Re: [6tsch] On the fly scheduling

Maria Rita PALATTELLA <> Thu, 03 October 2013 17:40 UTC

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From: Maria Rita PALATTELLA <>
To: Thomas Watteyne <>, 6TSCH <>
Thread-Topic: [6tsch] On the fly scheduling
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Date: Thu, 3 Oct 2013 17:21:23 +0000
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Subject: Re: [6tsch] On the fly scheduling
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Thomas, of course! the idea behind is similar, but the approach is different (centralized vs distributed).


Maria Rita, one big difference with TASA is that OTF scheduling is distributed.


On Thu, Oct 3, 2013 at 9:11 AM, Maria Rita PALATTELLA <<>> 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:<> [<>] on behalf of Pascal Thubert (pthubert) [<>]
Sent: Thursday, October 03, 2013 4:09 PM
To:<>; Prof. Diego Dujovne

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!


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.


From:<> [<>] On Behalf Of Xavier Vilajosana Guillen
Sent: jeudi 3 octobre 2013 15:46
To: Prof. Diego Dujovne
Subject: Re: [6tsch] On the fly scheduling


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?


On Thu, Oct 3, 2013 at 3:23 AM, Prof. Diego Dujovne <<>> 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.


Académico Escuela de Ingeniería en Informática y Telecomunicaciones
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