The equipment, including lines, that is used for digital multiplexing of telephone circuits, and that is provided by the network as part of the subscriber access.

A mechanism incorporated into a terminal or into equipment in the network whereby a duplex communication path may be connected back upon itself so that the digits sent on the transmit path are returned on the receive path. [After T1.206-1994]
Note: Loopback tests should be used only to check for circuit continuity and not for more subtle performance problems.

1. In digital telephony, a test signal consisting of eight 8-bit words corresponding to one cycle of a sinusoidal signal approximately 1 kHz in frequency and one milliwatt, rms, in power.
Note 1: The digital milliwatt is stored in ROM. A continuous signal of arbitrary length, i.e., an indefinite number of cycles, may be realized by continually reading out and… (Read More →)

1. The process of varying one or more parameters of a carrier wave as a function of two or more finite and discrete states of a signal.
2. The process by which some characteristic (frequency, phase, amplitude, or combinations thereof) of a carrier frequency is varied in accordance with a digital signal, e.g., one consisting of coded pulses or states.… (Read More →)

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.
Note 1: 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… (Read More →)

A device for combining several digital signals into an aggregate bit stream.
Note: Digital multiplexing may be implemented by interleaving bits, in rotation, from several digital bit streams either with or without the addition of extra framing, control, or error detection bits.

See integrated digital network.

The whole of the means of transmitting and receiving a digital signal of specified rate between the two digital distribution frames (or equivalent) at which terminal equipment or digital exchanges will be connected. [T1.206-1988]

Modulation in which the instantaneous phase of the modulated wave is shifted between a set of predetermined discrete values in accordance with the significant conditions of the modulating signal.

A phase-locked loop in which the reference signal, the controlled signal, or the controlling signal, or any combination of these, is in digital form.