Robert,
On 03/03/2021 10:58, Robert Raszuk wrote:
Hi Peter,
To your last point ...
Authors stated: "Whether egress queueing delay is included in the link
delay depends on the measuring mechanism."
I disagree with that statement - the Min Unidirectional Link Delay is
the value that does not include the queueing delay - that's why it is
called Min.
So sure there will be thresholds etc ... but this may very well depend
on the traffic.
no.
thanks,
Peter
Thx,
R.
On Wed, Mar 3, 2021 at 10:34 AM Peter Psenak <[email protected]
<mailto:[email protected]>> wrote:
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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