faxes

Faxes, or facsimiles, are systems for transmitting scanned documents over telephone networks. They exist as standalone fax machines, as features within multifunction printers, and as online services that route documents to or from fax numbers. While their use has declined in many settings, fax technology remains common in several industries, including healthcare, law, and finance, where direct device-to-device transmission of documents is valued.

Most fax transmission proceeds in a store-and-forward fashion. The sender scans each page, converts it into a bitmap, and compresses the image. The sending device negotiates capabilities with the recipient using an ITU-T protocol for fax communications, then transmits the data over a standard telephone line. The receiving device decodes the stream and prints or stores the page. Group 3 fax is the traditional dial-up standard and uses various compression methods; Group 4 is designed for digital networks and offers higher efficiency. Modern systems may also support faxing over IP using the T.38 protocol.

Key standards include ITU-T T.30 for session setup and document transfer, and ITU-T T.4 for image encoding in Group 3. Fax documents typically use standardized page sizes and line densities, and modern devices may integrate with digital workflows or email to provide alternative delivery methods.

A brief history places fax development in the 19th and 20th centuries, with commercial products becoming widespread in the mid- to late 20th century. The technology peaked in traditional office use in the late 20th century and has since been complemented by digital documents. Faxes remain in use where direct, paper-to-paper transmission is required or preferred due to regulatory or workflow considerations.