[aodvv2-discuss] Re: Metrics (removing references to alternate metric types)

  • From: Stan Ratliff <ratliffstan@xxxxxxxxx>
  • To: "aodvv2-discuss@xxxxxxxxxxxxx" <aodvv2-discuss@xxxxxxxxxxxxx>
  • Date: Sun, 27 Sep 2015 17:52:35 -0400

On Sun, Sep 27, 2015 at 5:31 PM, John Dowdell <john.dowdell486@xxxxxxxxx>
wrote:

Charlie

On 24 Sep 2015, at 21:48, Charlie Perkins <charles.perkins@xxxxxxxxxxxxx>
wrote:

Hello John,

Follow-up below...


Bandwidth is not a cost metric. The calculation of LoopFree() might be
more complicated. I don't like non-cost metrics for various reasons. One
reason is that they contradict the entire mathematical formulation for
metrics and metric spaces. On the other hand, some people in the IETF
don't have much respect for mathematics, it seems, and I get tired of
complaining about it.

Regards,
Charlie P.


Bandwidth is a metric (along with latency, both of which are declared as
metrics in DLEP). You can use it to influence routing decisions, but I’ll
agree that it doesn’t work to completely drive a route selection in the way
that hop count does.


So, let me construct a network scenario where I have two paths to a device:

Source------Router1--------Router2---------Router3-------Router4-------Destination

But, all of the dashed lines in the above description depict 10Gb/sec
copper.

Second path:

Source-----Router1-------------------Router3-------Router4------Destination

But the long dashed line between Router1 and Router3 is a satellite backup
link, at 1Mb/sec. I understand - it's a hypothetical case. But stuff like
this pops up all the time in real networks.

First route, hop count 5. Second route, hop count 4. Based on Charlie's
protestations, I should assume the second route is better than the first?
FWIW, I don't. If there's any way on earth I can take the first route, I
will.

Stan






I believe it is also impossible to calculate LoopFree() just using
bandwidth, so maybe you’d have to use a combination of hop count and
bandwidth, but that is a discussion for another draft.

Regards
John

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