality, I continue to get the sense that gear manufacturers and network carriers are not really telling the full story.  They seem to leave the impression that a packet possessing a QOS tag has some guarantee of timely delivery.  If doesn’t.  It simply means that if a device in the path is going to respect the tag (they don’t always), it will handle the packet with the higher QOS tag first.  Of course this is if the device is presented with two packets to handle at the same time and it possesses the bandwidth to handle them. It does not mean it guarantees delivery — not even to the next hop.

Sounds kinda like an ‘Air Mail’ stamp, eh? (Pardon my Canadian).

So what does actual Quality of Service look like…. Well it’s a bit more than simply tagging a packet on the way into the WAN.  In order to realize the benefits of a true SD-WAN with real-time end to end QOS, the network devices handling these tagged packets need to know the real time performance characteristics of every path in the network.  Further, they also must know that if they send a packet into the WAN, the links and devices on the other side of the network can handle the packet with priority when it gets there — not just best effort if they happen to respect the tag.

QOS — it’s more than a stamp.

Categories: Application Performance/Application Quality, Software Defined WAN (SD-WAN)