T.38 is a recommendation of the ITU-T for transmission of fax messages over packet-switched networks such as the Internet. Due to compression methods and runtime fluctuations in the IP telephony it is not possible to transmit faxes according to the transmission standards G2 and G3 of the ITU without interference. With T.38, the information is not transmitted with modem tones as in the normal telephone network, but digitized at the gateway and transmitted with the UDP or TCP protocols that are customary in IP networks.
