architectures may benefit from such a solution additionally the olt may also use data about the geographical location of the onus collected during system startup a procedure often referred to as ranging and derive preamble lengths based on that information when onus located far apart geographically needs to transmit after each other a longer preamble may be used the round trip time rtt of communication between the olt and onu is the main interest when taking the geographical location into account to take into account that timing parameters in the system might change on a short time scale depending on such effects as which devices need to transmit jitter wander phase looked loop pll drift or other device or network dependent parameters one may a vary only the part of the preamble that is used for deciding the optimal threshold and leave the preamble part that is used for the burst mode clock and data recovery cdr fixed or b regularly do new ber measurements to adapt to the changing conditions fig3 shows an example of method according to the present invention in a first step 301 data is received from an onu and bit error ratio is measured 302 or determined the olt takes the ber data into consideration when scheduling 303 in accordance with the ber finally appropriate scheduling parameters such as burst ordering and or overhead length is transmitted 304 to each onu.