Re: [tcpm] Reviewed for draft-ietf-tcpm-accurate-ecn-23

Gorry, I've addressed all your points in my editor's local copy, also on 
github.

See [BB3] for 3 further notes...

On 26/03/2023 18:57, Gorry Fairhurst wrote:
> See below,
> Gorry
>
> On 26/03/2023 18:11, Bob Briscoe wrote:
>> Gorry, See [BB2] I think we're close to converged.
>>
>> On 26/03/2023 14:51, Gorry Fairhurst wrote:
>>> On 26/03/2023 03:06, Bob Briscoe wrote:
>>>> Gorry,
>>>>
>>>> Thank you as always for your extensive review. See responses tagged 
>>>> [BB] inline.
>>>> No comment = proposal accepted.
>>>
>>> I see you have a plan, I made a few additional comments [GF2].
>>>
>>>>
>>>> On 25/03/2023 17:28, Gorry Fairhurst wrote:
>>>>> I have just reviewed draft-ietf-tcpm-accurate-ecn-23 for a WGLC.
>>>>>
>>>>> This ID is significantly easier to read than an earlier version I 
>>>>> read, but still is not an easy read - and I did not have time to 
>>>>> re-check all the logic, but I did look at the text and have the 
>>>>> following set of comments. Most of these relate to sentences were 
>>>>> clarity could be improved, or RFC2119 language could be more 
>>>>> explicit about the subject. Many of these could be resolved by 
>>>>> simple text changes, and where possible I have provided the text 
>>>>> from the ID, and in most cases a suggestion remedy.
>>>>>
>>>>> Best wishes,
>>>>>
>>>>> Gorry
>>>>>
>>>>> P.S. When you complete all the updates after the WGLC, I suggest 
>>>>> you post a review request to TSVWG, just to keep the process good 
>>>>> - because this does plan to update a TSVWG spec.
>>>>>
>>>>> =========
>>>>>
>>>>> This statement causes concern:
>>>>> AccECN is intended to be a complete replacement for classic 
>>>>> TCP/ECN feedback, not a fork in the design of TCP.
>>>>> Is it possible the intent is:
>>>>> AccECN is intended to offer a complete replacement for classic 
>>>>> TCP/ECN feedback, not a fork in the design of TCP.
>>>>> - To me the importance being that this does not immediately 
>>>>> obsolete current TCP, it simply provides a negotiated mechanism to 
>>>>> replace it.
>>>>>
>>>>> ===================
>>>>> Section 1
>>>>> ===
>>>>> Recently, proposed mechanisms like Congestion Exposure (ConEx 
>>>>> [RFC7713]), DCTCP [RFC8257] or L4S [RFC9330] need to know when 
>>>>> more than one marking is received in one RTT which is information 
>>>>> that cannot be provided by the feedback scheme as specified in 
>>>>> [RFC3168].
>>>>> - Add comma, so that:
>>>>> Recently, proposed mechanisms like Congestion Exposure (ConEx 
>>>>> [RFC7713]), DCTCP [RFC8257] or L4S [RFC9330] need to know when 
>>>>> more than one marking is received in one RTT, which is information 
>>>>> that cannot be provided by the feedback scheme as specified in 
>>>>> [RFC3168].
>>>>> ===
>>>>> This document specifies an update to the ECN feedback scheme of 
>>>>> RFC 3168 that provides more accurate information and could be used 
>>>>> by these and potentially other future TCP extensions.
>>>>> - could we note this is an alternative rather than replacement:
>>>>> This document specifies an update to the ECN feedback scheme of 
>>>>> RFC 3168 that provides an alternative more accurate information 
>>>>> and could be used by these and potentially other future TCP 
>>>>> extensions.

[BB3] Sorry, I overlooked this in the first pass.
AccECN is definitely not an alternative (as explained in the sentence 
"not a fork in the design of TCP"). It is a superset.
I know you are trying to avoid any implication that AccECN obsoletes 
RFC3168, but there was no such implication in this sentence as it stood. 
That is captured by the well-understood word "update".

Nonetheless, I would like to add the following important point to this 
sentence, which doesn't seem to have been said anywhere in the Intro:
     This document specifies an update to the ECN feedback scheme of RFC 
3168 that provides more accurate information and could be used by these 
and potentially other future TCP extensions*, while still also 
supporting the pre-existing TCP congestion controllers that use just one 
feedback signal per round*.

A later sentence makes it even clearer that RFC3168 feedback has not 
gone away:
     "AccECN feedback complements TCP's loss feedback and it can coexist 
alongside 'classic' [RFC3168 <https://www.rfc-editor.org/info/rfc3168>] 
TCP/ECN feedback."

>>>>> ===
>>>>> This documents specifies a standards track scheme
>>>>> - remove s
>>>>> This document specifies a standards track scheme
>>>>> ===
>>>>> Then terminology is defined
>>>>> - do we need a comma:
>>>>> Then, terminology is defined
>>>>> ===
>>>>> Section 1.2
>>>>> ===
>>>>> Therefore an AccECN receiver aims to act as a generic (dumb) 
>>>>> reflector of congestion information so that in future new sender 
>>>>> behaviours can be deployed unilaterally.
>>>>> - why /aims to/ ... why does this not specify this?
>>>>> - is /dumb/ necessary, it's an unfortunate word choice - simple 
>>>>> could be alternative?
>>>>
>>>> [BB] Yes, 'aims to' should be moved to the later part of the sentence.
>>>> The terminology 'dumb' was borrowed from the "intelligent vs dumb 
>>>> network" phrasing of the e2e argument. 'Simple' would lose the 
>>>> intended nuance of 'mechanistic' or 'robotic', and the former is 
>>>> least overloaded with other meanings these days (robotic is 
>>>> starting to mean the opposite!). So how about:
>>>>
>>>>     Therefore an AccECN receiver acts as a generic (mechanistic) 
>>>> reflector of congestion information with the aim that in future new 
>>>> sender behaviours can be deployed unilaterally.
>>>>
>>>> There are other occurrences of 'dumb reflector' - so I'll change 
>>>> them all.
>>>>
>>>>
>>> [GF2] Seems OK to me.
>>>>> ===
>>>>> Classic ECN: the ECN protocol specified in [RFC3168].
>>>>> - Upper case /The/ to be consistent?
>>>>> ===
>>>>> Classic ECN feedback: the
>>>>> - Upper case /The/ to be consistent?
>>>>> ===
>>>>> which ensures the signal is received reliably even if ACKs are lost.
>>>>> - well not if all are lost! Could this be:
>>>>> which provides resilience of the signal to loss or reordering of 
>>>>> ACKs.
>>>>> ====
>>>>> Para after table talks of a TCP sender, but the terminology talks 
>>>>> of a data sender and a TCP server; but not a TCP sender. 
>>>>> Presumably this is a data sender.
>>>>> ====
>>>>> - It might be useful to say that a TCP connection between a TCP 
>>>>> client and a TCP server provides bidirectional communication 
>>>>> between two pairs of TCP senders and TCP receivers, forming two 
>>>>> independent half connections/.
>>>>
>>>> [BB] Yes, we use half connection a number of times later, and this 
>>>> would be a good place to introduce it.
>>>>
>>>>> ====
>>>>> I think the whole of section 2 could be informative? ~If it is, 
>>>>> can we say this?
>>>>
>>>> [BB] We do already; in the first para of §2:
>>>> "This section provides an informative overview of the AccECN 
>>>> protocol that will be normatively specified in Section 3 
>>>> <https://datatracker.ietf.org/doc/html/draft-ietf-tcpm-accurate-ecn-23#accecn_Spec>"
>>>>
>>> [GF2] Oh, fine.
>>>>> ====
>>>>> The RFC 2119 conformance terms are defined in 1.3, but then are 
>>>>> followed by an informative set of sections. I for one, would much 
>>>>> prefer that definition block moved to the start of section 3.
>>>>
>>>> [BB] Much of the other terminology defined in §1.3 is needed 
>>>> sooner. So, to do as you ask, we'd have to to split up the 
>>>> terminology section, which I don't want to do. It's not incorrect 
>>>> as it is, so let's leave it.
>>>>
>>> [GF2] I still think splitting the terminology would be better to 
>>> include the RFC declarations at the start of the section that uses them.
>>
>> [BB2] It is very common RFC practice to stick all RFC2119 boilerplate 
>> and other terminology in an early section (often after the Intro), 
>> whether or not it will be immediately used in the subsequent section. 
>> Including in your latest RFC [RFC9268] actually :P
>>
> [GF3] There can still be feedback on requests containing normative and 
> informative sections, andyway, I'm not the shepherd, so no further 
> comment from me on this point.
>>
>>>>> ===
>>>>> but it is more likely to suffer from middlebox interference.
>>>>> - I think we could be more future-looking, and propose:
>>>>> but is currently more likely to suffer from middlebox interference.
>>>>> ===
>>>>> However cycling is still a possibility at the Data Sender because 
>>>>> a whole sequence of ACKs carrying intervening values of the field 
>>>>> might all be lost or delayed in transit.
>>>>> - This is about reception of ACKs? I wasn't sure first read, could 
>>>>> we write:
>>>>> However ACKs received at the Data Sender could still cycle because 
>>>>> a whole sequence of ACKs carrying intervening values of the field 
>>>>> might all be lost or delayed in transit.
>>>>> ===
>>>>> had been an infeasibly long sequence of ACK losses.
>>>>> - what does infeasible mean here, it seems very imprecise. It 
>>>>> would have been easier not to judge the feasibility and simply 
>>>>> said /a long/...
>>>>
>>>> [BB] 'long' is less precise than 'infeasibly long', which conveys 
>>>> the meaning of 'not just long, but so long that we do not need to 
>>>> consider the possibility of it occurring in practice'.
>>>> The main meaning of Infeasible is impracticable, so I would like to 
>>>> leave this as-is.
>>>>
>>> [GF2] Not a huge issue to me.
>>>>> ===
>>>>> Therefore, as long as the AccECN Option is available
>>>>> - unfortunate use of /as long/ just after discussing length of ACK 
>>>>> drops?
>>>>> Providing that the AccECN Option is available
>>>>> ===
>>>>> is provided in order to protect
>>>>> - ordering is not implied, this could be:
>>>>> is provided to protect
>>>>
>>>> [BB] The intended meaning was not "provided in order, to protect." 
>>>> Rather it was "provided in_order_to protect." So your suggestion 
>>>> does indeed remove the ambiguity.
>>>>
>>>>> ===
>>>>> The TCP server MUST NOT set one of these 4 combination of flags on 
>>>>> the SYN/ACK unless the preceding SYN requested support for AccECN 
>>>>> as above.
>>>>> - What is the client response if this does happen?
>>>>
>>>> [BB] To rephrase your question into a stand-alone question, "What 
>>>> does a non-AccECN client do if it somehow receives a SYN-ACK that 
>>>> implies the server supports AccECN?
>>>>
>>>> This draft doesn't specify what non-AccECN clients do, and it would 
>>>> be pointless to try, because they are already out there, and their 
>>>> specs already say what they do.
>>>> Nonetheless, FYI, clients implementing either of the two non-AccECN 
>>>> specs currently out there would both handle a randomly appearing 
>>>> AccECN SYN-ACK correctly. Specifically:
>>>>
>>>> 1) RFC3168, §6.1.1:
>>>>          If a host has received at least one [...]
>>>>          non-ECN-setup SYN-ACK packet, then it SHOULD NOT set ECT on
>>>>          data packets.
>>>>          ...
>>>>          Receivers MUST correctly handle all forms of the non-ECN-setup
>>>>          [...] SYN-ACK packets.
>>>>
>>>> Even if an RFC3168 client only checked the last 2 flags of the 3 
>>>> AccECN flags, none of the three 2-bit combinations that imply 
>>>> AccECN support would be expected by an RFC3168 client (by design of 
>>>> AccECN).
>>>>
>>>> Therefore:
>>>>
>>>>   * An RFC3168 client would handle a randomly appearing AccECN
>>>>     SYN-ACK correctly,
>>>>       o whether it checked all the TCP flags (as required by the
>>>>         second sentence quoted from RFC3168 above)
>>>>       o or even if it only checked CWR and ECE.
>>>>
>>>>
>>>> 2) RFC9293:
>>>> Altho this recommends TCP implementations support RFC3168, there 
>>>> are many RFC793 TCP implementations that do not. Such a non-ECN TCP 
>>>> client will have no logic to check the ECN flags during the 3WHS 
>>>> and therefore it will not notice that a SYN-ACK is (incorrectly) 
>>>> responding as if it was asked to support AccECN.
>>>>
>>>> Therefore, again,
>>>>
>>>>   * a non-ECN TCP client will handle a randomly appearing AccECN
>>>>     SYN-ACK correctly, just continuing to not support any form of ECN.
>>>>
>>>>
>>> [GF2] Thanks for this explantion, I think setting these bits defines 
>>> the mode - so it's a little weird as a requirement, but I get it.
>>>>
>>>>> ==
>>>>> interference than other intermittent causes of loss, e.g. 
>>>>> congestion, wireless interference, etc.¶
>>>>> - two uses of the word /interference/ with different meaning, 
>>>>> could the second be replaced by /loss/?
>>>>
>>>> [BB] Good point. I think "transmission loss" would be better.
>>>>
>>>>> ==
>>>>> It MUST NOT send an ECN-setup SYN [RFC3168] within the same 
>>>>> connection as it has sent a SYN requesting AccECN feedback.
>>>>> /as/when/ or something else?
>>>>> It MUST NOT send an ECN-setup SYN [RFC3168] within the same 
>>>>> connection when it has sent a SYN requesting AccECN feedback.
>>>>
>>>> [BB] I don't see the problem here. "The same ... as" is correct 
>>>> English, whereas "the same ... when" is not.
>>>> A similar sentence proves this is a correct construction: "It MUST 
>>>> NOT send a message within the same millisecond as it has sent 
>>>> another message"
>>>>
>>>> If this makes the reader stumble, we could rephrase entirely:
>>>>     It MUST NOT send an ECN-setup SYN [RFC3168] during a connection 
>>>> in which it has also sent a SYN requesting AccECN feedback.
>>>> However, I don't think that's any better, so I'd prefer to leave it 
>>>> as-is.
>>>>
>>> [GF2] That proposal seems much clearer to me, I understand now.
>>>>> ===
>>>>> It MUST NOT send an ECN-setup SYN/ACK [RFC3168] within the same 
>>>>> connection as it has sent a SYN/ACK agreeing to use AccECN feedback.
>>>>> /as/when/ or something else?
>>>>> It MUST NOT send an ECN-setup SYN/ACK [RFC3168] within the same 
>>>>> connection when it has sent a SYN/ACK agreeing to use AccECN 
>>>>> feedback.
>>>>
>>>> [BB] Ditto.
>>>>
>>> [G2] I'd prefer to find a way to make this one more clear.
>>
>> [BB2] I'll try. Brain's not in best trim at the mo.
>>
>>>>> ===
>>>>> It is still obliged to respond appropriately to AccECN feedback 
>>>>> that indicates there were ECN marks on packets it had previously sent
>>>>> -Please explicitly say what is "it"?
>>>>> The Data Sender is still obliged to respond appropriately to 
>>>>> AccECN feedback that indicates there were ECN marks on packets it 
>>>>> had previously sent
>>>>> ==
>>>>> In general, it is obliged to respond to congestion feedback even when
>>>>> - what is it? Receiver/Sender?
>>>>> In general, the Data Sender is obliged to respond to congestion 
>>>>> feedback even when
>>>>> ===
>>>>> Unlike an RFC 3168 data sender, it MUST NOT set CWR to indicate it 
>>>>> has received and responded
>>>>> - what is it? Receiver/Sender?
>>>>> Unlike an RFC 3168 data sender, a Data Receiver MUST NOT set CWR 
>>>>> to indicate it has received and responded
>>>>
>>>> [BB] The problem you've identified occurs because there is an aside 
>>>> about all the 'switching feedback negotiation' bullets, just before 
>>>> all the 'congestion response' bullets.
>>>> This tends to lose the thread of the Data-Sender context.
>>>>
>>>> Nonetheless, I've also noticed that:
>>>> * some of the bullets under "As a Data Sender" are about sending 
>>>> control packets, not data.
>>>> * some of the bullets under "As a Data Receiver" are about 
>>>> receiving control packets, not data.
>>>>
>>>> So I shall have to restructure the whole section.
>>>> Let me do that, then give it to you to review again.
>>> [GF2] OK
>>>>
>>>> ==
>>>>> if it receives an ECN-setup SYN or ECN-setup SYN/ACK [RFC3168] 
>>>>> during the same
>>>>> - to avoid doubt in citing this RFC2119 requirement, can we write:
>>>>> if a Data Receiver receives an ECN-setup SYN or ECN-setup SYN/ACK 
>>>>> [RFC3168] during the same
>>>>> ===
>>>>> If for any reason it is not willing to
>>>>> - to avoid doubt in citing this RFC2119 requirement, can we write:
>>>>> If for any reason the Data Receiver is not willing to
>>>>> ===
>>>>> it MUST NOT use reception
>>>>>
>>>>> - to avoid doubt in citing this RFC2119 requirement, can we write:
>>>>>
>>>>> A Data Receiver MUST NOT use reception
>>>>
>>>> [BB] As above, I'll restructure the whole of this section before 
>>>> giving to you to review again.
>>>> Sorry about this.

[BB3] I've done the restructuring.
I just wanted to explain why we didn't use phrases like "A Data Receiver 
MUST NOT use reception ..."
It's because we would need to repeat each time "A Data Receiver *in 
AccECN mode* MUST NOT use reception ..."
I wanted to avoid continually repeating this rather long phrase.

>>>>
>>>>
>>>>> ===
>>>>> correct ECN feedback logic, as the packets
>>>>> - could we replace /as/?
>>>>> correct ECN feedback logic, because packets
>>>>> ===
>>>>> Whenever a host feeds back the value
>>>>> - Is that the Data Receiver? Sender? or both? - it would better to 
>>>>> match the clauses above.
>>>>
>>>> [BB] Yes, this could s/host/Data Receiver/
>>>> But I will also make it clear that the stuff about the feedback 
>>>> being on a retransmission is about a retransmission for the other 
>>>> half connection.
>>>>
>>> [GF2] I see.
>>>>> ===
>>>>> When a host first enters AccECN mode, in its role as a Data Receiver
>>>>> - could this be more simply said:
>>>>> When Data Receiver first enters AccECN mode,
>>>>
>>>> [BB] Not really, because a host enters AccECN mode as a whole (not 
>>>> separately per half connection).
>>> [GF2] That was not clear, ... I think this applies to several 
>>> places, so maybe a clear statement that explains this in th eirght 
>>> place would be best?
>>
>> [BB2] OK. But, actually, I just went to do it, and it's already there 
>> in §3.1.1:
>>
>>     "If a TCP server (B) that is AccECN-enabled receives a SYN with 
>> the above three flags set, it MUST set *both its half connections* 
>> into AccECN mode."
>> ...
>>     "Once a TCP client (A) has sent the above SYN to declare that it 
>> supports AccECN, and once it has received the above SYN/ACK segment 
>> that confirms that the TCP server supports AccECN, the TCP client 
>> MUST set *both its half connections* into AccECN mode."
>>
> [GF3] It was the word "host" that I didn't see mentioned.
>>
>>>>
>>>>> ==
>>>>> When a host enters AccECN mode, in its role as a Data Sender
>>>>> - could this be more simply:
>>>>> When Data Sender first enters AccECN mode,
>>>>
>>>> [BB] Ditto.
>>>>
>>>>> ==
>>>>> A host MUST NOT interpret the 3
>>>>> - Is that the Data Receiver? Sender? or both? Client? Server?
>>>>> A Data Receiver MUST NOT interpret the 3
>>>>
>>>> [BB] This does really mean "a host".
>>>> It applies across the 3WHS and data transfer, so it's not just 
>>>> about Data receiver or Data sender. And it applies to client and 
>>>> server. So it is a general statement about what hosts interpret.
>>>>
>>>>> ==
>>>>> An implementer MAY develop an alternative algorithm as long as it 
>>>>> satisfies these requirements.¶
>>>>> - doesn't seem like a /MAY/ can this be /may/ or /is permitted to/?
>>>>
>>>> [BB] I've checked the definition of 'MAY' in RFC2119, and I'm 
>>>> pretty sure we really do mean 'MAY', but I'm always willing to be 
>>>> corrected.
>>>> Can you try to explain why your understanding of 'MAY' would be 
>>>> inappropriate here?
>>>>
>>>> I'm guessing that perhaps "an implementation MAY do x", but "an 
>>>> implementer may do y"?
>>>> If that's your concern, I would say in this case, "an implementer 
>>>> may produce code that MAY do y," so I don't see a great difference.
>>>>
>>> [GF2] I do not mind on this one at all, check and see what works.
>>>>> ==
>>>>> the Data Sender SHOULD believe the ACE counter, unless it can be 
>>>>> sure that it is counting all control packets correctly.¶
>>>>> - what does believe mean? use?
>>>>
>>>>     '...SHOULD consider the ACE counter to be correct (and its 
>>>> count of control packets to be incomplete)'
>>>>
>>>>> ===
>>>>> Section 3.2.3. The AccECN Option
>>>>> - Could we please add RFC-Ed instructions to ensure replacement of 
>>>>> TBD1 and TBD2 during final edit?
>>>>
>>>> [BB] In my local editor's copy, we already have the early 
>>>> assignment numbers now.
>>>>
>>>>> ===
>>>>> All implementations of a Data Sender that read any AccECN Option 
>>>>> MUST be able to read in AccECN Options of any of the above lengths.
>>>>> - I think /in/ seems odd.
>>>>> - This makes me wonder what happens if they do not?
>>>>> - REQUIRED to implement?
>>>>
>>>> [BB] I can s/read in/read/
>>>> For any spec (not only AccECN), if an implementation does not 
>>>> implement a 'MUST', it is not an implementation of the spec. So all 
>>>> bets would be off.
>>>>
>>>> All this is clarifying is that, altho' it is optional to implement 
>>>> the AccECN Option, if you do implement it, you have to be able to 
>>>> read all the valid option lengths.
>>>>
>>>>> ==
>>>>> Whenever the Data Sender receives ACK carrying
>>>>> - add /an/
>>>>> Whenever the Data Sender receives an ACK carrying
>>>>> ===
>>>>> If the ACK has not been superseded,
>>>>> - please explain superseded!
>>>>
>>>> [BB] I'll add '(see Appendix A.1)', which defines superseded precisely.
>>>>
>>>>> ===
>>>>> AccECN is for congestion control, which SHOULD generally be 
>>>>> considered important relative to other TCP options.
>>>>> - what does important mean here?
>>>>> - Does this have to be a /SHOULD/ could it be a should and explain?
>>>>
>>>> I'll reword as
>>>>     "which implementations SHOULD generally prioritize over other 
>>>> TCP options when there is insufficient space for all the options in 
>>>> use."
>>>> Then I think 'SHOULD' becomes appropriate.
>>>>
>>> [GF2] - yes.
>>>>> ===
>>>>> it (the server) has to have confirmed
>>>>> - why not just say the server?
>>>>> the server has to have confirmed
>>>>
>>>> [BB] In a SYN cookie scenario, the server deliberately forgets what 
>>>> it would normally remember. So I had to use 'it', because the 
>>>> server is reverse engineering what 'it' did earlier, where 'it' is 
>>>> another incarnation of itself that it doesn't remember. Otherwise, 
>>>> just saying "it can assume that the server has to have 
>>>> confirmed..." makes it sound like some other server.
>>>>
>>>> A little rephrasing is needed here anyway, so I've tried to say 
>>>> this another way:
>>>>
>>>> ORIGINAL:
>>>>
>>>> If a TCP server using SYN Cookies supports AccECN and if ..., and 
>>>> if ...,
>>>> it can assume that:
>>>> *  the TCP client has to have requested AccECN support on the SYN
>>>> *  it (the server) has to have confirmed that it supported AccECN
>>>>
>>>> PROPOSED:
>>>>
>>>> If a TCP server using SYN Cookies supports AccECN and if ..., and 
>>>> if ...,
>>>> the server can infer the first two stages of the handshake:
>>>> *  the TCP client has to have requested AccECN support on the SYN
>>>> *  then, even though the server kept no state, it has to have 
>>>> confirmed
>>>>    that it supported AccECN
>>>>
>>>>
>>>>> ===
>>>>> Each host needs to maintain eight additional counters. The hosts 
>>>>> have to apply some additional tests to detect tampering by 
>>>>> middleboxes,
>>>>> - Is this sender or receiver code?
>>>>
>>>> [BB] Here, 'hosts' is appropriate because this is a general 
>>>> statement about all the additional tests; some are during the 3WHS 
>>>> (when either client or server is comparing what it received against 
>>>> what it sent); while other tests are conducted by the Data Receiver 
>>>> part of a half-connection.
>>>>
>>>>> ===
>>>>> I would suggest section 3.3 is made a separate top level section 
>>>>> (section 4), to really call-out that this is not the TCP sender 
>>>>> and receiver but the part that other people need to read.
>>>>
>>>> [BB] That would have been a really good idea earlier. I'd like to 
>>>> do this. But I'm going to think long and hard before doing it now 
>>>> though. I'm concerned that there might be cross refs within this or 
>>>> other documents to §3.3 or §4 -- §8 that might break.

[BB3] The co-authors have decided we'd rather not promote the section 
no. of the middlebox section. Richard pointed out there could be x-refs 
from code and/or test results into specific section numbers.

We added a sentence at the end of the abstract: "The document also 
specifies the treatment of this updated TCP wire protocol by middleboxes."
And, in the doc roadmap, we have promoted this subsection up so it gets 
a mention.

>>>>
>>>> Whether we do this or not, an additional piece in the doc roadmap 
>>>> about this section would be useful.
>>>>
>>>>> ---
>>>>> With the importance of section 3.3 in mind, I was surprised to see 
>>>>> the top-level section had no text. Surely some text belongs here 
>>>>> to say that deployment of AccECN places new requirements on 
>>>>> networking equipment that forwards TCP, and inspects the TCP 
>>>>> header information!
>>>>
>>>> [BB] I believe that section headings are powerful ways to say 
>>>> exactly this, without having to repeat the same words with a few 
>>>> gratuitous little words added to make sentences. Specifically:
>>>>
>>>> 4. AccECN Compliance Requirements for TCP Proxies, Offload Engines 
>>>> and other Middleboxes
>>>>  4.1. Requirements for TCP Proxies
>>>>  ...
>>>>  4.2. Requirements for Transparent Middleboxes and TCP Normalizers
>>>>  ...
>>>>  4.3. Requirements for TCP ACK Filtering
>>>>  ...
>>>>  4.4. Requirements for TCP Segmentation Offload
>>>>  ...
>>>>
>>>> Again, if this idea had come earlier, I might have been more 
>>>> inclined to add a sentence or two. But I'm not a fan of adding 
>>>> significant amounts of text at this stage. Will probably add a 
>>>> little tho.
>>> [GF2] Little - even one sentence was what I had in mind. :-)
>>>>
>>>>> ===
>>>>> End of 3.3.2:
>>>>> However, to comply with
>>>>> - I could live without the "However", which to me at least gives 
>>>>> more weight - could even be a separate para to help this stand out!
>>>>
>>>> [BB] I can see the need to emphasize, but a new para wouldn't work 
>>>> - the 'However' sentence is very much a continuation of the same 
>>>> flow of thought.
>>>>
>>> [GF2] The problem with some of these /However/ is that they 
>>> follow-on a sentence which then becomes normative. I'm happiest when 
>>> the normative statements are single sentences that can be read on 
>>> their own...
>>
>> [BB2] Understood, but in this case, there's no danger of the first 
>> sentence being read as a requirement, because it says the opposite of 
>> the subsequent normative MUST NOT sentence.
>>
>>>>> ===
>>>>> I think 3.3.4 is different to 3.3.1 and 3.3.2, and really belongs 
>>>>> with the rest or directly following 3.2. The reason is this, is 
>>>>> about implementing TCP.
>>>>
>>>> [BB]
>>>> This is a question of whether separate processors are independent 
>>>> even if they run off the same power supply, or they're in the same 
>>>> housing. Similar questions apply on where you draw the line between 
>>>> an API and a protocol.
>>>>
>>>> In a similar vein, TCP Proxies /are/ TCP implementations. So they 
>>>> ought not to be outside §3.
>>>> So it seems we're now tending towards the idea that §3.3.1 and § 
>>>> 3.3.4 ought to remain in §3.3, while §3.2 & §3.3 would be moved to 
>>>> a new §4.
>>>>
>>>> But then we return to your original point that the types of company 
>>>> that build all the functions of all four sections (§3.3.1-§3.3.4) 
>>>> tend to be "networking equipment vendors" rather than end-system 
>>>> developers. So we want to direct their eyes to their own section. 
>>>> But then NFV blurs the distinction. This is not clear-cut. As I 
>>>> said, I will think on it.
>>>>
>>> [GF2] OK, I think the text works best when grouped into topics that 
>>> a specific group of readers would look at. 
>>
>> [BB2] I got that. But the problem is that even different subsections 
>> of §3.3. are already addressable to different parts of the industry. 
>> It's not clear cut. Not to mention the danger of late structural change.
>>
>> We might still do this (I would definitely have been in favour of it 
>> if we'd thought of it earlier), but let's see whether there are other 
>> views in the WG.
>>
> [GF3] I suspect you'll do the right thing, even if that's only to make 
> super clear in the ouline of the document's contents.
>>
>>>>> ===
>>>>> Section 4
>>>>> For the avoidance of doubt it would have been nice to have one 
>>>>> starting sentence that explains if these statements in section 4 
>>>>> are *additional* requirements to section 3, which I think they are 
>>>>> likely not, or a list of the impact of the changes in section 3 on 
>>>>> RFC3168?
>>>>
>>>> [BB] Good point. You're right. They are not additional, which needs 
>>>> saying.
>>>>
>>>>> ===
>>>>> I don't have a strong opinion, but I think section 6 is much 
>>>>> easier to read than some of the other materials, and seeing this 
>>>>> after section 2 mighty have been good. Equally could it be moved 
>>>>> to join other material before annexe B?
>>>>
>>>> [BB] It is intended to be like a 'Conclusions' section. The idea is 
>>>> that it comes after the detailed spec, to sum up whether it meets 
>>>> the original requirements. On that basis, it can't really come 
>>>> before the detailed spec. I'd like to leave it where it is. But 
>>>> would it help to change the title to 'Summary: Protocol Properties'?
>>> [GF2] That would help, or just a couple of extra words.
>>>>
>>>>> ===
>>>>> Section 10 looks like it should have an RFC-Ed comment to request 
>>>>> removal before publication.
>>>>> ===
>>>>> Of course, other ways could be resorted to in order to extend 
>>>>> AccECN or ECN in future
>>>>> - could we be simpler and just say:
>>>>> Other ways could have been used to extend ECN
>>>>
>>>> [BB] Certainly, we can remove 'Of course'.
>>>>
>>>> But you're suggesting we change the sense from 'could be in future' 
>>>> to 'could have been in this spec'. That would be contrary to the 
>>>> purpose (and headings) of this appendix. So we'd rather not do that 
>>>> part of your suggestion.
>>>>
>>> [GF2] I'm less sure of the future, but do what people agree.
>>>>> ===
>>>>> In section 2:
>>>>> could give conflicting feedback on the same segment
>>>>> - which segment - the received segment or the segment that carries 
>>>>> the feedback?
>>>>
>>>> [BB] We'll s/on/about/ which is what the conflict concern is.
>>>>
>>>>
>>>>> ===
>>>>> In section 2.4:
>>>>> If the option is stripped,
>>>>> - Maybe worth explaining in parenthesis
>>>>> If a middlebox strips the option (removes the option from a TCP 
>>>>> segment),
>>>>> ===
>>>>> In section 2.4:
>>>>> Feedback in bytes is provided in order to protect
>>>>> - seems one to confusion, can we remove /in order/ to avoid 
>>>>> potential misunderstanding of ordering
>>>>> Feedback in bytes provides protection against a receiver using 
>>>>> attacks similar to 'ACK-Division' to artificially inflate the 
>>>>> congestion window, which is why [RFC5681] now recommends that TCP 
>>>>> counts acknowledged bytes not packets.
>>>>> ===
>>>>> Can the last para of section 2.4, be modified like this to allow 
>>>>> it to appear in the guidance on middle boxes? :
>>>>> Feedback in bytes protects from middlebox attacks similar to 
>>>>> 'ACK-Division' that seek to artificially inflate the congestion 
>>>>> window, which is why [RFC5681] now recommends that TCP counts 
>>>>> acknowledged bytes not packets.
>>>>
>>>> [BB] A sentence directed at bad actors, boasting that we've 
>>>> designed this so they cannot build middleboxes that mount this 
>>>> particular attack wouldn't fit in the middlebox section.
>>>> The section on middleboxes is guidance for /willing/ middlebox 
>>>> implementers.
>>>>
>>>> The original sentence justifies a design choice of the AccECN 
>>>> protocol. So it would be appropriate to just
>>>>     s/against a receiver/against a receiver or middlebox/
>>>>
>>>>
>>>>> ===
>>>>> If it has set itself into classic ECN feedback mode it MUST then 
>>>>> comply with [RFC3168].
>>>>> - Can we replace the /it/s:
>>>>> If a Data Receiver has set itself into classic ECN feedback mode 
>>>>> it MUST then comply with [RFC3168].
>>>>
>>>> [BB] Yes, except s/Data Receiver/TCP client/, as per the preceding 
>>>> sentence in the draft.
>>>>
>>>>> =================
>>>>> Terms:
>>>>>
>>>>> /ECN bits/ is mentioned 3 times, but should always be /ECN Field/
>>>>
>>>> Agree on occurrences 1 & 2.
>>>>
>>>> Occurrence 3 is about the TCP flags - that needs
>>>>     s/using the ECN bits in the TCP header/using three flags in the 
>>>> TCP header already assigned to earlier ECN schemes/
>>>>
>>>>>
>>>>> /ECN Field/ is not defined, should be as per [RFC3168] and define 
>>>>> the ECN codepoint.
>>>>
>>>> [BB] OK. This just needs a change to the first sentence in §1.4 
>>>> Recap of Existing ECN Feedback in IP/TCP.
>>>>
>>>> OLD:
>>>>     ECN [RFC3168 <https://www.rfc-editor.org/info/rfc3168>] uses 
>>>> two bits in the IP header.
>>>> PROPOSED:
>>>> [RFC3168 <https://www.rfc-editor.org/info/rfc3168>] defines the 
>>>> two-bit ECN Field in the IP header, consisting of four codepoints.
>>>>
>>>> Table 1. is titled "The ECN Field in the IP header" and recaps the 
>>>> definitions of the ECN codepoints, and the para before it describes 
>>>> the semantics.
>>>>
>>>>>
>>>>> endpoint and end-point are variously used, please be consistent.
>>>>>
>>>>> /Data Sender/ is defined and then /ECN sender/ used in the text. 
>>>>> Do we need to define both terms? or are they the same?
>>>>
>>>> [BB] For the one occurrence, we'll
>>>>     s/an ECN sender/a sender that supports ECN/
>>>> and
>>>>     s/in the IP header/in the IP header of a data packet/
>>>>
>>>>>
>>>>> /TCP client/ and /TCP server/ use lower case, whereas Data 
>>>>> Receiver and Data Sender use upper case. the text later about a 
>>>>> /TCP sender/ lower case. These ought to be consistent?
>>>>
>>>> [BB] OK. I'll upper case TCP client and server.
>>>>
>>>> Of the 5 occurrences of 'TCP Sender', the middle 3 are within 
>>>> quotes from RFC3168 (where it is defined) and the 1st & 5th ought 
>>>> to be in quotes and upper-cased, because they are describing what 
>>>> RFC3168 says.
>>>>
>>>> That's it.
>>>> As I said, I'll just do everything with no comment.
>>>>
>>>> Thank you v much again.
>>>>
>>>> Cheers
>>>>
>>>>
>>>>
>>>> Bob
>>>>
>>>>
>>> It looks like the next revision will address these issues,
>>>
>>> Gorry
>>>
>>
>> [BB2] Will try.
>>
>> Cheers
>>
>>
>> Bob
>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> tcpm mailing list
>>>>> tcpm@ietf.org
>>>>> https://www.ietf.org/mailman/listinfo/tcpm
>>>>
>>>> -- 
>>>> ________________________________________________________________
>>>> Bob Briscoehttp://bobbriscoe.net/
>>>
>>>
>>
>> -- 
>> ________________________________________________________________
>> Bob Briscoehttp://bobbriscoe.net/
>
> Gorry
>

-- 
________________________________________________________________
Bob Briscoehttp://bobbriscoe.net/