Hi, Jensen: Speak as individual, My answer to your following question is false as well, even based on RFC7285, defining hopecount as float point value seem also weird. I think we can rely on implementation or some automation tools for constraints checking, but it is not scope of this document. For other comments, I think Richard have addressed in v-13. Please double check it. Thanks
-Qin [alto] Review for draft-ietf-alto-performance-metrics-12 Jensen Zhang <jingxuan.n.zh...@gmail.com> Tue, 13 October 2020 04:17 UTCShow header<https://mailarchive.ietf.org/arch/msg/alto/qZrkPza-vEUcIqQMR3OJfk8G-uw/> Dear ALTOers and authors of draft-ietf-alto-performance-metrics-12, Below is my review for draft-ietf-alto-performance-metrics-12. Best regards, Jensen ============================================== General issue: The document is well written. I only have one question about the design part: the base ALTO protocol only uses the cost-mode to infer the value format, e.g., "numerical" infers the cost value MUST be a floating-point value; but this document requires different value formats for different cost-metrics, e.g., "delay-ow" requires the non-negative floating-point value, and "hopcount" requires the non-negative integer value. But based on Sec 11.3.2.3 of RFC7285, in the "constraints" field, "ALTO servers SHOULD use at least IEEE 754 double-precision floating point [IEEE.754.2008] to store the cost value". I wonder if a test constraint expression like "eq 3.1" for the cost-metric "hopcount" is valid. Should the ALTO server reject such a request? According to RFC7285, it should be valid. But according to this document, it is clearly always false. ============================================== Nits and writing suggestions: Section 1., paragraph 5: > The purpose of this document is to ensure proper usage of the > performance metrics defined in Table 1; it does not claim novelty of > the metrics. The Origin column of Table 1 gives the RFC which > defines each metric. Origin -> Origin Example (to be consistent with the table) > We can rough classify the performance metrics into two categories: > those derived from the performance of individual packets (i.e., one- > way delay, round-trip delay, delay variation, hop count, and loss > rate), and those related with bandwidth (TCP throughput, residue > bandwidth and max reservable bandwidth). These two categories are > defined in Section 3 and Section 4 respectively. Note that all > metrics except round trip delay are unidirectional. Hence, a client > will need to query both directions if needed. Section 2., paragraph 1: > When defining the metrics in Table 1, this document considers the > guidelines specified in [RFC6390], which requires fine-grained > specification of (i) Metric Name, (ii) Metric Description, (iii) > Method of Measurement or Calculation, (iv) Units of Measurement, (v) > Measurement Points, and (vi) Measurement Timing. In particular, for > each metric, this document defines (i) Metric Name, (ii) Metric > Description, and (iv) Units of Measurement. The Measurement Points > are always specified by the specific ALTO services; for example, > endpoint cost service is between the two end points. end points -> endpoints Section 2.1., paragraph 11: > A particular type of "estimation is direct "import", which indicates > that the value of the metric is imported directly from a specific > existing protocol or system. Specifying "import" as source instead source -> the source > of the more generic "estimation" may allow better tracing of > information flow. For an "import" metric, it is RECOMMENDED that the > "parameters" field provides details to the system from which raw data > is imported. In particular, one may notice that the set of end-to- > end metrics defined in Table 1 has large overlap with the set defined > in [RFC8571], in the setting of IGP traffic engineering performance > metrics for each link (i.e., unidirectional link delay, min/max > unidirectional link delay, unidirectional delay variation, > unidirectional link loss, unidirectional residual bandwidth, > unidirectional available bandwidth, unidirectional utilized > bandwidth). Hence, an ALTO server may use "import" to indicate that > its end-to-end metrics are computed from link metrics imported from > [RFC8571]. Section 2.2., paragraph 2: > percentile, with letter p followed by a number p: a number p -> a number Section 2.2., paragraph 16: > If a metric has no <stat> (and hence no - as well), the metric MUST recommend adding " surrounding -, or using dash character instead; if possible, giving the precise BNF grammar will be better, as I see some metrics names also include the dash character ("-"). > be considered as the 50 percentile (median). Since this scheme is > common for all metrics defined in this document, below we only > specify the base identifier. Section 3., paragraph 1: > This section introduces ALTO network performance metrics including > one way delay, round trip delay, delay variation, hop count, and > packet loss rate. They measure the "quality of experience" of the > stream of packets sent from a resource provider to a resource > consumer. The measures of each individual packet (pkt) can include > the delay from the time that the packet enters the network to the > time that the packet leaves the network (pkt.delay); the number of the time that -> the time when > network hops that the packet traverses (pkt.hopcount); and whether > the packet is dropped before reaching destination (pkt.dropped). The destination -> the destination > semantics of the performance metrics defined in this section is that > they are statistics (percentiles) computed from these measures; for > example, the x-percentile of the one-way delay is the x-percentile of > the set of delays {pkt.delay} for the packets in the stream. Section 3.1.3., paragraph 1: > Intended Semantics: To specify spatial and temporal aggregated delay spatial -> the spatial > of a stream of packets from the specified source and the specified > destination. The spatial aggregation level is specified in the query > context (e.g., PID to PID, or endpoint to endpoint). Section 3.1.4., paragraph 2: > "sla": Many networks provide delay in their application-level service > level agreements. It is RECOMMENDED that the "parameters" field of > an "sla" one-way delay metric provides a link ("link") to the SLA I assume that the second link (the one surrounding with ") means a field called "link", and the first link (the one without ") means the value of this field is a URI. Please make it clear. Adding an example could be better. > definition. Section 5.3., paragraph 2: > To address this issue, the only defined "routingcost" metric can be > ONLY "estimation". "ONLY" is not an RFC 2119 key word, doesn't have to be uppercase. Section 7., paragraph 3: > Since he This document requests the creation of the "ALTO Cost Source > Registry" with the following currently defined values: This paragraph seems to be incomplete and repeated to the next one.
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