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Weekly Report




Test results have been coming in, and are pretty much going exactly as expected.

Packet colouring can find loss within 2 seconds, as you would expect. BFD takes a long time to notice low rates of packet loss, but will detect at least as low as 2% eventually. Basically it has to send in the order of 1/(n^3) packets to detect a packet loss rate of n. That all has brought me to the conclusion that packet colouring combined with the in-built link down detection in openflow is by far the most efficient way of finding loss. Link loss is detected immediately, and everything else is detected in 2 seconds.

The counters on the pronto are still pretty dodgy. Using packet counters with multiple bridges on the one device seems a bad idea. My packets are being handled by one bridge but are being counted towards flows on the other.

I've started building path calculators, I have one which tries to exploit openflow fast failovers, so when a link goes down, it only modifies the path at the point where the link down is detected. This could potentially require the smallest number of flows, but unless your network fits certain topological constrains it probably wont. I'm currently implementing the 2 flows per switch version, which may involve very long paths in certain circumstances (basically longer paths end up being prioritised over shorter paths in a lot of circumstances), and I will implement the patented version too, (unless someone tells me not to---I really have no understanding of patent law) just for a comparison.