Point-to-multipoint telecommunication system with downstream frame structure

A point-to-multipoint telecommunication system can be made more flexible by providing upstream units with generators and locators for generating at least two subsequent overhead cells located next to each other and neighbouring a larger number of data cells for supplying system information. Downstream units are provided with detectors for detecting the subsequent overhead cells. This new signal flame structure allows a larger number of data cells to be exchanged without being interrupted by an overhead cell. Each cell consists of at least 53 bytes in accordance with the Asynchronous Transfer Mode or ATM standard. The at least two overhead cells comprise two overhead cells for supporting 54 data cells, or comprise three overhead cells for supporting 103 data cells. The point-to-multipoint telecommunication systems comprise passive optical networks, with upstream units corresponding to line terminators, and with downstream units corresponding to network terminators.