Fax Machine settings for VoIP

Improve Faxing over VoIP by Changing a few Fax Settings

Using a fax machine connected to VoIP often ends in frustration with many failed transmissions.Check for these settings for VoIP fax. For occasional faxing, initiating a few straightforward changes to the fax machine's settings, as well as using the proper VoIP codec, can improve your success. With these settings relatively stable faxing over VoIP can be accomplished.

Businesses that depend on faxing, including those companies that transmit and receive multipage documents, a traditional fax connected to copper phone line or a virtual fax service is essential.

These Fax Machine Settings will help Faxing over VoIP

  • Reduce the fax machine's transmission speeds or BAUD rate. Change the settings for both Tx (transmission) and Rx (receiving) to 9600 bps. Some fax machines, such as HP, use parameter numbers which represent a specific transmission speed.
  • Disable or turn off ECM (Error Correction Mode). On by default in most fax machines, this setting over VoIP frequently generates needless retransmissions.

Some VoIP services use a compressed codec which will cause fax transmissions to fail. Additionally, a few services offer a "fax" setting which forces the connection to use G711. If you discover a setting "bandwidth saver" it should not be enabled.

Your VoIP Connection should not use a Compressed Codec

  • It is critical that your VoIP connection uses G711, a Non-Compressed Codec. There are several compressed codecs often used, including G729 that reduces bandwidth which will cause faxes to fail.


Faxing over a VoIP connection has improved over years, but businesses that do more than an occasional fax should remain with a traditional PSTN fax line rather than fax over VoIP. We find that in regulated corporations like insurance, healthcare, financial services, legal and real-estate, fax remains an essential requirement. However, some excellent virtual fax service providers are modest in cost and offer exceptional applications. Perhaps the ideal solution is to switch to a reliable cloud-based fax service.