Faxing over VoIP can be a trying experience, but with a few configuration changes on your current fax machine, you may find fairly reliable faxing over your VoIP line. 

Faxing over a VoIP connection.

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First some background on faxing and VoIP.

Faxing has been around for years and most of the protocols were written with the intent of sending those signals over traditional phone circuits using sounds.  Those sounds were turned back into data by the receiving fax machine, which expects a constant, steady transmission of data, without any loss.  If there is some loss of data the receiving fax machine will shut down the transmission. 

The problem is that the codecs used by VoIP IADs are designed to compress voice, not the analog signals sent and received by modems.

In a VoIP Internet world, voice is first converted into packets and then they are sent over the connections that make up our our vast Internet.  They may take slightly different times to arrive at their destination.  In doing so some packets may be discarded, but the end result is that the receiving VoIP device has enough packets to make a clear and understandable conversation. 

So by making a few setting changes on the fax machine; slowing the transmission rate down, and allowing the machine to continue receiving the transmission, even though a few bits of data were lost, faxing over VoIP can become more consistent.

G711 or Non-Compressed Codec

First make sure that your VoIP connection for you line that you fax on is set to G711.  This is a non-compressed codec.  G729 uses compression and will make the fax fail.  Some providers have a "Bandwidth Saver" setting.  This would be a compressed codec.  Make sure this is Not enabled.  If you do not have access to this setting call your provider and make sure your connection is set for G711.

 

You will want to make these changes:

• Slow down the transmission speed.  Set the BAUD rate of the fax machine to 9600 bps or even lower (7200 bps would be the next lower setting). 
• Turn off or disable ECM error correction mode, a setting, usually defaulted on, that many fax machines have.

More on Baud rates & ECM settings:

We have added some additional information about these two important settings and included some instructions on making these adjustments on some fax machines.  more

 

There are some other things that you will want to check, especially if you are still experiencing communication errors.  Some fax machines, especially Brother, have an Overseas Mode, which can be enabled before a fax. This setting makes temporary changes to the fax tones to accommodate noise and static and should be set before each outgoing fax. Check for the following:

• Use a direct connection from the IAD to the fax machine.  Try removing any splitters and other devices in that line.  Some devices may interfere with the fax transmission, such as, answering machines and caller IDs.
• Try enabling Overseas Mode.
• Change the resolution setting to Standard, rather than super fine.  This limits the amount of packets that need to be transmitted.
• If your fax machine is not connecting to the receiving fax machine try disabling or clearing any stutter tones that may be present on the line.  Many VoIP providers use a stutter tone to notify the user of new Voice Mail.  These stutter sounds will confuse the fax machine.
• Try plugging in the power adapter (cord) directly into a wall socket, rather than a power strip or surge protector. 
• Try placing a DSL filter in reverse position between the ATA and the fax machine.

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If you having problems connecting and are getting a fast busy signal when faxing, your fax machine is most likely not getting connected. (Try dialing the fax number from a different phone, and first check if you hear rings and then receive the traditional fax tone, as a test.)  If so, then you will want to check the fax connection for the following:

• Do you have dial tone at the fax machine and is the connection into the proper IN-Line port of the fax machine?
• Is the fax machine dialing the proper number?  If a 1 needs to be added to long distance, is it being added correctly?

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Integrating an Alarm system with VoIP.

Alarm companies are currently coming to grips with the realization that they will need to make their services work with VoIP.  Some companies can get their equipment to make the necessary communications and line seizure, but many cannot and will not support the service over VoIP.  The only way to know for sure is to call your alarm professional.  Introduction of voltages into a telephone line connected to VoIP can interfere with the VoIP connection.  In the event that you experience dropped calls or other issues with line quality, and have an alarm system integrated into the same wiring, try to connect a phone directly to the VoIP device, as a test.  If the issue stops occurring, then it could be a result from voltage introduced by the alarm system.

 

Dial-up Modems, Credit Card machines and Tivo.

Unfortunately, these devices will not work with any consistency over a VoIP connection and would not be recommended or supported by most providers.  The codecs used by IADs have been designed to compress voice, not the analog signals sent and received by modems.  (Some users have had limited success by slowing down the transmission rates to very slow speeds, but the network connections would need to be very stable and a G711 codec supported.  Some older machines are being used with some success, probably because they have slower BAUD rates.) 

In the case of Tivo, some people have had limited success by making the following changes:

• Make sure that your ATA connection is set to use the G711 codec.  (This codec is uncompressed and in some cases is referenced to 90kbps, as that is the approximate bandwidth needed.)
• Turn off Dial Tone Detection and Phone Detection.
• Some providers offer a dialing prefix of *99, if so use this setting.
• Try other dial in numbers.  (Some Tivo users say that they have better success with certain numbers rather than others.)  To change your dial in number, change the dialing prefix from ,#319 to ,#319,,xxxx where all symbols including commas are used and the xxxx represents the actual number to dial to.