Hello John,
If you mean to say that we should have another draft specifying the use
of bandwidth as an acceptable metric, that sounds just fine with me!
And, moreover, the experience of DLEP would be helpful.
No matter which specific metric you pick, it's not going to work for all
applications. Otherwise, we wouldn't have so many zillions of dollars
invested into QoS.
I know a good way to specify a cost metric that allows selection of the
path with the highest aggregate bandwidth. If you'd like to make a
draft along those lines, please let me know. If it would be useful for
DLEP, so much the better.
Regards,
Charlie P.
On 9/29/2015 1:36 AM, John Dowdell wrote:
Charlie
Stan, Vicky and I (not forgetting to mention Rick) have spent five years trying to work out how to get bandwidth and latency metrics from modems into routing protocols, so those metrics can be used to direct traffic in some fashion. There are lots of opinions on how best to do the directing so I’m not even going to go there, but suffice to say that I believe we should make an effort to incorporate outputs of DLEP into AODVv2. I will be the first to agree this is a non-trivial task, so I would be happy to vote for making this feature a separate draft.
On the other hand, from some observations of colleagues work in this area, I would suggest that a collection of metrics are often used to direct traffic according to some mathematical function. I would suggest it is not sensible to use bandwidth alone to prefer one route over another in the way that hop count has been used for decades, but most effectively when factored into such a calculation. Perhaps we should add some text on this point, which could then be used to placate the critics.
Regards
John
On 28 Sep 2015, at 06:38, Charlie Perkins <charles.perkins@xxxxxxxxxxxxx <mailto:charles.perkins@xxxxxxxxxxxxx>> wrote:
Stan,
It's not a problem at all to construct routes where hop count is not the best metric.
Was this at issue? Where did I say hop count was always best?
Or were you trying to suggest that bandwidth, as a non-cost metric, was sometimes useful? Well, yes, of course it is.
There are well-known cost metrics that enable comparisons of routes to select the one with the best bandwidth. I have mentioned them before in conversations on this list about this subject.
If my part of the discussion is simply to be dismissed as protestations, I wish someone would just tell me. I'd much prefer to know how to participate in a constructive discussion.
Regards,
Charlie P.
On 9/27/2015 2:52 PM, Stan Ratliff wrote:
On Sun, Sep 27, 2015 at 5:31 PM, John Dowdell <john.dowdell486@xxxxxxxxx <mailto: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
