Abstract: A quadrature coder for a two-wire digital loop communication system is described in which data is sampled and quadrature encoded by being divided into two bit streams, one of which comprises every other bit in the original bit stream and the other one comprises the remaining bits. One of the divided bit streams is delayed by 90.degree. from the other. The delayed and undelayed bit streams are then recombined and transmitted over a two-wire loop.

Abstract: A method and apparatus is described for transmitting and receiving data signals and voice band signals over a single pair of wires, wherein the energy content of the data signals in the voice band is transferred to a higher frequency to avoid interference between the two. This is accomplished by sinusoidally encoding the data pulses in the frequency domain. The encoding is equivalently performed in the time domain by linearly combining weighted delayed and advanced versions of the data pulses, in accordance with a weighting formula. A transversal filter is used to multiple delayed and advanced versions of the data pulses by a scaling factor times the ratio of m!/m-i)!i! factorial wherein i is the ith version being weighted, m is an integer greater than one and ! indicates the factorial function.

Abstract: An echo canceler is disabled by sending two signals to it or in the alternate, by sending a single signal. The two signals are bit shifted replicas of each other. The nature of the sequence of the bits within the signals assures that one of the two signals or in the alternate case, a single signal will disable the echo canceler. All of these signals are not necessarily comprised solely of tone at a predetermined frequency; rather they may merely have sufficient energy at a disabling frequency and sufficient signal noise ratio to disable the echo cancelers.

Abstract: A means is provided within an interface to data terminal equipment for obtaining call progress information. The call progress information provides relevant data as to the progress of a call initiated by the data terminal equipment. The interface is designed to be used in a portion of the telephone network that lacks byte alignment. Such portions of the telephone network do not currently receive call progress tones. The interface is preferably a data service unit that includes a receiving means processor and a display means. The data service unit interprets signals sent from the DDA/OCU that encode the progress or absence of call progress tones sent from the destination node of an initiated call.

Abstract: A method and apparatus is described for transmitting and receiving data signals and voice band signals over a single pair of wires, wherein the energy content of the data signals in the voice bands is transferred to a higher frequency to avoid interference between the two. This is accomplished by sinusoidally encoding the data pulses in the frequency domain. The encoding is equivalently performed in the time domain by linearly combining weighted delayed and advanced versions of the data pulses, in accordance with a weighting formula. A transversal filter is used to multiple delayed and advanced versions of the data pulses by a scaling factor times the ratio of m!/(m-i)!i! factorial wherein i is the ith version being weighted, m is an integer greater than one and ! indicates the factorial function.

Abstract: A post-equalizer and pre-equalizer circuit for use in communicating between nodes in a pulse amplitude modulated digital communication system is described. The post-equalizer circuit comprises a first variable zero circuit, a second variable circuit, and a gain shaper circuit wherein the gain and frequency location of the zeros in the zero circuits combined with the gain of the gain shaping circuit are simultaneously controlled by a control circuit which generates a control voltage which is a monotonically increasing function of cable loss. The control voltage generates a signal equal to the difference between the equalized signal and the original transmitted signal which is used to vary the resistance of voltage variable resistors in the form of FET's in each of the zero circuits and gain shaper circuits.

Abstract: A digital data service transmission system is described in which 19.2 kbps data rate AMI encoded local loop signals are formatted for reliable transmission at 64 kbps rates over unqualified digital facilities and re-formatted for entry into DDS network hierarchy.

Abstract: A line interface module and selected channel unit modules are replaced in a digital terminal which couples time multiplexed digital communications lines to a plurality of voice signal lines. The line interface unit is provided with means for responding to a controller to insert PCM data into selected time slots of the PCM signal on the digital line and to latch data received on the line. In addition to receiving pulse amplitude modulated signals from a receive unit in the terminal, voice channel units may also receive the PCM code. A state machine in the channel unit recognizes control sequences of insert data. By means of the insert data, the controller may direct provisioning of the channel unit with such adjustments as gain control and equalization. It may also direct the channel unit to switch to a loopback mode of operation for diagnostics. PCM corresponding to tones may also be inserted by the line interface unit to assist in diagnostics.

Abstract: A post-equalizer and pre-equalizer circuit for use in communicating between nodes in a Pulse Amplitude Modulated (PAM) digital or analog communication system is described. The post-equalizer circuit comprises a first variable zero circuit, a second variable zero circuit, and a gain shaper circuit wherein the gain and frequency location of the zeros in the zero circuits combined with the gain of the gain shaping circuit are simultaneously controlled by a control circuit which generates a control voltage which is a monotonically increasing function of cable loss. In the case of a PAM digital communication system, the control voltage generates a signal equal to the difference between the equalized signal and the original transmitted signal which is used to vary the resistance of voltage variable resistors in the form of FET's in each of the zero circuits and gain shaper circuits.