[PLUG] VoIP on DSL?

[Kyle Hayes]

On Friday 16 April 2004 14:02, AthlonRob wrote:
> On Sun, 2004-04-11 at 12:20, Kyle Hayes wrote:
> > Different codecs have different bandwidth requirements.  G.723.1
> > is one of the lowest with around 7-8kbps.  G.729 is better
> > quality but a little higher bandwidth.  About 12kpbs IIRC.  This
> > is just for the codec audio stream, not other overhead!
>
> What's a kpbs?
>
> I'm sure it isn't Kilobits per second, as 12k really isn't very
> much bandwidth, in the grand scheme of things.  Guess I could host
> a lot of those on my 512/256 slow-ass DSL.

It is kilobits per second.  With a decent codec, voice doesn't take 
much bandwidth.  That's why all the backbone voice carriers are 
slowly rolling out VoIP onto existing fiber.  They can get a lot more 
conversations on a single fiber with a good codec than they can with 
uncompressed data.

Uncompressed voice uses 64kbps.  Compressed can do about 8-9 times 
better.  Seems funny that you should get such good compression until 
you realize a few things:

1) the human voice is in a very narrow frequency band.

2) the human voice can be modelled relatively well with a fairly small 
number of parameters.

3) around 30% of all the time in a conversation is dead silence.  This 
can be between words, between sentences, little audible pauses etc.

Given those three things, the bit rates look a lot more reasonable.  
Even with overhead for UDP/RTP etc. two conversations on a solid 28.8 
connection is possible.  The latency is ugly though :-P

Best,
Kyle