Subject: [Roll] Question about non-storing mode in RPL

From: Hamidreza Kermajani <[email-masked]>
Date: Fri, 29 Oct 2010 16:50:05 +0200

Hi all,

According to RPL (v.14) that says :
"
9.5. Triggering DAO Messages
Nodes can trigger their sub-DODAG to send DAO messages. Each node
maintains a DAO Trigger Sequence Number (DTSN), which it communicates
through DIO messages.
1. If a node hears one of its DAO parents increment its DTSN, the
node MUST schedule a DAO message transmission using rules in
Section 9.3 and Section 9.4.
2. In non-storing mode, if a node hears one of its DAO parents
increment its DTSN, the node MUST increment its own DTSN.
"

1 - Is the first rule for both mode of operation? or only for storing mode?

As far as I understand, when a node adds a new parent to its DAO parent set
it must to send a DAO message to root, to inform the root about this case,
that's why in each time the root node has a route to other DODAG nodes.

Now my question is :

2 - When a non-storing node must send its DAO message to the DODAG root,
while sending packet to root ,Why should it send the packets to root via its
preferred parent( first to its preferred parent), not directly to the root ?
What's the reason?

Best Regards,
Hamidreza.

---

From: Matteo Paris <[email-masked]>
Date: Fri, 29 Oct 2010 11:49:27 -0400

Hi Hamidreza,

The first rule applies to both modes, the second only to non-storing 
mode.  Note that in non-storing mode, the DTSN is controlled by the 
root.  This is discussed in the 5th paragraph of section 9.5.

For your second question, see section 9.7 Non-storing Mode.  There it 
says "DAOs are sent directly to the root along a default route 
installed as part of the parent selection."  DAOs do not need to be 
sent via a particular parent in non-storing mode, since the IP 
destination of the DAO is the root.

Matteo

At 4:50 PM +0200 10/29/10, Hamidreza Kermajani wrote:
>As far as I understand, when a node adds a new parent to its DAO 
>parent set it must to send a DAO message to root, to inform the root 
>about this case, that's why in each time the root node has a route 
>to other DODAG nodes.
>
>Now my question is : 
>
>2 - When a non-storing node must send its DAO message to the DODAG 
>root, while sending packet to root ,Why should it send the packets 
>to root via its preferred parent( first to its preferred parent), 
>not directly to the root ? What's the reason?
>
>
>
>Best Regards,
>Hamidreza.
>
>_______________________________________________
>Roll mailing list
>[email-masked]
>https://www.ietf.org/mailman/listinfo/roll

---

From: Hamidreza Kermajani <[email-masked]>
Date: Fri, 29 Oct 2010 18:33:01 +0200

Hi Matteo,

First thanks for answer.

regarding my second question, I know that all non-root nodes in non-storing
mode send their DAO messages to the root. my question is about data
transmission, because according to Dario Tedeschi's email (in 19th August)
under title
"[Roll] Question on path to grand children in non-storing mode "He said that
to data transmission, first, a node must to send its data to its parent, and
other people have confirmed it.
That's why I asked this question. If it's true, what's the reason.

Best Regard,
hamidreza.

---

From: Matteo Paris <[email-masked]>
Date: Fri, 29 Oct 2010 14:11:48 -0400

Hi Hamidreza,

For a non-root router in a non-storing DODAG, the only next hops in 
its routing table are its parents.  All data traffic, to any 
destination, will necessarily be routed to one of the node's parents 
as the next hop.

(Exceptions: If the IP destination is a one-hop neighbor, the node 
may send the packet directly.  Or, the node may support additional 
routing mechanisms such as 
http://tools.ietf.org/html/draft-ietf-roll-p2p-rpl-01.)

The email you refer to, 
http://www.ietf.org/mail-archive/web/roll/current/msg05292.html
illustrates this fact in the special case of a linear topology.  The 
only next hop in C's routing table is B, so it has no choice of next 
hop for the data packet to E.  In general in a non-storing network, 
for any two routers, the root is their only common ancestor with 
downward routing information, so all point-to-point traffic flows 
through the root.

See section 4.3 Point-to-Point Traffic for further clarification.

Matteo

At 6:33 PM +0200 10/29/10, Hamidreza Kermajani wrote:
>Hi Matteo,
>
>First thanks for answer.
>
>regarding my second question, I know that all non-root nodes in 
>non-storing mode send their DAO messages to the root. my question is 
>about data transmission, because according to Dario Tedeschi's email 
>(in 19th August) under title
>
>"[Roll] Question on path to grand children in non-storing mode "
>
>He said that to data transmission, first, a node must to send its 
>data to its parent, and other people have confirmed it.