| 摘要 |
1,049,841. Automatic exchanges. STANDARD TELEPHONES & CABLES Ltd. Jan. 8, 1965 [Jan. 15, 1964], No. 959/65. Heading H4K. [Also in Division G4] An allotter comprises a ring counter provided with means for indicating failure if its stepping rate departs by more than a predetermined amount from standard. The first and last stages of a group 1-6 open an AND gate 72 if they operate at the required rate, and so also for other groups and AND gates 73-75. AND gates 72, 73 and AND gates 74, 75 are likewise coupled to turn flipflop 81 alternately on and off. Correct operation marks lead 85 but failure energizes inverter 86 to bring up an alarm and switch in a stand-by allotter 63. The allotter may assign groups of circuits for service (Fig. 3, not shown) each group having a predetermined or a random order of preference. Any circuit which is already busy is automatically excluded. A test is made as to whether the calling subscriber is permitted the class of service demanded before a circuit is finally assigned. If the selected circuit in a group is faulty the primary allotter steps to the next group. Distribution of service is therefore improved and a faulty circuit in one group disables a limited amount of equipment. Preference in a group may be determined by stepped decrements of potential at the base of each NPN transistor round the ring from a conducting transistor (Fig. 7, not shown). |
