[Nml-wg] Transitivity of hasPort
Jeroen van der Ham
vdham at uva.nl
Fri Aug 7 08:59:39 CDT 2009
Freek Dijkstra wrote:
> 2) Transitivity from Node to Service:
> If there is a hasPort relation between a Node and a Port, and also a
> hasService between the same Node and a Service, then it is implied that
> there is also a hasPort relation between the Service and the Port,
> _provided that the Port is on the same layer as the Service_. This
> scenario was discussed in the call, and we added this condition to cope
> with Nodes with services on multiple layers.
This seems like a good idea to me. It also makes it a lot easier to map
GMPLS descriptions to NML. In GMPLS the port contains all the
information about the layer and the switching capability. You can then
easily map that to a port on a layer and a service on a node.
> 3) Transitivity from Service to Node:
> If there is a hasPort relation between a Service and a Port, and also a
> hasService between a Node and the same Service, then it is implied that
> there is also a hasPort relation between the Node and the Port.
>
> This last scenario was not discussed, but I think it makes more sense:
> this way we would not need the additional condition that the Port is on
> the same layer as the Service.
> Less conditions = better.
This makes sense, but then I have problems with the word "Service".
A "Service" in my mind is a generic thing that can be provided by many
providers, it is up to you to pick the service-provider you want.
In this case we are talking about an action that is specific to this
device, and will need a unique identifier. Then there cannot be two
"Services" that are exactly the same.
What we actually seem to be talking about is that we have a
SwitchingMatrix in a device, which performs the Service of switching at
a specific layer.
Then a switchingmatrix is a unique component to a device, so it is fair
to assume that any port attached to a SM is also part of the node. The
way that switching is done is a Service, which should be equal between
SMs on the same layer.
Jeroen.
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