[Nml-wg] Transitivity of hasPort

[Guy Roberts]

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 at 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.
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