Most of my experience is in private networks. I've used QoS a lot for companies that run voice on their network. Predominately I've used QoS to guarantee delay, latency and jitter. I've also used it to protect certain types of network traffic (ssh and routing protocols, so I can guarantee they will work under excessive load). I don't think I have ever used it to determine traffic to drop (although it can obviously be used for that). If a customer is reaching the point where their pipes are so saturated they are losing traffic then they should upgrade to the next size pipe. On lower speed pipes you can get high jitter and delay every when the pipe is not saturated due to the serialisation delay. I've never ran into a case where the "pipes" where so big that QoS was not required. Never. You can really tell on a VoIP networks when QoS is not enabled, and I can't imagine a customer not wanting it turned on. So I can't agree with several of the comments below. However, I do agree, the public Internet is quite different. In a private network you have end to end trust, so QoS is so much easier to setup. If we tried to establish a QoS model in a public network then I can guarantee it that someone will abuse it. And I can only see it being seconds before P2P software notice QoS markings has an impact, and start marking all their own traffic. I tend to agree the only solution is bigger pipes. The only special case I can think of is when you can't get bigger pipes (or rather, the cost is too prohibitive). I also suspect that if the demand was so great for QoS fabric then a market would spring up to support the financial demand. But I think this would more likely be done with private point to point links, rather than a QoS IX. And I would surely like an ISP to deliver my packets as fast as they can, but let's face it, that's not what happens. They choose the most economic route for packet delivery, not the fastest. And even then, if it's the wrong type of packets there is a chance they'll police them even further guaranteeing packet loss will occur (which is a response to the ISP experiencing congestion and demand exceeding what they can supply - oh oh, artificial QoS!). -----Original Message----- From: Joe Abley [mailto:jabley(a)hopcount.ca] Sent: Tuesday, 31 March 2009 5:38 a.m. To: David Robb Cc: nznog Subject: Re: [nznog] QoS-IXPs ... It's perhaps easier to see that this is the case if you use the phrase "selective throwing away of customer packets" instead of "quality of service". The goal of an ISP is surely to deliver packets for customers and bill them for doing so. Nobody wants to throw away customer packets if there's a way to avoid it. Nobody wants "quality of service" if there's a way to avoid it.
For short term problems eg abnormal traffic flows causing congestion, sure. For long term traffic management - get bigger tubes.
Amen. Joe