Subject: [Roll] draft-ietf-roll-routing-metrics-07 - link/path/local/global metric

From: Omprakash Gnawali <[email-masked]>
Date: Sun, 13 Jun 2010 23:37:17 -0700

I had a comment on the terminology used in draft-ietf-roll-routing-metrics-07.

Lets take ETX as an example.

There is the notion of link ETX. Then, there is the path ETX - ETX
aggregated over the links on a path.

In the draft, ETX is described under the section link metrics. So, I
thought we were talking about link ETX. But near the end it says:

"   The ETX object is a global metric or constraint."

So, we are talking about path metric it seems.

Then, in section 8.1 Routing Objects, we are talking about Link ETX:

"   IANA is requested to create a registry for Routing objects.  Each
   Routing object has a Routing object type value.

  Value     Meaning                          Reference
     1       Node State and Attribute      This document
     2       Node Energy                   This document
     3       Hop Count                     This document
     4       Link Throughput               This document
     5       Link Latency                  This document
     6       Link Quality Level            This document
     7       Link ETX                      This document
     8       Link Color                    This document
"

For metrics such as latency and etx, I find it much clearer to use the
phrases link metric and path metric (e.g, link etx/latency, path
etx/latency) rather than local and global metric.

- om_p

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From: JP Vasseur <[email-masked]>
Date: Mon, 14 Jun 2010 10:08:15 +0200

Hi Omp,

> etx/latency) rather than local and global metric.

Thanks for your comments. The reference "link" versus "node" allows  
for making the disctinction
between a metrics that applies to a link or a node. Now, when the ETX  
metric is included in the
DAG Container, it reflect the ETX of the path, made of a set of link  
ETX (which may have been
added, multiplied, ... etc), as indicated by the A flag.
The notion of local versus global is different. When a metric is  
local, it is only passed to a direct
neighbor (and of course consequently as you pointed out never refers  
to a path ).

Hope this clarifies.

Thanks.

JP.

>
> - om_p
> _______________________________________________
> Roll mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/roll

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From: Alexandru Petrescu <[email-masked]>
Date: Mon, 14 Jun 2010 20:11:47 +0200

Le 14/06/2010 10:08, JP Vasseur a écrit :
> Thanks for your comments. The reference "link" versus "node" allows for
> making the disctinction
> DAG Container, it reflect the ETX of the path, made of a set of link ETX
> (which may have been
> The notion of local versus global is different. When a metric is local,
> it is only passed to a direct
> neighbor (and of course consequently as you pointed out never refers to
> a path ).

Hi JP,

Let me add to the metrics discussion.

I have suggested numerous times that a _link_ energy metric (not ETX, 
not node) be added to the draft.  I have suggested detail encodings and 
behaviour.  I am surprised none appears.  Should I re-send?

I have also seen discussion about the asymmetric link metrics, to which 
I suggested there are means to suggest asymmetric behaviour of energy 
spent to send a packet.  The energy link metrics I suggest do respect 
the asymmetricity aspect.  Should I re-send?

Alex

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From: JP Vasseur <[email-masked]>
Date: Wed, 16 Jun 2010 07:47:50 +0200

Hi,

On Jun 14, 2010, at 8:11 PM, Alexandru Petrescu wrote:

> I have suggested numerous times that a _link_ energy metric (not  
> ETX, not node) be added to the draft.  I have suggested detail  
> encodings and behaviour.  I am surprised none appears.  Should I re- 
> send?
>

Please do. As I recall, there was no consensus to add it. With a co- 
author hat, I expressed my sketicism but if there is a consensus at  
some point, it should be added.

> I have also seen discussion about the asymmetric link metrics, to  
> which I suggested there are means to suggest asymmetric behaviour of  
> energy spent to send a packet.  The energy link metrics I suggest do  
> respect the asymmetricity aspect.  Should I re-send?
>

Sure.

JP.