Using a fax machine connected to VoIP often ends in frustration with many failed transmissions. 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 often be accomplished.
Businesses that depend on faxing, including those companies that transmit and receive multipage documents, a traditional fax connected to a copper phone line or a virtual fax service is essential.
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 a part of the transmission to be lost, which then triggers a retransmit signal to be sent, until an error free frame is received. Resulting in more re-transmits over VoIP because of some packet loss, latency, or jitter, which may exist on an Internet connection. These re-transmits increase the call duration, quickly adding to the instability of the fax, resulting in additional retransmits. Which then leads to a fax failure, with a communication error reported by the receiving fax machine.
Disabling ECM results in the receiving fax machine accepting a transmission with some frames having bits of information missing. And still producing a completed fax, which should be of acceptable quality.
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.
Faxing over a VoIP connection has improved over the years, but businesses that do more than an occasional fax should remain with a traditional PSTN fax line rather than faxing 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.