[Ecn-sane] cctrace prototype

[Jonathan Morton]

> On 20 Mar, 2019, at 2:41 am, Pete Heist <pete at heistp.net> wrote:
> 
> So I’m starting work on a tool to make congestion signal plots in xplot.org format. It’s in Go for now and reads pcap files, producing one plot for each flow of the timestamp vs signal proportion. I’ll merge it to tcptrace later if needed, this is just faster for getting it started.
> 
> Here are screenshots and xpl files of one flow from a 10 second, 16-flow iperf upload with fq_codel_fast:
> 
> https://www.heistp.net/downloads/cctrace/
> 
> For each point, right arrow is used for upstream and left for downstream.
> 
> You can see that the SCE signals start sooner before CE takes over, which could theoretically prevent CE with a cooperating TCP.

Well, it's not *very* easy to see - but that is the idea in theory.  It might be easier to analyse such things (at this early stage of development) with a single flow, or possibly a pair with staggered start times.

One thing I'm noticing is that the SCE rate drops off very sharply when the CE marking rate rises, but the latter doesn't read higher than 50%.  Check your axis scale and your window average function for fenceposts.

> It needs some work, and I’m not yet satisfied with the windowing behavior. Choose a window size too low and the proportion value is visibly quantized. Too high and changes aren’t well reflected. I might be able to make a reasonable choice automatically through.
> 
> Thoughts? Ok to discuss this on ecn-sane?
> 
> Also, feel free to imagine what else would help visualize CC (different plot entirely? combined with throughput / RTT / TCP window?) and I’ll try to make it happen...

I'd like to see a sequence plot with the ECN codepoint indicated by colour coding, and similarly for ECE/NS/CWR on the ack path.

I'd also like to see a dynamic estimate of cwnd (or rather, in-flight data), with similar colour coding and/or labelling, for correlation.

 - Jonathan Morton