Digital subscriber carrier system including drop terminals and bypass and loopback means and alarm indication means

摘要

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. When the drop terminals are connected to the inward cable pair each terminal has associated therewith a circuit for looping back the system at the terminal upon the occurrence of a cable fault condition. The loopback circuit operates automatically and independently of the central office. An alarm mechanism is provided to allow a serviceman to easily locate the fault condition.