| 摘要 |
A telephone-network signals calls to destination terminal equipment by either of two categories of ON/OFF ringing signal: one category, called a short-ring and having ON periods less than a time-interval T, is used to signal calls intended for automatic answering; the other, having ON periods longer than T, is used to signal "telephony" calls which need the attention of a person from the start of the end-to-end connection. Upon receipt of a ringing signal, equipment at the terminal will seek assured detection of any prescribed short-ring cadence and then provide prompt automatic answering, but will stop seeking short-ring detection if an ON period exceeds T and then rely on an audible or other telephony alerting signal to elicit manual answering. The network may be instructed in 3 ways to signal a call with a short-ring: if the call originates from some designated terminal or network facility, or when number dialling has been preceded by a special pre-code (e.g. involving characters * and #), or when the number dialled has been selected from a plurality of numbers allocated to the receiving end-connection.
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