| 摘要 |
A device for permanent installation in series with a time division multiplex digital data transmission line for accessing data signals carried by the line without interruption or degradation of the signals. The device, referred to as a line access module (LAM), operates in a throughput mode in which incoming signals pass through the device without modification and a bypass mode in which the incoming signals are bypassed to an external common electronics circuit and reinserted in the outgoing transmission line. The LAM includes a controllable electronic switch for breaking the normal data signal throughput of the transmission line, for terminating the incoming line, and for bypassing the incoming data signals to the external common electronics circuits; a data insertion circuit for receiving the bypassed data signals from the common electronics circuits and transmitting these signals over the outgoing transmission line; and a delay circuit in the normal data signal throughput path for equalizing the transit time of data signals through the LAM in the normal throughput mode and in the bypass mode. A principal application of the LAM is as an element in a test system for verifying the integrity of individual subscriber channels of the digital data bit stream. The common electronics circuits generally include means for recognizing the framing pattern of a designated data subscriber channel, and for selectively deleting the incoming data content of the designated channel, and inserting locally generated data such as a test code in place thereof for transmission over the outgoing transmission line. Through the use of a duplex arrangement having a LAM in both the SEND and RECEIVE transmission lines, the response to the inserted test code data in the SEND line can be extracted from the RECEIVE line and decoded. In a system having a multiplicity of transmission lines, a LAM is installed in each line and all are controlled by a single common electronics circuit which may include a computer. Accessing an individual channel of the data bit stream is accomplished without interruption or degradation of the other subscriber channels.
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