DS1C

communications 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 "pulsestuffing". 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)