ONU State and Activation Process of ONU
Initial-state (O1)
The ONU in this state has just been powered on and is still in LOS / LOF. Once the downstream is received, the LOS and LOF eliminate, and the ONU moves to the standby state (O2).
Standby-state (O2)
The ONU in this state has been received to the downstream flow and is waiting for the network parameters to be received. When the ONU receives the Upstream_Overhead message, configure the ONU based on these network parameters (e.g., delimiters, power mode, preset equalization delay) and transferred to the serial number state (O3).
Serial-Number-state (O3)
The OLT sends Serial-Number Request messages to all ONUs in that state to discover the new ONUs as well as their Serial numbers. When the OLT discovers the new ONU, the ONU waits for the OLT to assign it the ONU-ID. The OLT assigns the ONU-ID through the Assign_ONU-ID message. ONU transfers to ranging state (O4) after obtaining ONU-ID.
Ranging-state (O4)
The transmitted signals from different ONUs should be synchronized when they arrive at the OLT, for which each ONU needs an equalization delay, which is measured in the ranging state. The ONU receives the Ranging_Time message and moves to the operational state (O5).
Operation-state (O5)
Onus in this state can send data and PLOAM messages under the control of OLT, and ONUs in this state can also establish other connections as required. When the ranging is successful, all ONUs send signals according to their equalized delay to maintain the synchronization of the uplink frame. Signals sent by different ONUs will arrive at the OLT separately, but each signal will appear exactly where it should appear in the uplink frame. Suspend the ONU in operation: During normal operation, the OLT may suspend the ONU to send signals to obtain the sequence number of other ONUs or to measure the distance of other ONUs. The OLT stops authorizing all uplink bandwidth for a period of time, and the ONU works in the normal way. Since no authorization is received, no signal will be transmitted, resulting in a quiet period, so that the OLT makes all ONUs suspend transmitting signals.
POPUP-state (O6)
The ONU in the operating state (O5) enters this state when it detects LOS or LOF. In this state, the ONU immediately stops transmitting signals, so that the OLT will detect the LOS alarm of this ONU. When the ODN fiber is interrupted, many ONUs will enter this state. For the sake of network reliability, one of the following methods should be used:
If guard switching is enabled, all ONUs will switch over to the standby fiber. At this time, all ONUs will conduct ranging again, for which the OLT sends a Broadcast POPUP message to inform all ONUs to enter the ranging state (O4).
If there is no protection switching but the ONU has internal protection capability, the OLT sends a Directed POPUP message to notify the ONU to enter the operation state (O5). When the ONU enters the O5 state, the OLT needs to detect the ONU first and then
Restore the ONU’s service. If the ONU does not recover from LOS or LOF, the ONU will not receive the Broadcast POPUP message or the Directed POPUP message, and the ONU enters the initial state (O1) after TO2 time.
Emergency-Stop-state (O7)
When the ONU receives a Disable_Serial_Number message with the “Disable” option, the ONU enters the emergency stop state (O7) and turns off the laser. In state O7, the ONU is forbidden to transmit signals. If the ONU does not successfully enter the O7 state and the OLT can still continue to receive the signal sent by the ONU, the OLT will generate a Dfi alarm. When the fault of an ONU is resolved, the OLT sends a Disable_Serial_Number message with the “Enable” option to activate that ONU. After receiving the message, the ONU enters the standby state (O2), and all the parameters (including the sequence number and ONU-ID) will be rechecked.
The above points of knowledge are about the explanation process of ONU status and activation brought by Shenzhen HDV Phoelectron Technology LTD., which is a manufacturer specializing in communication equipment as its main products. The related equipment involves: OLT ONU/ IntelligentONU/ AC ONU/ Fiber ONU/ CATV ONU/ GPON ONU/XPONONU/OLT equipment/OLT Switch/GPON OLT/ EPON OLT and so on, welcome users to come to the product consultation.
