The user and service reuse functions include assembling the information from each user, distributing the information to be transmitted to each user, and connecting a single service interface. The transmission multiplexing function includes analyzing the signal coming from the ODN and taking out the part belonging to the ONU and arranging the information to be sent to the ODN reasonably; The ODN interface function provides a series of opto-physical interface functions, including optical/electrical and electrical/optical conversion.

  If each ONU uses more than one optical fiber to connect to the ODN, then there is more than one physical interface. The ONU service function block provides user functions, including providing user service interface and adapting user information to 64kbit/s or n×64kbit/s. This function block can serve one or more users and can provide signaling conversion function according to its physical interface. The ONU general function block provides power supply functions and system operation, management, and maintenance (OAM) functions. The power supply function includes AC to DC or DC to AC. The power supply mode is local power supply or remote power supply. Several ONUs can share one power supply.