The DS0 rate was introduced to carry a single digitized voice call.
Because of its fundamental role in carrying a single phone call, the DS0 rate forms the basis for the digital multiplex transmission hierarchy in telecommunications systems used in North America.
To limit the number of wires required between two involved in exchanging voice calls, a system was built in which multiple DS0s are multiplexed together on higher capacity circuits.
E0 (standardized as ITU G.703) is the European equivalent of the North American DS0 for carrying a single voice call.
This article incorporates public domain material from Federal Standard 1037C.