2016-11-11 17:14 GMT-03:00 Prof. Diego Dujovne <[email protected]>:
> Yasuyuki, > -02 version does not take into account symmetry. > In fact, we do not specify which type of cells (RX,TX) we > are allocating, we only say that we need to allocate them as > an introduction to the section. > We implicitly assume that we are allocating TX > traffic (which is RX from the point of view of the neighbour). > The opposite sense is correct: If the neighbour needs TX traffic, > it is RX for the node. > We do not specify on the draft where (i.e. from which > neighbour) > the incoming traffic comes from. In fact, the incoming traffic can arrive > from any neighbour. However, if we assume that we are using RPL, all the > traffic from the child nodes is forwarded to the parent in the TX sense, > while downstream traffic would be parent->node->slave. > IMHO, I believe you are right when you say that taking into > account only the outgoing traffic is a good estimator on the number of > required cells, since it includes not only the locally generated traffic > but also the > traffic from the neighbours traversing the node to that neighbour. > Furthermore, it would be more accurate (and overprovisioning could be > smaller) > because we assume also that we are not using track nor flow identifiers to > map incoming traffic from the other nodes to the neighbours. > I think the symmetry interpretation comes from > the idea that we are measuring the incoming cell requests from > a specific neighbour and then adding the outgoing number of cells > to the same neighbour and calculate the total amount of required cells. > But we still have to differentiate between TX and RX cells. > Hope this helps. > Let me know your thoughts about it. > Regards, > > Diego Dujovne > > > > > > > 2016-11-11 14:20 GMT-03:00 Yasuyuki Tanaka <[email protected] > >: > >> Hi all, >> >> I'd appreciate it if someone could help me understand SF0 Cell >> Estimation Algorithm mentioned in draft-ietf-6tisch-6top-sf0-02... >> >> https://tools.ietf.org/html/draft-ietf-6tisch-6top-sf0-02#section-5 >> >> What I've read from the draft is that the Cell Estimation Algorithm >> tries to have at least as many TX cells to a neighbor as RX cells >> which has been allocated for the neighbor as requested. It seems the >> algorithm assumes the communication triggering SF0 is symmetric. >> >> This idea explains why REQUIREDCELLS is given "by adding the current >> number of effectively used cells and the new incoming cells >> requirement." In the draft, cells requested to the allocation policy >> by the cell estimation algorithm are always TX. The numbers of >> SCHEDULEDCELLS and REQUIREDCELLS are only about TX cells. >> >> Is it correct? If this is the case, I wonder where the assumption, >> communication with a neighbor is symmetric, comes from. >> >> Supposing communication is asymmetric, where a node which has >> allocated RX cells for a neighbor rarely sends data to it, TX cell >> allocation triggered by an incoming cell requirement could not only be >> in vain but also cause unnecessary 6P transactions. With this >> scenario, it seems better that the estimation algorithm does not to >> take into account "incoming cell requirements." I may overlook >> something... >> >> I have another thing to ask, but I'd like to clarify the above first. >> >> Best, >> Yatch >> >> _______________________________________________ >> 6tisch mailing list >> [email protected] >> https://www.ietf.org/mailman/listinfo/6tisch >> > > > > -- > DIEGO DUJOVNE > Profesor Asociado > Escuela de Informática y Telecomunicaciones > Facultad de Ingeniería - Universidad Diego Portales - Chile > www.ingenieria.udp.cl > (56 2) 676 8125 > -- DIEGO DUJOVNE Profesor Asociado Escuela de Informática y Telecomunicaciones Facultad de Ingeniería - Universidad Diego Portales - Chile www.ingenieria.udp.cl (56 2) 676 8125
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