Re: [6tisch] Comment on draft-ietf-6tisch-msf-01

[Simon Duquennoy <[e-mail]>]

Hi Christian,

I understand your concern.
In the current draft we maintain a Tx cell for each known neighbor, and
this might end up draining resources.
Maybe we should leave more flexibility on maintenance of autonomous cells?
One could even choose to install autonomous cells only on-demand: when a
packet is queued to a given neighbor, install cell towards that neighbor,
then remove it after sending.

Best,
Simon


On Wed, Oct 24, 2018 at 2:29 PM Christian Hopfner <
[e-mail]> wrote:

> Hi all,
>
>
>
> I have some question comments on latest draft of msf.
>
>
>
> 3. Autonomous Unicast Cells
>
> MSF nodes MUST initialize Slotframe 1 with a set of default cells for
>
> unicast communication with their neighbors. These cells are referred
>
> to as ’autonomous cells’, because they are maintained autonomously by
>
> each node. Each node has:
>
>
>
> 1. One cell to receive, at a [slotOffset,channelOffset] computed as
>
> a hash of the node’s EUI64 (detailed next). The cell options for
>
> this cell are RX=1.
>
>
>
> 2. For each neighbor in the IPv6 neighbor table, one cell to
>
> transmit, at a [slotOffset,channelOffset] computed as a hash of
>
> the neighbor’s EUI64 (detailed next). The cell options for this
>
> cell are TX=1, SHARED=1.
>
>
>
> CH I’m not sure if this 2nd item makes sense discussion it with the
> background of low-power and bandwidth capacity. Assuming we have space for
> 30 neighbor entries within my neighbor table this will lead to 32 cells
> being allocated within my schedule. 30 neighbors, my autonomous RX cell and
> shared minimal. This will reduce available bandwidth for the node
> tremendously. And might increase power consumption in parallel if we do not
> a have an intelligent scheduler which keeps the device in sleep even for
> active TX cells if we know in advance that there is no packet in the queue
> for the specific neighbor.
>
>
>
> What about considering only RPL neighbors for allocation TX, S cells to.
> This will keep the amount of allocated cell at least at a minimum necessary
> cells. If it comes to network transformation due to changing RPL parameters
> the Parent Switch functionality of msf will take care of reallocating
> installed cells.
>
>
> Mit freundlichen Grüßen I Best regards
>
> Christian Hopfner
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