Re: [Roll] Querying PDAO

["Pascal Thubert (pthubert)" <[e-mail]>]

Hello Michael:

I'd reward saying that DAO is the centralized way of doing what P2P RPL achieves in a distributed reactive fashion: a local DODAG that implements the concept of a 6TiSCH Track.
With the current spec the packets flow down the DODAG only, against the DODAG orientation. The root the DODAG is the source of the packets, and the RPL classical forwarding apply for storing and non-storing.  
The difference is in the control: there is no DIO messaging on the local DODAG, and the DAO messaging is initiated by the main root as opposed to the distributed nodes.
If we need a return channel well need to introduce a DIO that would be flooded the other way, or a DODAG in the other direction like AODV does.

So yes, P DAO installs routes, normally as different DODAGs typically as source-local RPL instances. The PCE may be hidden within or separated behind the main root, in which case the main root acts as proxy.
The expectation so far was that the request o establish a path would come from the application but the general DetNet model also enables the host to make that request.
With P DAO that means a message from the node to the root with a TSPEC that allows the root to compute a constrained DODAG. Can be a DIS.

The DODAG is decomposed in linear segments that are installed separately using the PDAO messaging in a same local instance owned by the local root. We probably need to explain all that a lot better. 
RAW would be how we optimize the runtime of the projected DODAG.

All the best,

Pascal

> -----Original Message-----
> From: Roll <[e-mail]> On Behalf Of Michael Richardson
> Sent: jeudi 25 juillet 2019 11:38
> To: Routing Over Low power and Lossy networks <[e-mail]>
> Subject: Re: [Roll] Querying PDAO
> 
> 
> Li Zhao (liz3) <[e-mail]> wrote:
>     > Correct. If the application on node X wants to ask a nearest path to
>     > node Y, PDAO draft doesn't provide any mechanism.
> 
> P2PRPL tries to do this, but you are suggesting that instead of learing it, the
> root should just know it.  This goes to some of the PCE cases, I think.
> 
> Is there PCE technology we can use?
> 
> DAO-projection does not create a route that is remembered, rather it prefixes
> it to a particular packet.  So you'd want node X to be able to ask the root for
> such a source route?
> 
>     > I think PDAO draft need to cover this case. Maybe how and when to use
>     > PDAO is out of scope of this draft.
>     > But at least we need to reserve the asking capability and define the
>     > protocol.
> --
> ]               Never tell me the odds!                 | ipv6 mesh networks [
> ]   Michael Richardson, Sandelman Software Works        | network architect  [
> ]     [e-mail]  http://www.sandelman.ca/        |   ruby on rails    [
>