In telecommunications, a digital multiplex hierarchy is a hierarchy consisting of an ordered repetition of tandem digital multiplexers that produce signals of successively higher data rates at each level of the hierarchy.^[1][2]

Digital multiplexing hierarchies may be implemented in many different configurations depending on; (a) the number of channels desired, (b) the signaling system to be used, and (c) the bit rate allowed by the communications media.^[1]

Some currently available digital multiplexers have been designated as Dl-, DS-, or M-series, all of which operate at T-carrier rates.^[1]

In the design of digital multiplex hierarchies, care must be exercised to ensure interoperability of the multiplexers used in the hierarchy.

Digroup is an abbreviation for digital group. In telephony, a basic group in the digital multiplex hierarchy.

In the North American and Japanese T-carrier digital hierarchies, each digroup supports 12 PCM voice channels or their equivalent in other services. The DS1 line rate (2 digroups plus overhead bits) is 1.544 Mbit/s, supporting 24 voice channels or their equivalent in other services.

In the E-carrier European hierarchy, each digroup supports 15 PCM channels or their equivalent in other services. The DS1 line rate (2 digroups plus overhead bits) is 2.048 Mbit/s, supporting 30 voice channels or their equivalent in other services.

• Plesiochronous digital hierarchy
• Synchronous digital hierarchy

•  This article incorporates public domain material from Federal Standard 1037C. General Services Administration. Archived from the original on 2022-01-22. (in support of MIL-STD-188).