The standard specifies the technical characteristics of equipment offering group 4 class 1 facsimile functions for attachment to the Integrated Services Digital Network (ISDN). The draft ETS is based upon CCITT Recommendation T.563 (1), ""Terminal Characteristics for Group 4 Facsimile Apparatus"" and CCITT Recommendation T.6 (2) ""Facsimile coding schemes and coding control functions for Group 4 facsimile apparatus"".