edVirtus Reference

What Is Facsimile?

How Does Facsimile Transmission Send Documents Over Communication Networks?

Facsimile, commonly known as fax, is a communication technology that transmits copies of printed documents, drawings, or handwritten pages over a communication network. The transmitting device scans the original document, converts it into digital image data, and sends the information to a receiving device, which reconstructs and prints a replica of the original page. Although fax originated on analogue telephone networks, modern systems increasingly use digital IP-based networks through Fax over IP (FoIP).

The basic principle is straightforward. A fax machine scans the document line by line, converting variations in light and dark areas into digital data. This data is compressed and transmitted across the communication network using standardised fax protocols. At the receiving end, the data is decoded and reproduced as an image that closely matches the original document.

A useful analogy is making a photocopy at a distant location. Instead of physically transporting the paper, the document's image is converted into electronic information, transmitted across the network, and recreated at the destination.

Traditional fax machines communicate over the Public Switched Telephone Network (PSTN) using standards developed by the International Telecommunication Union (ITU), particularly the ITU-T T.30 protocol. These systems establish a telephone connection, exchange capability information, and then transmit the scanned document using modem signals over an analogue telephone line. For many years, fax machines were widely used by businesses, government agencies, healthcare providers, and legal organisations because they provided a simple and standardised method of exchanging signed documents.

As communication networks have evolved, fax technology has adapted accordingly. Fax over IP (FoIP) enables fax transmissions to be carried across Internet Protocol (IP) networks rather than conventional analogue telephone circuits. Many FoIP systems use the ITU-T T.38 protocol, which transports fax data reliably across packet-switched networks while compensating for delay, packet loss, and jitter that can disrupt traditional fax modem signals. Some organisations also use store-and-forward Internet fax services, in which documents are exchanged as email attachments rather than through a real-time fax connection.

It is important to distinguish Fax over IP (FoIP) from Internet fax. FoIP preserves the traditional real-time fax process while transporting the fax data over an IP network using protocols such as T.38. Internet fax services, by contrast, often convert fax documents into email attachments or web-based documents without maintaining a conventional fax session. Although both use IP networks, they operate quite differently.

Today, traditional fax usage has declined as email, cloud storage, electronic document management, and secure digital signatures have become widespread. Nevertheless, facsimile transmission remains important in sectors such as healthcare, legal services, finance, and government, where established workflows and regulatory requirements continue to support its use. Modern Fax over IP technology enables these organisations to retain fax compatibility while taking advantage of contemporary digital communication networks.