Subject: [manet] #8: HopCount and alternate metrics in AODVv2

From: "manet issue tracker" <[email-masked]>
Date: Wed, 07 Nov 2012 16:56:47 -0000

#8: HopCount and alternate metrics in AODVv2

 Most of the language in the current specification for route metrics is
 actually specific to !HopCount.  It is proposed to rename existing metric
 fields to actually *be* !HopCount, to improve clarity.

 Following common practice up until now, the default route metric for
 AODVv2 is !HopCount.  Nevertheless, the document should allow for
 alternate metrics to be used.  To be compatible with RFC 5444 and the
 current reactive features, the following design guidelines are suggested.
  * a new AddTLV of type "metric" should be supported.  The metric AddTLV
    would supply metric values for each of the addresses in the !AddBlk
  * a metric 'type' should be supplied in a msg-TLV

 Whether or not the metric belongs in AODVv2 this year is a matter for
 discussion.  The design can be quite straightforward, requiring only an
 IANA registry for "metric type".  Given the flexibiity of RFC 5444 msg-
 header format, very general metrics could be supported.  Metric type '0'
 would be reserved for HopCount.

-- 
--------------------------------+-------------------------------------
 Reporter:  charliep@…          |      Owner:  Charlie Perkins
     Type:  enhancement         |     Status:  new
 Priority:  major               |  Milestone:
Component:  dymo                |    Version:
 Severity:  Active WG Document  |   Keywords:  route metric, hop count
--------------------------------+-------------------------------------

Ticket URL: <http://trac.tools.ietf.org/wg/manet/trac/ticket/8>
manet <http://tools.ietf.org/manet/>

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From: "JP Vasseur (jvasseur)" <[email-masked]>
Date: Wed, 7 Nov 2012 21:29:48 +0000

Hi Charlie,

> would be reserved for HopCount.

Completely agreeing. Although I love simplicity with only hop counts, it turns out not 
to always be the most relevant metric in MANET. It is not so rare to see shorter delays
on longer paths in terms of hop counts. Same comment for Packet Delivery Ratio (some
link may have really high ETX!).
Not suggesting to adopt a similar model as in RFC6551, but adding a bit of flexibility will
help in the future, even if we start with something very simple.

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From: Henning Rogge <[email-masked]>
Date: Wed, 7 Nov 2012 22:39:03 +0100

On Wed, Nov 7, 2012 at 10:29 PM, JP Vasseur (jvasseur)
<[email-masked]> wrote:
> to always be the most relevant metric in MANET.

In my experience Hopcount metrics don't work well in wireless networks
unless you have very specific links. Using hopcount as a metric means
you optimize for LONG links, which are often the ones that do not work
reasonable well. Without a well thought hysteresis your network might
just dissolve into a huge mess, especially for multirate networks like
IEEE802.11.

Saying "hopcount is the most relevant metric in MANET" is at best
shady... and at worst just wrong.

> It is not so rare to see shorter delays

I agree that not specifying the metric is a good idea (similar to the
way it has been done in OLSRv2), but hopcount only is a poor choice
for a metric.

Henning Rogge

-- 
Steven Hawkings about cosmic inflation: "An increase of billions of
billions of percent in a tiny fraction of a second. Of course, that
was before the present government."

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From: "JP Vasseur (jvasseur)" <[email-masked]>
Date: Thu, 8 Nov 2012 17:31:42 +0000

On Nov 7, 2012, at 10:39 PM, Henning Rogge wrote:

On Wed, Nov 7, 2012 at 10:29 PM, JP Vasseur (jvasseur)
<[email-masked]<mailto:[email-masked]>> wrote:
Hi Charlie,

we agree this is what I wrote ;-) … "Although I love simplicity with only hop counts, it turns out not
to always be the most relevant metric in MANET

indeed, this is why I was referring to the RFC6551 (being the editor of the document) although we may
not need all of these metrics.

JP.

Henning Rogge