Re: [rmcat] How we should handle feedback, and where the congestion should run

[Randell Jesup <[e-mail]>]

On 11/6/2015 11:33 PM, Xiaoqing Zhu (xiaoqzhu) wrote:
> In the eval-test-case draft, there is currently one test case dedicated
> for exploring impact of two-way traffic (Sec. 5.3.  Congested Feedback
> Link with Bi-directional RMCAT flows). Some corresponding graphs can be
> found below (they may not reflect the most up-to-date algorithm
> performance).
>
> * NADA:http://www.ietf.org/proceedings/92/slides/slides-92-rmcat-4.pdf
> (page #9 and #10)
> * SCReAM:
> http://www.ietf.org/proceedings/interim/2014/11/09/rmcat/slides/slides-inte
> rim-2014-rmcat-1-1.pdf (page #9)
> (Sorry, I was not able to find one with GCC yet.).

Thanks!  Those don't look too bad, though it can be hard to drill down 
into the details due to the PDF and thickness of the lines (and 
dense-ness of the graph); I found the closeups at the end of your pdf 
especially interesting (though not focused on this case).  One question 
that will be interesting as we develop a feedback mechanism is going to 
be the requirements from the algorithms on it, and the bandwidth it uses.

I note NADA seems to be slower to respond to delay, though it also seems 
to do much better against competing TCP flows (and likely the two items 
are linked, which will make for some interesting tradeoffs and tuning to 
do).

> Would like to know whether you think that current design of the test case
> has captured gist of the issue encountered by two-way calls, or any
> suggestions on additional test scenarios in that regard?

I think showing a graph similar to Scream's, with congested and 
non-congested feedback paths is a useful comparison - much easier to see 
the impact.  Feedback bandwidth would be useful, though that might be 
fairly fixed right now (multiple of packet rate), so unless it's 
surprising it may not need graphing (just noting on the graph).

-- 
Randell Jesup -- rjesup a t mozilla d o t com
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