| 摘要 |
To prevent the occurrence of an anomaly on a single data-sourcing slave channel from causing continuous transmission on that channel and thereby tying up the entirety of a multipoint network, a signal transmission quality monitoring mechanism is incorporated into the office channel unit of each data-sourcing channel. The signal transmission quality monitoring mechanism controls the participation of each monitored digital communications channel on the basis of a measure of the quality of digital signals received from each monitored channel. The control software of each slave channel's office channel unit is configured to include a bipolar violation detector which monitors the channel for the presence of errors exhibited as bipolar violations of alternate mark inversion (AMI)-formatted digital signals. In response to the occurrence of a prescribed number of illegal bipolar violations within a predetermined number of received signals (e.g. three errored seconds within a sliding ten second window), the channel is declared to be of "BAD" quality, and the office channel unit sends an 'ABNORMAL' station code upstream to a multipoint junction unit. Thereafter, during continued monitoring of the channel, in response to the lapse of a predetermined period of time (e.g. 30 seconds) during which the prescribed number of illegal bipolar violations has not occurred within the predetermined number of received digital signals, the channel is declared to be "GOOD", so that participation of the channel for the transmission of digital signals to the master site may be resumed.
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