Re: [AVTCORE] Mirja Kühlewind's Discuss on draft-ietf-avtcore-rtp-circuit-breakers-15: (with DISCUSS and COMMENT)

"Mirja Kuehlewind (IETF)" <ietf@kuehlewind.net> Tue, 10 May 2016 16:14 UTC

Return-Path: <ietf@kuehlewind.net>
X-Original-To: avt@ietfa.amsl.com
Delivered-To: avt@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 7290312D725 for <avt@ietfa.amsl.com>; Tue, 10 May 2016 09:14:32 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2.898
X-Spam-Level:
X-Spam-Status: No, score=-2.898 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RP_MATCHES_RCVD=-0.996, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001] autolearn=unavailable autolearn_force=no
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id oRVp6lSq3Nwi for <avt@ietfa.amsl.com>; Tue, 10 May 2016 09:14:30 -0700 (PDT)
Received: from kuehlewind.net (kuehlewind.net [83.169.45.111]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 4603912D71F for <avt@ietf.org>; Tue, 10 May 2016 09:14:30 -0700 (PDT)
Received: (qmail 28200 invoked from network); 10 May 2016 18:07:47 +0200
Received: from softdnserror (HELO ?10.189.54.194?) (192.54.222.12) by kuehlewind.net with ESMTPSA (DHE-RSA-AES256-SHA encrypted, authenticated); 10 May 2016 18:07:46 +0200
Content-Type: text/plain; charset="utf-8"
Mime-Version: 1.0 (Mac OS X Mail 9.3 \(3124\))
From: "Mirja Kuehlewind (IETF)" <ietf@kuehlewind.net>
In-Reply-To: <4FEBFDED-ADEE-40E5-954E-DA6FB072AAAA@csperkins.org>
Date: Tue, 10 May 2016 12:07:07 -0400
Content-Transfer-Encoding: quoted-printable
Message-Id: <19C46407-A326-4912-9510-3040EE54FB78@kuehlewind.net>
References: <20160503120321.7534.26562.idtracker@ietfa.amsl.com> <32C2F93E-9CB9-4645-9C42-320AA8B24ED5@csperkins.org> <2EC09917-2E05-407D-AA7F-38C73B179C4B@kuehlewind.net> <CACHXSv6vggo7KN1HOqQyjbzro6Eq0zGNcfJ9poKnfpBipBn7Vw@mail.gmail.com> <249B6CE6-805D-4B65-80DE-A8B5280A059B@kuehlewind.net> <4FEBFDED-ADEE-40E5-954E-DA6FB072AAAA@csperkins.org>
To: Colin Perkins <csp@csperkins.org>
X-Mailer: Apple Mail (2.3124)
Archived-At: <http://mailarchive.ietf.org/arch/msg/avt/G2mBcMR1_kR_LgZFN6ag27sAXEw>
Cc: avtcore-chairs@ietf.org, Magnus Westerlund <magnus.westerlund@ericsson.com>, draft-ietf-avtcore-rtp-circuit-breakers@ietf.org, avt@ietf.org, The IESG <iesg@ietf.org>, Varun Singh <varun@callstats.io>
Subject: Re: [AVTCORE] Mirja Kühlewind's Discuss on draft-ietf-avtcore-rtp-circuit-breakers-15: (with DISCUSS and COMMENT)
X-BeenThere: avt@ietf.org
X-Mailman-Version: 2.1.17
Precedence: list
List-Id: Audio/Video Transport Core Maintenance <avt.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/avt>, <mailto:avt-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/avt/>
List-Post: <mailto:avt@ietf.org>
List-Help: <mailto:avt-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/avt>, <mailto:avt-request@ietf.org?subject=subscribe>
X-List-Received-Date: Tue, 10 May 2016 16:14:32 -0000

Actually no, because the stable state of operation might cause a constant high level of markings (whereas you don’t want to have a high constant rate of loss).

Constantly increasing marking level might be an indication for congestion.

Mirja


> Am 10.05.2016 um 11:34 schrieb Colin Perkins <csp@csperkins.org>:
> 
> Hi Mirja,
> 
> Persistant ECN-CE marks indicates a flow is causing persistent congestion, no? 
> 
> Colin
> 
> 
>> On 10 May 2016, at 16:18, Mirja Kuehlewind (IETF) <ietf@kuehlewind.net> wrote:
>> 
>> Hi Varun,
>> 
>> I would say that parts of tsvg-circuit-breaker are so general that they also apply for this doc. 
>> 
>> However, in any case my point it that (while congestion control may or may not threat ECN-CE marks similar as loss), circuit breaker MUST NOT do that because only ECN-CE marks without loss clearly shows that everything is working right and there is not need for a circuit breaker to react. That is really important to get right!
>> 
>> Mirja
>> 
>> 
>>> Am 05.05.2016 um 16:43 schrieb Varun Singh <varun@callstats.io>:
>>> 
>>> Hi Mirja,
>>> 
>>> see inline.
>>> 
>>> Regards,
>>> Varun
>>> 
>>> On Wed, May 4, 2016 at 1:52 PM, Mirja Kuehlewind (IETF)
>>> <ietf@kuehlewind.net> wrote:
>>>> 
>>>>> Not sure I agree. The circuit breaker needs to treat lost and CE-marked packets the same as a congestion control algorithm, and the ECN specifications say that the response to CE marks needs to be the same as the response to loss.
>>>> 
>>>> I disagree, given the explanation above that ECN-CE marking indicate that all traffic have been transmitted correctly. It’s only an input for a control mechanism/loop and should not be used as input for a circuit breaker, at least not the same way as loss it used.
>>>> 
>>>> You could calculate the loss and ecn ratio separately and e.g. lower the k value if there is also a high level of CE marks. However, only CE marks without loss should not trigger a circuit breaker. This is also what ietf-tsvwg-circuit-breaker says:
>>>> "If Explicit
>>>>    Congestion Notification (ECN) is enabled [RFC3168], an egress
>>>>    meter MAY also count the number of ECN congestion marks/event per
>>>>    measurement interval, but even if ECN is used, loss MUST still be
>>>>    measured, since this better reflects the impact of persistent
>>>>    congestion.“
>>>> 
>>> 
>>> First, I believe the draft assumes ECN-CE should be considered as lost
>>> packets in addition to the lost packets.
>>> 
>>> Second, I am not sure the text from the tsvg-circuit-breaker applies
>>> in this case. Because the calculation in section 4.3 takes place at
>>> the sender. And the  sender receives the ECN-CE counter from
>>> the receiver in an RTCP XR report (RFC6679).
>>> 
>>> In RFC6679: the receiver reports the cumulative lost packets and
>>> cumulative ECN counters. So at the sender, there may not be
>>> sufficient information to say if the ECN-CE packets were
>>> accompanied by loss or not.
>>> 
>>> 
>>>>> 
>>>>>> ----------------------------------------------------------------------
>>>>>> COMMENT:
>>>>>> ----------------------------------------------------------------------
>>>>>> 
>>>>>> Few more minor comments:
>>>>>> 
>>>>>> 1) reference [I-D.ietf-tsvwg-circuit-breaker] should be normative
>>>>> 
>>>>> This was discussed in relation to Ben’s AD review. I think you can implement the RTP circuit breaker without reading the TSV draft, so informative seems correct. However, I don’t much care either way.
>>>> 
>>>> I will double-check this; was not aware of any previous discussions here. I still think it should be normative...
>>>> 
>>>>> 
>>>>>> 2) How is the loss rate in 4.3 calculated if some (but no all) RR are
>>>>>> lost?
>>>>> 
>>>>> There’s no obvious way for the receiver of the RRs to know that some were lost, so the calculation will proceed as if the reporting interval was longer.
>>>> 
>>>> Hm… what’s about using the (difference of )total number of losses instead?
>>>> 
>>> 
>>> As Colin indicated there is no way to know that the report was lost.
>>> 
>>> In (RFC3550), the fraction lost is defined to be the number of packets
>>> lost divided by the number of packets expected since the last report.
>>> And the formula in Section 4.3 does not rely on all receiving all
>>> reports. Furthermore, the RTT and fraction lost plugged into the
>>> formula are based on the same report.
>>> 
>>> Is the concern that the fraction lost may not be sufficiently
>>> indicative if the preceding RTCP RR was lost?
>>> 
>>> 
>>> 
>>> -- 
>>> Founder, CEO, callstats.io
>>> http://www.callstats.io
>>> Analytics and Optimizations for WebRTC.
>>> 
>>> We are hiring: www.callstats.io/jobs/
>>> 
>> 
> 
> 
> 
> -- 
> Colin Perkins
> https://csperkins.org/
> 
> 
> 
>