| 摘要 |
<p>A plurality of subscriber stations each with a plurality of outlets at which television signals broadcast over the system are to be made available, are connected to a plurality of switchpoints each connected to a respective group of subscriber stations. Each subscriber station is connected to its respective switchpoint by at least one optic fibre 16, and a plurality of optic fibre trunk cables 8-12 interconnecting the switchpoints and a plurality of television signal sources 1-5. PCM television signals are applied to each trunk fibre, each sample of each PCM television signal on a trunk fibre being allocated a respective time slot. Each switchpoint comprises a selector 13, 17 in respect of each outlet of each subscriber station in its respective group, the selectors being controllable from the respective subscriber station outlet to select a desired television signal by selecting samples of that television signal appearing in appropriate time slots. The switchpoint also comprises means 18 for allocating selected television signals to respective time slots on the fibre optic cable 16 leading to the subscriber unit, and each subscriber unit outlet comprises means for selecting the signal samples appearing in the appropriate time slots and for decoding the received signals to produce the desired television signal. The PCM coded television signals are distributed over the entire system so as to be generally available at each switchpoint but the final destination of the bit streams delivered to the switchpoints is determined by the recipients of those bit streams rather than from the head end of the system. <IMAGE></p> |
