Like the E transmission interfaces, the DS interface hierarchy (DS-0) is based on the Plesiochronous Digital Hierarchy (PDH) basic bit rate of 64 kbit/s (DS-0, 56 kbit/s plus 8 kbit/s). The designation "DS" ( Digital Signal) is used in North America, whereas the E designation is used in Europe.
The various DS interfaces (DS-0, DS-1, DS-2, DS-3, DS-4) form a multiplex hierarchy based on the basic bit rate:
DS-0 denotes a channel with a transmission rate of 64 kbit/s.DS-1 represents 24 64-kbit/s transmission channels, corresponding to a transmission rate of 1.544 Mbps. This transmission rate is also referred to as Transmission-Class-1, better known as T-1. This transmission rate is standardized in the ITU-T standard G.733. The transmission rate of the second PDH multiplex hierarchy, DS-2, is 6.312 Mbit/s and allows multiplexed transmission of four DS-1 channels at 1.544 Mbit/s or 96 DS-0 channels at 64 kbit/s. This transmission rate is known as T-2 and is standardized under G.743.
DS-3 can transmit seven DS-2 channels at 6.312 Mbit/s or 28 DS-1 channels at 1.544 Mbit/s or 672 DS-0 channels at 64 kbit/s multiplexed over one DS-3 line at a transmission rate of 44.736 Mbit/s. This transmission rate is standardized under G.743. This transmission rate is standardized under G.752 and also known as T-3. DS-4 designates a transmission channel with a transmission rate of 274.176 Mbit/s, which corresponds to 4,032 DS-0 channels.