[Nsi-wg] Topology properties for NSI - a minimalistic approach

[Evangelos Chaniotakis]

Hi all.

Here is my take on the topology issue:
- We SHOULD describe the topology properties that we think we will  
need for pathfinding.
- We SHOULD NOT assign too many semantics to the topology elements.
- We MUST NOT design a new topology schema.

Now for the things that I think are absolutely required properties for  
any topology:

1. The topology is a directed simple graph.
Note: Directed graph means each edge is an arrow with a start vertex  
and an end vertex. Simple graph means there are no parallel edges i.e.  
going the same direction between the same two vertices.
(I am on the fence for the "simple" requirement; do we need to make  
the topology a multigraph for some reason?)

2. We are allowed to separate the topology into mutually exclusive  
subgraphs. I will use Jerry's term "Network Domain" for these subgraphs.
Note: A subgraph is an arbitrary set of vertices and edges. It may  
consist of only edges, only vertices, or a mix thereof. A Network  
Domain is not necessarily a connected graph. (i.e. there is not  
necessarily a path between any two of its vertices).

3. The union of all Network Domains MUST equal (cover) the entire  
topology.
Rephrased: a given vertex or edge MUST belong to exactly one Network  
Domain.

4. A vertex belonging to a Network Domain MAY be connected to a vertex  
belonging to another Network Domain. In that case, that vertex for NSI  
purposes will be classified as a "Service Termination Point".

5. Edges and vertices MAY be annotated with attributes and metrics:  
i.e. framing, capacity, cost, etc.
Note: We MUST NOT specify those - this is a job for NML. But we SHOULD  
specify what we think we will need from these attributes.

6. Each vertex and edge MUST BE addressable through a globally unique  
identifier.


Note that in the above there are very few hard requirements for the  
topology graph - it can be as rich or as simple as necessary.

I have intentionally avoided assigned any names (such as "node",  
"port", "link", "point" etc) to the edges and vertices of the topology  
graph.

Finally, I think that the above requirements are enough to satisfy the  
needs of pathfinding. Can anyone think of any further requirements? Or  
is there a way we relax these even more somehow?



Here are a couple of examples of graphs (attached also in .graffle). I  
will work on more complex ones if needed but really, they will be  
pretty much equivalent to the graphs on Jerry's slides.

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