[Roll] Path control for non storing nodes

Costin Michaela Catalina-B06063 <B06063@freescale.com> Tue, 10 April 2012 08:21 UTC

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From: Costin Michaela Catalina-B06063 <B06063@freescale.com>
To: "roll@ietf.org" <roll@ietf.org>
Thread-Topic: Path control for non storing nodes
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Date: Tue, 10 Apr 2012 08:21:20 +0000
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Subject: [Roll] Path control for non storing nodes
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In RFC 6550, the path control field is generally associated with storing nodes.
In my understanding the path control is only used for preference on non storing nodes.

Consider the following scenario (DODAG), where the PARENT_SET_SIZE is set to 3 and PCS is set to 0:
                         RPL DODAG root
                             /        |            \
                          /           |              \
                       /              |                \
              NodeA     NodeB       Node C
                         \           |              /
                           \         |            /
                               NodeD

NodeD selects nodeA as preferred parent and NodeB and NodeC as parents. NodeD sends to RPL DODAG root a single DAO message containing the following:

*         RPL target option with NodeD global IPv6 address

*         3 Transit information options (sent exactly in this order over the air):

o   Transit information option containing the IPv6 global address for NodeB and path control set to 0x20 (medium preference)

o   Transit information option containing the IPv6 global address for NodeA and path control set to 0x80 (maximum preference)

o   Transit information option containing the IPv6 global address for NodeC and path control set to 0x20 (medium preference)

Now, my questions are:

1.       what is the RPL DODAG root going to do if PCS is set to any value smaller than 2 and it receives a DAO request with 3 Transit information options inside?

2.       Must NodeD send to RPL DODAG root a number of Transit information options equal to (PCS + 1)?

In my opinion:

1.       the RPL DODAG root should save all 3 routes to nodeD (no matter what the PCS value is set to). I think that for non storing nodes any PCS is valid as long as for each Transit information option at least one bit is set for path control.

2.       NodeD will always include in a DAO message all nodes in the parent set, no matter what value is set to PCS.

Do you have any comments on this?

Thanks,
Catalina