On 8/2/2012 6:10 PM, Varun Singh wrote:
Hi Piers,
comments inline. On Thu, Aug 2, 2012 at 9:14 PM, Piers O'Hanlon <p.ohanlon@gmail.com> wrote:
Hi Varun,
This looks interesting - it would be nice to see self-fairness performance as well. What model did you use for the
Yes, the graphs looked very interesting as a start.
The second set of experiments 2 RTP and TCP, which is not exactly evaluating for self fairness but the last two graphs show the two RTP flows stacked on top of one another.
codec in ns2 (EvalVid or mpeg_traffic or other) ?
I dont use either but, I'd have to use EvalVid_RA for this because AFAIK EvalVid does only fixed rate. On the other hand, we have an implementation which connects ns2 to a real codec over IPC, but the simulations take a lot of time and therefore preferred to do just packet simulations in the first iteration.
In these simulations, I simplify and use equal sized frames instead of a group of pictures (I would have to run more simulations to vary GoP and measure its impact and didn't want to pick a wrong GoP for these preliminary results).
For interactive traffic, GOPs should be irrelevant(**): recoveries occur as a result of loss; simple recovery is some level of IDR/iframe, more complex are slice repairs or using older or long-term reference frames. And if the RTT is low(*), the loss might be repaired with a retransmit. All other frames should be deltas (pframes). A first level approximation would be to simulate it sending an IDR/iframe only after being informed of a loss by the receiver. Also, the size of the iframe is relevant too - fixed-quantization iframes can cause problems. Complex recoveries will cause much smaller bandwidth spikes, so iframe recovery is worst-case (and what is actually done in the webrtc.org code today, ignoring NACK/re-xmits). Obviously, using a real implementation (at least codec + rtp/rtcp/control) will produce a more accurate result - but this should be a reasonable approximation.
I (and probably others) would be interested to have access to the ns2 RRTCC implementation - would it possible to release the source code? (Though I'd be surprised if Google haven't already implemented it in ns2/3 already as well ...)
The code is currently still work in progress as I am also experimenting with other types of congestion indicators/algorithms (and would need some more time for cleanup) but, I have been using http://code.google.com/p/webrtc/source/browse/#svn%2Ftrunk%2Fsrc%2Fmodules%2... as a guideline for the implementation.
-- Randell Jesup randell-ietf@jesup.org