Bandwidth refers to the rate at which data is transferred over the communication link. The underlying carrier technology depends on the bandwidth available. There is a difference in bandwidth points between the North American (T-carrier) specification and the European (E-carrier) system. Optical networks also use a different bandwidth hierarchy, which again differs between North America and Europe. In the U.S., Optical Carrier (OC) defines the bandwidth points.
In North America, the bandwidth is usually expressed as a digital signal level number (DS0, DS1, etc.), which refers to the rate and format of the signal. The most fundamental line speed is 64 kb/s, or DS-0, which is the bandwidth required for an uncompressed, digitized phone call. Serial connection bandwidths can be incrementally increased to accommodate the need for faster transmission. For example, 24 DS0s can be bundled to get a DS1 line (also called a T1 line) with a speed of 1.544 Mb/s. Also, 28 DS1s can be bundled to get a DS3 line (also called a T3 line) with a speed of 44.736 Mb/s. Leased lines are available in different capacities and are generally priced based on the bandwidth required and the distance between the two connected points.
OC transmission rates are a set of standardized specifications for the transmission of digital signals carried on SONET fiber-optic networks. The designation uses OC, followed by an integer value representing the base transmission rate of 51.84 Mb/s. For example, OC-1 has a transmission capacity of 51.84 Mb/s, whereas an OC-3 transmission medium would be three times 51.84 Mb/s, or 155.52 Mb/s.
The figure lists the most common line types and the associated bit rate capacity of each.
Note: E1 (2.048 Mb/s) and E3 (34.368 Mb/s) are European standards like T1 and T3, but with different bandwidths and frame structures.