[Asterisk-Users] Re: Slightly OT and mildly insane: Modems through VoIP :-))

Darren McIntosh dmcintosh at optushome.com.au
Tue Dec 16 02:51:07 MST 2003

> Message: 2
> Date: Mon, 15 Dec 2003 23:13:46 +0100
> From: Florian Overkamp <florian at obsimref.com>
> To: asterisk-users at lists.digium.com
> Subject: [Asterisk-Users] Slightly OT and mildly insane: Modems through
VoIP :-))
> Reply-To: asterisk-users at lists.digium.com
> Hi,
> First off, let me state that _YES, I am fully aware that what I am doing
> insane, prone to major havoc and bad for general health_ :-))
> Scenario: My GF needs an analog modem to use with her banking software
> (sodding backs don't supply a decent web-application for company use). I
> experimenting to see if we can get it to work (albeit slow) trough our
> talking g711 to Asterisk with chan_capi to the outside world. Should we
> there are more sane alternatives, but humour me :-))
> Now, with some modems on the other end I have received nice 26400bps
> handshakes, but it takes a long time and the successrate is about 25% :-)
> feeling is this should be better if we choose to slow it down more.
> But who can tell me what the best modem settings would be to try ? My
> dialect is rather old :-))
> Any experiences or hints are appreciated.
> -- 
> Best regards,
> Florian Overkamp
I've made data calls over g.711 voip from australia to the uk and they
trained up to 31k2 fine. What will throw them is packet loss. Just one lost
20ms frame was normally enough to force a retrain. Lose a packet during
retraining and the call would probably drop. Might pay to check the duplex
settings on your ata and whatever its connected to.
echo cancellers could possibly interfere with things but they should be
disabled by the 2100hz tone at the front of the call.


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