Abstract:
Error detection apparatus for a communications line includes an even/odd detection unit for detecting whether an even number of bipolar pulses or an odd number of bipolar pulses occur between a first pulse (violation pulse) interrupting an alternating pattern of bipolar pulses and a second pulse (violation pulse), and an output unit which determines that there is a line error in a target block defined by the first and second violation pulses when a detection result of the even/odd detection unit indicates an even number, wherein the first and second violation pulses occur in a code sequence in accordance with a predetermined coding scheme.
Abstract:
An optical communication system is disclosed in which a bipolar signal of the type transmitted in digital transmission systems is converted into a unipolar binary signal for transmission over an optical transmission medium. The three levels of the bipolar signal are converted into three pairs of bits in the binary signal. One pair of bits is not utilized in the conversion and is therefore labeled as a forbidden word. Synchronization is achieved at the receiving location for the purpose of decoding by detecting the presence of the forbidden word in the binary signal and in response to this detection an energizing pulse is produced. This energizing pulse drives a clock circuit which in turn drives a decoding apparatus utilized to translate the binary signal back into the bipolar signal. As a result of this type of word synchronization, individual errors introduced into the binary signal do not result in a framing error.
Abstract:
A pseudo-random, pseudo-ternary pulse train, which is representative of a PCM signal, is applied to one end of a cable pair. At the other end of the cable pair, the received pulse train is equalized and amplified to obtain a pulse train output in which pulses have very nearly the same peak amplitude as each transmitted pulse, plus a characteristic which is similar but not identical. A variable amplitude interfering tone is combined with the equalized and amplified received pulse train. If no errors are determined by an error detector with a 0 amplitude interfering tone, the amplitude is increased until errors occur. The interfering amplitude control is calibrated in terms of eye degradation factor. The magnitude of the eye degradation factor is determinative of the capability of the cable pair to transmit the PCM signal with an acceptable error rate.
Abstract:
A system for isolating the direction of communication errors in the local loop of a digital data network is described. A Network Interface Unit (NIU) located at the customer premises typically has a loopback feature, allowing for Bit Error Rate Tests (BERT) to be performed on the local loop from a remote test system located on the data network. The NIU loopback test isolates transmission problems at the customer premises from problems on the local loop. The present invention adds test pattern generation capability to the NIU, allowing the remote test system to determine whether the transmission problem on the local loop is in the network to customer premises direction or in the customer premises to network direction.