See facsimile.

In a communications network, a predefined address used to address only a specified set of users. Synonym collective address.

A service feature that (a) enables a controlling telephone to place a call to a specified number of telephones simultaneously, (b) enables the call to be recorded, (c) if any of the called lines is busy, enables the equipment to camp on until the busy line is free, and (d) rings the free line and plays the recorded message.

The busy hour for a given trunk group.

1. The rate of change of the total phase shift with respect to angular frequency, d/d, through a device or transmission medium, where is the total phase shift, and is the angular frequency equal to 2f, where f is the frequency.
2. In an optical fiber, the transit time required for optical power, traveling at a given mode's group velocity,… (Read More →)

In a group of waves that have slightly different individual frequencies, the time required for any defined point on the envelope (i.e., the envelope determined by the additive resultant of the group of waves) to travel through a device or transmission facility.

In frequency-division multiplexing, a distribution frame that provides terminating and interconnecting facilities at the group level, i.e., group modulator output and group demodulator input circuits of FDM carrier equipment.
Note: The basic spectrum of the FDM group is 60 kHz to 108 kHz.

In fiber optics, for a given mode propagating in a medium of refractive index , the velocity of light in vacuum, c, divided by the group velocity of the mode.
Note: For a plane wave of wavelength , the group index may also be expressed,

where n is the phase index of wavelength .

See patch bay.

1. The velocity of propagation of an envelope produced when an electromagnetic wave is modulated by, or mixed with, other waves of different frequencies.
Note: The group velocity is the velocity of information propagation and, loosely, of energy propagation.
2. In optical fiber transmission, for a particular mode, the reciprocal of the rate of change of the phase constant with… (Read More →)