Re: [Lsr] New draft on Flex-Algorithm Bandwidth Constraints

Tony Li <> Wed, 03 March 2021 18:14 UTC

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Subject: Re: [Lsr] New draft on Flex-Algorithm Bandwidth Constraints
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>> There are several link types in use that exhibit variable delay: satellite links (e.g., Starlink), microwave links, and ancient link layers that deliver reliability through retransmission.
>> Any of these (and probably a lot more) can create a noticeable and measurable difference in TWAMP. That would be reflected in an FA metric change. If you imagine a situation with multiiple parallel paths with nearly identical delays, you can easily imagine an oscillatory scenario.   IMHO, this is an outstanding concern with FA.
> yes, and that is what I referred to as "delay normalization", which can avoid that oscillation.

It can also negate the benefits of the feature. One might well imagine that Starlink would want to follow a min-delay path for optimality.  If the delay variations are “normalized” out of existence, then the benefits are lost.  The whole point is to track the dynamics.

>> Please note that I’m NOT recommending that we back away. Rather, we should seek to solve the long-standing issue of oscillatory routing.
> not that I disagree. History tells us that the generic case of oscillation which is caused by the traffic itself is a hard problem to solve.

Any oscillation is difficult to solve.  Positive feedback certainly can exacerbate the problem. But solving hard problems is why we are here.

Yours in control theory,