[Nml-wg] Adaptations

[John Vollbrecht]

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
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