Also known as Internet Fax Protocol (IFP). An ITU-T Recommendation originally issued in June 1998 for store-and-forward Fax over Internet Protocol (FoIP) via e-mail. T.38 addresses IP fax transmissions for IP-enabled fax devices and fax gateways, and defines the translation of T.30 fax signals and Internet Fax Protocol (IFP) packets. The specific methods for various T.38 implementations include fax relay and fax spoofing. Fax relay, also known as demod/remod, addresses the demodulation of standard analog fax transmissions from originating machines equipped with modems, and their remodulation for presentation to a matching destination device. Fax relay depends on a low latency IP network in order to avoid session time outs. Fax spoofing is used for fax transmissions over IP networks characterized by longer and less predictable levels of packet latency that could cause the session with the conventional fax machines to time out. T.38 provides for two transport protocols, User Datagram Protocol (UDP) and Transmission Control Protocol (TCP), and several optional means for error control. See also fax relay, fax spoofing, FoIP, T.30, T.37, TCP, and UDP.
An ITU standard for sending Group 3 faxes over IP networks in real time. T.38, which is known as a "fax relay protocol," is deployed in a fax gateway and converts a regular Group 3 fax into IP packets and vice versa. It is designed to adapt traditional fax machines to the Internet. See T.37, T.30 and fax gateway.