T1

Digital Signal 1 (DS1, sometimes DS-1) is a T-carrier signaling scheme devised by Bell Labs. DS1 is the primary digital telephone standard used in the United States, Canada and Japan and is able to transmit up to 24 multiplexed voice and data calls over telephone lines.

<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 "{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)