Source : Free On-Line Dictionary of Computing

DS1C
     
         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)