Hi Tony,
On 01/03/2021 21:47, Tony Li wrote:
Robert,
Constructing arbitrary topologies with bw constrain is useful work. For example
I want to create a topology without links of the capacity less then 1 Gbps. All
cool. Of course if I have a case where two nodes have 10 L3 1Gbps links nicely
doing ECMP I will not include those which may be a problem.
I agree that it may be a problem. Maybe it’s not the right tool for the job at
hand. That doesn’t make it a bad tool, just the wrong one. I try not to turn
screws with a hammer. And I try not to drive nails with a screwdriver.
I will happily stipulate that we need more tools and that these are not enough.
We should not reject a tool simply because it doesn’t solve all problems.
Let’s work towards the right set of tools. Linear algebra tells us that we want
an orthogonal set of basis vectors. What are they? Adding them one at a time is
not horrible progress.
However my observation is precisely related to your last sentence.
Is this extension to be used with static or dynamic data ? If static all fine.
But as William replied to me earlier link delay may be dynamically computed and
may include queue wait time. That to me means something much different if
Flex-Algo topologies will become dynamically adjustable. And I am not saying
this is not great idea .. My interest here is just to understand the current
scope.
Link delay was dynamic before this draft. As William mentioned, TWAMP can
already be used to provide a dynamic measurement of link delay. That, coupled
with the link delay metric already gave us dynamic path computation
requirements and the possibilities of oscillation and instability. We have
chosen to charge ahead, without addressing those concerns already.
TWAMP provided Min Unidirectional Link Delay is a dynamic one. On the
other side this value is calculated based on multiple measurements over
period of time and an average is used. Also, smart implementations can
normalize the value so that a small fluctuation of the delay is not
causing the traffic to shift or cause ECMP loss.
What is important here is that the Min Unidirectional Link Delay is a
link characteristic, not something that is affected by the amount of
traffic on the link or subject to queuing delay. Same applies to Maximum
link bandwidth.
thanks,
Peter
Regards,
Tony
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