[alto] link specific metric and aggregated metric

[Qin Wu <[e-mail]>]

Hi, Sabine:
As we know, link specific metric can be aggregated into a new network metric, let's call it path metric or end to end metric.
I am wondering whether we should introduce a new metric or we stick to the existing metric we defined in draft-ietf-alto-performance-metrics-01.
Take "availbw" as example, availbw is defined as TE specific metric or link specific metric(i.e., metric is measured on the link, if we want to introduce another metric to measure available bandwidth on the path from source to destination, we have two to do that:

1.       Define "path-availbw" metric, the measurement methodology for "path-availbw" is similar to one we used for link-availbw

2.       Stick to "availbw"metric we define in the document, but we use another parameter, e.g. using context-parameter to distinguish link availbw from path availbw. In this cse, the measurement methodology is same.
Another example is in draft-ietf-alto-performance-metrics-01, we define one way delay and round trip delay, there are two different cost metrics and measurement methodology for these two are different. I am wondering whether we should have a single metric delay metric and use some other parameter to distinguish one from another? Yes, context-parameter add a lot of flexibility and but also add complexity. How do you make sure the cost metric with different context can be parsed correctly.
What do you think of this? Comments and Suggestions?

-Qin