Re: [tcpm] Further comments on draft-ietf-tcpm-accurate-ecn

Bob Briscoe <> Mon, 16 July 2018 23:34 UTC

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To: "Scharf, Michael (Nokia - DE/Stuttgart)" <>, "" <>, "" <>
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From: Bob Briscoe <>
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Date: Mon, 16 Jul 2018 19:34:02 -0400
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Subject: Re: [tcpm] Further comments on draft-ietf-tcpm-accurate-ecn
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On 15/07/18 16:54, Scharf, Michael (Nokia - DE/Stuttgart) wrote:
> Hi all,
> While reading draft-ietf-tcpm-accurate-ecn-07, I noticed the following:
> Section 1. Introduction
>     It is likely (but not required) that the AccECN protocol will be
>     implemented along with the following experimental additions to the
>     TCP-ECN protocol: ECN-capable TCP control packets and retransmissions
>     [I-D.ietf-tcpm-generalized-ecn], which includes the ECN-capable SYN/
>     ACK experiment [RFC5562]; and testing receiver non-compliance
>     [I-D.moncaster-tcpm-rcv-cheat].
> [ms] I have commented on this section before. And I still dislike the term "likely". To me, "likely" is speculation. A neutral phrasing would be "... it is possible..." or "... it is useful...". Having said this, I observe that draft-moncaster-tcpm-rcv-cheat-03 was last updated in 2014. How "likely" is it that the AccECN protocol will be implemented along with a mechanism documented in an ID that has been written more than 10 years ago and not been updated for about 4 years? Are implementers indeed so interested in draft-moncaster-tcpm-rcv-cheat that an implementation is "likely"?

I agree. For ECN++, I think something like your suggestion of "useful", 
or even RECOMMENDED is what is needed here. I think the testing receiver 
compliance one could be removed from the intro. It's mentioned under 
testing for unexpected interference and under integrity checking, which 
are sufficient.

Also, this makes me notice that the word "includes" is wrong. ECN++ 
intends to obsolete RFC5562, but I don't think we need to mention that 
here (cos it might change before ECN++ gets published).


    It is likely (but not required) that the AccECN protocol will be
    implemented along with the following experimental additions to the
    TCP-ECN protocol: ECN-capable TCP control packets and retransmissions
<>], which includes the ECN-capable SYN/
    ACK experiment [RFC5562 <>]; and testing receiver non-compliance


    It is RECOMMENDED that the AccECN protocol is implemented along with
    the experimental ECN++ protocol [I-D.ietf-tcpm-generalized-ecn 

> Section 2.1.  Capability Negotiation
>     The TCP server sends the AccECN
>     Option on the SYN/ACK and the client sends it on the first ACK to
>     test whether the network path forwards the option correctly.
> [ms] According to Section 3.2.6, options are RECOMMENDED. While Section 2 is not normative, the whole Section 2 does not really describe well the actual requirements regarding options. This paragraph in Section 2.1 is one example for that. It would make sense to be more explicit in Section 2 to which extent options have to be supported.
OK, we need to review section 2, to ensure it is consistent with changes 
that have been made in the normative section 3 since it was written.

In this particular case, we already promised to check (offlist with an 
implementer) that there was no text that contradicted the optionality of 
the option stated at the end of Section 3.2.6.

I have already started this with a list I prepared (also offlist) of 
which middlebox checking sections an implementer could ignore if they 
were only reading but not sending the TCP options.


Bob Briscoe