Too large Optical attenuation leads to ONU recovery failure

In the network operation, if optical attenuation of Huawei MA5616 and MA5620 series ONU is too large that will lead to the same PON port of the other ONU configuration recovery failure. What’s the reason and how to solve it? In this article, we describe the situation in detail.

Huawei MA5616

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fault category

The quality of optical line



HG8546M optical signal loss

GEM channel loss

TF failure


Phenomenal description

18 units MA5616 connected to a GPON port of GPFD on Huawei MA5680T, via a 1:32 fiber splitter, with more than 10 units ONUs (Huawei MA5616 and Huawei MA5620) are configured. Configuration recovery failed. Individual ONU can be automatically recovered after a while, but it will appear the configuration state again, which influence on the business.


Alarm Information

HG8546M optical signal loss, HG8546M GEM channel loss, GPON port optical module sending failed (TF failure).


Probable Reasons

The attenuation of optical signal of the Huawei MA5616 or Huawei MA5620 received is too large.

The optical signal of PON port is disturbed.

There is something wrong with optical module.

Huawei MA5616.jpg

Operate steps

1. 10 of Huawei MA5616 and Huawei MA5620 appear this phenomenon, excluding the issue of device hardware.

2. Select one of Huawei MA5616 which configuration recovery failed, use undo ont ipconfig command to eliminate the related information of Huawei MA5616 IP address, and use snmp-profile delete command to cancel SNMP management template, then use ont activate to reactive the Huawei MA5616. But when use display ont info command to check “config state”, it still displays “failed”.

3. Estimated the approximately range of receiving optical power on Huawei MA5616: The average output power of the PON port is about 3dBm, the attenuation of 1:32 optical splitter is about 17dBm, insertion loss and optical fiber line is approximately 1dBm, so the received optical power of Huawei MA5616 is approximately: -16.5dBm, which basically meet the requirement.

4. Check whether the optical signal is connected to the optical signal of the non PON system, and didn’t find issues.

5. Check the history alarm again, found that No.12 MA5616 has the highest frequency of optical alarm. Learned that the optical path of this MA5616 is not very good, but it never be solved. Go to the spot immediately to measure the received optical power of the MA5616, the result is -34dBm, and other optical power of MA5616, which has been measured is about -16dBm, the difference of the two is 18dBm. The difference value does not match that under the same PON port, the difference value of the maximum and minimum optical attenuation of the MA5616 should be less than 15dBm. After fixing up the optical path of No.12 MA5616, all other MA5616 returned to normal.


Requirement and summary

The receiver range of Huawei MA5680T is within 15dBm, that is: the difference value of the maximum and minimum of the optical attenuation should be less than 15dBm, otherwise, once the dynamic range of MA5680T receiver is exceeded, it leads to the error rate increased, even lead to some MA5616 disconnection.


If a PON port of the MA5616 or other optical path is broken, it must be processed at once, otherwise it will influence on the entire PON port of the other MA5616


ONU GPON frequently online and offline

MA5616 under the GPON port is online and offline frequently, MA5680T will report a large number of MA5616 signal loss and recovery alarm.

Huawei MA5680T.jpg

Positioning ideas

The reason why MA5616 frequently online and offline is that MA5680T hardly received the signal of MA5616, which lead to MA5680T and MA5616 interaction message loss.

If the frequency of the MA5616 online and offline is very high, for example, the possibility of ODN problem is higher if drops per few second.

If the MA5616 drops per two hours or longer, may be the MA5616 failure leads to the device restart again and again.


When the MA5616 frequently online and offline, the fault range of positioning basis and possible reasons are as follows.

Fault  coverage Position basis Possible cause
MA5680T All the MA5616 under the PON port is frequently online and offline. The PON port is broken
All the MA5616 under the board is frequently online and offline. Board or slot is broken.

There are ODN related alarms in PON port. For example:
?  0x2e112002 GEM channel loss (LCDGi)
?  0x2e112003 ONT signal degradation (SDi)
?  0x2e112004 ONT signal failure (SFi)
?  0x2e112006 ONT frame loss (LOFi)

The poor quality of optical fiber links. ODU problem is usually due to the unreasonable design, construction, optical device selection in the optical path of larger reflection and bigger attenuation.
?   When a single or partial MA5616 is frequently online and offline, it may be the problem of branching optical fiber line and optical device.
?  When all the MA5616 under the PON port are frequently online and offline, it may be the problem of the main fiber line and optical devices.
MA5616 A single or part of the MA5616 is frequently online and offline. ? There is an abnormal MA5616, to interference other MA5616 can’t work properly.

? MA5616 repeated restart.



For the convenient of fault reporting, please save the execution result of all positioning operation and troubleshooting operation. 

This section relates to parameters information of optical module is CLASS B+, CLASS C+ and CLASS B+ are slightly different, please note that when you reference.


Operation steps

1. When appear “ONU is frequently online and offline”, using display ont info command to check Last down cause of MA5616. Check if MA5680T appears the following alarm:

Fault  coverage Related alarm
ODN ODN related alarm, for example:

? GEM 0x2e112002 channel loss (LCDGi)

? HG8646M 0x2e112003 signal degradation (SDi)

? HG8546M 0x2e112004 signal failure (SFi)

? HG8546M 0x2e112006 frame loss (LOFi)

? 0x2e11a001 main fiber broken or OLT detection is less than expected optical signal (LOS)
? 0x2e112007 branch fiber is broken or OLT is not detected by expected optical signal of HG8546M(LOSi/LOBi)

MA5616 ? Under 0x2e314021 port, existing illegal invasion of abnormal HG8546M
? The 0x2e314022 HG8546M is abnormal

Huawei ONT.jpg

2. To deal with the MA5680T problem, if you exclude the MA5680T problem, but MA5616 still can’t work properly.

Probably Reason Judgment Basis Handing Method
PON port fault Meet one of the following two conditions, you can determine the reason for this.
?  Using display port state command to check the state of the port, if there are abnormal project, please focus on inspection whether the optical module state (state Laser) is normal and whether TX power is in the normal range (1.5dBm ~ 5.0dBm).
? After transferring the business to other ports, MA5616 can work properly.
Replacing optical module or board
Board or slot fault All MA5616 under this board is frequently online and offline. First replace the board slot, if the faulty still existing, replace the board.


3. To deal with ODN problem, if you exclude the problem of ODU, but MA5616 still can’t work properly.

Probably Reason Judgment Basis Handing Method
Optical fiber connector port is dirty.
The dirty fiber connector port will lead to excessive attenuation, abnormal reflection and so on.
0. Using OTDR measurement and branch of trunk fiber optical fiber, there is abnormal reflection and loss.
1. On the spot using the “fiber end face detector” to inspect the port of the optical fiber connector, and find that the port is dirty.
Clean connector port. Cleaning method: please refer to the “clean optical fiber interface”.
There is a big bend in the optical fiber.
Bending radius is too small, it will lead to excessive attenuation.
2.Using OTDR measurement and branch of trunk fiber optical fiber, there is abnormal loss point.
3. On site inspection found that there is a large bending optical fiber.
Finishing optical fiber.

Connection is not close or different types of fiber optic connectors.


Connection of the connection is not close or different types of fiber optic connectors will lead to greater attenuation and reflection.

4.Using OTDR measurement and branch of trunk fiber optical fiber, there is abnormal loss point.
5.On site inspection found that the interface connection is not tight or the presence of PC (blue) connectors and APC (green) joints of the case.
?  If the connection is not tight, reconnect the fiber, to ensure that the connection is tight.
?  If there are different types of optical fiber interfaces, it is needed to re-manufacture the optical fiber interface or the replacement of the optical splitter and other related equipment.


If you need to open CATV business, it is recommended only use APC (green) connectors.

Having used the multi-mode optical fiber.
Multi-mode fiber can lead to the fast attenuation of optical signal, and the return loss becomes large.
0. Using OTDR to measure the main optical fiber and the branch fiber, the optical signal attenuation in the optical fiber is very big.
1. On site inspection of optical path, there are multi-mode fiber. Multi- mode optical fibers can be identified from the physical characteristics of color and other physical characteristics.
Replacement of multi-mode optical fiber as a single mode optical fiber.
Optical splitter fault or connector port is dirty. Optical power meter is used to measure the input light power and output optical power, and the attenuation is larger than the theoretical value.
OTDR can not penetrate the splitter to measure, so the optical splitter OTDR problems that cannot be used for positioning.
Replace the fault splitter  or clean the optical splitter port.
ODN planning is not reasonable.
State:?  The split ratio of the ODN link is not determined by the number of MA5616 connections,?  Once there is brightness decay, the split ratio should be calculated.

The difference between the optical power of the two adjacent MA5616 received by the MA5680T cannot be greater than 15dB.

Do not meet the requirements of ODN link planning and GPON Class B+ standard:
?  There are three optical levels.
?  ODN network coverage significantly exceeded  20km.
?  The standard of the exceeded splitter ratio, for example: The maximum split ratio of supporting by a board is 1:64, if split ratio of first level is 1:8, second level is 1:16, and the actual split ratio is 1:128, it is beyond the specifications.
?  A two optical path of the luminous attenuation is more than 15dB.
Optimize ODN network to meet the requirements and specifications of HUAWEI ODN construction.


4. To deal with ODN problem, if you exclude the problem of ODU, but ONU still can’t work properly.


Probably Reason Judgment Basis Handing Method
There are abnormal MA5616, interfering with other MA5616 cannot work properly.
When there are abnormal MA5616, which can’t be online normally may be normal, on the contrary, the MA5616 which can be online normally may be failure.

Meet one of the following conditions, you can determine the reason for this.
? There is an illegal alarm reported at MA5680T 0x2e314022 port.
? The 0x2e314022 appeared in the side of MA5680T is the abnormal HG8546M alarm.
? The optical fiber of PON MA5680T port is directly connected to the optical power meter to measure, as long as the optical power meter has the reading, which shows that there is a MA5616 constant or random luminescence.


Measurement of optical power can lead to business interruption, it is recommended only when the PON port does not have a business use, such as the start time.

For FTTH network, can refer to check the abnormal HG8546M to check whether exists abnormal HG8546M under the MA5680T PON port.


Replace the abnormal MA5616.
For FTTH+ scene, need to judge whether the abnormal HG8546M plug in the MA5658 plug box.
? Yes: Replace MA5658 box.
? No: Replace HG8546M.
Restart ONU repeatedly Check whether the MA5616 is due to the fault or the power supply voltage is not stable and repeatedly restart. Replace MA5616 or ensure the power supply is normal


From the whole passage, we’ve learnt the possible reasons and solutions to handle MA5616 recovery failure when optical attenuation is too large. If need more assistance, please email to

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