[R-C] LEDBAT - introductions?

[Michael Welzl]

On Apr 6, 2012, at 10:13 AM, Harald Alvestrand wrote:

> On 04/06/2012 01:45 AM, Matt Mathis wrote:
>> There is one especially useful design point to extract here.....
>>
>> I believe that by default ledbat has a 50mS set point.  That is, it  
>> regulates its rate/window size by sensing if the one way queue time  
>> seems to be above or below 50mS.
> That is - 50 ms more than the baseline (lowest observed) RTT?
> 50 ms absolute would make no sense, since intercontinental  
> conferencing has a longer baseline RTT.
>>
>> Would this be acceptable for RTCweb, or would it be necessary to  
>> choose some other set point?
> I generally don't like set-points, since they tend to make behaviour  
> converge on the set-point. Sliding scales like the Kalmann filter of  
> Stefan's proposal make more sense to me.

To take a short point out of my previous, maybe too long email:  
depending on the queue length, which is not under your control, saying  
"I want 0 delay on top of the baseline" may mean that you'd only get a  
very small amount of bandwidth.

One possibility would be to make that trade-off a knob for the user.  
Another one is to let the "at least as much as the TCP equation  
dictates" rule in Stefan's proposal take care of that, but then you  
don't really know how much delay you'll get... e.g., maybe users could  
even live with less bandwidth than what the TCP equation dictates, as  
long as the delay is smaller? I think that's not an option with the  
currently proposed scheme.

Cheers,
Michael