Well that’s a bold statement! QoS (Quality of Service) encompasses a range of techniques to prioritise important packets travelling through an IP network. The intent is to ensure that those important packets get through even when the IP network is busy.
This technology has also been talked about in relation to the whole Net Neutrality debate.
So why doesn’t it work? Well, it does … up to a point. You can prioritise a small amount of traffic and ensure that it gets through an IP network at the busiest times.
And the word busy is important here. Unless the network is full, congested, at capacity – whatever phrase you like to use – then QoS isn’t needed. If all bits can get through as they need then QoS makes no difference.
But during the busy hour, or busiest hours, it makes a difference – for a small amount of traffic only. VoIP is always the “application” used as an example of something that is sensitive to delay and could therefore theoretically gain some advantage during busy times.
Dan Bricklin has used the road as an analogy to explain why QoS is broadly ineffective. I’m going to borrow his good work to explain my point.
Consider a congested road. A QoS system exists for roads that allow emergency vehicles through during busy times. You pull over and/or slow down when the sirens and lights go on the emergency vehicle. But, that system itself slows everything else down. And if you try to add to the volume of priority traffic (say adding taxis, buses, then motorcycles, blue cars, convertibles etc.) you can see that it wouldn’t work any more. QoS only works for a very small percentage of the overall traffic. Try and prioritise too much and the system actually gets worse in an exponential cascading path to gridlock.
In addition there has to be some traffic flow to allow the small percentage of prioritised traffic through. QoS makes no difference with total gridlock. It only works (i.e. adds any value) in a very narrow range of utilisation. Low utilisation means it isn’t needed. Too much high priority traffic means it doesn’t work at all.
OK lets stretch the analogy a little. Lets add an HOV lane. This is what the opponents of Net Neutrality suggest. First of all that lane has to come out of the existing road capacity. That means congestion for non-prioritised traffic just got worse – all the time.
But now you still have the problem of the HOV system only working for a small percentage of the traffic. It can become congested itself very quickly.
And finally adding QoS is actually expensive. The computational power needed to tag and prioritise packets is an overhead that adds complexity and cost to the system.
So is there a better way? Yes. And it’s simple. Add more bandwidth. Sounds obvious and simple. And it is! We’ve modelled this many times over the years and in most cases for the majority of traffic profiles it is always more cost effective to simply add bandwidth than try and implement a QoS technology.
And, of course, it benefits ALL traffic.