A technique for facsimile (fax) transmission over the Internet or other IP-based packet network, rather than over the traditional public switched telephone network (PSTN). FoIP typically involves a fax gateway, which not only serves as a physical gate between the circuit-switched and the packet-switched networks, but also runs gateway protocols that convert from the PSTN to the IP-based packet network. Relevant IP fax standards include T.37, the specification for store-and-forward fax, and T.38, the specification for fax relay and fax spoofing. See also circuit switch, facsimile, fax relay, fax spoofing, Internet, IP, packet switch, PSTN, and store-and-forward.