Re: [tsvwg] Prague requirements survey

Ingemar Johansson S <ingemar.s.johansson@ericsson.com> Tue, 23 February 2021 08:45 UTC

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From: Ingemar Johansson S <ingemar.s.johansson@ericsson.com>
To: Bob Briscoe <in@bobbriscoe.net>, "De Schepper, Koen (Nokia - BE/Antwerp)" <koen.de_schepper@nokia-bell-labs.com>, tsvwg IETF list <tsvwg@ietf.org>
Thread-Topic: [tsvwg] Prague requirements survey
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Subject: Re: [tsvwg] Prague requirements survey
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Hi Bob

Please see inline [IJ2]

 

From: Bob Briscoe <in@bobbriscoe.net> 
Sent: den 22 februari 2021 21:35
To: Ingemar Johansson S <ingemar.s.johansson@ericsson.com>om>; De Schepper,
Koen (Nokia - BE/Antwerp) <koen.de_schepper@nokia-bell-labs.com>om>; tsvwg IETF
list <tsvwg@ietf.org>
Subject: Re: [tsvwg] Prague requirements survey

 

Ingemar,

On 10/02/2021 09:09, Ingemar Johansson S wrote:

Hi

Please see inline

/Ingemar

 

From: De Schepper, Koen (Nokia - BE/Antwerp)
<mailto:koen.de_schepper@nokia-bell-labs.com>
<koen.de_schepper@nokia-bell-labs.com> 
Sent: den 8 februari 2021 14:37
To: Ingemar Johansson S  <mailto:ingemar.s.johansson@ericsson.com>
<ingemar.s.johansson@ericsson.com>om>; tsvwg IETF list  <mailto:tsvwg@ietf.org>
<tsvwg@ietf.org>
Subject: RE: Prague requirements survey

 

Hi Ingemar,

 

Thanks for your contributions. I linked your doc to the
https://l4steam.github.io/#prague-requirements-compliance
<https://protect2.fireeye.com/v1/url?k=ae271499-f1bc2db2-ae275402-866038973a
15-a6d18987ee63d9e2&q=1&e=4b98878d-2d51-48b6-9518-92696e72501d&u=https%3A%2F
%2Fl4steam.github.io%2F%23prague-requirements-compliance>  web page (and
will do so for others).

[IJ] OK, great!

 

I didn't see any issues or objections mentioned to the current requirements
as specified in the draft. Does this mean you think they are all reasonable,
valid and feasible?

[IJ] There is a slight possibility that I misunderstood parts of the layout.
Even though SCReAM is only partially compliant in many cases I believe that
requirements are reasonable.  

 

Interesting observation (related to the performance optimization topic 1)
that for the control packets "RTCP is likely not using ECT(1)". Why is this
not likely? I assume this will impact the performance? Do we need to
recommend the use of ECT(1) on RTCP packets in the draft?

[IJ] Upon first glance I don't see that it is beneficial that RTCP packets
are ECT(1). But of course there is a possibility that RTCP packets go into a
queue with higher latency and that may affect performance. So. perhaps it is
reasonable that RTCP packets are ECT(1) too, but these are then to be
regarded as non queue building as it can be hard to rate control RTCP.


[BB] My knowledge is outdated, but RTCP used to be rate controlled in
multicast to prevent implosion (that was in the early days on shared
multicast, not single source). Are you saying all rate control mechanisms
have been removed? Is the problem that there's no feedback channel for
congestion indications on feedback? In 2-way RTP at least, couldn't you
infer the congestion of RTCP datagrams from the ECN on data running
alongside it? Or might they be disjoint paths?

[IJ2] Yes. It would of course be possible to set ECT(1) on RTCP/UDP/IP
packets and determine how large share of these packets that are marked. The
problem is then that there is not (currently) any RTCP feedback(on feedback)
format to carry that information back to the RTCP sender (==streaming
client) to make some rate control of the RTCP feedback possible. 
The RTCP bandwidth is indeed limited, the rule of thumb is that it should be
less than 5% of the RTP media bitrate scaled down by the number of
receivers. SCReAM is just one receiver and the RTCP bitrate is roughly 2% of
the medial bitrate. 

Incidentally, the attitude being taken to ECT on TCP Pure ACKs in AccECN is
in the AccECN draft. Basically, the info is now there for Ack CC if needed,
but no need to use it currently.


Bob




 

Thanks,

Koen.

 

From: Ingemar Johansson S <ingemar.s.johansson@ericsson.com
<mailto:ingemar.s.johansson@ericsson.com> > 
Sent: Monday, February 8, 2021 10:59 AM
To: De Schepper, Koen (Nokia - BE/Antwerp)
<koen.de_schepper@nokia-bell-labs.com
<mailto:koen.de_schepper@nokia-bell-labs.com> >; tsvwg IETF list
<tsvwg@ietf.org <mailto:tsvwg@ietf.org> >
Cc: Ingemar Johansson S <ingemar.s.johansson@ericsson.com
<mailto:ingemar.s.johansson@ericsson.com> >
Subject: RE: Prague requirements survey

 

Hi

Please find attached (hopefully) a Prague requirements survey applied to
SCReAM (RFC8298 std + running code)

 

Regards
Ingemar

 

From: tsvwg <tsvwg-bounces@ietf.org <mailto:tsvwg-bounces@ietf.org> > On
Behalf Of De Schepper, Koen (Nokia - BE/Antwerp)
Sent: den 6 februari 2021 23:20
To: tsvwg IETF list <tsvwg@ietf.org <mailto:tsvwg@ietf.org> >
Subject: [tsvwg] Prague requirements survey

 

Hi all,

 

To get a better understanding on the level of consensus on the Prague
requirements, we prepared an overview document listing the L4S-ID draft
requirements specific to the CC (wider Prague requirements), as a
questionnaire towards potential CC developers. If you are developing or have
developed an L4S congestion control, you can describe the status of your
ongoing development in the second last column. If you cannot share status,
or plan-to/would implement an L4S CC, you can list what you would want to
support (see feasible). In the last column you can put any
description/limitations/remarks/explanations related to evaluations,
implementations and/or plans (will implement or will not implement). Any
expected or experienced issues and any objections/disagreements to the
requirement can be explained and colored appropriately.

 

The document can be found on following link:
https://raw.githubusercontent.com/L4STeam/l4steam.github.io/master/PragueReq
s/Prague_requirements_Compliance_and_Objections_template.docx
<https://protect2.fireeye.com/v1/url?k=d16bc960-8ef0f066-d16b89fb-86ee86bd51
07-080c65bfd839440d&q=1&e=7dbb7494-67c3-4315-88a6-325f32e4e8b1&u=https%3A%2F
%2Fraw.githubusercontent.com%2FL4STeam%2Fl4steam.github.io%2Fmaster%2FPrague
Reqs%2FPrague_requirements_Compliance_and_Objections_template.docx> 

 

As an example I filled it for the Linux TCP-Prague implementation on
following link:
https://l4steam.github.io/PragueReqs/Prague_requirements_Compliance_and_Obje
ctions_Linux_TCP-Prague.docx
<https://protect2.fireeye.com/v1/url?k=f839c5f7-a7a2fcf1-f839856c-86ee86bd51
07-29dabadc5d0e673d&q=1&e=7dbb7494-67c3-4315-88a6-325f32e4e8b1&u=https%3A%2F
%2Fl4steam.github.io%2FPragueReqs%2FPrague_requirements_Compliance_and_Objec
tions_Linux_TCP-Prague.docx> 

 

Please send your filled document to the list (Not sure if an attachment will
work, so I assume you also need to store it somewhere and send a link to it,
or send to me directly). 

 

We hope to collect many answers, understanding the position of the different
(potential) implementers and come faster to consensus.

 

Thanks,

Koen.





-- 
________________________________________________________________
Bob Briscoe                               http://bobbriscoe.net/
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