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From: T H Panton <tim@pi.pe>
To: Dave Taht <dave.taht@gmail.com>
Cc: galene@lists.galene.org
Subject: [Galene] Re: using up more ports in ipv6 for better congestion control
Date: Sat, 10 Jul 2021 18:36:43 +0200
Message-ID: <35ECF0D3-B549-4C43-868F-58021E7F2BDD@pi.pe> (raw)
In-Reply-To: <CAA93jw58HfxwGTi6dwT+rGRYRrWQmBsaGatCmmNDc+KYPRLG+g@mail.gmail.com>



> On 10 Jul 2021, at 17:15, Dave Taht <dave.taht@gmail.com> wrote:
> 
> tim panton wrote me just now on linked in:
> 
> "It is still possible. Just set bundle-policy to max-compat and you'll
> get one stream for audio and one for video. Turn off rtcp-mux and
> you'll get 4 ports (voice, video, voice-RTCP, video-RTCP) - But your
> ability to connect will drop significantly (according to Google's
> data) and your connection setup time will increase. Even with port
> muxing congestion control is still possible, it just works
> _differently_ - which arguably it should, because realtime video has
> quite different needs from streaming or file transfer. Happy to have a
> chat about this...."
> 
> (so... chatting via email is preferred for me)
> 
> I am also under the impression that the congestion control
> notifications in rtcp are essentially obsolete in the rfc, mandating a
> 500ms interval instead of something sane, like a frame?

Oh, no, the congestion control is _very_ much alive in webRTC but under guise of 
bandwidth estimation - The ‘simplest' is google’s REMB RTCP message which basically
looks at the arrival time of packets and uses any _lengthening_ in the tof to deduce the onset of
additional buffering in the path. Transport CC tries to expand this to apply to all the streams muxed over a port
by adding an RTP header extension with an accurate (NTP) clock in it.

The thing that drives design this is that losing a packet is catastrophic for realtime video,  
one dropped packet makes seconds (aka megabytes) worth of data un-renderable.
At 50 fps the frame interval is shorter than the roundtrip time on the path (for VDSL users anyway - perhaps not fiber)
so a NAK/resend will fix it too late.

So the strategy is to dynamically estimate the capacity of the path and try to surf _just_ under that, ensuring minimal packet loss.

I realise this is anathema  to TCP folks, it certainly came as a shock to me….

T.

> 
> My other fantasy is to somehow start using udplite for more things.
> 
> The context for this of course is my never ending quest to have an IP
> based video and audio streaming system good enough to have a band
> playing with each other across town.
> 
> 
> -- 
> Latest Podcast:
> https://www.linkedin.com/feed/update/urn:li:activity:6791014284936785920/
> 
> Dave Täht CTO, TekLibre, LLC


  parent reply	other threads:[~2021-07-10 16:36 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-10 15:15 [Galene] " Dave Taht
2021-07-10 15:19 ` [Galene] " Dave Taht
2021-07-10 16:36 ` T H Panton [this message]
2021-07-10 16:48   ` Dave Taht
2021-07-11 11:19   ` Juliusz Chroboczek
2021-07-15 14:17     ` Sean DuBois
2021-07-16  1:36       ` Juliusz Chroboczek
2021-07-16 14:25         ` Sean DuBois
2021-07-15 16:26     ` T H Panton
2021-07-16  1:37       ` Juliusz Chroboczek
2021-07-16 14:46         ` T H Panton
2021-07-16 17:48           ` Juliusz Chroboczek

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