It seems that you may be debugging way too many things at once. Do you know much about the FAXBACK.COM internals? Just for a test you know you can bypass it. FreeSWITCH will work just fine on a windows box, using the FAXModem stuff, and com0com driver. That's what I use to have the M$ fax service talk to, and it works great. No hardware, and FS doing T38 right out of the Fax Service Server. At least if you test this way, you have FS logs and access to all the internals, and you can eliminate the "Black Box" in the middle. --Dave _____ From: Steven Schoch [mailto:schoch+freeswitch.org@xwin32.com] To: FreeSWITCH Users Help [mailto:freeswitch-users@lists.freeswitch.org] Sent: Tue, 15 Jan 2013 09:58:28 -0800 Subject: Re: [Freeswitch-users] FAX problems On Mon, Jan 14, 2013 at 5:12 PM, Michael Collins <msc@freeswitch.org> wrote: What does the FS log say? You should have some mod_spandsp log lines in there that mention what's going on with the fax attempt. Also, are you routing the call to the txfax app? Just curious how the fax call gets connected in the first place. The call is being routed from the Microsoft FAX plug in. The routing works like this: 1. FAX is initiated with Microsoft FAX on Windows 2. It goes through the faxback.com plug-in on the same machine. 3. The plug-in is configured to make a SIP connection to the FS pbx. 4. The FS pbx routes the call to the PSTN through sip.flowroute.com. 5. The call is received by a POTS line, connected to a modem. 6. The modem is connected with a serial line to a Linux machine. 7. The Linux machine runs Hylafax (www.hylafax.org). Steps 4-5 work for voice calls, using Polycom phones. Steps 5-7 work for other FAX calls, received often. The log for the faxback.com plug-in is at http://pastebin.freeswitch.org/20448. The FS log is at http://pastebin.freeswitch.org/20449. The Hylafax log is at http://pastebin.freeswitch.org/20450. New info: I put a test set on the PSTN fax line. (Yes, I'm old school telephony.) I hear the fax modem giving the normal terminating fax pre-message signal, and the originating fax sending the normal CNG tones. However, these tones don't stop. It's like the originating fax can't hear the pre-message signal from the fax modem. -- Steve