[Roll] Question about non-storing mode in RPL

[Hamidreza Kermajani <[e-mail]>]

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.