| 摘要 |
<p>Two to nine telephones (TI1-TI9) are connected to a telephone cable (20) by control or signalling devices (CD1 to CD9), there being one per telephone. The devices (CD) together act as a telephone exchange distributed along the cable (20). The cable may be directly connected to an outside telephone company line (21). In one version, each signalling device (CD) is able to receive on only one frequency unique to that device, but is able to transmit on any selectable one of the reception frequencies of the devices (CD). Each device (e.g. CD1) responds to the selection by its telephone TI1 of another (e.g. TI2) of the telephones to signal to the device (CD2) associated with another telephone (TI2) to establish a two way communication link. Multiway links are also possible, as are links to the outside line. Preferably all signals transmitted and received by the devices (CD) are of magnitude less than the maximum magnitude of noise permitted in the external line by the telephone company.</p> |
