hi Ben. thanks for your review. comments/replies inline.
> From: Ben Campbell [mailto:[email protected]]
> Sent: Thursday, June 20, 2013 4:07 PM
>
> I am the assigned Gen-ART reviewer for this draft. For background on
> Gen-ART, please see the FAQ at
>
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>
> Please resolve these comments along with any other Last Call comments
> you may receive.
>
> Document: draft-thornburgh-adobe-rtmfp-07
> Reviewer: Ben Campbell
> Review Date: 2013-06-20
> IETF LC End Date: 2013-06-25
>
> Summary: This draft is almost ready for publication as an informational RFC.
> However, I have some
> concerns about the purpose and intended status of the document that I think
> should be considered prior
> to publication.
>
>
> Note: This is an informational draft that describes what I understand to be
> an existing protocol as
> implemented by commercial products. Therefore, this review does not attempt
> to evaluate the protocol
> itself. I assume the protocol is what it is, and it is not up to the IETF to
> agree or disagree with
> it.
>
> *** Major issues:
>
> -- Why does this need to be published as an IETF stream RFC? If I understand
> correctly, this
> documents an existing protocol as implemented by commercial products. I agree
> with Martin's comment
> that there is value in publishing this sort of thing, but I applaud the Adobe
> and the author for
> publishing it so other implementations can interoperate with their products.
> But that could have done
> that in an independent stream document, or even in an Adobe published
> document. (Perhaps even in a
> prettier format ;-) ) If we publish this as an IETF stream document, then I
> think it needs stronger
> clarification that it is not an IETF consensus doc than just its
> informational status.
this memo documents an existing network transport protocol that is widely
deployed and in widespread use in the Internet. we felt that the IETF
community (and in particular the participants in the Transport and Services
Area) is the most appropriate community with which to share this work: 1)
members of this community have the necessary and relevant expertise not only to
understand the protocol, but to make use of it potentially in new applications
beyond Flash; 2) it is a transport protocol similar in many ways to TCP and
SCTP and widely deployed and used; 3) Adobe is interested in pursuing
standardization of this protocol (with all that entails) if there is community
interest, and the IETF is definitely the right place for that.
we are very grateful that Martin Stiemerling chose to sponsor this document.
with regard to comments in later messages in this thread, i'd be happy to
include some (IESG-supplied) boilerplate in the document to clarify that it is
not the product of an IETF WG. however, note that both the title and first
sentence of the Introduction indicate that this is "Adobe's blahblahblah",
consistent with other vendor-protocol RFCs and consistent with IESG editorial
insistence (as told to me by a former TSV AD). see RFC 4332 and RFC 6802 for
two examples of vendor-specific/supplied protocols. see also the IESG note in
RFC 4332 as an example disclaimer that could be added.
> Along those lines:
>
> -- Is this document the authoritative specification? (I suspect not.)
> Who owns change control? I
> assume that to be Adobe and/or the authors. What expectation do readers of
> this draft have that it
> represents the current version of RTMFP at any point in time?
this memo is the authoritative specification for Adobe's RTMFP. Adobe owns
change control. i believe the second and third paragraphs of the Introduction
indicate to a reader that this draft represents RTMFP as deployed in the named
Adobe products at the time of writing.
> -- Under what circumstances would one desire to implement this? I can
> infer that from the
> introduction, but it would be nice to see some sort of applicability
> statement making it explicitly
> clear that this is not an IETF protocol, and that one would implement it in
> order to interoperate with
> certain Adobe products. I know that some of this may be implied by the fact
> that this is informational
> rather than standards track. But I don't expect readers who are not IETF
> insiders to understand that
> subtlety without some explicit words to that effect. In particular, it would
> be good to clarify the
> difference between this and the many "not quite accepted as standards track
> by some working group"
> nature of a number of our informational RFCs that describe protocols.
i will expand on applicability beyond what i specify in the first paragraph of
the Introduction, in general terms such as the kinds of functionality we use
this protocol for in Flash. note that interoperation with certain Adobe
products, such as Flash Player, requires additional information such as the
Flash-specific Cryptography Profile and syntax/semantics of mapping Flash's
"Real Time Messaging Protocol (RTMP)" messages onto RTMFP flows. these
Flash-specific profiles and mappings are application-layer for RTMFP, analogous
to HTTP over TCP.
> That all being said, this is overall a well written document. The rest of my
> comments are mostly
> pedantic nits.
>
> *** Minor issues:
>
> -- section 1.2:
>
> I find the use of "MUST ONLY" confusing. I gather it means "you are _allowed_
> to do X only under
> certain conditions" rather than "you are _required_ to do X under certain
> conditions." If correct, I
> think the words "MAY ONLY" would be more clear. If not, then I think the
> construct would be better
> handled using existing 2119 language.
you're not the first person to be confused by that construct. i will change
instances of "MUST ONLY" to "is allowed only if" (or similar) and remove the
definition for "MUST ONLY" from Section 1.2.
> -- section 3.2:
>
> Do I understand correctly that all endpoints are expected to be able to
> present certificates? Do you
> find that common in the field? I realize the nature of the certs will depend
> on the security profiles.
yes, all endpoints have certificates. in the RTMFP-for-Flash world, these
certificates are not X.509 certs, and are anonymous and ephemeral.
> -- sections 3.2 and 5
>
> Do I assume correctly that endpoints need a common crypto profile to
> communicate? Is there a
> repository where one might find crypto profile documentation? Is there a
> commonly implemented one to
> which this draft could refer?
yes, endpoints need a common cryptography profile to interoperate. there is no
repository for crypto profile documentation at this time. currently, there is
one defined cryptography profile (the one used for Flash communication) that is
not publicly documented, because i do not yet have permission to publish it. i
(meaning me personally) hope that a memo documenting the crypto/application
profile for Flash communication (as being a widely deployed and used profile
for RTMFP) would also be published someday as an I-D and hopefully an
Informational RFC.
> -- section 3.2: "Multiple endpoints SHOULD NOT have the same identity."
>
> Why not MUST? Will things not break if two endpoints do have the same
> identity?
this should be "It is RECOMMENDED that multiple endpoints not have the same
identity." if two endpoints have the same identity, then they will be
indistinguishable. this will not break RTMFP, but might confuse an
application. that being said, there could potentially be reasons to have
different endpoints with indistinguishable identities and that potential should
not be normatively prohibited.
> -- "Authenticity MAY comprise verifying an issuer signature chain in a public
> key infrastructure"
>
> Is that really normative, or just an observation of fact?
that "MAY" should be "can".
> -- " Canonical Endpoint Discriminators for distinct identities SHOULD be
> distinct."
>
> What if they are not? Do things break? It might be worth making this a MUST,
> or adding some additional
> guidance about what might happen if the SHOULD is violated.
i will add a note that if the canonical EPD is the same for two distinct
identities, then the "duplicate session" logic in section 3.5.1.1.1 (paragraph
6 step 1) might abort a new opening session to the second identity, which might
not be desired.
> -- "A comparison function MAY comprise performing a lexicographic ordering..."
>
> Is that really normative, or just an example of something one might do?
that "MAY" should be "can".
> -- "A test SHOULD comprise testing whether the certificates are identical."
>
> What if it doesn't? Also, what constitutes "identical"? All fields match
> values? Bitwise match? Is it
> simply including the same identity or identities? Maybe an identity function
> provided by the crypto
> profile?
again, that SHOULD should be reworded to RECOMMENDED. i will change
"identical" to "bitwise identical".
> -- 3.5, last paragraph:
>
> Can you offer guidance on reasonable buffer size and number ranges?
i assume you mean "3.4, last paragraph" (referring to packet reassembly
buffers). i will add some guidance and a "for example". the guidance will
depend on how that RTMFP will be used and the expected amount of resources
available to it.
> -- 3.5.1.1.1, 3rd paragraph:
>
> What are the consequences of having a tag with less than 8 bytes of length?
> Is the SHOULD reasonable
> here?
both of those SHOULDs should be RECOMMENDEDs.
> -- 3.5.1.1.1 throughout, and following sections:
>
> Does the upper case AND have special meaning?
upper case is the closest to bold face available in this format. the intention
is to emphasize (since there are multiple conditionals) that all conditionals
are required to hold.
> -- 3.5.1.4, Deployment Note:
>
> How would a redirector know which endpoints might do this? Or should it never
> initiate a session?
this is guidance for designing and deploying an RTMFP system. the redirector
wouldn't know -- the designer should design the system such that the described
circumstance doesn't happen (for example, by having the redirector never
initiate a session). this is properly a SHOULD NOT since doing so can cause
undesired behavior (as described). it is not desirable to give a normative
prohibition or recommendation against a redirector initiating any sessions. i
feel this paragraph gives the narrowest normative limitation and an explanation
for that limitation.
> -- 3.5.2:
>
> Do I infer correctly that two endpoints need not share the same congestion
> control algorithm to
> communicate?
correct. the timestamp echo facility, ack behavior (as described for flow
receivers), and limitations on aggressiveness in 3.5.2/.* impose the normative
envelope in which any congestion control algorithms should interoperate.
> -- 3.6.2.3.2, 2nd paragraph: "...an implementation SHOULD encode a Next User
> Data chunk instead of a
> User Data chunk"
>
> I'm not sure why this needs to be normative, as I assume its just normal
> behavior. But if it does need
> to be normative, why not a MUST? Can the far endpoint reasonably handle
> things if the SHOULD is
> violated?
this should be a RECOMMENDED. the far end will work just fine if Next User
Data is never used.
> *** Nits/editorial comments:
>
> -- General: There's quite a bit of inconsistent use of third-person vs
> second-person language.
i will try to clean that up.
> -- 3.1: It would be nice to see the overview earlier in the draft. I found it
> difficult to read
> through all the data format stuff prior to section 3 putting them into
> context.
others have commented that they'd prefer sections 2 and 3 to be swapped. i
resisted that as this order ("here are the pieces" and then "here's how they
fit together") is my preferred way of explaining stuff. also swapping those
sections would be a huge editorial change which might have significant
cross-reference and forward/back reference implications and could introduce
hard-to-detect errors into the spec. however, i think i can move the overview
(or a summary thereof) to earlier in the spec (probably in Section 1).
> -- 3.5.1.4, Deployment Note:
>
> s/which/that
good catch.
> -- 3.5.1.6, last paragraph:
>
> Which diagram? (An explicit cross-ref would help.)
oops. that paragraph used to be the postamble of the figure, so it obviously
meant "this figure". i'll change "the figure" to "Figure 17".
> -- 3.5.2:
>
> What is meant by "aggressive" in this context? Aggressive in avoiding
> congestion, or aggressive in
> sending data?
aggressive in sending data. i'll make that clarification.
> -- 3.6.2.3.1 and subsequent sections:
>
> Does the all-caps "FIRST" have special meaning?
it is all-caps for typographical emphasis.
thank you!
-michael thornburgh
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