Hi David, I replied inline:
On Fri, Apr 10, 2020 at 12:27 AM David Hauweele <david.hauwe...@umons.ac.be> wrote: > Dear 6TiSCH, > > In the last few months, we performed a small scale study of the > behavior of 6TiSCH's minimal scheduling function (MSF) under stress. We > were especially interested in the dynamics of MSF's automated > adaptation to traffic load. Some of our conclusions have been > summarized in a paper that we submitted to IEEE ISCC 2020. A copy of > the evaluation section of our submission is attached to this mail. > Congrats on the published paper! > > Among our surprising findings, we observed that > > 1) The time required for MSF to adapt to a traffic change depends on > the current number of cells allocated. To give an example, it takes > much longer to go from 0 to 10 cells than from 10 to 20 cells. We > attribute this behavior to the way MSF measures cell occupancy by > counting the number of used and passed cells. Adaptation only occurs > when the number of passed cells reaches a maximum. However, with light > cell allocation, it takes longer to reach that maximum than with higher > cell allocation. > Cool! I have the similar results when evaluate the MSF performance. There are two things influencing the response time to the traffic changes 1. The value of MAX_NUM_CELLS, which you mentioned. It is configurable. By setting it to a small value, the response time can be reduced in case the traffic load changes frequently. 2. The number of cells to be added/deleted each time. In MSF, for the simplicity, we only add/delete 1 cell every time. An advanced version of MSF could add/delete cells according the percentage of cell usage. > > 2) MSF can lead to severe over-provisioning, which can be harmful in an > environment where the resources are scarce. We noticed that releasing > cells was especially hard for MSF due to the fixed hysteresis > thresholds. Indeed, the estimated cell occupancy must drop below 25% > for cells to be released. > The over-provisioning is designed intentionally to avoid the fluctuation of 6P transactions. It costs additional 50% cells in average, as a trade-off, it could reduce the cost of sending 6P frames, and the latency caused by 6P transaction. No sure if there is a perfect way to cover every aspects? > > We already have ideas to improve MSF's traffic adaptation mechanism, > that we plan to put under test in the coming weeks. We can also provide > you with more details if you wish. If you see interest in our evaluation > and proposals, we are eager to discuss this further with the WG. > Very interesting to see your approach to improve MSF ! Referring to the MSF standardization process , as said by Pascal, we won't be able to made big changes. We can adapt some minor changes. Unless there is a flaw in the draft, I would prefer to keep the draft as it.. Tengfei > > Best regards, > David, Bruno, Aris and Georgios > _______________________________________________ > 6tisch mailing list > 6tisch@ietf.org > https://www.ietf.org/mailman/listinfo/6tisch > -- —————————————————————————————————————— Stay healthy, stay optimistic! Dr. Tengfei, Chang Postdoctoral Research Engineer, Inria www.tchang.org/ ——————————————————————————————————————
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