Fax Machine Settings for VoIP Faxing
WE RECOMMEND THE FOLLOWING SETTINGS FOR BEST VOIP FAX RESULTS:
G711 or a Non-Compressed Codec
Make sure that your VoIP fax connection (the line you use for faxing) is set to G711, which is a non-compressed codec. G729 uses compression which will make faxes fail. If your VoIP provider has what may be called a "Bandwidth Saver" setting, then this setting would be a compressed codec. Make sure this setting is not enabled. You may have to talk with tech support for your VoIP service who will verify what type of codec your connection uses and to make sure your connection is set for G711.
Slow the transmission speeds on the fax machine settings. Both the Tx and Rx settings. This is called the BAUD rate of the fax machine. The best and fastest setting should be 9600 bps.
Disable ECM (Error Correction Mode). ECM is usually on by default on most fax machines. This setting needs to turned off.
Why ECM should be disabled:
Fax machines (also multi-function machines) set ECM as a default to on. This setting causes the receiving fax machine to analyze the received data frames and detect any data that may be corrupted. Any noise, lost packets, or poor signal strength can cause part of the transmission to be lost which then triggers a retransmit signal to be sent until an error-free frame is received. This causes retransmits more often over VoIP due to some packet loss, latency or jitter which exists on an Internet connection. These retransmits increase the call duration, quickly adding to the instability of the fax, requiring additional retransmits which then cause a failure with a communication error reported by the receiving fax machine.
Disabling ECM, will result in the receiving fax machine to accept a transmission with some frames that may have bits of information missing, but still resulting in a completed fax, which should be of acceptable quality.
Faxing over VoIP - When other alternatives are not available.
Companies that depend on multiple page faxes inbound and outbound should first and foremost use a dedicated copper phone line. A great alternative later technology choice would be to use an Internet fax service.
Where technology is taking faxing.
Better fax protocols for transmissions over IP have been in existence for some time, but this has not seemed to alleviate many user's major issues with faxing over VoIP. Anything but traditional copper lines are still suspect when it comes to faxes for heavy users. However, now VoIP services are offering services that work extremely well and provide apps that can benefit organizing and distributing faxes.