T38

ITU Recommendation T.38, covered in RFC 3362, describes the transmission of fax data over packet-switched data networks. T.38 is for the real-time transmission offax messages over IP networks by encapsulating a fax data stream according to T.30: Fax over IP( FoIP).

The typical scenario with T.38 involves a fax machine sending T.30 faxes over packet-switched data networks to a T.38 gateway, which converts the encapsulated T.30 protocol into a T.38 data stream. This is sent either to a fax server or fax device that supports T.38, or to another T.38 gateway that converts the data stream back and terminates the fax on a T.30 device.

The T.38 recommendation defines how the TCP protocol and the UDP protocol transport the T.38 data packets. It also deals with faulty, lost and retransmitted data packets.