computers and the like in fig4 a schematic block diagram of the receiver r ont 1 of a protected optical network terminal ont 1 is shown receiver r ont 1 comprises for each optical network pon a pon b an optical receiver unit or 1 or 2 a cell delineation and descrambling unit cdd 1 cdd 2 coupled to a ploam cell analysis unit pca 1 pca 2 the receiver also includes an adaptive delay buffer adb 1 comprising a memory to store data a downstream protection switch control unit dpsc 1 and a data conversion unit dc 1 data from optical network pon a and pon b are received by optical receivers or 1 and or 2 respectively and converted from the optical to the electronic domain from the receiver or 1 or 2 the data are sent to the cell delineation and descrambling units cdd 1 cdd 2 and analyzed for loss of signal los a los b and loss of cell delineation lcd a lcd b coupled to cdd 1 cdd 2 the ploam cell analysis units pca 1 pca 2 check the received ploam data for errors err a err b loss of ploam frame synchronization frml a frml b and loss of operations administration and maintenance data oaml a oaml b the ploam cell analysis units pca 1 pca 2 send their error related data to the downstream protection switch control unit dpsc 1 grant information gr 1 gr 2 for upstream transmission to the respective optical line interface pon lt 1 pon lt 2 is sent to the transmitter part of the optical network terminal.