[Nml-wg] About modelisation of the network description

[Aurélien Cedeyn]

Le samedi 01 mars 2008, Freek Dijkstra a écrit :
> Aurélien Cedeyn wrote:
> > I send you a little document that i made which describes a new object in
> > the NML : the model object. All the description and motivation about this
> > addon are in the attached document.
>
> Aurélien, thank you so much! Very good write down! These are the
> contributions that will help the NML workgroup a lot.
>

Hi Freek,
What an impressive mail :)
I'll try to answer shortly but clearly to your questions.

> I wholeheartedly agree with what you write, although I use different
> terms, and I don't understand all details of what your propose yet.
> Allow me to ask a bit, so I'll understand.
>
> > The NML goal is to instance modelisations of the real topology. This
> > real topology is too complex regarding the description needs of
> > applications, some informations are not needed.
>
> True, and true. But I think that modelling of the real topology is only
> ONE OF the goals of NML. What you write is that you also like to see NML
> capable of describing "modelisations" of the real topology (I would call
> it abstractions of the real topology). I wholeheartedly agree that that
> should also be another goal of NML.
>
> First a rather academic remark: what exactly is a "real topology" and a
> "modelisation" or "abstracted" topology? Most network engineers, even
> when asked for the "real topology" will describe fibers and devices, but
> still abstract a lot: they often leave out patch panels, and the
> internal workings of devices itself: because they either find it
> irrelevant (decribing patch panels is only relevant if you care about
> inventory management, or power loss details) or because they simply
> don't know the information (few people know how exactly devices work on
> the component level). In short: nearly everything is already a
> "modelisation", although the level of abstraction greatly differs
> between each model, and it is there where the discussion starts.
>

Exactly, that's what i mean with "Modelisations". The question is : "Does NML 
have to provide the extrem details of a real network such as patch panel ?"

> You propose an object "Model" for the abstraction of networks. So far
> I've seen "network", "domain" (in the perfSONAR schema),
> "abstract_link", "topology_point" (in cNIS), "AdminDomain", and
> "NetworkDomain" (NDL). I'm trying to figure out how these relate.
>
> Your examples seems to imply that there can be multiple Model objects
> for each domain, one for each abstractions. So the first example has a
> model with the layer 2 devices in a network, and a model with the layer
> 3 device in the same network. Is that correct, or is it a model
> describing the layer 2 switching capabilities and a model describing the
> layer 3 switching capabilities (rather than the layer 2/3 devices).
> The functionality compares to a single AdminDomain in NDL plus two
> SwitchMatrix instantiations (describing respectively the layer 2 and
> layer 3 switching capabilities), although the object relations are
> slightly different.
>
> Your second example is a new thing, which I have not seen before in one
> of the schemas discussed on this list. You seem to describe filtered
> views of a network. That is an interesting idea, but it seems different
> from an "abstracted view" of a network. In my opinion, a filter only
> describes part of the resources, while an abstraction describes the
> functions of all resources, but leaves out implementation details.
>
> Finally, while you did not describe it in text, your picture has a very
> important concept: you want to relate the network description (interco
> information) to other resource descriptions ("cluster information" and
> "frontend information"). I take it that is a similar concept as what
> Cees de Laat is presenting that -in that case RDF- can be used to link
> together different resource descriptions (see e.g. slide 20 presented at
> OGF 20, http://staff.science.uva.nl/~delaat/talks/cdl-2007-05-07.pdf)
>
> These are 3 different examples (describe capabilities, describe filtered
> view, link resources together), I at first did not understand the
> relation and what exactly a "Model" object represents. Am I correct that
> a "Model" simply means "a collection of resources"? If so, do you
> propose that the NML workgroup only describe this "grouping" object, or
> would you suggest to describe also dedicated grouping objects (e.g. also
> a "network" or "domain" object that describe specific groups of resources).

For me, the "Model" object groups objects which have relation between each 
other, they are "connected". Moreover, this group represent the network 
itself with a particular point of view. I think that with this concept we 
will be able to view cloud or a black-box as a network. Because whatever how 
deeply you describe your network, some information will be masked 
(constructor specs or some information you can not get).

I don't know if i answer to your questions, if not, feel free to ask me again.

>
> Regards,
> Freek
>
> (PS: sorry for the long mail)



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