[Nsi-wg] NML topology

[Martin Swany]

Hi All,

From a practical perspective, links are always "owned."  For a zero-cost
link at an exchange point, the ownership may be less clear, but even in
that case, our perspective has been that the egress part of the unidirectional
link is owned by the network/node/port that is driving it.  The link itself really
has few properties outside of propagation delay and loss, but has addressing
and queueing properties that are assigned to the port driving it and that port
*always* has an owner.

That said, I found John's slides and this point to be interesting and thought-
provoking.  But I would still encourage things to be expressed to the NML
in terms of requirements rather than terminology.  There are ports and links
and they are owned (at least by my definition above).  In the described case,
there are different policies that need to be applied for inter-domain links and
ports that dynamic.  I still don't think that we need a new a "thing" to describe
the same old "thing" with different roles and policies.

best,
martin

On Feb 22, 2010, at 6:00 AM, Guy Roberts wrote:

> Jeroen,
> 
> If we put aside the question of point vs port naming for the moment,  I think that John's slides raise an important question.  This is how best to describe connectivity between networks.
> 
> One option is to carry over the exiting NML concepts and assign a link as the connection between two networks.  In this case the link will have to be 'un-owned'  i.e. it is not within the control or ownership of either network.
> 
> The alternative option presented by John is to use a port or point concept to joint two ports on adjacent networks.  In this case there are no objects (i.e links) between networks - this solves the problem of un-owned resources.
> 
> To understand the implications of the existing NML model better, lets take the example of a fibre that connects two Ethernet switches in adjacent racks.  In this case I expect that the NML model will nominate the two Ethernet ports on the switches as 'Ports' and the fibre as a 'Link'. In this example it might be possible to replace the fibre with a transatlantic wavelength leased by one of the end networks. The question in my mind is how we allocate ownership of the inter-domain 'link'.
> 
> If we follow John's model and insist that there are no resources that are 'un-owned', then we need to allow the modelling of connectors that do not belong to switches.  So going back to my previous example, the demarcation point between networks moves from the Ethernet ports on the switches to a connector on a distribution frame that marks the boundary of physical ownership between the two networks.  In other words the schema would model the demarcation point between networks in a much more literal physical way.
> 
> The question in my mind is whether there is a real use-case for the second model.  Does NSI need to model the demarcation of ownership of items in the inter-network space, eg wavelengths or patch chords between providers?  This is a interesting question and needs a very clearly documented use-case.  
> 
> 
> Guy
> 
> -----Original Message-----
> From: Jeroen van der Ham [mailto:vdham at uva.nl] 
> Sent: 21 February 2010 21:08
> To: John Vollbrecht
> Cc: NSI WG
> Subject: Re: [Nsi-wg] NML topology
> 
> On 21/02/2010 18:20, John Vollbrecht wrote:
>> Attached is set of ppt slides to describe interdomain topology.  I
>> hope this helps - it is based on conversations in the NML group, and
>> is my understanding of what the Glossary of terms that Guy is
>> reviewing (and I think will review next Wed).
> 
> I just want to clarify my view of the conversation we have had in the 
> NML group about this issue. This was mainly a discussion between myself 
> and John wherein I tried to understand the NSI issue of describing 
> inter-domain topologies.
> 
> The current NML topology model does not have "Points". Nor do we 
> currently have plans to add them. *Unless* there is a use-case showing 
> the need of Points, which clearly outlines why it is not possible to 
> describe domain boundaries with the current NML Topology model. So far, 
> I have not seen such a clear and valid use-case for "Points".
> 
> Jeroen.
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