[Nsi-wg] Fwd: Thoughts on a basic topology model for NSI

[Jeroen van der Ham]

On 09/02/2010 15:42, John MacAuley wrote:
> Jeroen,
>
> I agree with the statement that the signal node model would perform more
> poorly for optimal path computation, but would the computation of the
> summarized meshed links not be a costly on an on-going basis? These
> meshed links would need to be updated anytime there is a reservation
> added to the network that could impact the availability of the existing
> precomputed links. I this model are you providing the summarized
> bandwidth available between nodes? This would be an extremely costly
> calculation summing all potential bandwidth.

Yes, there will be a cost in maintaining an up-to-date topology. Again, 
reflecting on the current situation, the time between reservation is 
measured in days, not miliseconds, so this is not really an issue right now.

Then again, if you're doing a single node aggregation, you will be 
getting a lot more false-positives, which means that the clients will 
have to do recalculations.
I am not sure how the amount of calcalations in the two situations 
balance out. I think that it will fall negatively towards the single 
node aggregation, because each client has to discover false positives 
himself. In the full mesh situation it's calculated once and then shared 
with everyone.

> Do you have description of the mechanism used to compute the meshed
> topology? I wouldn't mind understanding in more detail if possible.

I think there are several mechanisms to do that.
The one I used is very simple: for each border node we do a Dijkstra's 
towards all the other border nodes. If there is a path available, then 
we add a link in the full mesh topology. I don't do anything fancy with 
the metric, it's set to 1 on every link.

Jeroen.