Subject: [Roll] Nit: Rank a value or a function ('monotonic')? Options 'restricted to'?

From: Alexandru Petrescu <[email-masked]>
Date: Sun, 25 Jul 2010 01:26:54 +0200

>    The rank of a node is a scalar representation of the location of that
>    node within a DODAG version.

Ok a scalar, not a vectorial.

>  The rank is used to avoid and detect
>    loops, and as such must demonstrate certain properties.  The exact
>    calculation of the rank is left to the Objective Function, and may
>    depend on parents, link metrics, and the node configuration and
>    policies.
>
>    The rank is not a cost metric, although its value can be derived from
>    and influenced by metrics.  The rank has properties of its own that
>    are not necessarily those of all metrics:
>
>    Type:   The rank is an abstract numeric value.

Ok, a numeric value, not alphabetical.

>    Function:  The rank is the expression of a relative position within a
>            DODAG version with regard to neighbors and is not necessarily
>            a good indication or a proper expression of a distance or a
>            cost to the root.
>
>    Stability:  The stability of the rank determines the stability of the
>            routing topology.  Some dampening or filtering might be
>            applied to keep the topology stable, and thus the rank does
>            not necessarily change as fast as some physical metrics
>            would.  A new DODAG version would be a good opportunity to
>            reconcile the discrepancies that might form over time between
>            metrics and ranks within a DODAG version.
 >
>    Properties:  The rank is strictly monotonic,

But we said rank were a 'scalar', 'numeric' (like '1' or '0.5').  These 
can't be monotonic, functions could.  Is the rank a function?

Or is it 'the range of values of a rank could only be output by a 
monotonic function'?  (or similar).

> and can be used to
>            validate a progression from or towards the root.  A metric,
>            like bandwidth or jitter, does not necessarily exhibit this
>            property.

I think these can't be 'monotonic' because they aren't functions either.

>    Abstract:  The rank does not have a physical unit, but rather a range
>            of increment per hop, where the assignment of each increment
>            is to be determined by the Objective Function.

Ok, I get Abstract.  Could the rank also be 'decrement' per hop?  Or is 
it restricted to being always incremented?

>    The rank value feeds into DODAG parent selection, according to the
>    RPL loop-avoidance strategy.  Once a parent has been added, and a
>    rank value for the node within the DODAG has been advertised, the
                     ^^^ you mean 'this' node?  (not 'the' node)?

>    nodes further options with regard to DODAG parent selection and
      ^^^^^ node's?  nodes'?

>    movement within the DODAG are restricted in favor of loop avoidance.
                                    ^^^^^^^^^^^^^^^^^^^^^^ restricted to?
                                                    refused in favor of?
                                                    limited to?

'reduced, favoring loop avoidance' would mean it still has some options 
other than loop avoidance.

Alex