Subject: Re: [Roll] [roll] #37: Feed-back fron IPSO interop

From: "roll issue tracker" <[email-masked]>
Date: Mon, 14 Jun 2010 08:03:01 -0000

#37: Feed-back fron IPSO interop
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 Reporter:  jpv@…               |        Owner:  pthubert@…                        
     Type:  defect              |       Status:  closed                            
 Priority:  minor               |    Milestone:                                    
Component:  rpl                 |      Version:                                    
 Severity:  Active WG Document  |   Resolution:  fixed                             
 Keywords:                      |  
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Changes (by jpv@…):

  * status:  new => closed
  * resolution:  => fixed

Comment:

 Email from Pascal:

 Dear WG:

 We just published RPL 08 (also) addressing the IPSO feedback. I think that
 we can now close the ticket:

 In more details:

 Feedback-I:
 DAO rank: It seems there very couple of different interpretations for
 setting this value.
 A. Several implementations were setting the DAO rank to be equal to  the
 node rank (value sent in DIO rank). Each node relays this info in the DAO
 towards the root. However this does not convey any differentiating info to
 the receiving nodes when the DAOs are received thru multiple paths in
 order to install the best route.
 B. The other implementation was to set the value to 0 (or 1) by the  node
 and have the intermediate nodes increment it as the DAO rides up to the
 root. The DAO rank in this case is more of a hop count and the receiving
 nodes can make a decision based on the lowest value received when[Pascal]
 installing the DAO route.
 Pros: Decision is optimized based on hopcount. Relatively simple.
 Cons: Hopcount does not take link cost into account.
 C. A third proposal was to set the DAO rank equal to the node rank  and a
 link cost in the metric container as each nodes propagates the DAO.
 The receiving nodes would make a decision based on the link cost.
 Pros: Decision is optimized based on link cost  > Cons: The DAOs would
 need to carry additional info in the packet  (biggerDAOs) and more
 processing needed in the nodes to parse and process.

 I think we need some more details the spec for describing the value to  >
 be set in DAO rank.

 [Pascal] The Rank is gone from the DAO entirely. It was replaced by
 Roger's path control. The rationale is that the routing is computed by the
 router upon DIO. DAO merely informs the above about that decision. In case
 of source route, the root is expected to optimize the preference of the
 path that it is selecting.

 Feedback-II:
 DIO Sequence number: The issue was what should be the initial value of
 this field. The spec is not clear on what should be the initial value  set
 by the root. This has implications at the LBR in reload/reboot
 conditions. For example, if the initial value is set to 1 and is  >
 incremented to say 10. When the LBR reloads/reboots, it would start the
 sequence number with 1 but its DIOs will be rejected by the nodes as
 having stale sequence number. The LBR can store the sequence in persistent
 memory. An easier option could be use 255 as the starting sequence number.
 Using this value will make sure that the sequence number is always valid.

 Comments?

 [Pascal] 10 now has a mechanism that derives from Radia Perlman's
 lollipop. The mechanism includes a simple sequence counter comparison with
 desync detection.
 More at http://tools.ietf.org/html/draft-ietf-roll-rpl-09#section-6

 : )

-- 
Ticket URL: <http://trac.tools.ietf.org/wg/roll/trac/ticket/37#comment:2>
roll <http://tools.ietf.org/wg/roll/>