Re: [EToSat] Interop runner with satellite links

On Sat, Feb 26, 2022 at 3:40 AM Christian Huitema <huitema@huitema.net>
wrote:

>
> On 2/21/2022 10:16 AM, Su, Chi-Jiun wrote:
> > Hi Sebastian,
> >
> > Thanks for the great work.
> > Some comments/questions.
> >
> >    *   Sec. IV,D, 5: Interesting to know "picoquic" does speculative
> retransmission. As you argue, this may not always help. Did you confirm
> with the author?
>
> This is indeed supported in picoquic. There are APIs that allows the
> implementation to turn the feature on or off:
> `picoquic_set_preemptive_repeat_policy(quic_context, do_repeat)` is used
> to set the policy per Quic context, i.e., for all new connections;
> `picoquic_set_preemptive_repeat_per_cnx(connection_context, do_repeat)`
> is used to set the policy for a specific connection.
>
> The speculative retransmission happens at the lowest priority, i.e.,
> only happens if there is nothing else to send. It is subject to
> congestion control and rate limiting. The "nothing to send" rule means
> that it will only kick after all data of a stream and the FIN mark have
> been sent. The selection of data for speculative retransmission is based
> on stream level acknowledgements. The code deduces the acknowledged
> parts of a data stream from the packet acknowledgements. It will look at
> data that has been sent, but not yet acknowledged.
>
> As you say, this does not always help. If the packet loss rate is low,
> most of the preemptively repeated packets will be useless. On the other
> hand, when sending a file over a lossy link, the application may wait a
> long time for retransmission of packets lost in the last RTT. If loss
> rate and data rates are high enough, some of these packets will have to
> be repeated twice, or maybe three times. So we have a tradeoff: waste
> bandwidth, or waste time. The API allows the application to consider
> that tradeoff and decide whether it is useful or not.
>
> I would very much like to replace the current implementation of
> preemptive repeat by some version of FEC. FEC in general is a poor fit
> for transmission of big files, because it is always less bandwidth
> efficient than just repeating the packets that are lost. But if the
> application knows that the file transmission is almost complete, because
> there is just one CWIN worth of data left, it could turn own FEC for the
> the duration of the last RTT. It will "waste" a modest number of FEC
> packets, while drastically reducing the impact of packet losses on the
> duration of the file transfer. We could even imagine only sending the
> FEC packets after the FIN mark has been sent, making sure that FEC does
> not increase the duration of transfer if there were no errors.
>
> On the interaction between congestion control and coding, you may be
interested in looking at :
https://datatracker.ietf.org/doc/html/draft-irtf-nwcrg-coding-and-congestion-12

There have been other interesting contributions on the integration of FEC
in QUIC :
- https://datatracker.ietf.org/doc/html/draft-swett-nwcrg-coding-for-quic-04
- https://datatracker.ietf.org/doc/draft-roca-nwcrg-rlc-fec-scheme-for-quic/
-
https://inl.info.ucl.ac.be/publications/quic-fec-bringing-benefits-forward-erasure-correction-quic.html

I think the proposed approach (sending FEC packets when the file
transmission is over) had been experimented and will investigate whether
the results can be shared.

> -- Christian Huitema
>
>
> >    *    The results show loss-based CC does not perform well compared to
> BBR
> >    *   Production software performs well more like picoquic or not ?
> >       *   how big difference is between production vs these
> implementations in the test?
> >    *   Any Time-Offset graphs for EUTELSAT case ?
> >    *   Research overview page: additional column on emulated or real Sat
> link will be helpful
> >
> > Good useful work.
> > thanks.
> > cj
> > ________________________________
> > From: QUIC <quic-bounces@ietf.org> on behalf of Sebastian Endres <
> basti.endres@fau.de>
> > Sent: Friday, February 18, 2022 7:02 AM
> > To: etosat@ietf.org <etosat@ietf.org>; quic@ietf.org <quic@ietf.org>
> > Cc: joerg.deutschmann@fau.de <joerg.deutschmann@fau.de>
> > Subject: Re: [EToSat] Interop runner with satellite links
> >
> > **EXTERNAL EMAIL**
> >
> > Dear all,
> >
> > we've published a pre-print of our paper in which we present the
> QUIC-Interop-runner extended to include satellite scenarios and our
> measurement results using numerous publicly available QUIC implementations:
> >
> >
> https://urldefense.com/v3/__https://arxiv.org/abs/2202.08228__;!!Emaut56SYw!mFvp0jheUG95wMrw7L6ZHr3AUjZZgp63MEXhAZnEYvwEkQITw9uIFauoKkW-JRj-Kg$
> >
> > Best regards,
> >
> > Sebastian
> >
> > On Mittwoch, 29. September 2021 21:38:05 CET Sebastian Endres wrote:
> >> Dear all,
> >>
> >> for my master's thesis we ran measurements of all publicly available
> QUIC implementations over an emulated satellite link. The results are
> available online:
> https://urldefense.com/v3/__https://interop.sedrubal.de/__;!!Emaut56SYw!mFvp0jheUG95wMrw7L6ZHr3AUjZZgp63MEXhAZnEYvwEkQITw9uIFauoKkUlf0EgaQ$
> >>
> >> A click on the results also shows time-offset plots, but are not
> available for every combination.
> >>
> >> In general, the performance of QUIC over high latency (e.g.,
> geostationary satellites) is rather poor, especially if there is packet
> loss.
> >>
> >> Would it make sense to add such tests with challenging link
> characteristics to the official QUIC interop runner?
> >>
> >> Best regards,
> >>
> >> Sebastian
> >>
> >>
> >> _______________________________________________
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> >> EToSat@ietf.org
> >>
> https://urldefense.com/v3/__https://www.ietf.org/mailman/listinfo/etosat__;!!Emaut56SYw!mFvp0jheUG95wMrw7L6ZHr3AUjZZgp63MEXhAZnEYvwEkQITw9uIFauoKkXTZO8rhQ$
> >>
> >
> >
> >
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