[Nml-wg] Topology Model and Pathfinding

Wed Feb 10 13:10:40 CST 2010

Hello John,

I'm replying to the NML list, because I strongly believe that this issue 
must be discussed there.

I think I understand your point now, I've created a diagram (attached) 
that I think describes the situation.

The top view shows the physical topology, there are two networks, 
connected by an inter-domain link, which is owned by a third party.

At the bottom I've tried to capture the way that you would like to 
describe this situation. Is that correct? I've attached the graffle file 
too so that you can correct it if I'm wrong.

Jeroen.

On 10/02/2010 09:51, John Vollbrecht wrote:
> Hi Jeroen --
>
> I cc some others in case they have comments.
>
> The issue is what I was discussing with you at JTs. I will try to
> describe it better over the next few days. I certainly agree (as I said
> when we discussed this) we should talk about it at OGF or before.
>
> Let me try a bit to describe the issue now - comments will be helpful in
> getting a good description.
>
> I think the basic thing is that the atomic element in NSI is the set of
> resources that is controlled by a NRM (network resource manager). Those
> resources include switches/nodes a links in your terminology. For sake
> of argument call such a set of resources a network.
>
> I think network could be covered in NML by calling such a set of
> resources a group or a network group. For NSI (as I understand it) edge
> of a network is a port, where a port may be on either a link or node in
> NML terminology. This is where NML topology is missing a terrm - the
> concept of a port at the end of a link. If that were there we could have
> a simple mapping between NML and NSI concepts.
>
> Networks interconnect by joining ports together at a point. A point
> might be considered to be where a male and female connector join -
> either physically or logically. This is essentially the ASON (ITU
> G.8080) model for interconnection of subnetworks. If NML has the concept
> networks connecting at ports then I think there would be good mapping
> between NML, NSI and ASON.
>
> If we use this model, then the NSI topology is of a set of networks
> interconnected at points (or by connecting ports). By definition network
> can (potentially) make a connection between any two points - so from a
> graph point of view, a network is a vertex and a point or joined ports
> are edges.
>
> Some conversation --
> To help resolve this and help possible conversation about it, I offer my
> understanding of the NML issue with this. Please correct me if I have it
> wrong. From a topology point of view NML assumes both ends of a Link are
> the same and can be identified by the node to which they connect. Adding
> ports to the end of links increases the number of items that must be
> defined in a topology which makes definition of a topology longer and
> longer. Further, since topology is well defined as between node and link
> it is not clear why treating networks as supernodes with links between
> them doesn't work.
>
> There may be some way to combine these that I haven't thought of or
> understood yet. The problem I see from a inter-network (NSI/ ASON) point
> of view is that links are resources that are part of one or another
> network, not something outside them. From a reservation and provisioning
> point of view each network must make a connection between its ports.
> Ports from two networks are connected in a topology so when connections
> across the networks are provisioned, the concatenated connection across
> both networks is provisioned.
>
> Perhaps there is a way that topology and resources can be separated so
> that links don't have to have names and are implied. From a provisioning
> and monitoring view the control is certainly in a node, and so there may
> be a difference between what is the resource termination point and the
> control points.
>
> The one problem that having implied names doesn't seem to be able to
> handle is when a link is a resource independent of nodes at either end.
> In this case the link is a network which must be included in the
> topology for resource reservation and scheduling even though it is not
> included in the control topology.
>
> ---
> I am interested in comments and suggestions - of course. I think this is
> a very important concept to work through between groups.
>
> John
>
>
>
> On Feb 10, 2010, at 11:07 AM, Jeroen van der Ham wrote:
>
>> Hi John,
>>
>> The NML set out to create a topology model that is sufficient to do
>> pathfinding, at least on the topological level. I understand from the
>> discussion with you that you feel that NML is currently not providing
>> enough terminology to fulfill the needs of NSI pathfinding.
>> I think it is important that this is discussed in the NML group.
>> However I don't feel I have enough understanding of your problem to
>> make a good case for it. Would you mind explaining your problem to the
>> NML mailinglist?
>>
>> Thanks,
>> Jeroen.
>
>
>

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