FAX Support - Fax Troubleshooting

Table of Contents

Errors on Incoming Faxes over Analog Card using FXS Connected to a Fax Machine:

1. The fax machine must be connected directly to the port on the analog card with an FXS module. Any other way of connecting the fax machine is completely unsupported.

2. Make sure your fax machine has an analog extension on the Switchvox and is hooked up to the correct channel of the Analog card. In Setup > Channel Groups > Default Fax Extension you can verify the correct extension is entered for the fax machine.

3. In the Channel Group for the FXS port, Fax Detection should be set to No. Go to Setup > Channel Groups > modify the analog channel group setup for the FXS card. Go to Advanced Options > Click on Hide Advanced Group Options > change to Show Advanced Group Options settings. Set Fax detection to No. Also, set Relax DTMF recognition to Yes.                          

4. Incoming fax detection for the Provider must be disabled. Under Setup > Incoming Call Route > set Incoming Call Type to Voice Calls. Any Incoming Call Routes for the Fax DID cannot have Treat All Calls as a Fax enabled. If fax detection is enabled at all, then fax calls will not reach the fax machine. Instead, the faxes will be delivered to the extension inbox.

5. Check the error logs for fax errors: go to Server > Error Logs. Do you see any fax errors? These will usually give information on why the faxes are failing.

6. If you are not getting a dial tone, or the analog channels are showing in red alarm then you will need to troubleshoot the analog card. Go to Server > Connection Status > Hardware Devices. Are the analog card channels showing green or a red alarm? If they are in red alarm you should refer to these troubleshooting tips.

7. If there is no hardware problem, nothing more can be done to correct the problem. This is an unsupported configuration and is not an approved method of faxing with Switchvox. You will need to use a supported method of faxing. For a list click here. 

Errors on Incoming Faxes to an Extension’s Mailbox: 

1. What version of Switchvox is running? It must be an SMB version (cannot be used on Cloud Server).

2. Is the Fax License installed? Go to Tools > Sangoma Addon Products to check for fax software. Make sure it doesn’t show RESFAX ERR ERR next to the license key.  For instructions on correcting this error click here.

3. Check the Incoming Call Routes to see if the call route is setup for both Voice and Fax Calls (Server > Incoming Calls). The only Provider types that are supported are PRI & Analog (SIP using T.38 protocol: while not supported should work if the SIP Provider supports T.38). For T.38 faxing over SIP, verify that ports 4000-4999 UDP are opened on your firewall.

4. Check Reporting > Call Logs > Phones > select the extension > View Log to see if the call is reaching the extension.

5. Verify the Incoming Call Route is setup for Voice Calls and Faxes.

6. Check the Server > Error Logs: Are there any fax errors showing? For Technical Support: enable VPN access and check the system log file. Or, users can download the TSR report to check the /var/log/switchvox/fax_log file (Technical Support can review this file).

7. Is this happening from only one fax machine (or fax number) or is it occurring from different fax machines? 

8. Are there audio problems on voice calls? 

9. If it is a PRI or Analog card then the Channel Group settings (for the Bearer Channel) can be modified. CAUTION: Saving changes in the Channel Groups will drop all calls and restart the software! Change one setting at a time:

   1. Number of Fax Buffers: try increasing to 32, send a test fax and check the error logs if fax fails. 

   2. Fax Buffer Policy (change one at a time and send a test fax to see if the issue resolves). Selections are Half, Full, Immediate. Try changing to Full and send a test fax. If it fails check the Error Logs to see if the same error is occurring.

   3. Perform Automatic Gain Correction set to Yes. Then, send a test fax to see if this resolves the problem.

   4. Rx/Tx Gain affects the volume of audio and therefore the fax tones that are sent or received. Rx Gain controls the volume of audio received from this channel group, so that would affect incoming faxes.  It will also affect the volume of calls as well. Can try making changes from -5 to + 5 (in decibels). Try changing in small increments (2) and see if a test fax can be received.

   5. Fax Detection set to Yes is required any time you want the Switchvox to process a fax and deliver it to an extension mailbox.

   6. Run an Asterisk Command Line Interface Debug while attempting to receive a fax. Technical Support can review this file for you. Here is an article on how to run the debug session.

Errors on incoming faxes over SIP:

1. Does the SIP provider fully support T.38 protocol for faxing? If the provider uses inband audio then this will not work reliably.

2. Is the Fax License installed? Go to Tools > Sangoma Addon Products to check for fax software. Make sure it doesn’t say ERR next to the license key.

3. Verify that the ports 4,000-4,999 UDP are opened to the server IP address. 

4. Run a packet capture to see if the fax is reaching the server. Here are the steps to run a packet capture:

5. Try different settings in Setup > VOIP Provider > Fax Settings: Set the Minimum transfer rate for transmissions to 9600. Try a different Fax Detection setting.

6. Disable Error Correction Mode: Setup > VOIP Provider > Fax Settings > Error Correction Mode for T.38 Faxes = None.

7. Check the Call Logs for the extension to see if the call is reaching the extension. Verify the Incoming Call Route is setup for Voice Calls and Faxes.

Problem sending outgoing faxes from an extension’s Outbox:

1. For Technical Support: Enable VPN access and check the system log file. Or, users can download the TSR report to check the /var/log/switchvox/fax_log file (Technical Support can review this file)

2. Are there numerous messages regarding pending faxes? (“Not sending fax for (1108) to xxxxxxxxxx because fax is at status of:failed”)  Delete all failed faxes from users Outbox on their extension. Anytime a fax fails to send, it must be deleted from the Outbox on the extension if it fails to delete automatically.

3. Using an analog line to fax from desktop, check how the 'Automatically Determine Call Progress' option is set:

   1. Setup > Channel Groups > modify Analog group > Advanced Options > Click on Hide Advanced Group Options > change to Show Advanced Group Options settings.

   2. Change Automatically Determine Call Progress to No.

4. Change the Min Transfer Rate for Fax Transmissions to 9600: Go to Setup > Manage > Login to the extension > Voicemail/Fax > Fax Options > Sending/Receiving > Advanced Options > and change the Min Transfer Rate (this is the minimum transfer rate used during fax rate negotiation).

5. If faxes are still failing and it is a SIP provider, run a packet capture while sending out a fax. If the faxes are being sent over a PRI connection, run a PRI Debug. Technical Support can review this file for you.

Other questions to consider:

• Is the problem reported by only one fax user, or from/to only one particular phone number?

• Is the problem reproducible? Is it intermittent or happening consistently?

• Are there call quality problems with voice calls? This will affect faxes too.

• Is the disk full? Go to Server > Disk Usage to check.

• Are there Load Alerts or other performance issues on the server? Check the Error Logs and Server > Server Information.

• ​For more information see Supported Faxing methods.