An update to my dial-up ISP project. I got a two node modem pool working a PCI card to add more serial ports. Instead of my Verizon line, I patched these modems into my PBX running asterisk with a Grandstream ATA with 4 internal lines. The PBX takes incoming calls from a new number and uses a basic hunt group to connect to caller to the next free line.

Got a dialup modem? Feel free to give a call and let me know what OS you are using, how it goes. Details at

@Famicoman Have you been able to get the modems to talk to each other through SIP? I played a lot with that and it took some doing. I have grandstream HT702's hooked to my Panasonic PBX. About 300 was all I could do reliably to the SDF dial in number.


@junkman Yeah I've got speeds of 33.6kbps with few issues. I haven't tested any POTS lines, it is all VoIP. I've been doing Verizon voip to and my friend has been testing Google Voice to and we usually get something close to that. I think all I did on the ATA was make sure to prefer G.711 and turn off any echo cancellation. It might just be luck that there isn't much lag in the connection.

@junkman It's down right now but the dogemicrosystems guide has tips for ATA configuration,

I think that's really the only bit of that page I used as I am running Win Server right now, though I do want to switch things over to Linux at some point.

I'm using a Granstream HT504 myself so I imagine it isn't too big a jump for a 7XX model.

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