Re: [tsvwg] Fwd: Qs on your 5G L4S slides

["Smith, Kevin, Vodafone Group" <[e-mail]>]

Hi Ingemar,

Just to ask, was there also a variant of the test with no L4S but with the dedicated bearer? I'd be interested to see that comparison.

@Bob, regarding UPF placement: the ability to virtualise network functions in 5G Core allows easier scaling of UPFs as required.

All best,
Kevin





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From: tsvwg <[e-mail]> On Behalf Of Bob Briscoe
Sent: 10 March 2021 17:41
To: tsvwg IETF list <[e-mail]>
Subject: [tsvwg] Fwd: Qs on your 5G L4S slides

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tsvwg,

Fwd'ing to list, with permission...
In case anyone else had the same questions


-------- Forwarded Message --------
Subject:

RE: Qs on your 5G L4S slides

Date:

Wed, 10 Mar 2021 14:33:42 +0000

From:

Ingemar Johansson S <[e-mail]><mailto:[e-mail]>

To:

Bob Briscoe <[e-mail]><mailto:[e-mail]>

CC:

Ingemar Johansson S <[e-mail]><mailto:[e-mail]>



Hi
Please see inline [IJ]

/Ingemar

-----Original Message-----
From: Bob Briscoe <[e-mail]><mailto:[e-mail]>
Sent: den 10 mars 2021 14:46
To: Ingemar Johansson S <[e-mail]><mailto:[e-mail]>
Subject: Qs on your 5G L4S slides

Ingemar,

#5 "Dedicated bearer / QoS flow for L4S traffic"
Is this a per-app microflow or a per-user flow?
[IJ] It is per-user flows, i.e each bearer can handle many flows


And I think you'll need to explain where the UPF is typically located. I believe
it's close to the edge, isn't i?
Further into the network (beyond the UPF) these flows just become an
aggregate of all the users.
[IJ] The UPF is close to the edge somehow, it is hard to say for certain where they are located, they can be real close to the base stations or >100km away.


#6 Question:
Do you have any feel for qDelay & throughput if a "Classic ECN AQM" like PIE
or CoDel was used?
[IJ] No, it was not studied in the master thesis work.


#6 - #11:
Is the DBS scheduler between users, or between flows?
[IJ] Per user (bearer)


#12: L4S is meant to greatly reduce the throughput-delay tradeoff, and in our
results it did.
Any idea why not here? I guess, with video, it's the 'getting up to speed' fast
problem (that I'm working on with Joakim).
[IJ] One reason is the large variation in frame sizes that video coders generate.
Another is that SCReAM paces out the video frames as 50% higher rate than the nominal video target bitrate. This pacing overhead can be configured lower but then the video frames (RTP packets) are more likely to become queued up in the sender instead. I really believe that it can be done better, was hoping to have time to improve SCReAM in this respect but the work hours fly in other directions .
With that said. Also a DCTCP flow (with L4S) marking will get a reduced throughput compared to e.g a Cubic flow (without L4S) over cellular. The reason is that the large buffers with Cubic absorb the fast fading dips in LTE and NR. With DCTCP + L4S some extra headroom is needed to avoid queue build up.



Bob

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