Faxing with an ATA


You may use an ATA to connect a fax machine to the Phone.com network, but we can only offer “best effort” compatibility. Fax machines vary widely, and successful fax transmissions depend on many factors beyond our control. We encourage you to use Phone.com’s e-fax service as an alternative. If a physical fax machine is required, we recommend that you pair it with a Cisco SPA122 purchased from Phone.com. If you plan to use this setup, we will provide recommendations that can assist in the reliability of your fax transmissions.



Faxing protocols were originally developed when sound was sent over fixed circuits. Faxes are data turned into sound. Those sounds are turned back into data by the receiving machine. If too much data is missing, the connection is terminated.

Although protocols have arisen to deal with faxing over VoIP, there are still two fundamental difficulties:

  1. The fax data is converted to audio and then into a different form of data before being transmitted.
  2. The data is sent all over the internet, not a steady, fixed path.

Although voice traffic can often overcome these issues, faxing cannot always do so.

We have little control over the second item. Each packet might take a different route and could arrive at different times, or even be dropped completely. And if the packets don’t form an understandable message, the transmission fails.

Faxing with physical fax machines over VoIP is challenging, but with a few tweaks you might be able to increase the reliability of faxing in a VoIP environment.


ATA Settings

We may be able to automatically configure your ATA so that it’s optimized for fax machine use.

Please reach out to our Customer Support team if you plan to use this setup.


Network Changes

Network hardware that employs SIP ALG can interfere with fax performance even if it doesn’t obviously impact voice calls.

If you cannot disable SIP ALG on your network hardware, consider replacing that hardware.


Extension and Number Settings

Log into your Control Panel and make the following changes to your ATA’s extension and any number pointing to it.

  • Disable voicemail for the extension so the inbox doesn’t intercept inbound faxes
  • Disable call waiting
  • Make sure the outbound Caller ID is set to a number that has no Call Handling Rules other than to ring the fax machine’s extension
  • Make sure anonymous calls are allowed


Fax Machine Settings

  • Set the baud rate to 9600 or below
    • Menu options might refer to setting as “transmission speed,” “compatibility mode,” or “VoIP mode”
    • Slower speeds can help ensure more data gets to its destination
    • Higher speeds increase the chance of failure from packet loss, jitter, and latency
  • Disable Error Correction Mode (ECM)
    • ECM tells the machine to retransmit when noise, poor signal strength or packet loss is detected
    • But packet loss, jitter, and latency exist on the Internet normally, so the retransmits increase call duration, increasing instability
    • Disabling ECM prevents this retransmit signal
    • Although this could result in a fax of poorer quality, it isn’t likely to be noticeable
  • Set fax resolution to “normal” instead of high, fine, or ultra-fine
  • Disable dial tone detection if it fails to dial outbound properly
  • Disable any remote fax codes (numbers required after answer to send / receive)


Fax Troubleshooting

Testing Within the Phone.com Network (Required)

If you have problems sending or receiving faxes, run some tests within the Phone.com network by faxing either between two Phone.com ATAs, or between an ATA and a virtual extension in your account.

Make sure all above recommendations have been followed before proceeding.

Send 10 test faxes. If you had two or more failures:

  1. Record your network’s statistics for jitter, loss, and delay
  2. Get a copy of your ATA’s configuration to send to Customer Support
    1. In your web browser, go to the following URL to see the configuration file:
    2. Save the file with a filename like “<mac_address>.xml” using your device’s MAC address
  3. Identify the type of fax machine connected to the ATA
  4. Contact Phone.com Customer Support


Testing Outside the Phone.com Network (Optional)

Only proceed with this test if the above in-network testing had a 100% pass rate.

Use the HP Fax Test Service to confirm your fax is working after initial setup or to check for connection issues.

Send a one-page black and white text fax to 888-HPFaxMe (888-473-2963). When the service receives your fax, a return confirmation fax is sent within five minutes. This verifies that you can both send and receive a fax.

Read the following guidelines and tips if the test fax fails to send or the confirmation fax is not received.

  • Add your fax number in the fax header: The service uses the header number to send the confirmation fax. Make sure your full 10-digit fax number is in the header, and that it matches the number of the phone line connected to the fax.
  • Remove conflicting phone line services: Services such as voicemail, call waiting, anonymous call rejection, privacy manager, and caller ID can interfere with incoming faxes.
  • Run a Fax Test or Fax Test Report: Print a fax test report to identify any issues with the printer, phone line connection, or machine settings. Review the report for any tests that failed and follow any instructions provided.

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