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

Abstract

A method to determine a switching moment (Ti) of a switch (SWi) is provided. The switch is coupled to an optical combiner (OC) of a tree-like optical network. The optical combiner enables multiple access of information signals (IN,, . . . , INi, . . . INn) which are upstream transmitted from network units (NU,, NU,′, NU,″, . . . , NUi, . . . , NUn) to a line terminator (LT) via the cascade connection of dedicated branches (B,, . . . , Bi, . . . , Bn), the optical combiner and a common branch (BC). The switch passes an information signal (INi) at an approximated switching moment (APP-Ti) when the information signal is present and interrupts the branch when the information signal is not present. The method includes the steps of: a) capturing downstream grant information by a control network unit (CTRL-NU) which is coupled between the switch and the line terminator; and b) determining the approximated switching moment by the control network unit based upon the downstream grant information; and c) upstream transmitting by one of the network units coupled to this one dedicated branch a predefined bit pattern (PAT) similar to the information signal. In the event when the predefined bit pattern is passing through the switch, the predefined bit pattern is truncated and a truncated bit pattern (PAT-TR) is provided which is related to the approximated switching moment; and d) detecting by the line terminator reception of the truncated bit pattern; and e) determining by the line terminator a measure of how much the predefined bit pattern 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 control network unit in order to determine the switching moment in function of the calibration value and the approximated switching moment.