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 DS1SIgnals 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)