| 摘要 |
In caller ID telephone service system, if a calling party does not want to display his telephone number on the called party side, the calling party takes an authorized key number (hereinafter called "blocking key number") with the telephone exchange office. The key number is composed of a 3 or 4 digit numerical signal, like a push-phone tone, when the subscriber calls any subscriber (called party) telephone number in this service area. If he dials that key number first and then the conventional number, the telephone exchange office detects that key number, then blocks (stops) sending the calling party telephone number to the called party side. On the other hand, the called party side has a device with a relay which functions to take out the associated telephone set from the telephone line after one ring because the device cannot detect telephone number information between the first ring and second ring. However, the telephone ring signal still comes successively via the telephone line and can activate a Telephone Answering Device (TAD).
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