[GGIE] Low latency and high bandwidth

Bob Briscoe <ietf@bobbriscoe.net> Mon, 22 July 2019 19:35 UTC

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To: Justin Uberti <juberti@google.com>, ggie@ietf.org
From: Bob Briscoe <ietf@bobbriscoe.net>
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Date: Mon, 22 Jul 2019 15:35:32 -0400
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Subject: [GGIE] Low latency and high bandwidth
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Justin, and MPOS-ers, if that's a thing.

Here's links to the work on making sure your low latency high throughput 
video isn't screwed up by intermittent other traffic sharing the queue.

L4S = Low Latency Low Loss Scalable throughput (L4S) is nearing 
completion in the transport area.

      1/ Demo of L4S at the Jul 2015 IETF that kicked off the work

Still worth seeing. It shows a panoramic cloud-rendered video of a live 
football match, panned and zoomed by finger-gestures on a tablet, over a 
data centre - core - backhaul - 40Mb/s broadband DSL access - home 
network (7ms base delay), with multiple TCP downloads (L4S and non-L4S) 
running through the same queue:
You'll see it appears to stick to the finger (sub-1ms queuing delay).

      2/ Low Latency DOCSIS

IETF L4S was adopted for DOCSIS a couple of years ago. The updated 
DOCSIS specs were published in Jan'19, with vendor products now planned 
for early 2020 (operators in various countries have deployment plans).

See the annex of the white paper 
at the end of the above page entitled "Low Latency AND High Throughput: L4S"
There's an IETF draft of the same paper, but the pictures aren't so good ;)

      3/ Google BBRv2 will use L4S

At the Mar'19 IETF, Neal Cardwell announced 
that BBRv2 will switch to exploiting L4S where the path supports it 
("DCTCP-inspired ECN").

      4/ Even more impressive demo

At the MMSYS'16 demo session.

      5/ Latency Performance

Our most evil test traffic mix: 600 web session arrivals per second and 
two TCP downloads (all half and half L4S and non-L4S).
99th percentile queuing delay: 2ms for /all/ the L4S packets: web and 
downloads [see log CCDF plot 

      6/ Code?

All the pieces via the code section of the landing page 
TCP Prague is most mature, but there's an L4S variant of rmcat SCReAM, 
and QUIC there too.

      7/ Are there ops issues to work through?

Sure. See the ops & management sections of the drafts 
Let's discuss.


Bob Briscoe                               http://bobbriscoe.net/