| 摘要 |
In order to provide unbalanced ringing when an exchange line card provides a balanced ringing output the interface provides a ringing detector in circuit with a customer pair. On detecting balanced ringing signals from the line card, the interface takes over the customer line pair and provides unbalanced ringing signals to the customer and monitors for customer answer. By inserting the interface in circuit at the main distribution frame of an exchange, legacy customer premises equipment which is unable to respond to balanced signalling can be provided with an appropriate ringing signal without the necessity to provide differing line cards at the exchange.
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