Subject: [Roll] question about broken link detection

From: "Jetcheva, Jorjeta" <[email-masked]>
Date: Mon, 3 Jan 2011 11:13:35 -0800

Hi everyone,

Happy New Year!

I am trying to understand how RPL deals with broken links in non-storing mode so I wanted to run several scenarios by the group.  When a packet is transmitted downstream and reaches a broken link, e.g., from node A to node B,  and the transmitting node (node A) doesn't get a link layer ack from the downstream next hop (node B) after sending several retransmissions, it can send an ICMP destination unreachable packet to the root.  The root can then try to use other routes it has to the destination or if it doesn't know of any other ones, it can:

1.        Increment its DTSN, triggering all nodes in the DODAG to send it a DAO, at which point the downstream node adjacent to the broken link (node B) will detect that the link to its parent (node A) is broken and will select a new preferred parent (assuming it has other possible parents) and send a DAO.

2.       Wait for the downstream node in the broken link (node B) to detect that its parent (node A) is not reachable

A.      When the downstream node (Node B) observes that it hasn't gotten a DIO from its parent (node A) for a while, and it would select a new preferred parent (assuming it has other possible parents) and send a DAO to the root

B.      If traffic happens to be flowing upstream, the lack of per-hop/link layer acks would indicate the upstream parent (node A) is no longer reachable and a new parent will be selected, and a DAO would be sent to the root.
Are these the options for detecting a broken link when forwarding a packet downstream in non-storing mode?  Is there a preferred mechanism for this?

Thanks!

Jorjeta

---

From: "Don Sturek" <[email-masked]>
Date: Thu, 6 Jan 2011 06:19:33 -0800

Hi Jorjeta,

I think the point to point draft
(http://datatracker.ietf.org/doc/draft-dt-roll-p2p-rpl/) attempts to take up
the issue of pro-active route repair using RPL.   I have not closely
followed the draft but know that was in scope.

Don

From: [email-masked] [mailto:[email-masked]] On Behalf Of
Jetcheva, Jorjeta
Sent: Monday, January 03, 2011 11:14 AM
To: [email-masked]
Subject: [Roll] question about broken link detection

Hi everyone,

Happy New Year!

I am trying to understand how RPL deals with broken links in non-storing
mode so I wanted to run several scenarios by the group.  When a packet is
transmitted downstream and reaches a broken link, e.g., from node A to node
B,  and the transmitting node (node A) doesn't get a link layer ack from the
downstream next hop (node B) after sending several retransmissions, it can
send an ICMP destination unreachable packet to the root.  The root can then
try to use other routes it has to the destination or if it doesn't know of
any other ones, it can:

1.        Increment its DTSN, triggering all nodes in the DODAG to send it a
DAO, at which point the downstream node adjacent to the broken link (node B)
will detect that the link to its parent (node A) is broken and will select a
new preferred parent (assuming it has other possible parents) and send a
DAO.

2.       Wait for the downstream node in the broken link (node B) to detect
that its parent (node A) is not reachable 

A.      When the downstream node (Node B) observes that it hasn't gotten a
DIO from its parent (node A) for a while, and it would select a new
preferred parent (assuming it has other possible parents) and send a DAO to
the root

B.      If traffic happens to be flowing upstream, the lack of per-hop/link
layer acks would indicate the upstream parent (node A) is no longer
reachable and a new parent will be selected, and a DAO would be sent to the
root.

Are these the options for detecting a broken link when forwarding a packet
downstream in non-storing mode?  Is there a preferred mechanism for this?

Thanks!

Jorjeta

---

From: [email-masked]
Date: Thu, 6 Jan 2011 09:40:53 -0600

Hi Jorjeta,

The P2P mechanism could be deployed
as a band-aid means to repair the link in the DAG, but it is not meant
for that.  If node A wants to transmit to node B within the LLN, RPL
(in non-storing mode) would require the packet to traverse to the LBR and
then be source routed back down to the destination.  If the packet
should happen upon a broken link, it would be feasible that a P2P request
could be made at that point to re-establish a link and complete the journey.
However since P2P is not an integral part of RPL, this would be a
proprietary solution.  The packet would get to the destination, but
the LBR would not know about the broken link so there would be no persistence
of this link repair.

The more likely scenario would be that
Node A sends a packet to Node B via the LBR as noted above.  Node
A times out the Node B response and determines the packet has been lost.
Rather than continue to retry through the DAG and LBR hoping the
link has been re-established; Node A rather defines a direct link to Node
B using the P2P mechanism.  Here, rather than traversing the entire
DAG up and down through the LBR, the packet can be efficiently sent directly
from A to B through the appropriate hopping nodes.

This is the intent of the P2P draft.
Hope this helps.

Jerry

From:

"Don Sturek" <[email-masked]>

To:

"'Jetcheva, Jorjeta'" <[email-masked]>,
<[email-masked]>

Date:

01/06/2011 08:20 AM

Subject:

Re: [Roll] question about broken link
detection

Hi Jorjeta,

I think the point to point
draft (http://datatracker.ietf.org/doc/draft-dt-roll-p2p-rpl/)
attempts to take up the issue of pro-active route repair using RPL.
I have not closely followed the draft but know that was in scope.

Don

From: [email-masked] [mailto:[email-masked]]
On Behalf Of Jetcheva, Jorjeta

To: [email-masked]

Hi everyone,

Happy New Year!

I am trying to understand how RPL deals
with broken links in non-storing mode so I wanted to run several scenarios
by the group.  When a packet is transmitted downstream and reaches
a broken link, e.g., from node A to node B,  and the transmitting
node (node A) doesn’t get a link layer ack from the downstream next hop
(node B) after sending several retransmissions, it can send an ICMP destination
unreachable packet to the root.  The root can then try to use other
routes it has to the destination or if it doesn’t know of any other ones,
it can:

1.        Increment
its DTSN, triggering all nodes in the DODAG to send it a DAO, at which
point the downstream node adjacent to the broken link (node B) will detect
that the link to its parent (node A) is broken and will select a new preferred
parent (assuming it has other possible parents) and send a DAO.

2.       Wait for the downstream
node in the broken link (node B) to detect that its parent (node A) is
not reachable

A.      When the downstream
node (Node B) observes that it hasn’t gotten a DIO from its parent (node
A) for a while, and it would select a new preferred parent (assuming it
has other possible parents) and send a DAO to the root

B.      If traffic happens
to be flowing upstream, the lack of per-hop/link layer acks would indicate
the upstream parent (node A) is no longer reachable and a new parent will
be selected, and a DAO would be sent to the root.

Are these the options for detecting a broken
link when forwarding a packet downstream in non-storing mode?  Is
there a preferred mechanism for this?

Thanks!

Jorjeta_______________________________________________

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