Abstract: A central office line unit (COLU) for a pulse code modulation (PCM) upstream and downstream system in a universal digital loop carrier (UDLC) includes a hybrid circuit for transmitting/receiving an analog signal to/from a switch. An analog-to-digital converter is provided for receiving the analog signal from the hybrid circuit and converting the analog signal to a converted digital signal. A digital transmission circuit transmits/receives a digital signal to/from a remote terminal. A quantizer is provided for evaluating and processing the converted digital signal so that only valid states of the converted digital signal are transmitted to the digital transmission circuit for transmission to the remote terminal. A receiver is used for receiving the digital signal from the digital transmission circuit and for evaluating and processing the digital signal so that only valid states of the digital signal are outputted from the receiver.

Abstract: An electronic module having a chassis and a single backplane disposed within the chassis. A plurality of bridge circuit cards is disposed within the chassis and is electrically connected to the single backplane. Each of the plurality of bridge circuit cards is for converting between a local area network protocol and a wide area network protocol. A hub circuit card is disposed within the chassis and is electrically connected to the single backplane so that the hub circuit card is electrically connected to each of the plurality of bridge circuit cards. The single backplane is connectable to each of a plurality of remote units for respectively electrically connecting each of the plurality of remote units to each of the plurality of bridge circuit cards. The single backplane is connectable to a data network for electrically connecting the data network to the hub circuit card.

Abstract: A conditioner unit is wired in parallel with a pair gain test controller used to test a digital loop carrier telephone network. The conditioner unit senses a signal intended to request test results from the pair gain test controller and provides a response signal which indicates that the pair gain test controller performed a successful test, even though the pair gain test controller was not activated. This allows testing of the network without use of a bypass pair or the need to interface the digital loop carrier network with the pair gain test controller.

Abstract: Phase locked loops adapted to filter and store data indicative of the control signal applied to an oscillator permit suppression of tracking in the event of a step change in the phase difference between the reference clock signal and the feedback signal in the phase locked loop. Such phase locked loops further facilitate compensation for drift of the oscillator. Such phase locked loops are suitable for use in timing circuits of communications systems.

Abstract: A housing for a plurality of electronic circuit cards is provided. The housing includes a shell and a single door adapted to selectively close the shell. The housing has a first shelf having opposing first and second edges in frictional engagement with the shell to thermally couple the first shelf to the shell. Moreover, the housing has a second shelf having opposing first and second edges directly contacting the shell to thermally couple the second shelf to the shell. The first and second shelves define a space therebetween for containing the plurality of electronic circuit cards. A backplane is disposed within the shell. The second shelf is removably attached to the shell to enable the backplane to be installed or removed via the single door.