> So for us Dummies out here :) who just know it works.

Yep, it sure does, I thought it was something people might find interesting. Its 
certainly been a challenging subject for me to try and provide reliable and high 
quality voice service over ADSL. In my experience it seems to depend a hell of a lot 
on the QoS deployed on the ATM network behind the DSLAM's. Obviously a single cell 
being dropped every 5 cells would effectively cause every G.711 IP packet to be lost.

Here in Holland I ported my KPN (legacy incumbent) telephone number to my home VoIP 
service about 4 months ago. It has been  running over a BBNED ADSL service and works 
great 99.9% of the time. Although during recently virus/worm outbreaks I have found 
people complain they hear my voice choppy, probably due to the contention of all the 
other ADSL connection upstreams as they propagate those viruses/worms.

> This would mean that if you had a 512/256 aDSL and a 256 ISDN connection 
> you would be able to have more channels over the ISDN?

Thats right, I am not aware of any ADSL providers that actually provide their stated 
service level at an IP layer rather than  at the ATM layer but maybe they are out 
there ...

The exact calculation depends on how your encapsulating IP over the 256k ISDN 
connection. I will assume your actually getting 4x B channels with either multi-link 
PPP (haven't calculated the overhead for this one) or a CSU/DSU converting to 
X.21/V.35 (preferable). You should be able to push 3 concurrent G.711 channels over 
that 256k ISDN service assuming 86Kbps per channel.

> David

Here's a little table I put together for our capacity planning team:

G.711 over Ethernet     = 95 Kbps per channel
G.711 over IP/PPP               = 86 Kbps per channel
G.711 over ADSL/ATM     = 108 Kbps per channel

G.729 over Ethernet     = 39 Kbps per channel
G.729 over IP/PPP               = 30 Kbps per channel
G.729 over ADSL/ATM     = 45 Kbps per channel



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