| 摘要 |
A telephone line incoming call filtering device. A ring-through of an incoming call to a subscriber's controlled telephone is reserved to a second call attempt quickly following a succession of a first call and a hang-up. As a result, nuisance calls such as trash calls from telemarketeers and other unwanted calls may be simply diverted to an answering machine. This nuisance call filtering is transparently obtained without even bothering the subscriber when the first call attempt rings more often than one or two times. On the other hand, repeating a rapid-fire succession of incoming calls where the first call attempt is allowed to ring only once or twice followed by a second call attempt are allowed to ring-through directly to the subscriber's telephone set. Filtering of unwanted calls is achieved by permitting the ring-through to occur only when the first call attempt is allowed to ring only a few times and distinctly a less number of times than ordinarily attempted by casual or nuisance callers. Then the second call attempt, when it follows the first call attempt in quick time succession is recognized as possibly valid and the ring-through occurs. Filtering may also be obtained by recognizing and storing the caller-ID of the first call attempt and then a second immediately occurring call attempt is intercepted and if the caller-ID of this second call matches the stored caller-ID of the second call, the ring-through to the subscriber's telephone set is permitted.
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