Subject: [tcpm] I-D Action: draft-ietf-tcpm-accurate-ecn-12.txt

From: [email-masked]
Date: Wed, 28 Oct 2020 05:47:31 -0700

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.

Internet-Drafts are also available by anonymous FTP at:
ftp://ftp.ietf.org/internet-drafts/

---

From: Bob Briscoe <[email-masked]>
Date: Wed, 28 Oct 2020 13:03:31 +0000

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, [email-masked] wrote:
> _______________________________________________
> tcpm mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/tcpm

-- 
________________________________________________________________
Bob Briscoe                               http://bobbriscoe.net/
                PRIVILEGED AND CONFIDENTIAL

---

From: "Scharf, Michael" <[email-masked]>
Date: Wed, 28 Oct 2020 15:55:56 +0000

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.

There have been other related comments, e.g. from Ilpo.

Best regards

Michael (with no hat)

> -----Original Message-----
> From: tcpm <[email-masked]> On Behalf Of Bob Briscoe
> Sent: Wednesday, October 28, 2020 2:04 PM
> To: [email-masked]
> Cc: Scheffenegger, Richard <[email-masked]>; Mirja
> Kuehlewind <[email-masked]>
> Subject: Re: [tcpm] I-D Action: draft-ietf-tcpm-accurate-ecn-12.txt
> 
> TCPM folks,
>

---

From: Bob Briscoe <[email-masked]>
Date: Wed, 28 Oct 2020 17:17:20 +0000

Michael,

> 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. Ne…

[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