Optical network unit and registration method thereof

An optical network unit (ONU), communicatively connected to an optical line termination (OLT), the ONU comprising:

• an ONU media access control (MAC) circuit configured to perform the following processes:
• determining whether a network parameter configuration message broadcasted by the OLT is received in a standby state;
• in response to determining that the network parameter configuration message is received, entering a serial number state, and generating a timing duration;
• receiving at least one serial number request message from the OLT in the serial number state;
• transmitting a serial number response message to the OLT upon each receipt of the serial number request message in the serial number state while the timing duration does not exceed a discovery time, and determining whether an identifier allocation message is received, wherein a duration of the discovery time is a time interval that allows the ONU to receive at least two sequence request messages in the serial number state;
• and
• in response to determining that the identifier allocation message is received while the timing duration does not exceed the discovery time, entering a ranging state;
• and
• a discovery time generation circuit connected to the ONU MAC circuit, wherein the discovery time generation circuit is configured to generate the discovery time, which is provided to the ONU MAC circuit.