T1 is a digital data transmission medium capable of handling 24 simultaneous connections running at a combined 1.544 Mbps. T1 combines these 24 separate connections, called channels or time slots, onto a single link. T1 is also called DS1.
The T1 data stream is broken into frames. Each frame consists of a single framing bit and 24 8-bit channels, totalling 193 bits per T1 frame. Frames are transmitted 8,000 times per second, at a data transmission rate of 1.544 Mbps (8,000 x 193 = 1.544 Mbps).
As each frame is received and processed, the data in each 8-bit channel is maintained with the channel data from previous frames, enabling T1 traffic to be separated into 24 separate flows across a single medium. For example, in the following set of 4-channel frames (without a framing bit), the data in channel 1 consists of the first octet of each frame, the data in channel 2 consists of the second octet of each frame, and so on:
Chan. 1 Chan. 2 Chan. 3 Chan. 4 Frame 1 [10001100][00110001][11111000][10101010] Frame 2 [11100101][01110110][10001000][11001010] Frame 3 [00010100][00101111][11000001][00000001]