Re: [tcpm] I-D Action: draft-ietf-tcpm-accurate-ecn-13.txt

Hi Yoshi,

not sure if that really saves that much as you don’t need to send the option with every packet, as such you can manage the overhead dynamically as you can decide how often to send. Also in a scenario where most of the traffic flows only in on direction the AccECN is sent in the other direction.

Mirja

From: tcpm <tcpm-bounces@ietf.org> on behalf of Yoshifumi Nishida <nsd.ietf@gmail.com>
Date: Friday, 6. November 2020 at 09:54
To: Bob Briscoe <ietf@bobbriscoe.net>
Cc: "Scheffenegger, Richard" <Richard.Scheffenegger@netapp.com>, "tcpm@ietf.org" <tcpm@ietf.org>, Mirja Kuehlewind <ietf@kuehlewind.net>
Subject: Re: [tcpm] I-D Action: draft-ietf-tcpm-accurate-ecn-13.txt

Hi Bob,

Sorry for the late comments, I have a naive question about the encoding schemes in the options.
The byte counters will be incremented by every byte the receiver receives. But, do we really need this level of granularity?
I am thinking if we can byte-shift the counter values to some extent, we might be able to save option space.

Thanks,
--
Yoshi

On Mon, Nov 2, 2020 at 4:09 PM Bob Briscoe <ietf@bobbriscoe.net<mailto:ietf@bobbriscoe.net>> wrote:
Michael,

1/ I just posted a draft-13 that has the two AccECN TCP Option orders.

There are also htmlized versions available at:
https://tools.ietf.org/html/draft-ietf-tcpm-accurate-ecn-13

As agreed, it keys the two option orders on two different Option Kinds,
which I've requested in the IANA section (TBD0 and TBD1). This replaces
using the initial values of the fields. I've reverted all the
complicated text about:
* varying the initial field values dependent on option order,
* having to keep consistent order throughout a connection,
* and choosing which order from each end.
All of which is irrelevant now.

It is much simpler (I guess we all knew that). Thank you.

As mentioned, I found my other ToDo list:
2/ We also introduced considerably more guidance on middlebox handling,
esp. ACK filtering and Segmentation Offload. There was enough extra text
to be worth breaking that section into subsections.

The guidance on ACK filtering for connections with AccECN negotiated
updates the (non-)guidance in RFC3449 (BCP69 which said ACK filtering in
the presence of ECN was a research issue). But there is still no
guidance for ECN connections when AccECN has not been negotiated.

3/ I also added a SHOULD requirement I had on my ToDo list: Each Data
Sender SHOULD disable ECT in one direction if all the feedback for three
or four rounds from the start is CE. That's already done in Linux, and
in the TCP in iOS and MacOS at least.

Bob

On 28/10/2020 17:17, Bob Briscoe wrote:
> Michael,
>
> On 28/10/2020 15:55, Scharf, Michael wrote:
>> Hi Bob,
>>
>> What is the future plan regarding the option encoding proposed by the
>> authors?
>>
>> This has been discussed in past meetings and on the list, for
>> instance:
>> https://mailarchive.ietf.org/arch/msg/tcpm/zo-1OR0nRfhHocX8yvTvpC4BNMo/
>>
>> I have explained several times my pushback against the encoding
>> currently described in the document, most notably the requirement to
>> keep state in the endpoints to decode the format of a TCP option. I
>> have not changed my mind.
>>
>> I have also mentioned that, for instance, two option codepoints would
>> IMHO be a better engineering approach ("KISS principle"). That would
>> be a very simple change to the content to the document. Needless to
>> say that there are other alternatives for marshalling parameters in
>> an unambigous way.
>
> [BB] Whoops. In my head I had already shifted to your scheme with
> two-option kinds. But I see that, in the draft,  I haven't. Whoops -
> that was a bug in my ToDo list processing. Sorry about that. I'll
> submit another draft before the deadline with that scheme replacing
> the current one.
>
> I've just found some other entries in my ToDo list for this draft
> which I missed as well. I'll include them too.
>
> Sorry again.
>
>
> Bob
>
>>
>> There have been other related comments, e.g. from Ilpo.
>>
>> Best regards
>>
>> Michael (with no hat)
>>
>>> -----Original Message-----
>>> From: tcpm <tcpm-bounces@ietf.org<mailto:tcpm-bounces@ietf.org>> On Behalf Of Bob Briscoe
>>> Sent: Wednesday, October 28, 2020 2:04 PM
>>> To: tcpm@ietf.org<mailto:tcpm@ietf.org>
>>> Cc: Scheffenegger, Richard <Richard.Scheffenegger@netapp.com<mailto:Richard.Scheffenegger@netapp.com>>; Mirja
>>> Kuehlewind <ietf@kuehlewind.net<mailto:ietf@kuehlewind.net>>
>>> Subject: Re: [tcpm] I-D Action: draft-ietf-tcpm-accurate-ecn-12.txt
>>>
>>> TCPM folks,
>>>
>>> Back in May'20, it was decided to hold back the AccECN (and the ECN++)
>>> drafts for a while until the position on L4S in tsvwg was clearer.
>>> There
>>> is no formal dependency on the L4S drafts in tsvwg, but it made sense
>>> not to burn codepoints without more certainty.
>>>
>>> I've just refreshed the AccECN and the ECN++ drafts, which had expired.
>>>
>>> I included the following minor changes to AccECN, which you can see via
>>> the diff link below, but in summary:
>>> * moved wrongly categorized "action if unwilling to provide f/b" to the
>>> group of bullets relevant to the receiver
>>> * removed refs to long-expired ecn-fallback draft
>>> * fixed table 1 after xml2rfc changed formatting
>>>
>>> Thanks to those who pointed these out.
>>>
>>> No changes to ECN++ other than update of some refs.
>>>
>>> Cheers
>>>
>>>
>>> Bob
>>>
>>> On 28/10/2020 12:47, internet-drafts@ietf.org<mailto:internet-drafts@ietf.org> wrote:
>>>> A New Internet-Draft is available from the on-line Internet-Drafts
>>>> directories.
>>>> This draft is a work item of the TCP Maintenance and Minor
>>>> Extensions WG of
>>> the IETF.
>>>>           Title           : More Accurate ECN Feedback in TCP
>>>>           Authors         : Bob Briscoe
>>>>                             Mirja Kühlewind
>>>>                             Richard Scheffenegger
>>>>     Filename        : draft-ietf-tcpm-accurate-ecn-12.txt
>>>>     Pages           : 58
>>>>     Date            : 2020-10-28
>>>>
>>>> Abstract:
>>>>      Explicit Congestion Notification (ECN) is a mechanism where
>>>> network
>>>>      nodes can mark IP packets instead of dropping them to indicate
>>>>      incipient congestion to the end-points.  Receivers with an ECN-
>>>>      capable transport protocol feed back this information to the
>>>> sender.
>>>>      ECN is specified for TCP in such a way that only one feedback
>>>> signal
>>>>      can be transmitted per Round-Trip Time (RTT).  Recent new TCP
>>>>      mechanisms like Congestion Exposure (ConEx), Data Center TCP
>>>> (DCTCP)
>>>>      or Low Latency Low Loss Scalable Throughput (L4S) need more
>>>> accurate
>>>>      ECN feedback information whenever more than one marking is
>>>> received
>>>>      in one RTT.  This document specifies a scheme to provide more
>>>> than
>>>>      one feedback signal per RTT in the TCP header.  Given TCP header
>>>>      space is scarce, it allocates a reserved header bit, that was
>>>>      previously used for the ECN-Nonce which has now been declared
>>>>      historic.  It also overloads the two existing ECN flags in the
>>>> TCP
>>>>      header.  The resulting extra space is exploited to feed back
>>>> the IP-
>>>>      ECN field received during the 3-way handshake as well.
>>>> Supplementary
>>>>      feedback information can optionally be provided in a new TCP
>>>> option,
>>>>      which is never used on the TCP SYN.
>>>>
>>>>
>>>> The IETF datatracker status page for this draft is:
>>>> https://datatracker.ietf.org/doc/draft-ietf-tcpm-accurate-ecn/
>>>>
>>>> There are also htmlized versions available at:
>>>> https://tools.ietf.org/html/draft-ietf-tcpm-accurate-ecn-12
>>>> https://datatracker.ietf.org/doc/html/draft-ietf-tcpm-accurate-ecn-12
>>>>
>>>> A diff from the previous version is available at:
>>>> https://www.ietf.org/rfcdiff?url2=draft-ietf-tcpm-accurate-ecn-12
>>>>
>>>>
>>>> Please note that it may take a couple of minutes from the time of
>>>> submission
>>>> until the htmlized version and diff are available at tools.ietf.org<http://tools.ietf.org>.
>>>>
>>>> Internet-Drafts are also available by anonymous FTP at:
>>>> ftp://ftp.ietf.org/internet-drafts/
>>>>
>>>>
>>>> _______________________________________________
>>>> tcpm mailing list
>>>> tcpm@ietf.org<mailto:tcpm@ietf.org>
>>>> https://www.ietf.org/mailman/listinfo/tcpm
>>> --
>>> ________________________________________________________________
>>> Bob Briscoe http://bobbriscoe.net/<https://protect2.fireeye.com/v1/url?k=94a9aab2-cb32939f-94a9ea29-8692dc8284cb-827b8e584d366b78&q=1&e=b9141f6c-0f70-4414-9212-82cae72b93fc&u=http%3A%2F%2Fbobbriscoe.net%2F>
>>>                  PRIVILEGED AND CONFIDENTIAL
>>>
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>

--
________________________________________________________________
Bob Briscoe                               http://bobbriscoe.net/<https://protect2.fireeye.com/v1/url?k=1641fe24-49dac709-1641bebf-8692dc8284cb-0283475ef4fa8e27&q=1&e=b9141f6c-0f70-4414-9212-82cae72b93fc&u=http%3A%2F%2Fbobbriscoe.net%2F>

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