Introduction

Fax over IP, or FoIP, is a modern alternative to traditional faxing. Instead of using old copper phone lines, faxes travel over the internet. For many companies, this means fewer hardware problems, lower costs, and the ability to send or receive faxes from anywhere-not just from a machine standing in the office.

What Is Fax over IP (FoIP)?

FoIP lets you send and receive faxes through an IP network, the same type of network your VoIP calls use.

You can use FoIP in several ways:

  • connect a regular fax machine through an ATA adapter,
  • use an IP fax device that supports T.38 or G.711,
  • rely on a cloud fax service,
  • receive faxes through a virtual fax number that forwards them to email.

In other words, FoIP keeps the idea of faxing, but removes the limitations of physical phone lines.

How FoIP Works

Here’s what happens behind the scenes when you send a fax via FoIP:

  1. The document is scanned by a fax machine or uploaded digitally.
  2. The signal is converted into digital packets.
  3. These packets travel over the internet.
  4. The receiving system assembles them back into a fax and delivers it to the recipient.

Two main protocols are used:

  • T.38 — built specifically for faxing over IP, more stable on imperfect connections.
  • G.711 — a codec normally used for voice calls; it works with faxing but is more sensitive to delays and packet loss.

Most businesses prefer T.38 because it handles real-world network conditions better.

Using FoIP in Business

FoIP is especially useful for companies that still rely on faxing but no longer want to depend on analog phone lines. It works well for medical centers, logistics companies, legal firms, financial institutions, and any business that exchanges documents daily.

With FoIP, you can:

  • stop paying for separate phone lines just for faxing,
  • access faxes from any device,
  • cut down on paper documents,
  • store documents digitally for easier search and archiving,
  • support remote and hybrid teams without extra equipment.

Example 1: Medical clinic

A clinic receives test results and insurance forms throughout the day. With FoIP, all incoming faxes go directly to a secure email inbox. Staff don’t need to wait near a fax machine-they get documents instantly and can forward them where needed.

Example 2: Logistics company

A logistics team uses several virtual fax numbers-one for dispatch, one for customs, and one for warehouse operations. Each fax lands in the correct department’s email, which saves time and avoids mix-ups.

FAQ

What is FoIP?

FoIP stands for Fax over IP. It’s a way to send and receive faxes through the internet, using VoIP technology instead of traditional phone lines.

How does FoIP work?

The fax signal is converted into digital data, sent over the internet, and then turned back into a fax document on the receiving side. You can use a fax machine with an ATA adapter or a fully digital setup.

Can a regular fax machine work with FoIP?

Yes. A standard fax machine can work with FoIP if it’s connected through an ATA adapter that supports T.38. This lets the device communicate over an IP network without needing an analog line.

What protocols are used?

FoIP mainly uses two:

  • T.38 — the recommended standard for faxing over IP,
  • G.711 — a voice codec that can carry fax signals but is more sensitive to connection issues.

What problems might occur?

If the internet connection is unstable, FoIP faxes may fail or come through partially. Common reasons include packet loss, outdated equipment, or incorrect settings. A properly configured VoIP system (such as Freezvon’s cloud PBX) reduces these issues significantly.

In simple terms

FoIP lets you fax through the internet instead of using a phone line. It’s faster, easier to manage, and works even if your team isn’t in the same office.