I am having trouble connecting a conventional fax machine up via an ATA or via a TDM400P (like countless others I’m sure).

My frustration stems from the fact that if my fax machine is connected to Asterisk, then I have about 70% failures. If I take that same conventional fax machine with the same settings and register it directly to my VoIP provider (VP Connect), then my success rate jumps to around 90% or better. It’s an incredible difference.

I don’t know exactly what I may be doing wrong other than having a few settings screwed up maybe. I’m not running fax detect or any of the special fax options (I have tried them, and most of them are for converting faxes to PDFs, etc.).

I have disabled echocancel in zapata.conf and other “fixes” that could interfere with the signal.

When using the ATA, I change no settings other than the register info. Of course I’m forcing g711u, and I have a fat pipe with low latency (~40-50ms to VP Connect), packet loss is nil, and QoS running on both the LAN and WAN segments of my network interfaces.

Any ideas?

Faxing behind VOIP can be a frustrating experience. Even when it works well you will only receive 90% of the faxes, and the ones you need the most will always fall in the 10% category. I would suggest getting either an analog phone line for faxing or an efax account.