Fax over IP

Some folks might think fax is outdated, but the truth is, it just needs a little bit of modernization—which is where FoIP comes in.

First things first. What is fax over IP (FoIP)?

Fax over Internet Protocol, or FoIP for short, is a method of sending or receiving faxes through the internet.

Not only does it remove the need for a clunky fax machine in the corner of your office, but it can also help you cut costs, work more efficiently, and even increase the security of your fax process.

One huge advantage of FoIP is that it uses the same SIP platform as VoIP (that’s Voice over Internet Protocol). While there might be a lot of confusing acronyms (sorry) this actually makes things simpler for you in the long run. For one, by integrating faxing into your IP telephony solutions, you can streamline the number of communication tools you’re using.

And if you work in industries like healthcare or insurance, faxing isn’t old-fashioned. It’s necessary. For these types of businesses and organizations, it’s still the best way to send important documents over long distances. With FoIP, you can keep all the benefits of faxing—without the clunkiness of old fax machines.

Dialpad’s FoIP solution is a great way to manage your business faxing needs through your existing network infrastructure.

Of course, if you still love that old fax machine, you can keep it around (maybe you’ve got an ‘80s themed office, who are we to judge?)—but why do that when you can send faxes through email?

How does fax over IP work?

Brace yourself: it’s time to get technical.

Once you’ve set your fax to send, it’s broken up into small data packets—just like with voice calls made through VoIP, actually.

These packets are sent, via your router, through the internet. When it reaches the other end, these packets are reassembled and presented to the recipient. The whole process takes seconds—just like an email!

Getting nerdy: With an entirely online fax, everything is digital. But, you can link in traditional paper fax machines... if you want. SIP involves gateways that convert the analog signal to a digital one. From there, it’s exactly as we explained above. The same goes in reverse too—if you’re sending an online fax to a traditional machine, the gateway will convert the digital data packets into analog information.

4 benefits of using FoIP

So, why would you want to use faxing through the internet? Let’s look at some of the main benefits of FoIP.

1. It’s cheaper

As we mentioned, reducing network complexity will in most cases save you money. This isn’t the only way FoIP can save you money either.

Because you don’t have to install new hardware, that means less equipment costs overall. And since you don’t have to pay for a phone line, the expense will already be factored into your internet package.

For example, if you use Dialpad to send faxes online, you’ll get 100 pages for free per month, which makes it incredibly cost-effective:

Our customers love it too:

dialpad fax review from g2

2. It reduces your network complexity

Since you’re just using your existing IP network, FoIP reduces network complexity and administrative overheads.

You don’t need to run a separate phone line just for your fax machine anymore—instead, it uses the same internet connection that your other communication tools do.

Not only does this mean less cables and hardware, it also means lower maintenance costs and cost savings.

3. It’s a more effective way of managing documents

With traditional fax solutions, you’d have to file away boxes and boxes of paper documents. With online faxes, you have many more (space-friendly) management options.

You can save, archive, email, and share all your docs with just a click of a button. It’s also easier to track and organize—and more eco-friendly too.

Virtual faxing improves disaster recovery capabilities too (especially if you store things in the cloud) so if you want to be on the safe side, go with this option. Not only will you streamline the way you work, it’ll also let anyone on your team access documents more easily.

4. You can work and send faxes from anywhere

There are many offices (and home offices) without fax lines. But almost everyone has the internet.

And let’s face it, with the rise of remote working, who wants a big clunky machine in their home office? FoIP is an essential step if you want to allow your team to work from the clinic, or the office, or from home—or even while they’re on the go.

Everyone on your team will get access to the same functionality, no matter where you’re located. Just one of the many perks of taking your faxing needs online.

How to send faxes over IP

If you have a traditional fax machine that allows for fax over IP, you’d simply set it up as you normally would. The difference is that instead of a phone line connection, you’d use an Ethernet cable to connect it to the internet. (Some FoIP-enabled fax machines might also have phone line functionality, allowing them to work both ways.)

👉 Dialpad tip: As you’re configuring your FoIP fax machine, check what forms of fax communications it actually allows. For faxing between FoIP-enabled devices, you need the destination IP address. For SIP, you would need the fax to communicate with an SIP-enabled phone number. And for a FoIP, you’d simply need a regular phone number connected by a VoIP gateway.

To enjoy the best FoIP experience, it’s best to use a unified communications platform. If you’re already using a business phone system or a similar software, this is just simpler compared to having a separate tool for faxing.

For example, Dialpad’s virtual fax feature lets you send and receive faxes through your computer—saving you all the hassle of the above steps!

Now, let’s use Dialpad as an example to look at how you can do different things related to faxing (most fax over IP options should let you do something similar):

How to add or remove fax numbers

To add a fax number on Dialpad, head to Admin Settings.

  1. Go to the Department you want to add a fax number for, then select Add a fax number:

  2. Enter the country of origin and area code.

  3. Confirm the addition of this fax number.

If you want to add a number as a Team Member, head to Admin Settings > Office > Users.

Choose the user, then go to Options > Calling > Add a Fax Line. Input the country of origin and area code, then confirm the addition of this fax number.

To remove a number, just choose the user, then select Options > Calling > Remove Fax Line alongside the fax number

How to purchase a fax license

Before you actually add a fax number, you have to do this! (Can’t have a number without a license…)

In Dialpad, you can purchase a fax license for a fax number before assigning it to a Shared Line or someone on your team.

  1. From Dialpad.com, just navigate to Admin Settings > Billing

  2. Select Buy Licenses.

  3. Enter the amount of fax number licenses you want to purchase, then select Next > Confirm Purchase. That’s it!

How to send or receive faxes

On your Dialpad desktop app (which you can also use to make phone and video calls), you can send a fax from your Main Line, Department, Call Center, Shared Line or your individual account.

To fax from your direct line, get your Admin to add a fax line to your account.

  1. Click on Send a Fax to open a new Compose screen.

  2. You may search for your recipient or type in their number manually. If you’re sending using the shared line, you can adjust the ID from the New Fax From drop-down:

After selecting your recipient, upload your file, which needs to be less than 10 MB and has to be one of these file types:

  • .doc and .docx

  • .pdf

  • .ppsx

  • .ppt and .pptx

  • .tif

  • .jpg and .jpeg

  • .png

  • .xls and .xlsx

  • .txt

  • .html

  • .gif

Once you’ve chosen the file you want to fax, it’ll be sent as a fax and the text under the fax icon will change from "Pending" to "Success" with a timestamp. You’ll then be able to see this fax transmission in the conversation thread!

When someone sends you a fax, you’ll get an incoming message notification. Click on it will open the conversation thread. Dialpad will also send you an email with a link to download the fax. 😉

How to fax to an international number

Need to fax to an international number? You can do that too with FoIP! (With Dialpad, for example, these are the available countries and related costs) Other than the charges being different, the process is exactly the same.

A few best practices for fax over IP (and other things to keep in mind)...

There are some standard practices that can help you integrate your fax machine with your VoIP network for the best FoIP fax results:

1. T.38 fax relay is the recommended choice for FoIP.

Typically, the most important decision related to FoIP is about the protocol you use. Your primary concern should be whether you want real-time fax or a fax received by email (as in a store-and-forward fax option).

The T.38 real-time fax protocol mimics the traditional fax transmission, which makes it important for critical fax documents. If you need to work with third-party fax devices, like fax servers or voice gateways, then T.38 protocol is your best choice.

2. Packet loss is just as harmful to FoIP (fax) as it is to VoIP (phone calls).

With VoIP, you’ll get dropped calls—with FoIP, you simply won’t get the fax that was sent. The only way to make sure packet loss doesn’t impact your fax calls is to implement the right Quality of Service (QoS) policies in your network.

Another option is to use the T.38 relay and take advantage of its redundancy features enabled.

3. Keep security in mind.

Anything you fax needs to be securely transmitted. Of course, nothing is as secure as a traditional fax machine.

But even if you work in the financial or healthcare sector, you can still use FoIP as a reliable form of communication—if you choose an option that lets you transfer your documents directly with full encryption. Make sure that your faxing tool keeps your sensitive data safe and helps you comply with federal regulations.

👉 Dialpad tip: Of course, it’s not just sending fax data that needs tight security: there’s the storage part too. While physical faxes would need to be filed away safely, it’s sometimes easier to protect faxes that are sent virtually (whether that’s through secure cloud storage, or through an extra layer of password protection).

FAQs about fax over IP

Does faxing over IP work in real-time?

The answer to this is simple: yes! It definitely does.

The fact that you can transfer documents almost immediately between two different people has always been a major advantage of fax. The internet is just as fast (if not faster) than a phone line—this doesn’t change.

What are the challenges of faxing over IP networks?

Unfortunately, no technology comes without challenges. (Not even good old faxes…)

Some major issues stem from the fact that while you might be using the internet to transmit your fax, the receiving end could be a conventional fax machine. Here are some of the biggest challenges of FoIP:

Lost or out-of-sequence packets

Lost packets of data can be caused by network congestion. (Back to being technical again!) This can lead to fax failure, meaning the fax call fails and the fax isn’t transmitted because there is no sequence to read. Emails can sometimes resequence packets, and this can also cause the fax to drop.

There are a few ways to mitigate packet loss—one way is through redundant packets. This is essentially an error correction technique where each packet has its own data and the data from the one before it, which means two consecutive packets would have to be lost for any data to be lost. (Other techniques include increasing bandwidth or adjusting the quality of service on your router.)


When the fax signal data is delayed beyond a certain time frame, the receiving end might end the call—which means they never receive the fax you’ve sent. This is more likely when faxing from a digital device to a traditional machine, since the connections are pretty sensitive to network timing. This is because transmission of information can be corrupted if the timing is off in a fax session.

FoIP delays can be caused by things like high latency, network hold-ups due to high traffic, and jitter buffers.

Jitter buffers delay packets on the receiving end so everything is received and delivered in the right order. Usually this is a good thing, but if it’s not programmed correctly, this can “confuse” the machine. Luckily, you can use a dynamically managed jitter buffer to avoid this, which keeps the connection open until the complete fax is received.

Routing and interoperability (network complexity)

Unfortunately, there are quite a few different fax protocols, and they don’t all work in conjunction with each other. FoIP connections often cross different carrier networks, and not all of them have implemented T.38 (more on this below). If this happens, it requires protocol conversion within the call. There are several operating issues that could affect protocol conversion.

Rather than changing your entire IP infrastructure, you can avoid problems with routing through use of a software bundle that acts as a bridge between two protocols. This converts fax signals to digital data and vice versa. The fax/protocol component coordinates the actual T.38 timing with the T.30 expected timing.

What are the different types of FoIP technology?

We’ve already mentioned fax protocols a few times, but let’s take a look at what they actually are.

T.38—sends in real-time

This is the fax protocol that allows you to send a fax over a Voice over IP network. To send a fax through T.38, you need a VoIP gateway and a virtual fax capable fax machine, fax card or fax software. The International Telecommunication Union (ITU) introduced the T.38 protocol for sending faxes through the internet.

T.38 has a handy correcting mechanism for missing and delayed packets. These are called fax-aware buffer mechanisms and they are used to fool fax machines into thinking that they are dealing with telephone lines and not network lines. Enabling T.38 can reduce the required data network bandwidth and correct packet loss and jitter.

Two things to remember about T.38: Fax messages are sent in real-time, and faxes are sent and received at the same time—and not automatically stored.

T.37—stores and forwards

T.37 is an ITU protocol for sending faxes using email. A fax machine configured to T.37 will send a fax to an email address.

First, the document will be converted to an image, attached to an email and sent using SMTP (that’s Simple Mail Transfer Protocol). The receiving end will get the email and print out the image. T.37 can be used with fax gateways to make it compatible with regular fax machines. These gateways will convert emails to faxes and vice versa.

A T.37 fax machine can also send a fax to phone numbers as long as there’s a telephone network available.


The T.30 protocol is the industry standard for old-school analog fax (the type that uses phone lines and PSTN). The T.30 can help make up for noise and dropouts common with voice communication lines. Fax machines are digital and the T.30 protocol is used to convert digital info into analog signals (that's on the sending end) and to decode those analog signals back into digital information (on the receiving end).

The T.30 protocol can be used to send fax over IP, but generally it’s not your best option. Choosing between this one and T.38 comes down to experimentation, and which of the two will work best for you depends on the quality of your telephony service provider's IP link.


The G.711 protocol exists as a backup to be used if a T.38 call doesn’t go through. There are a few problems with this protocol, because the signal can be compressed. (This can be corrected with proper software in your VoIP line though.)

This fax method has a gateway and server to handle the fax message, which makes it an easy-to-implement faxing solution that can work with just about any established business system.

Ready to get started with fax over IP?

With the right configurations and a few handy best practices, you can easily fax more efficiently—and from anywhere. The most common challenges tend to come up because of vendor incompatibilities and poor network performance, but FOIP is a leap forward, and using a cloud-based internet fax service is truly the best of this technology.

With FoIP, there doesn’t really need to be any changes on the recipient’s end. And that, along with the heightened security it offers, makes it the most secure, flexible, and efficient way to transfer important documents today.