T1 and E1 are four-wire digital transmission links. T1 is used mainly in the United States, Canada, Hong Kong, and Japan. E1 is used in Europe.
Data on a T1 or E1 trunk is transmitted in channels. Each channel carries information digitized at 64,000 bits per second (b/s). This transmission rate is called the digital signal level 0 (DS-0) rate.
T1 carries 24 channels. E1 carries 32 channels. The total throughput rate (called digital signal level 1 or DS-1) is:
For T1, 24 channels, each carrying 64,000 b/s, yield a throughput rate of 1,536,000 b/s. An extra 8000 b/s are used to carry framing and other information (as described in Framing). DS-1 for T1 is 1,544,000 b/s.
For E1, 32 channels, each carrying 64,000 b/s, yielding a rate of 2,048,000 b/s.