Re: [6tisch] The channel hopping scheme seems to be suboptimal

[[e-mail] (Dale R. Worley)]

Thomas Watteyne <[e-mail]> writes:
> You raise a valid point. There are a couple of points, though, that make an
> "Absolute Slot Number" more favorable compared to an "Absolute Slotframe
> Number":
> - if you schedule multiple cells between two nodes in a single slotframe,
> you want those different transmissions to happen at a different frequency

Although you could construct the schedule so that the nodes have
different channel offsets for the different slots within the schedule.

> - ASN is used to construct a nonce when securing link-layer frames.
> Security is such that we never want to re-use the same nonce.

Although you could construct the nonce to be (ASFN * nSlots +
slotOffset).  And you need to do a construction like that to make sure
that different nodes with different channel offsets during the same slot
do not use the same nonce.

I suspect the main reason is that several slotframe schedules of
different lengths can be active at the same time in one network.
Keeping a separate ASFN for each schedule would require a lot of work.

Dale