Good to know
Outbound faxing via VoIP (using an ATA) is always a bit tricky and it means you'll have to play with the settings and it may even be affected by the ATA, the fax machine or how well those play together.
As 'fax' as a standard is notoriously badly followed by (all) manufacturers.
Our system support T38 fully so that really can't be the issue, it is often the interoperability between ATA and fax machine (and/or any other devices in the mix and the settings in any of those) that creates possible issues.
PS Just so you know, if you have a fax line with us the Inbound faxes are caught and processed on our systems and sent to you as PDFs, so there is no worry about that working :-)
Setting up your ATA <> Fax machine
To set up your ATA you can use the same setup details as for a standard phone line with our systems, yes, we try to keep it easy.
This only goes for the account and connection towards us though and you will need to set other settings to make the AT play nice.
Please follow the manufacturers' instructions to do this part as every manufacturer, device and sometimes even version of the software on the device can require different settings and/or details.
Troubleshooting
All the following options and settings are mentioned in general terms, your device may not have all the options and/or call them slightly different, but you can usually recognise the matching one.
- Set the transmission speed to 9600 baud
(if the fax works perfectly, you can up it to 14.4k but that may be more troublesome if the network is the issue) - Set the codec to G711u
- Set the Preferred Codec Only to Yes
- Set FAX Passthru Method to NSE (if available) otherwise it will be protocol based (which should be fine)
- Try to use the UDP port type but, to see if this works better for you, you could also try if TCP may give a better result (always port 5060 though)
- Switch Call Waiting Off (possibly on both the ATA and the Fax machine)
- Switch Silence SuppressionOff
- Switch Echo Suppression Off
- Switch Echo Canceller Off (sometimes called ECAN)
- Switch error correction (ECM) off
- Turning Overseas Mode On (if available)
- Jitter: play with switching any jitter control on or off and if on, change the value and see if that gives some improvement.
Usually the bigger the value the more stable but also the slower it will work, so find the best option for your situation. - SIP ALG Off
(this often has to be done via the command line, not the web interface to switch off fully) - Adjust the TX volume as some ATAs could have an issue if set incorrectly
Optional, if still needed,
- Try different options in the FXS Settings such as TXgain and RXgain (if available)
- Test with different settings for the Calling Channel Codec Priority (if available)
- You could try if QOS (best on the modem/router, alternatively on the ATA) helps
If your faxes are still having issues going out, we can look at the log files to see if that clears anything up.
For us to look at such a fax/call issue we need to know the minimum call details of that very specific call to be able to find the correct log file.
(max 12-24 hours old, the more recent the better as log files get compressed because of the sheer volume there are).
So, the next one that breaks, let us know this and we can have a look if we can see anything specific in the log file that may help to understand this issue.
Recommendations
In all the years e have had Faxes connected to (our) VoIP solutions, we have seen the good the bad and the downright ugly. Some will work easily and reliably and some will never work.
In our experience, don't hold us to this as results may vary a lot, we have seen that the one combo seems to stand out in setting up and reliable workings.
This is the combination of a Linksys ATA, such as the Linksys PAP or PAP 2T, and an HP Fax machine.
(but even here, it depends a lot on the machine. Often the simpler the more reliable.)
Last updated: 01/01/2024
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