The CCITT considering (a) that the bearer rate recognized by the CCITT is 64 kbit/s; (b) that 64 kbit/s satellite channels on TDMA systems are not yet operational; (c) that 64 kbit/s channels on SCPC systems are under investigation; (d) that for an interim period only 48, 50 or 56 kbit/s channels via a satellite will be available in many cases; (e) that there is a requirement to interface transmission systems using an 8-bit envelope structure with such satellite systems.