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 of a multiplexing scheme for the interworking between two networks where both use 10-bit envelope structure but transmission is at a gross bit rate of 56 kbit/s, typically via an SCPC satellite system with forward error correction.