Hi Alessandro! And thank you for bringing this point about the BER. When I indicated the value of a BER 10^-12, I meant the BER at the receiver terminal input for the group signal. If I am not mistaken, this value is defined in rec. G.941.1 of ITU-T. However, if we are defining a plausible value for BER in a channel that is digital, i.e. Ethernet of SDH hierarchy, it will be equal to 10^-9, in accordance with corresponding recommendations for digital communications.