Stephane M wrote :
> Thanks guys for all this information...
>
> But I think about companies, which want to install a VoIP system....
> that seems to me not really suitable for companies..
>
> you can't ask people to stop downloading while phoning :-)

No, however, you can have a separate connection for voice, or choose an
ISP that can prioritise your traffic for you.

Employing QoS locally won't achieve all that an ISP can by shaping your
traffic - after all, using your router to provide QoS does nothing for
your packets after they leave your router, if you know what I mean.