Jonathan,
Picking up on an earlier point you made about avoiding heuristics by
ensuring the underlying algo is sound,... that's precisely why I'm going
through all the (9) PIE heuristics...
For PI2 we removed all but 2 and it worked the same or better than PIE
in all our tests. I have been assessing each of the other 7 one by one
for reinstatement. So far I've rejected 6. I think I can reject this
last one by making the sampling time of the base PI algo dependent on
the max link rate. Then when the queue goes idle, the base PI algo will
decay drop down to zero no slower than the queue drains, without needing
this extra heuristic. But I need to check that's realistic.
We will be writing all this up (probably in an update to the PI2 paper -
I don't think the IETF PI2 spec is the right place for a critique of
heuristics that it doesn't use).
Our aim is a completely sound AQM in a few lines of code and a few
operations so it can be implemented everywhere with minimal resistance
from developers due to performance concerns (e.g. cheap ethernet
switches, cheap home gateways, carrier-grade equipment for thousands of
users, etc).
Bob
On 28/03/17 07:25, Jonathan Morton wrote:
By all means, avoid dropping packets when the queue is actually empty - that
is, when you’re delivering the last packet in the queue. In that case, there
is no congestion to signal for. But there really is no need to have any
complex state-switching logic for that. If your underlying algorithm is sound,
it will naturally decay to zero packet drops if the empty-queue condition
persists.
- Jonathan Morton
--
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Bob Briscoe http://bobbriscoe.net/
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