[Nml-wg] Network and domain abstractions

[Freek Dijkstra]

Jeroen van der Ham wrote:

>> I do not see why it is necessary to know about the terminating device 
>> for links in the external view. It seems to me that all I need to know 
>> is the encoding of the link, the the capabilities of the domain 
>> ('network' in my terminology) to act on this link.
> 
> You need to know about the terminating device, otherwise you cannot find 
> a path to it.

So you are saying that you want to find a path *to a terminating device 
in a domain*? I would rather find a path *to a certain domain*, and 
don't care exactly which device it terminates at.

To clarify: With "terminating device" I mean the first device that I 
encounter when crossing the domain boundary. I do not want to know about 
that. (Perhaps I want to be able to find a path to a certain device in 
the middle of a domain, if that is my final destination, but that is a 
different discussion.)


Allow me to give a short example. If I connect to the Amsterdam Internet 
Exchange, I know I connect to a 10 GE port on a switch, with certain 
properties. That's all I need to know. I don't care about the name of 
that switch. In fact, 4 years ago or so, the AMS-IX stopped terminating 
customer links at the switch, but put a optical cross connect (OXC) in 
between the customer and the switch. Like so:

               :
CUSTOMER  ----------- OXC ---------- Core switch
               :         \
               :          \
        domain boundary    ---------- Backup switch

Now if the core switch crashes, the OXC flips mirrors and withing 
milliseconds, the data is forwarded to the backup switch.

So what is the terminating device in this case? The OXC, the core switch 
or the backup switch? I don't want the name to change if the OXC flips 
its switch, since that it an event I don't (want to) know about.

Honestly, I don't care. All I care about is the service. As a customer, 
I call this interface "A", and don't care if this interface "A" is an 
interface in the OXC, the core switch or the backup switch.

Regards,
Freek Dijkstra