[Roll] [roll] #5: DODAG

[Tim Winter <wintert at acm.org>]

Hi Julien, WG,


roll issue tracker wrote:
> #5: DODAG
> --------------------------------+-------------------------------------------
>  Reporter:  jpv at …               |       Owner:  wintert at …      
>      Type:  defect              |      Status:  new            
>  Priority:  major               |   Milestone:                 
> Component:  rpl                 |     Version:                 
>  Severity:  Active WG Document  |    Keywords:                 
> --------------------------------+-------------------------------------------
>  * This is currently being discussed by the RPL Author team *
> 
>  Email from Julien
> 
>  Is there a distinction between DAG and destination oriented DAG. From what
>  I read I feel all DAGs are destination oriented. If this is correct I
>  propose to remove the destination oriented DAG concept.
> 


The intent for -05 will be to make the unqualifed use of `DAG' in the text
consistent with `DODAG Iteration', as outlined below.  So in this use, a
`DAG' is a `DODAG' snapshotted by a single sequence number -- a `DODAG
Iteration'.  There may be cases in -04 where the text reads `DAG' and is in
fact referring to `DODAG'- we will be sure to clean these up.  Here below is
some additional explanation prepared by the author team-

Does this help to clarify?

Regards,

-Tim



Instance


     +----------------------------------------------------------------+
     |                                                                |
     |      (R1)                   (R2)                   (Rn)        |
     |      /  \                   /| \                  / |  \       |
     |     /    \                 / |  \                /  |   \      |
     |   (A)    (B)             (M) |  (N)     ...    (X) (Y)  (Z)    |
     |   /|\     |\             /   |   |\             |   |    |     |
     |  : : :    : :            :  (O)  : :            :   :    :     |
     |                             / \                                |
     |                            :   :                               |
     |                                                                |
     |                          Instance ID                           |
     |                                                                |
     +----------------------------------------------------------------+

                                 Instance


   An Instance is a routing topology over an LLN, optimized for a
   particular objective/application.  Discrete Instances may also be set
   up to offer optimized connectivity to different destinations when
   appropriate, for example to differentiate a Home Network LLN from a
   Utility Network LLN in a smart metering application where a meter may
   be configured to join both Instances.

   It consists of one or more Destination Oriented DAGs (DODAGs).

   It is uniquely identified by an InstanceID.

   Each instance is operated independently of other instances, and RPL
   defines operation over only one instance.  Operation among multiple
   instances is to be expanded upon in a future revision or companion
   specification.



Destination Oriented DAG (DODAG)


     +----------------+
     |                |
     |      (R1)      |            (R2)                   (Rn)
     |      /  \      |            /| \                  / |  \
     |     /    \     |           / |  \                /  |   \
     |   (A)    (B)   |         (M) |  (N)     ...    (X) (Y)  (Z)
     |   /|\     |\   |         /   |   |\             |   |    |
     |  : : :    : :  |         :  (O)  : :            :   :    :
     |                |            / \
     |     DAGID      |           :   :
     |                |
     +----------------+

                                   DODAG


   A Destination Oriented DAG is a DAG rooted at a single root node,
   which is a node with no outgoing edges.

   In the case where multiple nodes in the LLN coordinate over a
   backbone and expose the same DAGID (to support the same DODAG), it is
   conceptually as if there is a single virtual root over the backbone
   (not illustrated).  In some applications/implementations this may be
   a desired architecture; in other applications each DODAG may operate
   with indpendent uncoordinated roots exposing different DAGIDs.

   A DODAG is uniquely identified over the LLN by the tuple (InstanceID,
   DAGID).

   In RPL a node may belong to only one DODAG per Instance at a time.



DODAG Iteration


           +----------------+                +-----------------+
           |                |                |                 |
           |      (R1)      |                |      (R1)       |
           |      /  \      |         \      |     / |  \      |
           |     /    \     |    ------\     |    /  |   \     |
           |   (A)    (B)   |           \    |  (A)  (C)  (B)  |
           |   /|\     |\   |           /    |  /|\        |\  |
           |  : : :    : :  |    ------/     | : : :       : : |
           |                |         /      |                 |
           |   Sequence N   |                |  Sequence N+1   |
           |                |                |                 |
           +----------------+                +-----------------+

                              DODAG Iteration


   A DODAG Iteration is the DODAG that results from the iterative
   process that reshapes the DODAG as stimulated by the root.  It is a
   DAG as constrained by operation of RPL over a fixed Sequence Number.

   As the root node increments the Sequence Number, different types of
   node movement are allowed (e.g. moving `down') and a new DODAG
   Iteration is formed.

   A DODAG Iteration is uniquely identified over the LLN by the tuple
   (InstanceID, DAGID, SequenceNumber).



Scope

   o  The scope of an InstanceID is the whole network and it defines an
      instance

   o  The scope of a DAGID is an instance and it defines a DODAG within
      that instance

   o  The scope of a Sequence Number is a DODAG and it defines an
      iteration of that DODAG (DODAG Iteration)

   o  The scope of a rank is a DODAG Iteration and it defines a position
      of a node within that iteration.