Some types of dedicated line services available are:
- DDS or Dataphone Digital Services
- 56/64 kbps lines
- Fractional T1/T3 lines
- T1/E1 lines
DDS or Dataphone Digital Services, the first private digital lines offered by AT&T and North America’s digital transmission method initially deployed in the mid-1970s, provide a synchronous transmission of digital signals at up to 56 kilobytes per second (kbps). Subrate or lower speed services are also available at 2,400 to 19,200 bps. Most LEC (Local Exchange Carriers) and IEC (IntereXchange Carriers) offer similar services.
In Europe, 56/64 kbps lines provide a full 64 kbps. However, in the United States and Japan, 8 kbps are used for administrative and control overhead and the remaining 56 kbps are used for the subscriber. These lines are also available through dialup and undedicated lines.
A fractional T1 line, which is, as it suggests, only part of a T1 line, built up in increments of 64 kbps to a maximum rate of 768 kbps. It only allows customers to use a certain number of the 24 channels available on the T1 line, and allows for the same type of speed and security delivered on a T1 line. The channels not rented simply contain no data. T3s, built up in increments of 3 Mbps, are sometimes offered as a fractional service.
T1 lines, which are sometimes referred to as DS1 lines, provide 1.544 megabits per second (Mbps), which comes from 24 64 kilobit per second (kbps) channels, together with one 8 kbps framing channel, available in North America, Australia and Japan. In South America, Mexico and Europe, E1 services are the European format for digital transmission. They provide 2.048 Mbps, which comes from 32 64 kilobit per second (kbps) channels, with 2 channels reserved for signaling and controlling.
The availability and pricing associated to each of these types dedicated line services vary greatly among each other and among different geographical areas.