Re: [Roll] question about broken link detection

["Don Sturek" <[e-mail]>]

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: [e-mail] [mailto:[e-mail]] On Behalf Of
Jetcheva, Jorjeta
Sent: Monday, January 03, 2011 11:14 AM
To: [e-mail]
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