Re: [6tsch] On the fly scheduling

Thomas Watteyne <watteyne@eecs.berkeley.edu> Thu, 03 October 2013 20:27 UTC

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From: Thomas Watteyne <watteyne@eecs.berkeley.edu>
Date: Thu, 3 Oct 2013 13:11:15 -0700
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Subject: Re: [6tsch] On the fly scheduling
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That would indeed be clean.


On Thu, Oct 3, 2013 at 12:33 PM, Qin Wang <qinwang@berkeley.edu>; wrote:

> Hi all,
>
> +1 for the proposal.
>
> Regarding to how to approach, I agree with Thomas. There is an entity
> running on top of 6top, which reads queue information and other statistics
> information from 6top, sends instruction like create/delete softcells to
> 6top. I think we can use the design methodology of Objective Function in
> RPL, i.e. define the statistics information and the interface to/from 6top,
> and leave the specific algorithm open.
>
> What do you think?
>
> Qin
>
>
>
>
> On Fri, Oct 4, 2013 at 12:45 AM, Thomas Watteyne <
> watteyne@eecs.berkeley.edu>; wrote:
>
>> +1 for the proposal.
>>
>> I believe it could be a very simple and powerful approach. Diego, would
>> you agree that this can be considered a distributed mechanism sitting on
>> top of 6top?
>>
>> That is, 6top provides:
>>
>>    - commands to modify the number of soft cells in a bundle
>>    - commands to retrieve usage statistics of the cells/bundles
>>
>> The way I see it, your proposal consists of an algorithm which feeds from
>> the usage statistics and triggers changes in the number of soft cells in a
>> bundle. Correct?
>>
>> The questions to answer for now is whether 6top provides the right
>> statistics.
>>
>> Maria Rita, one big difference with TASA is that OTF scheduling is
>> distributed.
>>
>> Thomas
>>
>> On Thu, Oct 3, 2013 at 9:11 AM, Maria Rita PALATTELLA <
>> maria-rita.palattella@uni.lu>; wrote:
>>
>>>  Diego,( all)
>>>
>>> what you are suggesting (i.e., reserve cells based on queue size, delay)
>>> is actually the main idea behind TASA (Traffic Aware Scheduling Algorithm).
>>>
>>> TASA builds the schedule based on the local (number of pkt generated by
>>> the node) and global queue level ( i.e., local + pkt to be forwarded,
>>> generated by children). It gives priority to nodes with longer queues and
>>> it aims to reduce the latency for delivering the pkt. At the same time
>>> while building the schedule it minimizes the number of scheduled cells in
>>> order to reduce the network duty cycle.
>>> TASA is centralized and thus it assumes that the PCE has all the info
>>> needed for setting up the schedule. in other words, it knows the traffic
>>> generated by each nodes, and the paths followed by each pkt.
>>> With a "on the fly solution", we will not need to know all this info a
>>> priori. but we will use 6top monitoring functions and the control flows
>>> message for scheduling the cells.
>>>
>>> Btw, I agree with all the points raised up by Xavi.  We will have to
>>> address his questions.
>>>
>>> And I support Pascal's suggestions about how to deal with bundle.
>>>
>>> Maria Rita
>>>
>>>
>>>  ------------------------------
>>> *From:* 6tsch-bounces@ietf.org [6tsch-bounces@ietf.org] on behalf of
>>> Pascal Thubert (pthubert) [pthubert@cisco.com]
>>> *Sent:* Thursday, October 03, 2013 4:09 PM
>>> *To:* xvilajosana@eecs.berkeley.edu; Prof. Diego Dujovne
>>>
>>> *Cc:* 6TSCH
>>> *Subject:* Re: [6tsch] On the fly scheduling
>>>
>>>   +1 too.
>>>
>>>
>>>
>>> I think that the queue size matters at enqueue but the latency is really
>>> what we care for at dequeue, that is how long did this device keep this
>>> message in queue (even if we are far from
>>>
>>> buffer bloat conditions in such a device). If one of the 2 conditions
>>> (size at enqueue, latency at dequeue) is reached then the bundle should be
>>> increased.
>>>
>>>
>>>
>>> I agree with Xavi that we want to avoid changing the bundle size all the
>>> time. We discussed that with Qin and others earlier on the ML. One way of
>>> increasing the bundle dynamically at a very low cost (not even a
>>> hysteresis)  is to have it large amount of cells from the start but used
>>> like 10% by default (xmit/listen happens only once in 10 time slots). A bit
>>> in the frame indicates whether the next (normally unused) slot will indeed
>>> be used. The bit can be present in the data and acked in the ack. This can
>>> also implicitly be triggered for retries.
>>>
>>>
>>>
>>> Please keep us tuned!
>>>
>>>
>>>
>>> Cheers,
>>>
>>>
>>>
>>> PS Note that Cisco has IPR on chaining time slots and flagging whether
>>> the next is used or not. We already declared our IPR against the
>>> architecture draft and provided terms.
>>>
>>>
>>>
>>> Pascal
>>>
>>>
>>>
>>> *From:* 6tsch-bounces@ietf.org [mailto:6tsch-bounces@ietf.org] *On
>>> Behalf Of *Xavier Vilajosana Guillen
>>> *Sent:* jeudi 3 octobre 2013 15:46
>>> *To:* Prof. Diego Dujovne
>>> *Cc:* 6TSCH
>>> *Subject:* Re: [6tsch] On the fly scheduling
>>>
>>>
>>>
>>> Diego,
>>>
>>> +1
>>>
>>> it seems to a me a very interesting idea to explore. Maybe we can start
>>> putting some rules of this mechanism on the table and prepare a simulation.
>>> I am completely in with that idea.
>>>
>>> Some questions arise:
>>>
>>> 1-how fast do you react to changes on the queue size to avoid hysteresis
>>> -- i.e how do you maintain certain stability in the schedule (so you don't
>>> start installing and removing links very often)
>>>
>>> 2-how you map queue size (only one or if more than one queue) to actual
>>> link requirements
>>>
>>> 3-how you recover from link collisions in case of multiple nodes
>>> schedule the same cells.
>>>
>>> 4-how to decide to who (what neighbor) install more links according to
>>> queue size?
>>>
>>>
>>>
>>> cheers!
>>> Xavi
>>>
>>>
>>>
>>>
>>>
>>> On Thu, Oct 3, 2013 at 3:23 AM, Prof. Diego Dujovne <
>>> diego.dujovne@mail.udp.cl>; wrote:
>>>
>>> Dear all,
>>>             I've been looking into the idea of "on the fly scheduling",
>>> presented on the Sept 27th webex call as "on-the-fly decentralized
>>> reservation".
>>> The basic mechanism would be based on analysing the queue size
>>> on a node and dynamically adapt the number of reserved
>>> cells to satisfy queue size, delay and/or power
>>> consumption thresholds.
>>>             This mechanism would work inside 6top, between pairs of
>>> nodes.
>>> As a first approach, it would be based on the minimal draft.
>>> What do you think on this starting point?
>>> I (gladly) receive comments to add or modify this proposal.
>>>
>>>                                      Diego
>>>
>>>
>>>
>>>
>>> --
>>> DIEGO DUJOVNE
>>> Académico Escuela de Ingeniería en Informática y Telecomunicaciones
>>> Facultad de Ingeniería UDP
>>> www.ingenieria.udp.cl
>>> (56 2) 676 8125
>>> _______________________________________________
>>> 6tsch mailing list
>>> 6tsch@ietf.org
>>> https://www.ietf.org/mailman/listinfo/6tsch
>>>
>>>
>>>
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>>>
>>
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