[tcpm] Comments on ECN++ (rev 02)
Gorry Fairhurst <gorry@erg.abdn.ac.uk> Mon, 20 November 2017 06:03 UTC
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Date: Mon, 20 Nov 2017 07:03:28 +0100
From: Gorry Fairhurst <gorry@erg.abdn.ac.uk>
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Subject: [tcpm] Comments on ECN++ (rev 02)
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tcpm@ietf.org I reviewed this draft prior to the IETF-100 meeting, but did not manage to send notes until just now. Thanks for this revison! Overall, I had three observations and some comments on the writing iof the current ID. * It seems like a silly question, but as I read this I do wonder: Do we **need** to allow ECT(1) on SYN as in 3.2.2.1? * I think the AccECN studff requires a decision on how to present the info differently. This talks about recommending AccECN implementation, which implies a reader beds ti read both this and AccECN together. Both of these are long documents, and when you read these together one discovers many areas of overlap - but the pieces neded are in both drafts. ... One thing I suggest we consider is whether the ECN++ draft simply defines the method when AccECN is not supported. The AccECN draft appears to contain the machinery to allow ECT on SYN. One drawback is that the AccECN draft does not define mechanisms to react, but does define fallback. It could even be that the simplest is to write 3 drafts - having one just on AccECN+ECTonSYN? ... The considerations for reaction to CE-marked SYN and the implications of loss seem to be one area of experimentation, hence placing this in one place may help identify whether that experiment has suceeded. I'll type-up my notes on AccECN next. Whatever, the two drafts are not consistent on the use of caching, and specifying the SYN processing once I think would help to simplify things. If this is the direction, Table 1 could then be simplified, and one could add a column showing the section number where the topic is discussed? * The section 4 is quite long. I'm not sure of who is the real target (or tragets) for section 4 and I think this therefore needs to be made clearer, so that people would know beforehand whether they should read the whole of this section. Gorry --- Some more specific comments on the text in the -02 draft: (1) Style: The introduction sectionc contains a "RECOMMENDS: statement recommending AccECN. This comes before the IETF keyword declaration, and is not normal for an introduction. I suggest you avoid keywords in the intro. (2) Final para of 1.1 - I really dislike the way this statemnent somehow reads as asserting the value of "ongoing experimental efforts to promote the adoption of a ***slightly*** modified variant of DCTP". I suggest the should be English improved here, to avoid making the prior claim that this is "slight" (even if it may turn out to be so). e.g., if the WG thinks the work should be based on DCTP, I'm sure the ID can say ths, but I'd really prefer we simply state the effort to build an IETF transport for L4S. (3)Final para of 1.1: Is there really a problem with the SYN packet travelling via a different queue? The text suggests reordering is an issue, which I do not understand. I'd have thought a SYN packet was the only packet in flight when the connection is being setup, what is the ordering wrt? (4) I think in this case you could refer to the RFC: There is a phrase /When this specification/. This phrase always seems problematic in ID, with ambiguity to know whether it refers to the present document. (5) TEXT: "MAY be adopted if found to be more effective". - To me that seems like the document is almost defining working group process surrounding this. I don't think this document ought to do this. I suggest you delete the text, or at least don't use a RFC2119 keyword. (6) TEXT: "MAY also implement AckCC". - Is this a /It is RECOMMENDED that AckCC is implemented/ - from text elsewhere this seems correct. I think some people prefer to say "is RECOMMNDED" when the text refers to an implemementation requirement, rather than protocol requirement. (7) 3.2.3 - I do see the logic in not setting ECT unless there is feedback sup[ported to report CE. (8) 3.2.4 - Please rephrase the first para in terms of citing the ECN-Experiments ID (in TSVWG) that enables this, rather than talking of the prohibition that has passed and the need to ignore - there is no need for this, since the TSVWG ID *WILL* be published before this. (9) 3.2.6 - This recommends RFC5961. This seems an odd thing to suddently place an implementation requirement, if there are important requirements then I would hope these appear earlier in the document and are justified. I really encourage the WG to put all implementation requirements in a separate section, so implementors know what depends on what. (10) Setion 4 - The section seems to call out a number of things that need to be done. Some of these may be neded before WGLC... but I don't know see which? Some are evidently targeting IETF experimentation, some are discussion of the background (could be an appendix?). At the moment this makes for quite a long read. (11) Section 5.3, Para 1 The style of the SCTP discussion seems well-intentioned, but inappropriate, since it is based on a long-expired draft. (I strongly suggest we do not publish RFCs that discuss IDs that have not been progressed in WGs.) I suggest that more appropriate text could simply say "RFC4960 describes how ECN would be supported for SCTP, but at the time of writing there is no IETF Specification for this", or something similar. Gorry
- [tcpm] Comments on ECN++ (rev 02) Gorry Fairhurst