[Nsi-wg] Path Object information/function
Jerry Sobieski
jerry at nordu.net
Wed Jan 27 19:36:33 CST 2010
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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