Hi Qin and all, I agree with Dhruv's point. ALTO is expected to provide TE metric values on E2E paths. Therefore these values will necessarily be the result of a composition of link values (space aggregation). A typical operator on metrics related to available BW is the MIN of BW values on path links.
An E2E path may have heterogeneous links, of different dynamics, that may be monitored differently allowing thus no common parameters such as measurement intervals. We therefore assume that the path-wide E2E metric value is computed by the ALTO Server. So need to define ALTO TE cost value generation parameters that characterize the "accuracy" of the values: e.g. time aggregation ops. such as statistics, time interval on which the aggregation was done (e.g. at least MAX measurement interval on links), and other parameters to be discussed. Besides, I agree with Qin that percentiles are easy to process and usually trigger TE decisions as for example load thresholds. I think is useful to keep, in addition, full values on available BW (are related). The reason is that 50% of a capacity is not the same on a 10 Gb link than on a 10 Mb link. Last, the draft specifies a set of TE ALTO metrics that attempts to be as wide as possible. It does not mandate an ALTO Server to support all the metrics. Best regards Sabine -----Message d'origine----- De : Dhruv Dhody [mailto:[email protected]] Envoyé : mardi 22 juillet 2014 17:23 À : Qin Wu Cc : [email protected]; Y. Richard Yang; RANDRIAMASY, SABINE (SABINE) Objet : Re: statistics operators for ALTO cost metrics Hi Qin, One point to note that would be that metrics in IGP drafts are in terms of a TE link, in ALTO we need to worry about E2E cost ( or cost of an abstract link incase when ALTO also convey an abstract topology), so these cost metrics are composite metrics. ALTO server may rely on database populated by routing protocols, or a PCE, or a measurement system. Thus ALTO server rely completely on the source on how this cost metric is derived and all it can do is to specify the source (or composition mechanism) in its reply. Bandwidth is a bit different from the delay, jitter and loss which can be easily composed to an end to end metric. Bandwidth is well suited to filtering to get endpoints that can provide the requested bandwidth. As a cost it might either represent the bottleneck link for the E2E path. Question for us to consider is - do we need all of max bandwidth, max resv bandwidth, available bandwidth etc; and what format they should be in. Dhruv On Fri, Jul 18, 2014 at 8:13 AM, Qin Wu <[email protected]> wrote: > Hi, > > Motivated by RFC3630 and draft-ietf-isis-te-metric-extensions, we > define 11 alto cost metrics, > > The value of these alto cost metrics are high aggregated value, we may > have several statistics operators, e.g., > > Mean, variance, avg, percentile). > > In the current draft, delay and delay jitter are both on delay, we use > mean > > For delay and use variance for delayjitter. > > It is not clear these statistics operator are appropriate for them? > E.g., should we use percentile for bandwidth related cost metric? > > Any opinion? > > > > Regards! > > -Qin _______________________________________________ alto mailing list [email protected] https://www.ietf.org/mailman/listinfo/alto
