Subject: [Roll] Two questions about RPL: "RPL link" and "DAODealy"

From: Jiazi YI <[email-masked]>
Date: Sun, 08 Jan 2012 18:42:07 +0100

Hello dear all,

When reading the RPL draft, I have two questions:

1. In section 8.2.2.2. DODAG Roots:

> In a deployment that uses non-RPL links to federate a number of LLN
>    roots, it is possible to run RPL over those non-RPL links and use one
>    router as a "backbone root". 

What does the "non-RPL link" mean here? And what's "RPL link"? According
to the context, it seems to be "low power and lossy link"? I don't  see
why the *link* should be related to RPL.

2. In section 9.6. Triggering DAO messages

>   In the case of triggered DAOs, selecting a proper DAODelay can
>    greatly reduce the number of DAOs transmitted.  The trigger flows
>    Down the DODAG; in the best case the DAOs flow Up the DODAG such that
>    leaves send DAOs first, with each node sending a DAO message only
>    once. 

I don't know how each node only needs to send a DAO once in non-storing
mode if the DAO doesn't accumulate the path information?

cheers

-- 
Jiazi YI

www.jiaziyi.com
Hipercom@LIX, Ecole Polytechnique
91128 Palaiseau Cedex France

---

From: Alexandru Petrescu <[email-masked]>
Date: Mon, 09 Jan 2012 08:44:48 +0100

Le 08/01/2012 18:42, Jiazi YI a écrit :
>> In a deployment that uses non-RPL links to federate a number of
>> LLN roots, it is possible to run RPL over those non-RPL links and
>> use one router as a"backbone root".
>
> What does the "non-RPL link" mean here? And what's "RPL link"?
> According to the context, it seems to be "low power and lossy link"?
> I don't see why the *link* should be related to RPL.

I agree.  Maybe it better said "links on which RPL runs" or so.  "RPL
link" makes little sense, but for example "802.15.4 link" would make
more sense.

Alex

>> Down the DODAG; in the best case the DAOs flow Up the DODAG such
>> that leaves send DAOs first, with each node sending a DAO message
>> only once.
>
> I don't know how each node only needs to send a DAO once in
> non-storing mode if the DAO doesn't accumulate the path information?
>
> cheers
>
> -- Jiazi YI
>
> www.jiaziyi.com Hipercom@LIX, Ecole Polytechnique 91128 Palaiseau
> Cedex France
>
>
>
> _______________________________________________ Roll mailing list
> [email-masked] https://www.ietf.org/mailman/listinfo/roll

---

From: "Pascal Thubert (pthubert)" <[email-masked]>
Date: Mon, 9 Jan 2012 18:03:46 +0100

Hello Jiazi,

1)      I think this is a typo for non-LLN. This is the case where you
have a backbone such as Ethernet that federates multiple roots and the
backbone is not a LLN but still is used as the first hop of the RPL
network off the root... You'll note that in that case the whole network
is a single DAG.

You can alternatively make each root own its own DODAG in which case the
backbone is not RPL. 

Either way, you might want to run an additional routing protocol such as
OSPF over that backbone so that a packet from a node1 in subdag1
attached via  root1 to node2 in subdag2 attached via root2 will go
straight from root1 to root2 over the backbone. With RPL only, that
packet would go via a global root that is also on that backbone. This
illustrates the concept of boulevard that was discussed early in the RPL
process.

2)      Yes, this is storing only, since for all I know it refers to the
aggregation that happens in storing mode, where a single DAO message can
accumulate multiple targets. In non-storing, the DAO is unicast to the
root directly so no such aggregation happens. In storing, the DODAG
refresh could be optimized down to 1 DAO per router if, recursively, the
children have a lesser delay between the trigger and the DAO emission
than their parents do. So that a node gets all the targets for all of
its subdag before it sends an accumulation of those plus its own
information to a selection of its own parents. We used to have a
mechanism in storing mode to recursively update the whole subdag as we
do in non-storing (indicating that with a flag) but we abandoned that so
the optimization discussed here now may only apply to a
DODAGVersionNumber increment. The suggestion has lost most of its value
as RPL evolved and we should probably remove it since it's only creating
confusion.

Thanks for the review!

Pascal

From: [email-masked] [mailto:[email-masked]] On Behalf Of
Jiazi YI
Sent: dimanche 8 janvier 2012 18:42
To: roll WG
Subject: [Roll] Two questions about RPL: "RPL link" and "DAODealy"

Hello dear all,

cheers

-- 
Jiazi YI
 
www.jiaziyi.com

---

From: Jiazi YI <[email-masked]>
Date: Mon, 09 Jan 2012 21:32:18 +0100

Hello Pascal,

Thanks for you detailed answer.

1) It makes much more sense when "non-LLN" is used.

2) There is no problem if it's for storing only. However, in the current
draft, it's a little confusing. Hopefully it can be clarified.

regards

On 1/9/12 6:03 PM, Pascal Thubert (pthubert) wrote:
> network off the root... You'll note that in that case the whole
> network is a single DAG.
>
> You can alternatively make each root own its own DODAG in which case
> the backbone is not RPL.
>
>  
>
> Either way, you might want to run an additional routing protocol such
> as OSPF over that backbone so that a packet from a node1 in subdag1
> illustrates the concept of boulevard that was discussed early in the
> RPL process.
>
>  
>
> 2)      Yes, this is storing only, since for all I know it refers to
> the aggregation that happens in storing mode, where a single DAO
> message can accumulate multiple targets. In non-storing, the DAO is
> unicast to the root directly so no such aggregation happens. In
> storing, the DODAG refresh could be optimized down to 1 DAO per router
> if, recursively, the children have a lesser delay between the trigger
> and the DAO emission than their parents do. So that a node gets all
> the targets for all of its subdag before it sends an accumulation of
> those plus its own information to a selection of its own parents. We
> used to have a mechanism in storing mode to recursively update the
> whole subdag as we do in non-storing (indicating that with a flag) but
> we abandoned that so the optimization discussed here now may only
> apply to a DODAGVersionNumber increment. The suggestion has lost most
> of its value as RPL evolved and we should probably remove it since
> it's only creating confusion.
>
>  
>
> Thanks for the review!
>
>  
>
> Pascal
>
>  
>
> *From:[email-masked] [mailto:[email-masked]] *On Behalf
> Of *Jiazi YI
> *Sent:* dimanche 8 janvier 2012 18:42
> *To:* roll WG
> *Subject:* [Roll] Two questions about RPL: "RPL link" and "DAODealy"
>
>  
>
> Hello dear all,
>
> According to the context, it seems to be "low power and lossy link"? I
> don't  see why the *link* should be related to RPL.
>
> www.jiaziyi.com <http://www.jiaziyi.com>

-- 
Jiazi YI

www.jiaziyi.com