[Ecn-sane] comments: "Enabling ECN for Datacenter Networks with RTT Variations"

[Dave Taht]

On Sun, Dec 29, 2019 at 8:02 PM Dave Taht <dave.taht at gmail.com> wrote:
>
> this ecn# & codel in p4 paper had probably of most interest to me four points:
>
> 1) Codel like algorithm on a tofino switch, implemented in p4
> 2) with some source code published... Not the p4 code, darn it...
> unless I missed it?
>    but a detailed description of how they used the timestamp field was neat
> 3 Honestly I'd never thought about how much rtt variation a dc had,
> nor do I know if this model is correct

> 3) Not really clear what parameters the used for codel

For CoDel, the interval is set to 240µs while target is set to 10µs.

> https://resource.hpisys.com/seminar-papers/2019/paper/20191108_CoNEXT2019_Enabling%20ECN%20for%20Datacenter%20Networks%20with%20RTT%20Variations.pdf
>
> "Despite being successful, prior ECN-based transports have an
> important drawback: they adopt a fxed RTT value in calculating
> instantaneous ECN marking threshold while overlooking the RTT
> variations in practice. In this paper, we reveal that the current
> practice of using a fxed high-percentile RTT for ECN threshold
> calculation can lead to persistent queue buildups, signifcantly
> increasing packet latency. On the other hand, directly adopting lower
> percentile RTTs results in throughput degradation. To handle the
> problem, we introduce ECN!, a simple yet efective solution to enable
> ECN for RTT variations. At its heart, ECN! inherits the current
> instantaneous ECN marking (based on a high-percentile RTT) to achieve
> high throughput and burst tolerance, while further marking packets
> (conservatively) upon detecting long-term queue buildups to eliminate
> unnecessary queueing delay without degrading throughput. We implement
> ECN! on a Barefoot Tofno switch"
>
> --
> Make Music, Not War
>
> Dave Täht
> CTO, TekLibre, LLC
> http://www.teklibre.com
> Tel: 1-831-435-0729



-- 
Make Music, Not War

Dave Täht
CTO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-831-435-0729