In a fiber-optic broadband (FTTH) network, the ONU (optical network unit) is a key device at the user end, responsible for converting optical signals into electrical signals, enabling homes or businesses to access the Internet. However, in actual use, the ONU may encounter problems such as low optical power and inability to register, resulting in network interruption or reduced network speed. This article will introduce how to quickly troubleshoot and solve these faults, and provide actionable methods that even non-professionals can easily get started.
2.4g XPON ONU 1G3F+WIFI2.4+CATV+POTS
Ⅰ. Low ONU optical power: causes and solutions
1. What is optical power?
Optical power refers to the intensity of the optical signal received by the ONU, in dBm (decibel milliwatts).
The normal range is usually:
-8 dBm to -27 dBm (GPON/EPON)
-Below -28 dBm may cause network instability or disconnection
-Above -8 may cause ONU restart and registration instability
2. How to check the optical power?
Different brands of ONUs have slightly different ways of checking, but they can usually be checked in the following ways:
① Web management interface (such as 192.168.1.1, enter the administrator account password) → Status → Optical module information
② ONU indicator: If the LOS (loss of optical signal) light is red, it means that the optical power is too low or the optical fiber is disconnected
③ Use an optical power meter (commonly used by professional operation and maintenance personnel)
3. Common causes and solutions for low optical power
|
Cause Of Failure |
Troubleshooting Method |
Solution |
| Fiber is Bent Or Damaged |
Check whether the fiber is bent (especially at the joint) |
Straighten the fiber to avoid 90° bends |
| Dirty Fiber Connector |
Check whether the SC/APC/UPC connector is dusty |
Clean With Alcohol Cotton Or Dust-Free Cloth |
| The optical attenuation is too large (too far from OLT) |
Measure whether the optical power is lower than -28dBm |
Contact the operator to adjust the splitter or shorten the distance |
| Splitter Failure |
Are other users on the same PON port normal |
Operator replaces the optical splitter |
| ONU Optical Module Aging |
Replace Another ONU for Testing |
Replace a New ONU |
Note:
1. Do not look directly at the fiber end face, the laser may hurt your eyes!
2. If you cannot solve the problem yourself, it is recommended to contact the operator for repair, it may be a problem with the trunk optical cable.
Ⅱ. ONU registration failure: causes and solutions
1. What is ONU registration?
ONU needs to register with the operator's OLT (optical line terminal) to access the Internet normally. If the registration fails, problems such as flashing red network light and dial-up failure (PPPoE error) will appear.
2. How to determine registration failure?
①PON light is off/flashing (normally it should be on)
②The management interface displays "unregistered" or "authentication failed"
③When dialing up to access the Internet, it prompts "678/651 error" (may be different in different regions)
3.Common reasons and solutions for registration failure
|
Cause Of The Problem |
Troubleshooting Method |
Solution |
| LOID/SN Code Error |
Check if the LOID (broadband identification code) is Entered Correctly |
Re-enter the LOID (provided by the operator) |
| OLT version is incompatible |
Check whether the ONU Model Supports the Operator Network |
Replace the operator-certified ONU |
| Optical power is too low |
Check the optical power according to the first part |
Fix the optical power problem and register again |
| Operator binds MAC |
Try to clone the original ONU MAC address |
Contact the operator to unbind or replace the device |
| Insufficient PON port resources |
Too many users on the same PON port |
Operator adjusts PON port configuration |
Operation example (taking CeitaTech ONU as an example):
1. Enter the management interface (192.168.100.1) → enter the LOID (provided by the operator).
2. Click "Register" and wait for the PON light to be on to indicate success.
3. If it fails, try "Restart ONU" or "Restore Factory Settings" and then re-register.
Ⅲ. Quick check of other common problems
1. ONU can register but cannot access the Internet?
① Check whether the PPPoE account password is correct (provided by the operator).
② Try to change the network cable or router for testing.
2. ONU frequently disconnects?
① It may be the critical value of optical power (about -27dBm), and the optical fiber connection needs to be optimized.
② Check the heat dissipation of ONU to avoid instability caused by high temperature.
3. How to determine whether it is an ONU problem or an operator problem?
① Are other users under the same PON port normal? If they are all abnormal, it may be an OLT failure.
② Measure with an optical power meter. If the optical power is normal but cannot be registered, it may be an ONU failure.
IV. Summary: ONU troubleshooting process
1. Check the optical power first (whether it is between -8dBm and -28dBm).
2. Check the optical fiber and connector (whether it is bent or dirty).
3. Confirm that the LOID/SN code is correct (contact the operator to obtain it).
4. Restart the ONU or re-register after restoring the factory settings.
5. Still can't solve it? Contact the operator to report it (it may be a problem with the OLT or the trunk optical cable).
According to this process, most ONU faults can be quickly located and solved! If your ONU still has problems, you are welcome to contact us! WhatsApp/Phone:+86 13714107074
Post time: May-07-2025
