| 摘要 |
An automatic dialer for controlling access to a long-distance telephone network. The automatic dialer includes a read/write memory. Each time the user attempts to call through the network a telephone number inaccessible via the network, an entry representing the area code and/or exchange of that telephone number is made in the memory. Prior to calling the network, the dialer compares the destination telephone number with the entries in the memory; the call is placed via the network only if the area code and exchange of the destination number do not match any of the entries. The entries in the memory are ordered according to recency of attempts by the user to access a telephone number within the groups of telephone numbers represented by the entries; when the memory is filled, the oldest entry is deleted to make room for the newest entry. Memory entries may be erased manually or automatically, by the network control station, without human intervention, to remove entries corresponding to areas added to the network. Automatic erasure is accomplished by the network sending an appropriate command, using tone signalling, as part of a message that the user has attempted to call a location not covered by the network.
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