Analog vs. VoIP Faxing

Analog Faxing

Faxes have historically been sent over copper wires using sounds (analog). The sounds are converted back into data by the fax machine receiving the fax. If there is data loss during the transmission of an analog fax, the receiving fax machine has to terminate the transmission. This results in delays since the fax would need to be sent again.

Faxing Over VoIP

VoIP faxing allows you to conveniently send faxes from your computer without the hassle of printing out a document and feeding it into a fax machine to be sent. Unlike with analog faxing, a physical, dedicated phone line is not required to send a fax over VoIP as a fax's data is transmitted wirelessly over the internet.

To have your fax machine send faxes using VoIP, you will need…

• A fax machine that has had its settings configured for VoIP services.
• An Analog Telephone Adapter (ATA) for faxing connected and registered to your fax machine.
• An extra phone number that has been routed and configured for faxing with your fax ATA. 

To make the switch over the VoIP for faxing, contact our technical support department to explore your options.

Fax Machine Settings to Adjust for VoIP Faxing

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.

Enable Auto-Answer

To make faxing over VoIP more automated, auto-answer needs to be turned on in the fax machine's settings. If auto-answer is disabled, then each fax would need to be manually answered on the fax machine.

BAUD Rate

The BAUD Rate is the data transmission speed of a fax machine.  Some machines might display this as the Tx/Rx rates.  This should be set to 14400 bps.

Enable ECM (Error Correction Mode)

ECM is usually on by default on most fax machines (and multi-function printers), however this setting will need to be confirmed as enabled.

Why Should ECM be Enabled?

With VoIP services (whether voice or fax), packet loss, latency or jitter are inevitable aspects of internet connectivity.  This setting allows any errors in data transmission caused by noise, packet loss, or poor signal strength to be analyzed and detect data that might have been corrupted.  The machine triggers a retransmit signal to be sent until an error-free data frame is received.  This can increase a fax call duration until the fax is fully transmitted, which could subsequently result in other incoming faxes to not be answered and received by the machine before the call times out or hangs up and result in a failure for the sender.

Historically, disabling ECM would be recommended and still result in a completed fax of acceptable quality (assuming not too many data packets had been lost or corrupted during transmission).  This is no longer the case, and if ECM is disabled, fax attempts will instead result in errors being reported and ultimately failed transmissions.