[Nsi-wg] Pathfinding, Labels, and Topology (a bit long)

[Jeroen van der Ham]

Hello,

I think it's most important to identify the requirements that we have for the topology, and work from there:

- We need to have some distribution method for topology
- This method must be maintainable for changes in the network, so it should allow updates.
- It must be possible to request a connection from port A with VLAN X to port B with VLAN X.
- It must be possible to request a connection from port A with VLAN X to port B with VLAN Y.

Nice to haves:
- Dynamic availability information for both links and labels.

Do we also want to include a connection from port A to port B where you don't care about the label?

After we have the requirements, we can look at solutions, and how these solutions solve those requirements, and what the implications of those solutions are.

Jeroen.


On 30 Nov 2011, at 11:01, Jeroen van der Ham wrote:

> Hello,
> 
> On 29 Nov 2011, at 03:47, Jerry Sobieski wrote:
>> Hi everyone - this is long (sorry) but this is a long held response to the so called "label" issue.   We need to engage on this...
>> 
>> Our topology model works just fine for path finding.  Period.  As is.   It is critical for people to understand this. It works for flat VLANs, it works for swapping, it works for essentially any network connection service.  Try to get away from conventional signaling ways of thinking and look at how NSI is positioned to do this and the power it brings.   NSI is about *connections* - not VLANs, not waves, not LSPs...  The abstraction it presents to the user is a connection model that works regardless of underlying technologies.
> 
> Our current topology model works in that it has a 1 in 4 chance of getting the right VLAN across a network is acceptable. However, we're still using only 4 VLANs, once we go to 4096, we get to a 1 in 4096 chance.
> 
> Pathfinding currently is done by the Aggregator NSA handling the request. He looks at the current topology, sees thousands of parallel SDPs and for crossing several domain boundaries, he just has to pick one randomly. I don't know about you, but I don't consider that "working just fine".
> 
> In the demonstration at SC we relied on the human to make requests from one endpoint to another endpoint, using the same VLAN. I have not seen any requests made using different VLAN labels.
> Also, I have seen and heard that NSA implementations used the last part of the ID to figure out the correct label and use that in their pathfinding algorithms.
> I do not think that that is a desirable solution.
> 
> Let me reiterate:
> The current NSI implementation is completely unaware of labels. This makes it near impossible to make informed decisions about paths crossing several domains. For each domain a path crosses the chance of finding the right path decreases exponentially.
> 
> The only way to make label unaware pathfinding work is by making 4096 versions of each of the different domains in the global network. The connections between those different networks will then depend on the label-swapping capabilities of those networks. Even with that solution, it is still hard, due to availability, and correlations between paths (if I use 10gb on one label, I can't use it again on a different label).
> 
> Note also that the number of domain descriptions will increase exponentially as soon as we start considering multi-layer networks.
> 
> 
> Jeroen.
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