Freek, I like the idea of creating an explicit service call switchingMatrix (for circuits) or forwardingEngine (for packets). So as Jeroen says, as soon as an switchingMatrix/forwardingEngine is instantiated in a node, all of the ports in the switchingMatrix/forwardingEngine are inherited by the node. I wonder if we should not distinguish between switchingMatrix and forwardingEngine, these have unique properties, for example a forwarding engine will try and forward any incoming packet to its egress destination, but has the ability to drop packets, whereas a switchingMatrix can have blocking properties, so either everything or nothing is forwarded. The reason I like the idea of explicitly nominating services types is that it maps to reality which is always nice :) Guy -----Original Message----- From: Jeroen van der Ham [mailto:vdham@uva.nl] Sent: 07 August 2009 15:00 To: Freek Dijkstra Cc: Network Markup Language Working Group Subject: Re: [Nml-wg] Transitivity of hasPort 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. _______________________________________________ nml-wg mailing list nml-wg@ogf.org http://www.ogf.org/mailman/listinfo/nml-wg