Hi Peter, > if you read the DCM draft carefully, you will find out that what you put > below is maybe funny, but not more than that.
It’s also accurate. It’s very clear where the intellectual inspiration for DCM came from. Yes, you’ve changed the details, but you’re solving the same problem. You didn’t like our solution, so you came up with a worse one all on your own. And then you berate someone else for doing what you’ve done. > Here are the significant differences between the two: > > 1. TTE is based on a backup paths, DCM calculates its own offload paths More accurately, DCM offloads traffic onto an oscillating Flex Algo topology. You’ve exactly recreated the BBN SPREAD oscillator from the Arpanet, one of the classic mistakes in networking (https://www.cs.princeton.edu/~jrex/teaching/spring2005/reading/khanna89.pdf). SPF in an unstable topology is going to continually generate transient micro-loops. > 2. LFA/TI-LFA does not take congestion into account, DCM offload path is > calculated to be congestion free DCM’s calculation is at best optimistic. Traffic is fractal. Congestion happens in spikes. If you do detect congestion, DCM has to change the Flex Algo topology, thereby thrashing the IGP, and the entire network has to SPF for that topology. This turns a congestion event into an IGP churn and micro-loop. This is not better, this adds to control plane instability. Then after shifting traffic, the link is no longer congested, so is reinstated to the offload topology and the cycle repeats. > 2. TTE does not support multiple congested links in the network at the same > time. Using multiple LFA/TI-LFA paths simultaneously on different nodes can > easily lead to loops. One can avoid this via SSPF. > 3. TTE is proposed to be used for a short duration of the time and then the > TE is expected to recompute. DCM is meant to be used for long time and does > not need any TE action. DCM keeps the network thrashing indefinitely. > 4. As a result of (3), DCM offload path is fully protected by LFA/TI-LFA, TTE > paths are note protected. TTE paths are load balanced, until paths are recomputed, so enjoy full protection. DCM paths are necessarily transient. Tony
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