How to Diagnose Optical Fiber Faults


Optical fiber access stands out for its unique bandwidth advantage among many Internet access methods. As a fast channel in the era of information development, it has become an ideal choice for many network operators. Choosing the networking scheme of optical fiber access is also the best networking scheme in broadband applications. With the increase of access points, various fiber failures have also occurred.



The fiber fault is judged as follows:

Fiber failure 1: Power light does not light up


electricity failure

Optical fiber failure 2: Link light does not light up


The fault may be as follows:

a) Check whether the fiber optic line is broken

b) Check whether the loss of the optical fiber line is too large and exceeds the receiving range of the equipment

c) Check whether the optical fiber interface is connected correctly, the local TX is connected with the remote RX, and the remote TX is connected with the local RX.

d) Check whether the optical fiber connector is well inserted into the device interface, whether the jumper type matches the device interface, whether the device type matches the optical fiber, and whether the device transmission length matches the distance.


Optical fiber failure 3: Circuit Link light does not light up

The fault may be as follows:

a) Check if the network cable is broken

b) Check whether the connection type matches: the network card and routers and other devices use crossover cables, and switches, hubs and other devices use straight-through cables.

c) Check whether the device transmission rate matches

ftth cable

Fiber failure 4: Serious network packet loss

Possible failures are as follows:

1) The electrical port of the transceiver does not match the interface of the network device, or the duplex mode of the device interface at both ends.

2) There is a problem with the twisted pair cable and the RJ-45 head, check it

3) Optical fiber connection problem, whether the jumper is aligned with the device interface, whether the pigtail matches the jumper and the coupler type, etc.


Optical fiber fault 5: After the optical fiber transceiver is connected, the two ends cannot communicate

1) The optical fibers are reversed, and the optical fibers connected to TX and RX are reversed

2) The connection between the RJ45 interface and the external device is incorrect (pay attention to the straight-through and splicing)


The optical fiber interface (ceramic ferrule) does not match. This fault is mainly reflected in the 100M transceiver with optoelectronic mutual control function. For example, if the pigtail of the APC ferrule is connected to the transceiver of the PC ferrule, it will not be able to communicate normally. The optoelectronic mutual control transceiver has no effect.


Fiber failure 6: On and off phenomenon

1) It may be that the attenuation of the optical path is too large. At this time, an optical power meter can be used to measure the optical power of the receiving end. If it is near the receiving sensitivity range, it can be basically judged as an optical path failure within the range of 1-2dB.


2) It may be that the switch connected to the transceiver is faulty. At this time, replace the switch with a PC, that is, the two transceivers are directly connected to the PC, and the two ends are pinged.


3) It may be the failure of the transceiver. At this time, you can connect both ends of the transceiver to the PC (not through the switch). After the two ends have no problem with PING, transfer a large file (100M) or more from one end to the other, and observe it. If the speed is very slow (files below 200M are transmitted for more than 15 minutes), it can be basically judged that the transceiver is faulty.


Optical fiber failure 7: After a period of communication, the machine crashes, that is, it cannot communicate, and it returns to normal after restarting

This phenomenon is generally caused by the switch. The switch will perform CRC error detection and length check on all the received data. The packets with errors will be discarded, and the correct packets will be forwarded. However, some erroneous packets in this process cannot be detected in CRC error detection and length verification. Such packets will not be sent or discarded during the forwarding process, and they will accumulate in the dynamic buffer. (buffer), it can never be sent out. When the buffer is full, it will cause the switch to crash. Because restarting the transceiver or restarting the switch can make the communication return to normal at this time, users usually think that the problem is the transceiver.


Fiber Failure 8: Transceiver Test Methods

If you find a problem with the transceiver connection, please test as follows to find out the cause of the failure


a) Proximal testing:

If the computers at both ends can PING, it proves that there is no problem with the optical transceiver. If the near-end test cannot communicate, it can be judged that the optical transceiver is faulty.


b) Remote test:

The computers at both ends are connected to PING. If the PING fails, you must check whether the optical path connection is normal and whether the transmit and receive power of the optical fiber transceiver is within the allowable range. If you can PING, it proves that the optical path connection is normal. It can be judged that the fault lies in the switch.


c) Remote test to determine the fault point:

First connect one end to the switch, and both ends to PING, if there is no fault, it can be judged as the fault of the other switch


Troubleshooting fiber optics is a complex process. After receiving the customer's repair call, we must first understand the phenomenon of the failure from them, so as to roughly determine the cause of the failure, and further determine the failure point with the help of test equipment, and finally solve the failure for the customer. This is the general process of failure resolution.


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