Basic troubleshooting of ONU (optical network unit)

Introduction: ONU (Optical Network Unit) is divided into active optical network units and passive optical network units. ONU is a user equipment in optical networks, placed on the user end, and used in conjunction with OLT to achieve Ethernet Layer 2 and Layer 3 functions, providing users with voice, data, and multimedia services.

Description of ONU panel indicators:

POWER light: green off: power off on: power on

PON light: Green on: Long on indicates that the board has passed self test and the device is running normally

LOS lamp: not on: normal state

Determine user faults:

The faults are mainly optical path faults and ONU device faults. First, check whether the panel indicator light is normal. Check the PON lamp status for optical path faults: the PON lamp is normally lit in green, indicating that the optical path is normal, and the PON lamp is off, indicating that the optical path is broken.

Use an optical power meter to test the optical path. The acceptable range of optical power is: 1490nm: – 8db to – 28db. If the range is exceeded, it will affect the normal working quality of the ONU, and the user’s internet access will be affected. Check the upper level optical path, and go to the optical cable handover box to test the tail fiber of the splitter corresponding to the faulty user’s optical cable

Attenuation of 1:2 channel splitter is – 3 db

1:4 channel splitter attenuation is – 6db

The attenuation of the 1:8 channel splitter is – 9db,

1:16 channel splitter attenuation is – 12db,

The attenuation of 1:32 channel splitter is – 15 db,

The attenuation of 1:64 channel splitter is – 18db,

1、 If the output optical power of the splitter pigtail is qualified, please replace the fiber core between the optical cable junction box and the building. Generally, we will lay at least two fiber cores to the building, and then conduct the end testing after the replacement. If the optical power of the pigtail from the splitter is unqualified, please replace the remaining pigtail, and use the optical power meter to test a qualified one to connect to the building pigtail.

If it is an optical path fault: First, unplug the pigtail on the ONU to test the optical power. If there is no light or the power is unqualified, please find the one of the 1-32 pigtails corresponding to the ONU on the flange of the optical cable junction box, and unplug the pigtail from the flange to test the optical power. If the pigtail is unqualified, replace any one of the 1-32 idle pigtails. Remember that the main fiber of the splitter cannot be unplugged, which will affect all ONUs.

ONU device panel indicator light description Power green light permanently on: Device power on Off: Device power off LOS light: Off: PON port receives normal optical power Green light permanently on: Device completes discovery and registration Green light flashing: Device is not doing data Not on: PON port has no light or optical power is lower than reception sensitivity LAN1, LAN2, LAN3 LAN4 is an electrical port, FXS1 is a voice port, and troubleshooting: First, check whether the ONU device is operating normally (whether the indicator light on the device panel is normal). After the device is operating normally, find out other reasons. The procedure is the same as described above.

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