Re: [ippm] John Scudder's Discuss on draft-ietf-ippm-rfc8889bis-02: (with DISCUSS and COMMENT)
Giuseppe Fioccola <giuseppe.fioccola@huawei.com> Tue, 12 July 2022 17:41 UTC
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From: Giuseppe Fioccola <giuseppe.fioccola@huawei.com>
To: John Scudder <jgs@juniper.net>, The IESG <iesg@ietf.org>
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Thread-Topic: John Scudder's Discuss on draft-ietf-ippm-rfc8889bis-02: (with DISCUSS and COMMENT)
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Date: Tue, 12 Jul 2022 17:41:29 +0000
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Subject: Re: [ippm] John Scudder's Discuss on draft-ietf-ippm-rfc8889bis-02: (with DISCUSS and COMMENT)
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Hi John, Thanks again for your revision. Please find my answers inline tagged as [GF]. I plan to address your comments in the next revision. Best Regards, Giuseppe -----Original Message----- From: John Scudder via Datatracker <noreply@ietf.org> Sent: Tuesday, July 12, 2022 5:36 PM To: The IESG <iesg@ietf.org> Cc: draft-ietf-ippm-rfc8889bis@ietf.org; ippm-chairs@ietf.org; ippm@ietf.org; tpauly@apple.com; tpauly@apple.com Subject: John Scudder's Discuss on draft-ietf-ippm-rfc8889bis-02: (with DISCUSS and COMMENT) John Scudder has entered the following ballot position for draft-ietf-ippm-rfc8889bis-02: Discuss When responding, please keep the subject line intact and reply to all email addresses included in the To and CC lines. (Feel free to cut this introductory paragraph, however.) Please refer to https://www.ietf.org/about/groups/iesg/statements/handling-ballot-positions/ for more information about how to handle DISCUSS and COMMENT positions. The document, along with other ballot positions, can be found here: https://datatracker.ietf.org/doc/draft-ietf-ippm-rfc8889bis/ ---------------------------------------------------------------------- DISCUSS: ---------------------------------------------------------------------- Thanks for this document. As you may have noticed I had considerable difficulty with the definition of "cluster". Once I completed an end-to-end read-through, this was resolved (good!) but because RFCs are often consumed piecemeal (e.g. someone may just dip into a portion of a document rather than settling down with a nice cup of tea to read it end-to-end), I think it's important to fix this problem, on the assumption I'm not the only person who might be thrown off. [GF]: No problem. I agree with you. It is better to improve the readability. I'll leave the details in the COMMENT, but I will repeat one observation from my comment #3, which is that I count at least four separate (re-)definitions of "cluster" in the document. With so many, it's no wonder that they're inconsistent, and quite possibly the simplest solution would involve cutting the number of definitions down to as close to 1 as possible. [GF]: Your suggestion to keep only one definition of cluster makes sense to me. I can probably keep only the definition in the Terminology section and align the others or refer to section 2 where necessary. ---------------------------------------------------------------------- COMMENT: ---------------------------------------------------------------------- I support Roman's DISCUSS. 1. In §1, this While this document and its Clustered Alternate-Marking method is valid for multipoint-to-multipoint unicast flows, anycast, and ECMP flows. This is a sentence fragment (a naked subordinate clause). I'd suggest a rewrite but I can't make out what you are trying to say. [GF]: This is about the scope. Maybe I can replace "is valid for" with "apply to" 2. You have multiple definitions of "cluster" in the document, it seems. In §2 you have, Cluster: Smallest identifiable subnetwork of the entire monitoring network graph that still satisfies the condition that the number of packets that go in is the same as the number that go out. A cluster partition algorithm can be applied to split the monitoring network into clusters. As we have discussed in the past, according to this definition, a cluster is always a single router. I think in an earlier discussion you suggested that it could be corrected by saying something like "smallest subnetwork larger than a singleton router", which I think would work, "smallest non-trivial" would too (although it's less explicit). [GF]: I already revised the sentence in my local version and in draft-ietf-6man-ipv6-alt-mark as well. But then in §5 you have, In addition, it is also possible to leverage the data provided by the other counters in the network to converge on the smallest identifiable subnetworks where the losses occur. These subnetworks are named "clusters". As written, this makes nonzero losses a definitional attribute of a cluster. Now that I've taken in the entire document, I guess this is the incorrect definition. Possibly a fix would be to just drop the final sentence, which (incorrectly?) implies that losses are an essential element of the definition. [GF]: I see your point. I will delete that sentence and refer to the definition in the Terminology section For what it's worth, the algorithm of Section 5.1 is perfectly clear. I see the desire to have a prose description of what a cluster is trying to do, but I wonder if in the end it would be best to make the algorithm the canonical definition, referenced from the prose definition as in Cluster: Smallest identifiable non-trivial subnetwork of the entire monitoring network graph that still satisfies the condition that the number of packets that go in is the same as the number that go out. A cluster partition algorithm, such as that found in Section 5.1, can be applied to split the monitoring network into clusters. [GF]: Good suggestion. In this case I could probably move the prose description and the related example to an Appendix. 3. In §5, you have A cluster graph is a subnetwork of the entire monitoring network graph that still satisfies the packet loss equation (introduced in the previous section), where PL in this case is the number of packets lost in the cluster. I'd previously pointed out that this is problematic since the PL equation you mention is in the nature of a definition; since you don't supply a condition there's no way of saying whether it's "satisfied" or not. In response you said (https://mailarchive.ietf.org/arch/msg/ippm/iXSBuXrQaETl6MyeDH8DBaPiJ9Q/), ``` We can modify the wording in Section 5 accordingly: "A cluster graph is a subnetwork of the entire monitoring network graph that still satisfies the condition that the number of packets that go in is the same as the number that go out, if no packet loss occurs." ``` If indeed that is the right definition (see my earlier point, so probably inserting "non-trivial" or "with more than a single router") then I do think you should make that change, or in any case you should correct the current text somehow. [GF]: Already done in my local version. By the way, do you mean something subtly different by "cluster graph" than you do by "cluster"? Or do you just mean "the graph that represents the cluster"? I think my confusion over just what a "cluster" is would have been mitigated by fewer re-definitions of it. If "cluster graph" is indeed just another way of saying "cluster" it's the third of four definitions! (The two I mention in my point #2, this one, and the algorithm in Section 5.1.) With four definitions of the same thing, in different words, no wonder some inconsistency crept in! [GF]: Yes, with cluster graph I only meant the graph that represents the cluster. It is not a new definition. For this reason, I will probably remove some of these definitions and simply refer to Terminology section. 4. In §5.1, In summary, once a flow is defined, the algorithm to build the clusters partition is based on topological information; therefore, it considers all the possible links and nodes crossed by the given flow, even if there is no traffic. If a flow has no traffic, can we call it a flow? It seems counter to the normal English meaning of the word. Perhaps you mean possible links and nodes that could potentially be crossed by the given flow? [GF]: Yes, I will fix. 5. Thanks for reporting the outcome of the earlier experiment, in §9. As with my review of rfc8321bis, I think the RFC 2119 keywords need to be in a "Deployment Considerations" section or similar, which could be achieved by retitling this section or by separating the material into reporting the experiment outcome (this section) and a new subsection for deployment advice. [GF]: Agree. As per RFC8321bis I can retitle the section. 6. Again similarly to my review of the companion document, I think §9's "the Multipoint Alternate Marking Method is RECOMMENDED only for controlled domains" needs to be fixed. Please bring it into line with whatever language you choose for rfc8321bis. [GF]: Sure. Similarly to RFC8321bis, I will replace it with: "The Multipoint Alternate Marking Method MUST only be applied to controlled domains." Nits: 7. While the reference tags are in principle arbitrary strings, I wondered if it was a typo that you used "PNPM" to tag a paper titled "AM-PM"? [GF]: It was not a typo since PNPM stands for Packet Network Performance Measurement. But AM-PM can also be used. 8. In §7.1.1, This means that, in the calculation, it is possible to weigh the timestamps by considering the number of packets for each endpoints. s/endpoints/endpoint/ [GF]: Ok
- [ippm] John Scudder's Discuss on draft-ietf-ippm-… John Scudder via Datatracker
- Re: [ippm] John Scudder's Discuss on draft-ietf-i… Giuseppe Fioccola