Martin -This seems a good discussion - thanks. -- based on the fact that describing DCN is part of what NML should be able to do, I expand on your ideas below. It seems to me that one possible result is that we generate a "view" of the schema for DCN. This view would include only the aspects of DCN that are important for creating dynamic networks - e.g. networks, nodes, ports and links in the form we use right now. One specific is that for static connections between dynamic nodes, it is good to describe the statically configured devices for monitoring and debugging purposes, but these static devices are not needed when doing pathfinding or reservations. More below. On Jun 26, 2008, at 7:03 AM, Martin Swany wrote:
Hi John,
This is a great set of questions and get right at the heart of the problem.
From what you say, I assume that a logical link between two ports would be what in DCN I call a path segment. A path segment has uses some resource on a physical link. in this case, each logical link then can have an adaptation. This is ok - but --
where is a physical link described? how do I know how a physical link can be subdivided into dynamic logical links? how do I create an ete circuit that is a concatenation of logical links. How do I name the ete circuit and treat it as an entity that is time variant?
The physical link is described as another link (indicating that it is physical) and enumerating its characteristics.
To me the physical link is the basic element. Virtual or logical links may exist but are built by "relations" with physical links. Is this wrong.
Next, we'd need to describe the relationship between this physical link and the logical links atop it. In our model (where "our" is the topology schema folks in perfSONAR @ Internet2) we have an element called "relation". As I think I mentioned, this is one sense of the "adaptation" concept from the NDL. At any rate, we must represent the case you're highlighting. I think adaptation is also a G.805 term, and is perhaps a specific type of relation.
I think the implication of what you suggest is that there needs to be a switch between links on a node. Then there needs to be a way to specify which pieces of a link switch to which pieces of a different link. Do you agree? I think each link segment may be "adapted" in a way that deals with that stream so that it can be switched at a different level (or format - is switching between SONET and Ethernet swithcing levels or just formats?) Also, I don't think there is a name for a concatenated sequence of link segments (or whatever you call them). Perhaps there is some concept that I don't know.
These are what seems to me to be needed for DCN, to both create reservations and circuits, and to monitor the reservations and circuits.
Absolutely. Hopefully, this begins to address it.
best, martin
John Vollbrecht, Senior Network Engineer Internet2 office +1-734-352-4960 | mobile +1-734-395-7890