[Nml-wg] Metrics for pathfinding

[Freek Dijkstra]

On 06-06-2013 16:51, Paul Boven wrote:

> [...]
> At first glance, I would suggest adding attributes such as length,
> weight (preference) and bandwidth - as NML is extensible, should such
> extensions be coordinated by the NML-WG, or extensions that NSI
> themselves could create? Given the basic nature of these attributes, it
> would probably be best to have them centrally registered, to prevent
> multiple, incompatible versions (Length in m or km? Bandwidth in b/s or
> Mb/s?) from occurring.

I would like to see delay (in ms), (maximum) capacity of Links, and
(maximum) capacity and MTU of ports.

The problem with capacity is that it is highly non-trivial for the main
technology in use today, Ethernet. Two notes:
* Maximum achievable bandwidth of a channel (VLAN) depends on frame size
and interframe gap, and header size. (Most technologies define bandwidth
of the payload; to avoid these issues, Ethernet defines the bandwidth of
the underlying medium)
* Ethernet does not work with a achievable bandwidth, but instead
defines Committed Information Rate (CIR), Excess Information Rate (EIR),
Committed Burst Size (CBS), and Excess Burst Size (EBS).

For this reason, the proposal to make generic definitions was rejected
at OGF35, and it was suggested to define technology-specific definition
for each technology.

I agree that the above issues are irrelevant for a "rough estimate" as
you need. My fear is that we introduce a "rough estimate", an
application may later use it to check if it is possible to fit a data
flow within a pipe (thus is the bandwidth of the data flow is smaller
than the capacity of the pipe). GMPLS is doing this.

For reference, see http://tools.ietf.org/html/rfc6003#section-4.1 for
how GMPLS defined the bandwidth. I personally think it is way too complex.

Maybe we have to pick, and make some "experimental" parameter:
* Do you want a parameter that describes the capacity of the data flow
including or excluding the header?
* For Ethernet, do you want a parameter that defines the CIR or PIR
(=CIR+EIR), or do you prefer two (or four) parameters?

Freek