An optical network unit and an optical line terminal which efficiently
control the data receiving and dechurning processes in a passive optical
network. In a churning parameter memory subsystem, a first memory bank
stores churning parameters that are currently used, while a second memory
bank stores updates made to the churning parameters. Under the control of
the churning parameter memory subsystem, those first and second memory
banks change their roles with each other at a churning key updating time
point. A data dechurning unit receives a data stream consisting of a
plurality of frames and dechurns the information contained in the data
stream, according to the stored churning parameters. When an update is
done to the parameters in a certain frame, the data dechurning unit makes
the update effective at the next frame, thus starting data dechurning
operations from the next frame.