Recommendation ITU-T T.38 defines the procedures to be applied to allow Group 3 facsimile transmission between terminals where, in addition to the public switched telephone network (PSTN) or integrated services digital network (ISDN), a portion of the transmission path used between terminals includes an IP network, e.g., the Internet.

This revision of this Recommendation clarifies Recommendation ITU-T H.323, Recommendation ITU-T H.248.1, session initiation protocol (SIP) and session description protocol (SDP) call establishment and improves the compatibility between ITU-T T.38 gateways and Group 3 facsimile.