Subject: Re: [Roll] [roll] #53: How does an OF compute rank from metric values?

From: Mukul Goyal <[email-masked]>
Date: Thu, 17 Jun 2010 00:33:21 -0500 (CDT)

How about if we require a metric definition to provide a mapping to an equivalent rank value. Then, the job of objective function becomes easier; it just needs to combine equivalent values in the desired manner.

Why wont this scheme work??

Thanks
Mukul 

----- Original Message -----
From: "roll issue tracker" <[email-masked]>
To: [email-masked], [email-masked]
Cc: [email-masked]
Sent: Thursday, June 17, 2010 12:15:30 AM
Subject: [Roll] [roll] #53: How does an OF compute rank from metric values?

#53: How does an OF compute rank from metric values?
--------------------------------+-------------------------------------------
Reporter: jpv@… | Owner: wintert@…
Type: defect | Status: new
Priority: major | Milestone:
Component: rpl | Version:
Severity: Active WG Document | Keywords:
--------------------------------+-------------------------------------------
We have different types of metrics with different ranges. Examples:
ETX is 16 bits. Latency is 24 bits. How do we convert these numbers to
rank in an OF? Does the range of rank depend on the range and size of
the metric?

-- Ticket URL: <http://trac.tools.ietf.org/wg/roll/trac/ticket/53>
roll <http://tools.ietf.org/wg/roll/>

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From: Yoav Ben-Yehezkel <[email-masked]>
Date: Thu, 17 Jun 2010 09:10:38 +0300

Hi Mukul,

At least my understanding of the following is that the rank should not
necessarily be a direct mapping function of the metric. If it were, there
would have been no use for two different concepts (rank and metric). Not
just for the sake of ranges and granularities.

"
3.6.2.  Rank Properties

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

   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.
"

If we decide to go your way - I see some potential for simplification having
just one number that determines both cost and position in the DODAG.

Thoughts?

Regards,
Yoav

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Mukul Goyal
Sent: Thursday, June 17, 2010 8:33 AM
To: [email-masked]
Subject: Re: [Roll] [roll] #53: How does an OF compute rank from metric
values?

How about if we require a metric definition to provide a mapping to an
equivalent rank value. Then, the job of objective function becomes easier;
it just needs to combine equivalent values in the desired manner.

Thanks
Mukul

----- Original Message -----
From: "roll issue tracker" <[email-masked]>
To: [email-masked], [email-masked]
Cc: [email-masked]
Sent: Thursday, June 17, 2010 12:15:30 AM
Subject: [Roll] [roll] #53: How does an OF compute rank from metric values?

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From: [email-masked]
Date: Thu, 17 Jun 2010 10:03:37 -0500

I agree with Mukul.  The metrics
author should be compelled to draft the transfer function of metric to
rank.  This should then be explicitly noted in the draft.  Otherwise
interoperability will suffer since different implementations may not define
rank consistently.

The idea of melding the two measures
into one variable and making RPL simpler sounds even better!!!

Jerry

From:

Yoav Ben-Yehezkel <[email-masked]>

To:

Mukul Goyal <[email-masked]>, [email-masked]

Date:

06/17/2010 01:10 AM

Subject:

Re: [Roll] [roll] #53: How does an OF
compute rank from metric        values?

Hi Mukul,

"

3.6.2.  Rank Properties

The rank of a node is a scalar representation of the location of
that

node within a DODAG version.  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

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

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.

"

Thoughts?

Regards,

Yoav

-----Original Message-----

From: [email-masked] [mailto:[email-masked]]
On Behalf Of

Mukul Goyal

To: [email-masked]

values?

Thanks

Mukul

----- Original Message -----

Cc: [email-masked]

the metric?

[email-masked]

Roll mailing list

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