[Nsi-wg] Some thoughts on STP

[Jeroen van der Ham]

Hello,

Please allow me to bundle my feedback on the identifier scheme
discussion. A short summary of the issue as I see them currently:
There needs to be a globally unique identifier for Service Termination
Points. This id does not have to be related to a point in a network
topology, but the local NSA must be able to map an STP id to a service
and/or endpoint in the network.

One possible solution: "The identifier can be just a string"
I would strongly argue against this line of thought. Strings are not
simple objects. There is a very valid reason why the definition of urn
identifiers for OGF (and NML) takes up half a dozen pages. The
construction and equality of strings is not trivial to define and should
not be underestimated.

I am very much in favor of urn-style identifiers similar in style to
what GLIF is using currently, using
urn:<identifier>:<network-name>:<localpart>.

The <identifier> is the urn namespace, most easily is to use a
subnamespace of the ogf, urn:ogf:nsi: springs to mind.
The advantage of this is that it is easy to set up, constraints on
content and equality are already provided and reasonably clear to users.

The <network-name> can be the DNS namespace that the NSA represents.
This also allows you to use a simple out-of-band verification of the NSA
using DNS TXT records or something.

The <localpart> can then be defined by the local NSA itself, and it has
complete freedom to define this within the confines of the urn syntax
limits as described for the namespace.

The whole system allows for a very simple scheme that makes it
immediately obvious what the identifier is for, and easily ensures
global uniqueness. Knowing the purpose of the identifier is important
because these will probably be used in many different contexts, as they
are used as advertisement of the service.

The identifiers may become a bit long, but given the fact that the NSI
protocol seems to converge on XML as a dataformat, I do not feel that
string-lengths is a problem.

One last point on VLAN identification:
I have seen some examples where the VLAN number is part of the
identifier. There is also an argument for STPs to not map to the network
topology so as to avoid a problem with 4095 different labels.
As far as I know right now NML will not create labels for endpoints for
each different VLAN, wavelength, timeslot or whatever. This should
become a property of the object the identifier identifies, not part of
the identifier itself.

Jeroen.