[clue] Benjamin Kaduk's No Objection on draft-ietf-clue-protocol-19: (with COMMENT)
Benjamin Kaduk via Datatracker <noreply@ietf.org> Tue, 10 December 2019 02:08 UTC
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Date: Mon, 09 Dec 2019 18:08:29 -0800
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Subject: [clue] Benjamin Kaduk's No Objection on draft-ietf-clue-protocol-19: (with COMMENT)
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Benjamin Kaduk has entered the following ballot position for draft-ietf-clue-protocol-19: No Objection 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/iesg/statement/discuss-criteria.html for more information about IESG DISCUSS and COMMENT positions. The document, along with other ballot positions, can be found here: https://datatracker.ietf.org/doc/draft-ietf-clue-protocol/ ---------------------------------------------------------------------- COMMENT: ---------------------------------------------------------------------- I'm balloting No Objection, as the concerns noted in my previous Discuss ballot position are not necessarily blocking issues for an Experimental document, and in fact further experience might be helpful to reveal the appropriate values and behaviors to use for timeouts and loop-avoidance. My previous ballot position is preserved below; I note that some of the "substantial comments that do not rise to Discuss level" seem to still be present in the -19. DISCUSS Thanks for the generally clear and well-written document! I would like to discuss whether there needs to be more prominent coverage of timers/timeouts, especially as relating to the state machines. (I'd be happy to learn that this is well-covered elsewhere in the document set; I just haven't run into it yet.) In a similar vein, do we want to have any treatment of avoiding infinite loops (e.g., when a 'configure' or 'advertisement' is rejected in expectation of modification but the sending implementation continues to generate an identical message)? It is not clear to me that any change to the document text is needed in either case, but I don't know to what extent the topics have already been discussed. COMMENT I also have some substantial comments that do not rise to Discuss-level. How do I know which endpoint is the channel initiator and which is the channel receiver? draft-ietf-clue-signaling suggests that the DTLS client is the channel initiator, but even that is not explicit about it -- the protocol could be considered under-specified if there is insufficient clarity. Section 2 The MCU definition doesn't actually expand the acronym, which seems a little reader-unfriendly. Section 5.1 There are perhaps more XML extension points in here than is reasonable for some of these elements (e.g., <versionsListType>). Section 5.2 If the responseCode is between 200 and 299 inclusive, the response MUST also include <mediaProvider>, <mediaConsumer>, <version> and <commonExtensions> elements; Maybe re-mention that MP and MC are booleans here. Finally, the commonly supported extensions are copied in the <commonExtensions> field. Does this need to say that only extensions that are applicable to the negotiated protocol version are included? (Also, how does one handle an extension that exists for multiple major versions -- are there two <extension> elments for it in the <options> message?) Upon reception of the 'optionsResponse' the version to be used is the one provided in the <version> tag of the message. The following CLUE messages MUST use such a version number in the "v" attribute. The allowed extensions in the CLUE dialogue are those indicated in the <commonExtensions> of the 'optionsResponse' message. Couldn't this restriction on the "v" value apply even to the 'optionsResponse' message? Section 5.3 The 'advertisement' message is used by the MP to advertise the available media captures and related information to the MC. [...] I'd consider avoiding the definite article "the" to refer to MP/MC roles, since in many caess there will be 2+ of each, and we don't want to confuse the reader into thinking that there is an MP/CR equivalence or something like that. So, perhaps "each MP" and "the corresponding MC". Section 5.4 As it can be seen from the message schema provided in the following excerpt (Figure 6), the 'ack' contains a response code and a reason string for describing the processing result of the 'advertisement'. [...] [the reason string is part of the base clueResponseType] The text quoted here could be read as implying that the reason string is required in the 'ack' message, a stronger requirement than of the base clueResponseType where it has minOccurs=0. Some greater clarity in the text here is probably called for, especially since when the 'ack' is piggybacked on a 'configure' message, there is no provision for a reason string at all. Section 5.5 The <ack> element MUST NOT be present if an 'ack' message has been already sent back to the MP. I think you need to clarify that this is scoped to the current advSequenceNr. Section 5.6 It contains (Figure 8) a response code with a reason string indicating either the success or the failure (along with failure details) of a 'configure' request processing. [...] [Same comment about reason string as for 'ack'] Section 5.7 Such new response codes MUST NOT overwrite the ones here defined and they MUST respect the semantics of the first code digit. nit: is this "overwrite" or "override"? This document does not define response codes starting with "1", and such response codes are not allowed to appear in major version 1 of the CLUE protocol. The range from 100 to 199 inclusive is reserved for future major versions of the protocol to define response codes for delayed or incomplete operations if necessary. Response codes starting with "5" through "9" are reserved for future major versions of the protocol to define new classes of response, and are not allowed in major version 1 of the CLUE protocol. Response codes starting with "0" are not allowed. This text seems to also preclude extensions to major version '1' from defining 1xx or [5-9]xx reason codes; is that the intent? Section 6 When the CLUE data channel set up starts ("start channel"), the CP moves from the IDLE state to the CHANNEL SETUP state. nit: only one of "sets up" and "starts" is needed. When in the ACTIVE state, the CP starts the envisioned sub-state machines (i.e., the MP state machine and the MC state machine) according to the roles it plays in the telepresence sessions. Such roles have been previously declared in the 'options' and 'optionsResponse' messages involved in the initiation phase (see OPTIONS sections Section 5.1 and Section 5.2 for the details). [...] My reading of the initiation phase is that each CP sends only a boolean indication of whether it supports the MP/MC roles, and so each party has to determine on its own whether it will act as a MP and/or MC; is that correct? If so, do we need to say anything about how the boolean matrix translates to activating the respective sub-state machines? Section 6.1 'configure+ack' messages referring to out-of- date (i.e., having a sequence number equal to or less than the highest seen so far) advertisements MUST be ignored, i.e., they do not trigger any state transition. [...] Is this really less than or equal or just less than? Also, is "seen" the right verb, since IIUC these are sequence numbers that the MP has *generated* in its advertisements? Section 7 In other words, in this example, the MP MUST use version 1.4 and downgrade to the lower version. [...] nit: does the phrase "and downgrade to the lower version" add any value here? The word "downgrade" can have negative connotations in some other contexts, so if it's not adding value I'd suggest avoiding it. Section 8 As reported in Figure 13, the values of the fields of the <extension> element (either new information or new messages) take the following values: [...] o the major standard version of the protocol that the extension refers to. The XSL includes a full version (including minor), even though the semantics basically only use the major version. That said, why is the 'version' element minOccurs="0" -- what are the semantics when it is absent? Section 8.1 The CLUE data model document ([I-D.ietf-clue-data-model-schema]) envisions the possibility of adding this kind of "extra" information in the description of a video capture by keeping the compatibility with the CLUE data model schema. [...] nit: I don't think this is grammatical; maybe just "keeping compatibility". Section 10 This claims to be a "call flow" example, but the described flows only contain a single unidirectional media flow, which is not really consistent with the normal usage of the word "call". Buried in the body text there is a disclaimer: [...] For the sake of simplicity, the following call flow focuses only on the dialogue between MP CP1 and MC CP2. I would suggest making the presence of this simplification much clearer from the start, perhaps "CLUE protocol messages exchanged in the following call flow are detailed; only one direction of media is shown for simplicity, as the other direction is precisely symmetric". CP2 acknowledges the second 'advertisement' message with an 'ack' message (Section 10.7). In a second moment, CP2 changes the requested media streams from CP1 by sending to CP1 a 'configure' message replacing the previously selected video streams with the new composed media streams advertised by CP1 (Section 10.8). This might be an appropriate place to indicate that media from the previous configuration continue to flow during the reconfiguration process. It might also be worth noting again somewhere in here (or a subsection) that there are three (well, two, since we only show one direction of media) distinct sequence number spaces per sender, and that the discontinuity between Section 10.2 and 10.3's numbers is correct. Section 11 Thanks for the well-thought-through security considerations; in combination with the linked documents (particularly the framework), they cover all the considerations (especially privacy considerations) that I had in mind. Section 14.2 We appear to be citing both 5117 and 7667, whereas the latter obsoletes the former.
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