The PON network is mainly composed of four parts: the user equipment ONU (optical network unit), the central office equipment OLT (optical line terminal), ODN (optical distribution network) and EMS. It is connected to the BRAS (broadband remote access server) through the metropolitan area convergence network. ), downstream user equipment such as corporate LAN switches, wireless base stations, PCs and telephones, etc.
ODN is mainly composed of the optical distribution frame, single-mode optical fiber/optical cable, passive optical splitter, optical fiber adapter and optical fiber connector, etc.
A typical PON network is shown in the figure
PON Network Application Problem Case Analysis
PON link optical power attenuation is too small
Failure performance
The ONT can register normally, but the OLT side continuously reports "GEM cell loss", "GEM channel recovery", and "ONU signal degradation" alarm information.
Failure analysis
a) The normal registration of the ONT indicates that the optical path is connected. The received optical power value of the ONT is queried through the EMS, and it is found that the received optical power of the ONT is too large, which exceeds the normal operating range of the optical module.
b) Check the fiber connection and find that the ONT is directly connected to the OLT through a fiber. Add an optical splitter between the ONT and the OLT. After the ONT registers normally, the alarm will no longer appear.
Solutions
If the optical attenuation of the optical path between the ONT and the OLT is significantly less than 15dB, the received power of the ONT or the optical module of the OLT will be overloaded and work in an unstable state, which will affect the transmission of normal packets.
The SDH optical transceiver is incorrectly connected to the PON network, resulting in abnormal services of multiple ONUs
Failure performance
All ONUs under a certain PON interface of the OLT are offline or the communication is interrupted, but the OLT can still receive optical signals, and the EMS has not received the ONU power failure notification.
Failure analysis
The OLT can receive the upstream optical signal, indicating that a remote device is sending the upstream signal, and all ONUs that display offline or communication interruption are under the same OLT-PON interface, and there is no ONU power failure notification alarm. It can be preliminarily judged that there is a remote The end device emits abnormally.
Solutions
a) The PON system provides "rogue" ONU detection and control functions. Through this function, abnormally luminous ONUs can be detected and located, and commands can be issued to turn off the transmission of the "rogue" ONU optical modules.
b) The "rogue" ONU detection and control function is only applicable to the case where the remote abnormal light-emitting device is an ONU. If the measures in a) cannot locate the remote abnormal light-emitting device, and the abnormal light cannot be turned off. Currently, it is only recommended to manually check remotely one by one
Incorrect configuration of the optical modules at both ends of the device and the switch causes the link to be abnormal
Failure performance
The MA5680T is connected to the Layer 3 switch through the GE port multi-mode fiber. The optical port of the switch can receive light, and the optical port is always on; while the optical port of MA5680T cannot receive light, and the optical port is always off.
Failure analysis
a) Check the fiber, no problem. Changing the duplex mode of the MA5680T port to full-duplex, the problem remains; changing the negotiation mode of the MA5680T port to auto-negotiation, the problem remains, indicating that it is not a port negotiation problem.
b) Check the optical modules at both ends and find that the module models at both ends are different. The switch is single-mode (1310nm), while MA5680T is multi-mode (850nm).
c) Replace the optical module at one end to be consistent with the other end, and the fault is rectified.
Solutions
In addition to the influence of the optical fiber and port negotiation mode, the optical module at both ends receives and emits abnormalities, and the inconsistency of the optical modules at both ends must be considered. Under normal circumstances, the reasons for the above problems are:
a) There is a problem with the optical fiber.
b) The optical module is broken.
c) The interface mode is configured incorrectly.
d) Interface mode negotiation error.
