Re: [codec] #16: Multicast?

[Koen Vos <[e-mail]>]

Quoting "Raymond (Juin-Hwey) Chen":

>   One-way delay = codec-independent delay + 3*(codec frame size) +  
> (codec look-ahead) + (codec filtering delay if any)
>
> This formula was obtained from an experienced engineer who has been  
> working on IP phones related fields for more than a decade,

At Skype We have 100+ years of combined VoIP experience, and a focus  
on minimizing delay as part of our goal to maximize quality.  The  
consensus among our engineers is that the multiplier is closer to 1  
than to 2, at least for software VoIP applications over typical  
Internet connections.  Some years ago the situation was slightly worse  
because dial-up was more prevalent.


> Similar 3X multiplier is also observed in VoIP gateways.  Even with  
> a fast processor/system optimized from ground up to be low-delay,  
> the measured "codec-dependent" one-way delay of such a VoIP gateway  
> using the G.711 codec with a 5 ms frame/packet size is between 12  
> and 17 ms, or around 3X the frame size.

As I've pointed out before, that doesn't say much about how the delay  
increases with larger frame sizes.  Perhaps the 12~17 ms includes a  
constant delay of 7 ms, and the marginal growth of delay with frame  
size is 1x.

best,
koen.