Re: [6tisch] Questions on TSCH CSMA-CA retransmission algorithm in IEEE 802.15.4-2015

I agree with Fabrice's comments, that's how I read the document.

On Thu, Jun 14, 2018 at 6:07 PM Yasuyuki Tanaka <yasuyuki.tanaka@inria.fr>
wrote:

> Thank you, Fabrice!
>
> > the backoff window is selected randomly between 0 and 2^BE-1.
>
> According to you, the term of "the backoff window" seems to be used as the
> retransmission backoff or the retransmission backoff wait. If so, I was
> confused by a sentence in the third paragraph of the section, "A successful
> transmission in a shared link resets the backoff window to the minimum
> value."
>
> What is "reset" or the minimum value...?
>
> Perhaps, the backoff window there is meant (2^BE - 1) and its minimum
> value is (2^macMinBe - 1).
>
> > dedicated links > no collision / no backoff.
> > You transmit it without delay
> > (NB: you may have the first transmission during a shared link, and its
> retransmission in a dedicated one)
>
> Yes, that how it works.
>
> > If I understand correctly the standard, in that case, the dedicated link
> should not impact the BE value: the next packet will be picked in the
> queue, and transmitted with the same BE value as previously.
>
> Hmm, what if that next packet is not acknowledged in the first attempt?
>
> Will it use the *same* BE value in the following retransmission as
> perviously or use macMinBe as described in the standard, which could be
> different from the BE value used previously...?
>
> > "NB is the number of times the CSMA-CA algorithm was required to back
> off while attempting the current transmission"
>
> Aha, I see; then we need "NB=0" just after the "Retransmission?" box ;-)
>
> > I have also the same doubts as you for the figure 6.6….
>
> It'd be great if someone is woking on revising the figure... (>_<)
>
> Best,
> Yatch
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-- 
________________________________________

Thomas Watteyne, PhD
Research Scientist & Innovator, Inria
Sr Networking Design Eng, Analog Devices
Founder & co-lead, UC Berkeley OpenWSN
Co-chair, IETF 6TiSCH

www.thomaswatteyne.com
________________________________________