[Asterisk-Users] Small office requirements - Can this be done ?

Low, Adam ALow at Prioritytelecom.com
Tue Mar 2 04:43:24 MST 2004

> 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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