Michael.Dillon@radianz.com wrote:

You hit the nail on the head. Fundametally, any route optimization technique that tries to treat an aggregate of the network as a blob which can be measured will suffer the same type of problems as an IP over ATM network.

Observationally, IP over ATM has interesting latency effects. But it's rather defeatist to tar "any route optimization technique" with this critical brush. First, real products exist which do not require treating the /8 as a contiguous block - local (no-export) more specific injection is well understood (for those who believe it's even necessary). Second, to the extent that your point is about variance of one quantity of interest (latency), there are comparatively ancient statistical techniques for handling that - hardly new science.

There will always be a hidden layer of complexity that will affect your traffic flow and which you cannot influence.

Surely the same statement is true of almost all other products we can buy, not just bandwidth? There's hidden, important complexity in how airlines operate, how coffee is produced, how cars function. Somehow, though, we manage to make price-performance tradeoffs about these commodities all the time. In a network of networks, we cannot perform "strong TE" across everyone else's backbone. It does not follow that it's pointless to measure the other networks we rely on.

The same thing will happen with any measurement system that tries to classify a path through someone else's AS. You have no control over what happens in that AS and, more importantly, you have no control over the peering points bewteen ASes. Your measurements are as meaningless as measurements of an IP over ATM network.

So I agree with you that a /8, measured together, has a high signal to noise ratio. You're right that giving an extremely tight latency bound on a /8 aggregate is often impractical. It does not follow that it is impossible to extract signal from the noise; specifically, we routinely find concrete and stable (hours to days) instances where aggregate packet loss for a /8 will vary between various paths to reach it. No doubt someone hereabouts will scream "so buy more access", as if that means you can stop looking at off-net price/performance. For anyone who believes they don't need to look, fine - enjoy. For anyone who wants to evaluate the bandwidth they buy on an ongoing basis, tools exist, ranging from traditional network management pieces through to route optimization. The question, surely, is not whether off-net measurement is possible; it's whether it's useful to automate feedback from such a system into the network. Mike Lloyd CTO, RouteScience