I know this isn't exactly what you were asking, but we do a lot of faxing (receiving and sending) and usually it can come from various machines with various settings, so we needed something pretty flexible. We also wanted to keep our "regular" fax machines as that is what our users were accustomed to. In the end, we just bought a Cisco SPA112 ATA box for each fax machine. You just setup the extension to it and register it as a phone and then plug its analog port into the back of the fax machine. So far they have been working great. Here are my notes on setting them up in case you decide to go that route:
To make our current fax machines work, I'm using a Cisco SPA112 ATA (Analog Telephone Adapter). One will be at each fax machine. It basically takes a sip account, takes the sip calls, and turns it into a regular "line" for faxes. Here are settings/important notes:
Update the firmware!!! The firmware that comes shipped is terrible. Get to at least 1.4.1.
By default, the box will get a DHCP lease and the username and password are both admin. You can find the IP in the dhcp leases file by searching for SPA112
You can use the "Quick Setup" for the initial account setup. Enter the following:
Proxy: <Address of FreeSwitch server>
Display Name: whatever name you want it to have
User ID: (the extension number)
Password: (the password)
Per that guide, set the following under Voice->Line1:
SIP Settings:
SIP Transport: TCP
Network Settings Section -
Network Jitter Level: very high
Jitter Buffer Adjustment: no
Supplementary Service Subscription Section -
Call Waiting Serv: no
Three Way CAll Serv: no
Audio Configuration Section -
Preferred Codec: G.771u
Use pref. codec only: yes
Silence Supp Enable: no
Echo Canc Enable: no
FAX Passthru Method: ReINVITE
All other defaults should be good.