| 摘要 |
An access controller is placed in series with a subscriber's telephone set and includes an off hook detector, a ring detector, a central office simulator and DTMF circuitry which cooperate with a microcontroller or microprocessor suitably programmed to select one of a multiple providers of services by generating an access code corresponding to one of the service providers in accordance with an algorithm which provides a desired distribution of usage by the subscriber. The controller inserts a five digit prefix, namely the access code into the dialed number. The access code allows the call to be routed through a specific long distance service provider telephone network. By inserting the access code into the dialed number the device selects a particular long distance carrier for the duration of the call. Access codes are stored in a memory list of the access controller. Examples of algorithms used to select access codes from memory include a "rotating" algorithm for sequencing next access codes stored in memory in a predetermined order or sequence which are rotated one after the other. Another algorithm is a "time based" algorithm which employs a real time clock to establish preset time intervals during which each of the access codes are used. The controller can also use a "random selection" algorithm in which the controller selects an access code at random from those stored in a memory list. The controller is transparent to incoming calls and local outgoing calls, as well as certain excepted calls which commence with the digit "1". However, as soon as the controller detects an outgoing long distance call which commences with a digit "1", the controller inserts a prefix or access code to the dialed number to connect the subscriber's telephone unit with a long distance provider or carrier in accordance with the desired algorithm.
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