[Nml-wg] source/sink versus ingress/egress (was: Example topology of Automated GOLE)

[Jerry Sobieski]

Hi Freek-

Regarding the "connectedTo" or "mapsTo" terms in the NSI topology, those 
could be different strings if NML is already using them in a different 
sense.   We could in NSI use the term "sharesInterfaceWith" or 
"internallyTranslatesTo" for each of those respectively.   THis ould be 
a minor change for us.

More important to NSI is that there be the /semantics/ that those 
relations represent.

On a slightly different issue -
I saw a comment somewhere (maybe the minutes of THursday's call?) that 
said NSI was not using the SDP relations...  This is wrong.   NSI very 
much uses SDPs in the current topology.

SDPs are represented within an STP object with a "connectedTo" relation 
referencing another STP object.   Here is a OWL snippet:
<owl:NamedIndividual 
rdf:about="urn:ogf:network:stp:northernlight.ets:poz-1">
<rdf:type rdf:resource="http://www.glif.is/working-groups/tech/dtox#STP"/>
<connectedTo rdf:resource="urn:ogf:network:stp:pionier.ets:cphb"/>
</owl:NamedIndividual>
In this snippet, NorthernLight STP "poz-1" is in an SDP relationship 
with the Pionier STP "cphb".   The Snippet is the STP object defined for 
NothernLight.    A mirror image STP is defined in Pionier.   Thus a path 
finder traversing the networks in either direction will easily see the 
SDP relation.

There may be better ways to represent the SDP, this was what we did for 
the fall...We can discuss others...

The NSI topological _/representation/_ (i.e. the OWL/RDF form) could 
take other forms that we currently have as long as the semantics of the 
three key NSI objects are preserved: NSI Networks (service domains), 
STPs (edge ports/points), and SDPs (adjacencies).   These are I think 
represented in NML, though there is probably a different notion of 
"link" vs "SDP" that we need to reconcile...and maybe some of the 
mechanics of the "port" vs "STP" ...  These notions are very close.

Jerry

On 2/16/12 10:57 AM, Freek Dijkstra wrote:
> A somewhat related issue on source/sink. I don't think this was ever
> written down.
>
> Freek Dijkstra wrote:
>
>> The question at hand is basically how to describe the following (with
>> apologies with my poor ASCII art skills)
>>
>> port A    link X    port B    link Y    port C
>>    O------------------>O------------------>O
>>
> [...]
>> In the NML schema it is currently defined as:
>>
>>   link X
>>      relation=source
>>          port A
>>      relation=sink
>>          port B
>>   link Y
>>      relation=source
>>          port B
>>      relation=sink
>>          port C
> For the record, an alternative way to describe this is making the ports
> leading instead of the links:
>
>   port A
>       relation=egress
>           link X
>   port B
>       relation=ingress
>           link X
>       relation=egress
>           link Y
>   port C
>       relation=ingress
>           link Y
>
> Technically I think these are equivalent: the provide a directed
> relation between links and ports. Which one is syntactically better
> depends what is more common, a one-to-many or a many-to-one relation
> between ports and links.
>
> For the circuits, this is often a one-to-one relation.
> Since we implemented cross-connects as links, VLANs are likely also
> described as some kind of "link", but one with multiple sources and
> sinks. Hence, there is a one to many relation from link to port.
> This means that the source and sink relation we have now is more easy to
> convey in XML than the alternative ingress and egress relation.
>
> I personally think the source/sink stuff is still the best alternative
> we have.
>
> Regards,
> Freek
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