Abstract: A method and apparatus monitor the performance of a DDS loop connecting an information transmitter to an information receiver. The information transmitter is typically at a customer premises while the receiver is typically an OCU at the receiving local office. The DDS loop uses an alternate mark inversion communications protocol and the monitoring method and apparatus feature circuitry for determining a current imbalance on the DDS loop. The numbers of positive and negative pulses on the line are individually counted and if the count of the two counters used deviates either positively or negatively from each other by specified amounts, an error event is declared. If the error events meet a statistical timing criterion, a channel error is declared and appropriate steps are undertaken to prevent signals coming from the channel from interfering with other signals available at the local office.

Abstract: A digital subscriber loop termination device, such as an office channel unit, dataport unit, digital data bank unit or the like, employs a microprocessor for providing data transfer between customer lines and network lines operating at respective different data transmission rates. The microprocessor circuit responds to network sync pulses for providing transfer of network input bytes to customer output generators and for providing for transfer of customer input bytes to network output serial generators. Additionally, the circuit includes facilities for enabling operation at different customer rates.

Abstract: A circuit for restoring and converting bipolar customer data signals into a pair of binary signals at a customer data frequency equal to or less than 250 KHz includes a PCM integrated circuit repeater for restoring and converting 1.544 MHz communication signals and transmission lines. Use of the high frequency repeater is enabled by a buffer amplifier connected in series with the input of a repeater amplifier and which has an input connected to a parallel resistance and capacitance network which is connected in series with an ALBO diode of the repeater for automatically inserting loss characteristics in the input signal so that the input signal has characteristics resembling losses of a signal passing through a maximum length transmission line. Fixed equalizer and amplification circuitry restores the original pulse signal magnitude and characteristics.

Abstract: A multi-channel digital subscriber carrier system for serving a multiplicity of subscribers one or more of whom may be located at points between the central office and the subscriber (furthest remote) terminal. One or more drop terminals are provided to serve these inbetween subscribers. Each terminal has a receiver section for recovering the clock signal generated by a master oscillator located in the central office. The receiver section also synchronizes on the received signal and generates signals indicating times of occurrence of the channels in the received signal. The transmitter section of each terminal uses the above signals and the recovered clock to generate a digital signal wherein messages from the subscribers at the terminal are inserted in those channels associated with the subscribers for the messages received from the office for the subscribers. Each terminal has associated therewith a circuit for bypassing the terminal upon the occurrence of a terminal fault condition.

Abstract: A current regulator for a pulse code modulated (PCM) transmission line is interposed between a voltage potential and a load (consisting of repeater amplifiers along the PCM transmission line) for limiting the current flow to the load. During normal operation, the regulator provides a relatively low impedance path from the voltage potential to the load through a series pass transistor and a sensing resistor. During an overload condition, which is sensed by the sensing resistor, the series pass transistor is deprived of base drive thereby providing a high impedance path with an accompanying increased voltage drop across the series pass transistor of the series regulator. This voltage drop is used to drive a timer which turns the series pass transistor off and on, with a low on time or duty cycle, in order to minimize power dissipation during the overload condition.

Abstract: A telephone transmission system has repeaters spaced along both the transmit and receive legs of the transmission line, with a power supply for the repeaters including a current regulator having positive and negative supply lines connecting the power supply to the two legs of the transmission line. Current surge protectors are connected from the two legs of the transmission line to ground. A pair of current sensors responsive to the current levels in the positive and negative supply lines, between the power supply and the current surge protectors closest to the power supply, produce output signals representative of the respective current levels. A control signal generating means receives the output signals from the current sensors and produces a control signal in response to a deviation of the higher current in the supply lines from a preselected reference level. The control signal is supplied to the current regulator to maintain the higher current level in the supply lines at the preselected reference level.

Abstract: In a carrier system having a plurality of relatively wide band (or voice) channels which are time-division multiplexed and represented by N sequential coded pulses for each channel, it is sometimes desirable that the individual pulses of one or more of the relatively wide band channels be used for information or data. In such past arrangements, only (N - 1) of the pulses were used for transmitting information. The Nth pulse was reserved as a needed keep-alive pulse to provide proper operation of repeaters in the pulse coded system. The present arrangement provides means at the transmitter for detecting when (N - 1) of the channel pulses are all in an undesired code condition, and transmitting the needed keep-alive pulse as the Nth pulse. If any one of the (N - 1) channel pulses is in the desired code condition, the Nth pulse can transmit information.