Faxing is built on analog technology that is incompatible with digital VoIP phone systems that make calls over the Internet.
I’ll explain exactly why this is and share specific problems you might encounter when trying to send VoIP faxes. If you need to send a fax without a fax machine or landline, there are simple online fax services that work much better than trying to use VoIP to send a fax.
Well – that’s a quick rundown of the important information. Let’s dig into the details.
Why VoIP Fax Struggles
When you make a VoIP phone call, the sound of your voice is broken up and converted into small digital packets that travel over the Internet. Each packet contains information that identifies it in the entire series of signals. Even if it gets out of sequence, each fragment can be reassembled into its complete original message at the other end.
Fax machines are designed to send and receive the analog tones of the public switched telephone network rather than the digital packets associated with VoIP.
Unlike voice calls, fax data is highly time-sensitive and does not tolerate packet loss, jitter or delay.
Basically, the two technologies rely on different languages—you can’t just plug an analog device (a fax machine) into a digital network (the Internet) and expect them to communicate flawlessly.
Connecting an analog fax machine to a digital network requires a specific solution, such as a fax-specific protocol such as T.38. However, it depends on both VoIP provider and the receiving device supports the protocol to ensure compatibility.
See: Learn more about Differences between landline and VoIP communications.
What are the problems with VoIP fax?
VoIP technology was designed to digitize and transmit voice signals, not fax tones. Fax machines rely on analog tones that VoIP networks struggle to handle reliably. This creates several challenges when sending faxes over VoIP.
1. Packet Loss and Garbage
When fax machine tones are digitized and transmitted over a VoIP network, the data is broken into packets. These packets may experience delays, arrive out of sequence, or be lost entirely during transmission. Such problems, known as jitter and packet loss, make it difficult for the receiving fax machine to reassemble the data correctly.
See: Discover. How to Fix Network Errors.
2. Bandwidth limitations
Fax transmissions require more bandwidth than voice calls due to the amount of data involved. During periods of heavy network usage, insufficient bandwidth can lead to failed transmissions.
See: Learn. How to Optimize Your Network for VoIPfax, and other business communications.
3. Protocol interoperability
Fax machines must use the same protocol—usually T.30 or T.38—to communicate effectively. If the sending and receiving devices are not connected, errors occur, and transmissions may fail. The newer G.711 codec solves some of the compatibility issues but still relies on both machines supporting it.
See: Learn more about Using the correct VoIP codecs.
4. Network firewalls
Firewalls and NAT (Network Address Translation) filtering can block or prevent VoIP fax transmissions by extracting essential data from packets. Disabling features like SIP ALG can help but expose your network to security risks.
See: See Different Types of Network Address Translation and when to use each.
VoIP Fax Alternative
Use an online fax service.
When you send a fax using an online service, the platform processes it through its back-end infrastructure, converting it into a format suitable for the recipient’s device — whether it’s email, a web portal, etc. , or a physical fax machine. This ensures the reliability and compatibility of traditional faxes while eliminating the need for additional hardware on your end.
gave Best Online Fax Services There are interfaces that are extremely user-friendly, accessible through web browsers or mobile apps. While Internet access is required to initiate a fax, recipients using traditional fax machines do not need Internet access.
If you need to send faxes occasionally, free or per-use online fax services may suit your needs. If you need Fax the check. Or any other sensitive document, just remember it A fax is only as secure as its network. Using reputable providers is always a good idea.
For businesses, subscription plans offer enhanced features, such as secure document storage, integration with productivity tools, and support for high volumes.
Use Fax ATA.
Oh Fax ATA (analog telephone adapter) is a device that connects a fax machine to a modem or router, converting analog signals into digital data for transmission over a VoIP network.
It is a practical solution for those who want to move communications to digital channels while continuing to use existing devices.
The key to success with this setup is to choose a VoIP provider that clearly supports fax services as not all do. With the right provider, a fax ATA can provide reliable performance without the need to migrate to online fax services. For businesses that already have fax machines in operation and prefer to avoid additional costs or workflow changes, Fax ATA is an efficient and straightforward option.
See: Checkout Our RingCentral review To learn more about our favorite fax-enabled VoIP service.
Have separate phone lines for faxes
Dedicated landlines ensure reliable fax transmission, especially for businesses that send or receive large volumes of documents. Unlike some online fax services, you won’t face page limits or need to change established workflows. This can be a good setup for mass fax broadcasting, for example.
However, this approach comes with additional costs. Telecom providers typically charge $25 to $40 per month per landline, plus setup fees, which is quite expensive compared to similar ones. Small Business Online Fax Service.
It’s also important to note that the Federal Communications Commission (FCC) officially eliminated the requirement for landline support in August 2022. While landline faxing remains an option for now, the future availability of these networks is uncertain as carriers focus on new technologies.
For businesses with high fax volume and a need for reliability, maintaining landlines may still be worth the investment. However, those looking for a long-term solution can look for alternatives. Business phone services With T.38 protocol support and online fax services.