[Nsi-wg] Path Object information/function

[Jerry Sobieski]

Hi John-

I am deleting some of the text to make the email a bit more readable...

John Vollbrecht wrote:
>> Jerry wrote:
>> Not sure what you mean here...  From Jeroen's comments, we might have 
>> two indicator bits: one that says "This hop is strict", and a second 
>> that says "This hop is required".   The former means that this hop 
>> should be and is expected to be adjacent to the previous hop within 
>> the service transport layer.  
>
> So adjacent needs to be defined.  Do you mean ordered, in the sense 
> that other hops might be inserted but the order must be correct?  This 
> might be the case where a high level set of POs might be requested and 
> these might later include lower (hierarchically) paths.  Or is there a 
> definition of adjacent that requires lowest level POs (and what is 
> lowest)?
>
"Adjacent" means "directly next to each other."   I will get pedantic 
now(:-):  Two vertices in a graph are adjacent if they are connected by 
an edge.   Within our network topology model, two Nodes, A and B, are 
/adjacent/ if there exists a Link in the toplogy that has one endpoint 
on A and the other endpoint on B.   A Link, which represents an 
immutable transparent transport conduit between two Nodes in the 
topology,  by definition, establishes adjacency between those two nodes.

In the PO, a "strict" hop means simply that the path from hop(k) to 
hop(k+1) transits no (zero) intervening nodes. i.e. hop(k) and hop(k+1) 
should be or are expected to be /adjacent/ in the topology.    The 
latter hop, the k+1 hop in this example, would be flagged as "strict" in 
this case.     In the PO, the order of the hops is important, but the 
strict/loose tagging only implies something about the possible presence 
or absence of intervening nodes.

To be clear about adjacency, if a Link in the topology is realized over 
lower layer infrastructure - even if that infrastructure itself is part 
of the topologyDB - the Link still constitutes adjacency since the 
underlying supporting infrastructure is transparent to the layer at 
which the Link is defined in the topology (i.e. the nodes it connects).  
This allows us, for example, to allocate a GFP/SDH circuit over an SDH 
cloud and define the resulting ethernet connection in the topology as an 
Ethernet Link forming an adjacency between two Ethernet Nodes.

Jerry
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