T.38

T.38 Procedures for real-time Group 3 facsimile communication over IP networks or Fax over IP ( FoIP ) is a recommendation for sending faxes over the Internet.

Due to the compression method and run-time variations in IP telephony, it is not possible without interference to transmit faxes after the transmission standards G2 and G3 of the ITU. With T.38, the information is not transmitted with tones as in the normal telephone network, but with the adapted on UDP or TCP and IP network protocol Facsimilé Internet Protocol ( IFP).

Unlike T.37, in which the faxes via SMTP to be sent as e- mail, T.38 is a real- time system that transmits faxes without delay. To each shipped with T.38 fax is transmitted to a conventional fax machine, gateways between the two incompatible modes of transmission are required. Many providers of IP telephony now operate such gateways. To operate an ordinary fax machine to a T.38 -capable VoIP connection, the ATA used must ( or router with an integrated telephone function or IAD ) also contain a T.38 gateway.

Often an attempt is made to operate fax machines to a VoIP connection is not officially supported. This can work, but is by no means assured. The best chances of success with uncompressed audio codecs ( such as G.711 ) and a stable internet connection with the same low latency and low packet loss. The provider of IP telephony have in these cases explicitly to the experimental characteristics, and was close facsimile transmission officially from its terms of reference from. Some providers offer optional T.38 (fees may apply).