# Channels and transmission rates

T1 and E1 trunks are four-wire digital transmission links. T1 trunks are used mainly in the United States, Canada, Hong Kong, and Japan. E1 trunks are used in Europe.

Data on a T1 or E1 trunk is transmitted in channels. Each channel carries information digitized at 64000 bits per second (bps). This transmission rate is called the digital signal level 0 (DS-0) rate.

T1 trunks carry 24 channels. E1 trunks carry 32 channels. The total throughput rate (called digital signal level 1 or DS-1) is:

- For T1 trunks: 24 channels, each carrying 64,000 bps, yield a throughput rate of 1,536,000 bps. An extra 8000 bps are used to carry framing and other information (as described in Framing). DS-1 for T1 trunks is 1,544,000 bps.

- For E1 trunks: 32 channels, each carrying 64,000 bps, yield a rate of 2,048,000 bps.