Evangelos, I think your simple graph described in #1 will not hold and we will need more than a single link between nodes. If we are supporting #5 then we could need multiple links to represent different values for the physical connections, especially if we are doing route diversity. In addition, there my be multiple links as a result of topology at different layers between the nodes (unless these are considered separate graphs). John. On 10-02-10 8:09 PM, Evangelos Chaniotakis wrote:
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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