Re: [Bloat] DSLReports Speed Test has latency measurement built-in

[Mikael Abrahamsson <swmike@swm.pp.se>]

On Thu, 7 May 2015, Jonathan Morton wrote:

> However the more common characteristic is that delay is sometimes low 
> (link idle) and sometimes high (buffer full) and rarely in between. In 
> other words, delay samples are not statistically independent; loss due 
> to jitter is bursty, and real-time applications like VoIP can't cope 
> with that. For that reason, and due to your low temporal sampling rate, 
> you should take the peak delay observed under load and compare it to the 
> average during idle.

Well, some applications will stop playing if the playout-buffer is empty, 
and if the packet arrives late, just start playing again and then increase 
the PDV buffer to whatever gap was observed, and if the PDV buffer has 
sustained fill, start playing it faster or skipping packets to play down 
the PDV buffer fill again.

So you'll observe silence or cutouts, but you'll still hear all sound but 
after this event, your mouth-ear-mouth-ear delay has now increased.

As far as I can tell, for instance Skype has a lot of different ways to 
cope with changing characteristics of the path, which work a lot better 
than a 10 year old classic PSTN-style G.711-over-IP style system with 
static 40ms PDV buffers, which behave exactly as you describe.

-- 
Mikael Abrahamsson    email: swmike@swm.pp.se