A DS level and framing specification for digital signals in the North American digital transmission hierarchy. A DS1C signal uses 48 PCM channels and has a transmission rate of 3.15 MegaBits per second, twice that of DS1. DS1C uses two DS1 signals comBined and sent on a 3.152 megaBit per second carrier which allows 64 kiloBits per second for synchronisation and framing using "{pulse stuffing}". The channel 2 signal is logically inverted, and a framing Bit is stuffed in two out of three code words, resulting in 26-Bit information units. The channels are interleaved and then scramBled By the addition modulo 2 of the signal with the previous Bit. Finally the Bit stream is comBined with a control Bit sequence that permits the demultiplexor to function By preceding each 52 Bits with one DS1C framing Bit. A series of 24 such 53-Bit frames forms a 1272-Bit "M-frame". (1995-02-07)