Ecarrier

E-carrier, or E-carrier system, is a family of digital transmission formats used to transport multiple voice and data channels over a single circuit in European telecommunications networks. Developed within the ITU-T's PDH framework, it serves as the European counterpart to the North American T-carrier system and became standard in many national networks during the late 20th century.

The E-carrier hierarchy includes several levels defined by rate and multiplexing structure. E1 operates at 2.048 Mbit/s and carries 32 timeslots of 64 kbit/s; timeslot 0 provides frame alignment and timeslot 16 carries signaling information, leaving 30 DS0 channels for voice or data. Higher levels are formed by multiplexing four of the next lower level: E2 at 8.448 Mbit/s (four E1s), E3 at 34.368 Mbit/s (four E2s), and E4 at 139.264 Mbit/s (four E3s).

In practice, E-carrier circuits were widely used for inter-office and long-distance voice trunks, as well as early data services. The technology relied on plesiochronous timing and was gradually superseded by optical and packet-based networks, notably SDH/SONET and IP/MPLS infrastructures, though some E1 and E3 services remained in limited use in legacy systems and certain regions.

Today, E-carrier is primarily of historical and standardization interest, illustrating the evolution of European digital transmission and its role in shaping modern transport networks. It remains relevant for understanding PDH heritage, regulatory standards, and legacy interconnects.