VoIP Fax Might Work, But There Are More Reliable Options


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The same Voice over Internet Protocol (VoIP) network you rely on to make voice and video calls can also be used to send faxes. However, it’s not a super reliable solution.

Faxing is built on older technology that isn’t quite compatible with today’s internet-based phone systems. We’ll explain exactly why that is and share specific problems you may run into when attempting to send VoIP faxes. 

This isn’t all doom and gloom, though. When you need to send a fax, there’s actually a better and even simpler solution out there: using an online fax service.

Online fax services are designed to replace fax machines altogether while helping companies avoid the rampant issues with VoIP fax.      

How VoIP Fax Works

When you make a VoIP phone call, the sound of your voice is broken down and converted into smaller digital packets that travel over the internet. Each packet contains information that identifies it within the full series of signals. Even if it arrives out of order, each piece can be reassembled into its complete original message on the other end.  

Fax machines are made to send and receive the analog tones of the circuit-switched landline network rather than the digital packets associated with VoIP. 

Essentially, the two technologies rely on different languages. 

An ATA (Analog Telephone Adapter) can help them speak to each other, but it works imperfectly at best. 

With an ATA, VoIP fax can attempt to compress and convert analog tones in the same way it converts voice data. The small black box connects to your modem, router, or incoming cable outlet and automatically translates between systems. This solution can work as a stop-gap or temporary option, but it lacks the reliability and consistent quality of online fax services.

What Are the Issues With VoIP Fax?

VoIP technology was created to compress and convert vocal sound waves into a specific digital language that modern internet networks can quickly identify and easily transmit. 

Fax machines, on the other hand, use a tone-based language that cannot be so readily translated. 

In order for VoIP fax to work, it must first digitize the information. It does this by first attempting to translate the fax machine’s analog tones into sound waves it can recognize. Then, these sound waves are converted into a digital data packet. 

Remember when we mentioned that these packets are typically marked according to their specific order for easy reassembling? 

That aspect becomes a key part of the problem with VoIP fax—because such markings are glaringly absent once the data is converted into its digitized format.  

When an ATA converts a fax machine’s tones into VoIP-compatible data packets, it produces a rough translation that doesn’t include the crucial information necessary to reassemble it in its proper order. The packets then will get jumbled in transit, some are even delayed en route to their destination, and others simply go missing altogether. 

In the end, the destination fax machine can’t figure out how to put the pieces together. The process of converting the digital packets back into analog tones in their original order takes far too long—especially now that pieces are missing. 

Gaps of silence, also known as jitter, occur as the remaining packets are frantically assembled. In most cases, the machine times out waiting for these signals to come through. At other times, such gaps cause the device to determine that the signal stream has ended. Both actions result in transmission failure.

There are several additional aspects of VoIP fax that can cause a message to terminate. In some situations, the data stream is just too large. The analog-to-digital translation process typically requires more bandwidth than a voice call. This bandwidth may not be available, particularly during periods of heavy use.   

Even if all goes well and the data transmits successfully, the recipient’s device may terminate the conversation due to interoperability errors. Your machine and theirs must follow the same system protocols—usually T.30 or T.38—transmitting information at the same speed. Otherwise, they may fall out of sync with one another and experience the jitter-related problems caused by data digitization.

It’s worth noting that a newer G.711 codec was created to help fix these interoperability issues. While this approach certainly improves the experience, it still doesn’t provide the streamlined transmission of online fax. It also only works if the destination fax machine operates by the same protocol.   

Network firewalls are another major hurdle when it comes to using VoIP fax. Features like Network Address Translation (NAT) filtering and Session Initiation Protocol Application Layer Gateway (SIP ALG) technology strip even more identifying information from incoming data packets. As a result, the system encounters further confusion about how the pieces fit together. The connection is often blocked or dropped entirely, terminating the transmission. 

You can sometimes bypass this issue by temporarily disabling your firewall or turning off SIP ALG. But this can be risky, potentially allowing uninvited data into your system. We don’t recommend it.

Ultimately, an online fax solution manages this problem for you without the need for a complex work around.  

VoIP Fax Alternatives

Maintain Separate Phone Lines for Fax

If your team is already accustomed to fax machines, you don’t have to give them up in order to use VoIP technology. In fact, many VoIP providers will recommend that you set up Plain Old Telephone Service (POTS) lines to service these machines. After all, fax machines were designed with these copper wire networks in mind. They both speak the same language, eliminating the potential for translation errors. 

Keeping dedicated lines just for faxing purposes can help to ensure a smooth, reliable process when sending and receiving messages. You also won’t need to trouble yourself with page limits, as you might with an online fax service.

Note that this approach does add an extra operations cost. Telecom providers typically charge anywhere from $25 to $40 each month per landline, plus set up fees. This can get quite pricey if you’re managing multiple machines, but it may prove a worthwhile option if your fax volume is high.

Also keep in mind that the Federal Communications Commission (FCC) officially phased out POTS lines as of August 2022. Phone carriers are no longer required to service or support these copper wire networks. 

Although landline faxing is still an option at this time, their future applicability is unknown.

Use an Online Fax Service

An online fax service, also called e-faxing or virtual fax, replaces a physical machine and bypasses the shortcomings of VoIP. This cloud-based technology operates independently of the VoIP network, using common internet protocols such as HTTPS, TLS (Transport Layer Security), and SMTP (Simple Mail Transfer Protocol). 

Each fax is transmitted as a system file attachment—much like you’d see on an email—rather than a piece of communications data. Even larger files arrive fairly quickly and completely intact, delivered via your fax server and converted for email or fax machine receipt.

Most online fax interfaces are extremely user friendly, accessible by web browser or through a convenient app on a smart device. 

You don’t need any additional hardware, but keep in mind that both you and the fax recipient will need internet access to transmit over the network—which shouldn’t be an issue for most people.

If you just need to send an occasional fax, you might find that a free service works fine for your needs. 

If you’re sending or receiving higher volumes—10 pages or more per day—you’ll likely need a paid option. Even these are priced competitively, with some services charging per document and others per page. Certain subscription options offer monthly pricing starting as low as $9.99 for up to 500 pages. 

Using a virtual fax service not only streamlines your experience but also enables encrypted document storage on the cloud. Depending on your service provider, this approach can be more secure than traditional fax. You can even enjoy the convenience of a local virtual fax number or carry over your existing number to avoid loss of service. 

In a pinch, you can send or receive faxes over your VoIP network. For a more reliable long-term solution, consider getting a separate fax landline or using an online fax service. Both are viable options, depending on your fax volume and budget.

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