Re: [Roll] (Was: review of dao-projection -22)

[Abdussalam Baryun <[e-mail]>]

On Fri, Jan 14, 2022 at 12:21 PM Pascal Thubert (pthubert) <pthubert=
[e-mail]> wrote:

> Dear all: we had this thread as part of Li’s review:
>
>
>
>
>
> About “5.4 only the router with the lowest Interface ID in its registered
> address needs report the SIO, and the Root will assume symmetry.”
>
>
>
> [Li] -> Is it possible to add a flag to indicate the symmetry? Otherwise,
> if A chooses B as sibling, but B doesn't choose A as sibling, Root may
> treat SIO from A as symmetry incorrectly when only receiving SIO from A.
>
>
>
> [PT] we used to have that (B Flag for bidir) but we removed it for
> simplification. I’m OK to add it back, but we still lake a good description
> of how the node will know that the link is roughly symmetrical.
>
>
>
> [Li] Some physical layer measurements such as RSSI/LQI have forward and
> reverse direction. Can it indicate symmetrical?
>
>                   In layer 3, receiving DIO/NS messages from each other
> indicate symmetrical
>
>
>
> [PT] There’s a nuance between bidir and symmetrical.  Maybe the ping works
> but the link quality is very different in both directions. If so the Rank
> increment computation would differ widely and we would need both sides.
>
>
>
> At the moment the text says:
>
> “
>
>    B:  1-bit flag that is set to indicate that the connectivity to the
>
>       sibling is bidirectional and roughly symmetrical.  In that case,
>
>       only one of the siblings may report the SIO for the hop.  If 'B'
>
>       is not set then the SIO only indicates connectivity from the
>
>       sibling to this node, and does not provide information on the hop
>
>       from this node to the sibling.
>
> “
>
>
>
> We need to clarify what the B flag means, when it can be set, and what is
> expected from the Root/ PCE about path computation when it is set or not
> set.
>

I think the flag needs more than two possibilities for connectivity issues,
could we have two bits?

AB