T1, What is it?
Posted by Joseph Brochin
DS1 also known as T1. “T1″ has become synonymous with any circuit that has a 1.544 Mbit/s line rate. T2 and T3 circuits carry multiple T1 channels multiplexed together, producing rates up to 44.736 Mbit/s.
T1 format carries (24) pulse-code modulated speech signals that are time division multiplexed and encoded in 64 kbit/s streams that leave 8 kbits/s of framing information, also known as overhead, for signaling to allow the signals to remain synchronized and de-multiplexed at the receiving end.
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To better understand how the rate of 1.544 Mbit/s for a T1 was achieved we provide the following:
-Highest voice frequency which the telephone system transmits is 4000 Hz.
-Required digital sampling rate is 8000 Hz.
-T1 frames contain (1) byte of voice data for each of the 24 channels.
-Needs 8000 frames per second to maintain those 24 simultaneous voice channels.
-Each frame of a T1 is 193 bits in length.
(24 channels X 8 bits per channel + 1 framing bit = 193 bits)
-8000 frames per second is multiplied by 193 bits to yield a transfer rate of 1.544 Mbit/s.
(8000 X 193 = 1544000).
