Re: [tsvwg] L4S DSCP (was: L4S drafts: Next Steps)

Jonathan Morton <> Tue, 30 March 2021 17:47 UTC

Return-Path: <>
Received: from localhost (localhost []) by (Postfix) with ESMTP id AF8ED3A1C69 for <>; Tue, 30 Mar 2021 10:47:10 -0700 (PDT)
X-Virus-Scanned: amavisd-new at
X-Spam-Flag: NO
X-Spam-Score: -1.848
X-Spam-Status: No, score=-1.848 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_ENVFROM_END_DIGIT=0.25, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
Authentication-Results: (amavisd-new); dkim=pass (2048-bit key)
Received: from ([]) by localhost ( []) (amavisd-new, port 10024) with ESMTP id Ozpcv59pG9yE for <>; Tue, 30 Mar 2021 10:47:06 -0700 (PDT)
Received: from ( [IPv6:2a00:1450:4864:20::22f]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by (Postfix) with ESMTPS id F2CB83A1C66 for <>; Tue, 30 Mar 2021 10:47:05 -0700 (PDT)
Received: by with SMTP id 184so20819501ljf.9 for <>; Tue, 30 Mar 2021 10:47:05 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=20161025; h=mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=3leeALcnpTvtj/tnUG/UAG7aa0JkM/O2u6C66rgyvTU=; b=PSQMTVbbBTTPXEuU3CIdjfX9ps3cpXykyvtHo+AHAHvJpuRTSjKdIsxWXQpSGSffa/ dAAfqQV19ep7shvGELmnPVzzbHv5HE5i7GwWwr/RLmJrR+gyNZCkr2swajmj5R5eKl99 Yv02IsSb+j/3hJIsErc6Yl6akGkP7VpsQoM8WieLb9PPV31ZrOIj/PJP9XV21gnMjHJb Ar8gI67zF99FXeU0h1A0f8mXguGEKro4QKDjnTNN/bqG7A48o91aiOQCojzlw7qNie9L EKAMBlxVIujdLxgWg/vf50OHVgn8ulEaLQkhrnfa0xXCE8s1eNHxkcLkZXjI6Spv99N8 00MA==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;; s=20161025; h=x-gm-message-state:mime-version:subject:from:in-reply-to:date:cc :content-transfer-encoding:message-id:references:to; bh=3leeALcnpTvtj/tnUG/UAG7aa0JkM/O2u6C66rgyvTU=; b=Mz7mTIFrZbDDCSmEoKsPuaHRMEE16XkUFnMa7WprdmEWXopFr5AfQbi2i4Q3HyxLoe GJlDlTbiphfqGZQFr5eDioq62mHx1u0DwbdtcVv1dexplB47rMuYiHvTOy2+nfFYqBI1 WodX7nsxbcIwm2WeNPuC2NRRSyFtRTEhfoyrq6SexMigRxyVe8z7lk+A9wFhZTrKUFGS tUqLarIqBSxGkVuQOCVa49FrTDa3YRRZAvuc+DkrqESTe3Y8IsAtYy4fNpJoUw6ESv80 XLFdxY1v4tlMFJheovGdyi+cUswlW01N1HW+5tgnrHnmAmxtPPfMJ/4buwS7wPpwXzWl lvqA==
X-Gm-Message-State: AOAM533JTxGEfSyvYUtAl37NLgJKLqUfhnFqluB+BgDT5uTIBaw2iq38 uCgWpeHCaVgfSu023uOCdbY=
X-Google-Smtp-Source: ABdhPJwYtfY21GvqbEpmTffRCtqcrByp1+6cREU7kXqenC8fzVeTv0YmQD2zNRczu3MtAxJtDuhG7Q==
X-Received: by 2002:a2e:8084:: with SMTP id i4mr22412565ljg.122.1617126422970; Tue, 30 Mar 2021 10:47:02 -0700 (PDT)
Received: from jonathartonsmbp.lan ( []) by with ESMTPSA id y186sm2238203lfc.304.2021. (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Tue, 30 Mar 2021 10:47:02 -0700 (PDT)
Content-Type: text/plain; charset="us-ascii"
Mime-Version: 1.0 (Mac OS X Mail 11.5 \(3445.9.7\))
From: Jonathan Morton <>
In-Reply-To: <>
Date: Tue, 30 Mar 2021 20:47:00 +0300
Cc: Sebastian Moeller <>, "" <>
Content-Transfer-Encoding: quoted-printable
Message-Id: <>
References: <> <> <> <> <> <> <> <> <> <> <> <> <> <> <>
To: Bob Briscoe <>
X-Mailer: Apple Mail (2.3445.9.7)
Archived-At: <>
Subject: Re: [tsvwg] L4S DSCP (was: L4S drafts: Next Steps)
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: Transport Area Working Group <>
List-Unsubscribe: <>, <>
List-Archive: <>
List-Post: <>
List-Help: <>
List-Subscribe: <>, <>
X-List-Received-Date: Tue, 30 Mar 2021 17:47:11 -0000

> On 30 Mar, 2021, at 11:21 am, Bob Briscoe <> wrote:
> L4S does not involve a DSCP, so there is no need to discuss DSCPs in l4sops.

Okay, so what mechanism do you propose to contain the L4S experiment to the participating networks?

> The tunnel issue was central to the choice of the L4S identifier - you will find it mentioned all over the ecn-l4s-id draft.

Yes, you've gone to a lot of trouble to make sure that L4S traffic is identified to the network in many different situations.  But the problems all have to do with networks that don't know to look for that identifier, even though it is present and correct on the traffic in question.  That's why the experiment has to be contained to networks that do.

Ultimately the problems arise because the network does not identify to the receiver what type of congestion signal it is producing.  You can only detect that indirectly through heuristics and probing, and (so far) not at all reliably.  We have been waiting for a solution to that deficiency since it was formally raised at Montreal.

Focus on these problems, and we might get somewhere.  Dismiss them, and you will fail.

 - Jonathan Morton