[Nsi-wg] NML topology

[John Vollbrecht]

I  would like to propose something for discussion.  I realize this may  
not be "the" answer, but I am hoping it can generate some discussion  
that will help us come to a good coordination of NML and NSI  
requirements - which I think are pretty close but not totally matched  
yet.

A couple comments about viewpoints -

NML is mostly concerned with topology and path finding requirements  
(not exclusively I understand)
NSI is mostly concerned with ownership and authorization

NML and deals with networking units basically nodes and links
NSI deals with sets of networking units owned by a NRM - it call these  
sets networks

A NSI network can be describe as a NML group specifically owned by an  
NRM - I don't think there is any problem with this.  Nodes and links  
can have owners in NML.

NSI network could be considered a hierarchical "node".  However NRMs  
own links as well as nodes, and no NRM link exists outside a network.

So - the proposal so far is to call the edge of a network a port, and  
a port may be on a NML node or link.  This is a problem because NML  
links don't have ports, so the proposal is to allow links to have ports.

How this helps is that now topology for pathfinding can be described  
between nodes over links without worrying about ownership, and  
reservation can be done using resources without worrying about  
topology between networks.

Some discussion of whether a link is described with ends independent  
of nodes for resource purposes and if the ends are actually ports  
might be helpful (or not).

At any rate, I think it would be good to discuss the problem and  
possible solutions at OGF.

John


On Feb 22, 2010, at 6:29 AM, Martin Swany wrote:

> 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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