This Recommendation defines the network-independent basic transport service applicable to Teletex and Group 4 facsimile terminals connected to the types of network mentioned in (a) above in terms of: the transport services provided to the higher layer [the transport services are provided by the transport layer (layer 4) in association with the underlying services provided by the supporting layers 1 to 31].
ITU-T T.70 FRENCH-1993 history
1993ITU-T T.70 FRENCH-1993 NETWORK-INDEPENDENT BASIC TRANSPORT SERVICE FOR THE TELEMATIC SERVICES