[Nsi-wg] Determining the Network of an STP

[Freek Dijkstra]

Aside from the snarky comments, I guess we agree that solution #3 is
best from these listed solutions:

> A path computation engine needs to know in which domain a STP lies.
> 
> There are solutions to this:
> 1. The domain can be inferred by parsing the URN identifier of the STP.
> 2. Each domain announces a full list of it's STPs, and the path
>   computation engine keeps a table of all STP-Domain relations.
> 3. Each connection request must not only list the URN of the STP,
>   but the URN of the domain as well.

There is an open questions which variant to use:

A connection request must contain for each endpoint ...
3a. ... a globally unique identifier of the network (*)
    and a STP identifier that is unique within the context of
    this network.
or
3b. ... a globally unique identifier of the network (*)
    and a globally unique STP identifier.

For the record, ITU-T G.800 seems to follow 3a, while NML chose 3b. The
reason for NML was that 3b removed the need for scopes -- so NML would
also work in a scenario where the STP identifier is known, but the
Topology (network) identifier is unknown. Arguably this leads to a bit
of redundancy in the identifier in this use case. I nevertheless argue
that it is useful to use the same identifier as NML uses. The
alternative is either to maintain a NSI-NML identifier lookup table, or
a proposal to the NML group to revert the earlier choice, along with a
clear definition how to identify Ports, remembering that Ports can be
identified both in the scope of a network, as well is scope of a device
(without further knowledge of the network).

Freek

(*) I use the terms "topology", "network" and "domain" interchangeably
in this email. I'm referring to the concept of NML Topology or NSI Network.