Abstract: A processor controlled test set is disclosed for testing special service circuits of a telecommunication system. A microprocessor controls the overall operation of the test set, while a digital signal processor provides high speed timing signals to the various test circuits for generating the wave forms used in testing, as well as analyzes the test result signals that are converted into digital signals. A calibration of the test generator signals as well as the signal measuring path is carried out prior to the test sequence. The digital signal processor also provides gain control over a talking path to maintain stability thereof. An I/O circuit of the test set provides plural communication paths between remote equipment and the test set to initiate and carry out various tests. Processors in the I/O module are effective to convert the various protocols of the serial data, by way of software, to digital bit streams usable by the test set.

Abstract: A circuit for comparing transmitted and received data frames containing appropriate stuff symbols to detect when a channel is disconnected. Transmit data symbols consisting of frames of user data, each with a constant number of symbols, are separated by a sequence of symbols known as the frame pattern. At the end of each data frame, just before the next frame pattern, a small number of stuff symbols are added into the frame. The stuff symbols injected in the transmit signal are chosen to be identical to the last scrambled data symbol in the frame of user data. Stuff symbols in a recovered receive signal are chosen to look identical to data symbols which were scrambled at the remote transceiver. A frame-by-frame comparison between the transmit stuff symbols and the next received stuff symbols is carried out on a continual basis.

Abstract: In an identification apparatus for identifying an unknown system in response to a transmission input signal and an echo signal which includes multiple echoes sent through the unknown system, a plurality of adaptive filters each of which has a plurality of taps are supplied with the transmission signal in parallel to individually identify the multiple echoes by successively modifying tap coefficients in each adaptive filter. Information is transmitted from a j-th adaptive filter to a (j+1)-th adaptive filter to identify each of the multiple echoes. Each adaptive filter monitors modification times of tap coefficients or ERLE. Alternatively, a step size is changed from one to another to be delivered to tap coefficient generators and to accomplish high speed convergence.

Abstract: A communications system adaptive echo canceller integrally contains a test far-end talker signal generator, an echo signal generator for generating an echo signal with a simulated echo path, a residual echo detector for detecting a residual echo based on the output of a subtracter, and a switching unit for switching an input and output signal of the echo canceller into an echo canceller test mode. Further, it provides a bypassing unit for, in a test mode, separating a call/talk connected to the echo cancellers from the echo cancellers and forming a bypass path between trunk circuits and a transmission circuit. The bypassing unit results in being able to realize a test for the echo canceller while a talk is alive.

Abstract: A method for estimating an amount of phase roll on a transmission channel. A signal of known frequency is transmitted over the channel by a near end modem. An average noise autocorrelation matrix is subtracted from an average signal plus noise autocorrelation matrix, both as received by a near end modem. The eigenvector of the resulting matrix is computed. The complex root of a quadratic with coefficients equal to the eigenvector elements is computed to solve for a difference between the frequency of the transmitted signal and the echoed receive signal to determine the phase roll.

Abstract: A device for establishing a desired operator audio level in an operator position means, is disclosed, comprising a processor means for processing digital signals for generating a desired receive audio level in an operator position means for use by an operator, conversion means for converting analog speech transmit signal from a telephone transmit means to digital for input to said processor means and for converting digital receive signal from the processor means to analog receive signal for input to a telephone receive means, and means for connecting the processor means to a telecommunications network. The processor means includes control means for the operator for permitting the operator to modify the desired receive audio level.

Abstract: In accordance with the present invention, local loop testing in an echo canceller based modem is provided in a manner in which proper operation of both the receiver and echo canceller can be assessed simultaneously. Specifically, the modem includes means for generating data and interfering symbol sequences and for applying the interfering sequence to both the echo canceller and the modem transmitter, while applying the data sequence only to either the transmitter or the echo canceller. During closed loop testing, the modem connection to the transmission line is opened, and a portion of the output of the modem transmitter is applied to the modem receiver via a leakage path through the hybrid. The received symbol is subtracted from the echo canceller output, resulting in application to the receiver of only a version of the data symbol sequence. Advanced knowledge of the characteristics of the data symbol sequence allows proper receiver operation to be verified.

Abstract: A method for providing and for testing adaptive echo cancellation in an apparatus including transmission equipment for data communication. The apparatus includes a 2-wire to 4-wire hybrid circuit which receives a signal from a remote end which is cut off for purposes of the testing method. A signal consisting of randomly occurring ones and zeros is applied to the send end of the apparatus. Also included in the apparatus is an adaptive echo canceller which cooperates with the send end and with a filtered signal received from the hybrid circuit to produce a correction signal which is fed back to the adaptive echo canceller and which is also compared with threshold values for purposes of testing the function of the apparatus.