Multifunction Fax Machines (Fax MFPs)

What a multifunction fax machine is

A multifunction fax machine — commonly called a fax MFP or all-in-one — is an office machine that incorporates the functionality of several devices in one, combining some or all of printing, scanning, photocopying, and faxing in a single unit. In this class the fax capability is not a standalone product but one function among several: the same chassis prints documents, scans and copies originals, and sends and receives faxes. From the 1980s to the 2010s multifunction printers commonly included fax functionality, which is how the fax MFP became a typical way offices faxed once converged devices displaced dedicated fax machines. On contemporary all-in-ones fax is increasingly treated as an optional feature rather than a defining one.

The fax function: Group 3 over the telephone network

The fax subsystem in these machines is almost always Group 3, the facsimile system standardized by the ITU-T (formerly CCITT). Two recommendations define it. T.4, "Standardization of Group 3 facsimile terminals for document transmission," specifies how the page image is encoded, using the Modified Huffman and Modified READ compression schemes. T.30, "Procedures for document facsimile transmission in the general switched telephone network," governs how two terminals negotiate and carry out a call over ordinary telephone lines. Under T.4, Group 3 sends at 204 × 98 dpi in standard mode and 204 × 196 dpi in fine mode. Because Group 3 runs over the analog telephone network, a fax MFP needs only a standard phone line to interoperate with other fax machines.

Transmission speed: Super G3 and earlier Group 3 modems

Group 3 fax speed is set by the modulation the two terminals agree on during the T.30 handshake. Many later fax MFPs support Super G3, which uses V.34 modulation to reach up to 33.6 kbit/s and is defined in Annex F of ITU-T T.30. Earlier and fallback Group 3 modes run more slowly — up to 14.4 kbit/s using V.17 and up to 9.6 kbit/s using V.29 — and a call drops back to a lower rate when line conditions require it. Higher speed shortens per-page transmission time but does not change the Group 3 image resolutions defined by T.4.

Plain-paper output on a laser or inkjet engine

Because the fax function shares the multifunction unit's own print engine, a fax MFP produces incoming faxes on plain paper rather than the heat-sensitive roll paper used by early standalone thermal fax machines. In commercial and enterprise machines that engine is typically laser (electrophotographic); in personal and small-office (SOHO) machines it is typically inkjet. This plain-paper output is a practical advantage of the class: received faxes look like ordinary printed documents, do not fade the way thermal-paper faxes can, and use the same consumables and paper path as the machine's printing and copying functions.

A shared scanner for copy, scan, and fax-send

The same scanning mechanism the machine uses to photocopy and to scan to file also captures outgoing fax pages, often fed through an automatic document feeder. Integrating one scanner, one print engine, and one telephone interface is what lets a single device stand in for a separate printer, copier, scanner, and fax machine — the core value proposition of the multifunction category. The fax portion still operates as an independent Group 3 terminal on the telephone line; the integration lies in the shared hardware and control panel rather than in the fax protocol itself.

Relation to standalone and Group 4 fax machines

Multifunction fax machines sit between dedicated desktop fax units and general office printing. Compared with standalone thermal-paper fax machines, the fax MFP trades a single-purpose design for shared print, scan, and copy hardware and plain-paper output. It should also be distinguished from Group 4 facsimile, a separate digital class defined by ITU-T T.6 (which specifies the Modified Modified READ coding) and T.563 (terminal characteristics) that operates over 64 kbit/s ISDN circuits rather than the analog telephone network. Most office fax MFPs implement Group 3 over the PSTN, not Group 4. Related class pages in this reference cover plain-paper, laser, inkjet, and Super G3 fax machines in more detail.

Reference scope

This page describes the multifunction fax machine as a class, at family level. It does not list resolution, speed, memory, or price for any individual model, and it states no per-model specification that cannot be traced to an authoritative source. Class-level facts about the fax subsystem are drawn from the ITU-T facsimile recommendations, and the multifunction-device definition from general reference material; anything that could not be sourced is omitted rather than estimated. It is not a buying guide and quotes no current pricing or availability.