Optical line termination in ATM-based PON

A churning method in an asynchronous transfer mode, comprising the steps of:

• a) requesting a new churning key through a new key request message to an ONU, wherein the ONU completes a distance measurement;
• b) transmitting the new churning key to an optical line termination (OLT) through the new key request message;
• c) in case where the OLT receives the new churning key predetermined times, transmitting a churning key update message to the ONU predetermined times at a predetermined interval together with a transmission numbers;
• and
• d) after receiving a first correct churning key update message, transmitting an acknowledge signal representing a message reception to the OLT.

A method for allocating a down message in an optical line termination, comprising the steps:

• a) in case where a current state is not an express message slot and a message memory is empty, transmitting a serial number mask message and a request password message one time;
• b) transmitting the other message three times, thereby determining the transmission numbers according to a message identification read out from a memory;
• and
• c) in case where the message memory is empty and is not the express message slot, transmitting a NO message.