A METHOD TO DETERMINE A SWITCHING MOMENT AND A LINE TERMINATOR, A CONTROL NETWORK UNIT AND A NETWORK UNIT REALIZING SUCH A METHOD AND A TREE-LIKE OPTICAL NETWORK INCLUDING SUCH A LINE TERMINATOR, SUCH A CONTROL NETWORK UNIT OR SUCH A NETWORK UNIT

摘要

A method to determine a switching moment (Ti) of a switch (SWi) isprovided. The switch is coupled to an optical combiner (OC) of a tree-likeopticalnetwork. The optical combiner enables multiple access of information signals(IN1, ..., INi, ... INn) which are upstream transmitted from network units(NU1,NU1', NU1", ..., NUi, ..., NUn) to a line terminator (LT) via the cascadeconnection of dedicated branches (B1, ..., Bi, ..., Bn), the optical combinerand acommon branch (BC). The switch passes an information signal (INi) at anapproximated switching moment (APP-Ti) when the information signal is presentand interrupts the branch when the information signal is not present. Themethod includes the steps of : a) capturing downstream grant information by acontrol network unit (CTRL-NU) which is coupled between the switch and thelineterminator; and b) determining the approximated switching moment by thecontrol network unit based upon the downstream grant information; and c)upstream transmitting by one of the network units coupled to this onededicatedbranch a predefined bit pattern (PAT) similar to the information signal. Intheevent when the predefined bit pattern is passing through the switch, thepredefined bit pattern is truncated and a truncated bit pattern (PAT-TR) isprovided which is related to the approximated switching moment; and d)detecting by the line terminator reception of the truncated bit pattern; ande)determining by the line terminator a measure of how much the predefined bitpattern is truncated and providing thereby a truncation measure (.TR); and f)calculating in function of the truncation measure a calibration value (CAL-SWi)for the switching moment; g) providing the calibration value to the controlnetwork unit in order to determine the switching moment in function of thecalibration value and the approximated switching moment.