Causes and Solutions of Common Faults in Optical Fiber Transceivers

- Sep 18, 2019-

According to the problems of daily maintenance and users, I hope to bring some help to the maintenance staff, to judge the reasons according to the fault phenomena, to find the fault point, and to "prescribe the remedy to the case".

1. When RJ45 port of transceiver is connected with other devices, what kind of connection is used?

Reasons: RJ45 port of transceiver connects to PC network card (DTE data terminal equipment) using cross twisted pair, HUB or SWITCH (DCE data communication equipment) using parallel lines.

2. What is the reason why the TxLink lamp is not on?

Answer: 1 Misconnected twisted pair

2. Poor contact between crystal head of twisted pair and equipment, or quality problems of twisted pair itself

3 The equipment is not connected properly.

3. What's the reason why TxLink lights are always on when the optical fibers are connected normally without flickering?


1. The fault is usually caused by too long transmission distance.

Compatibility with Network Card (Connecting with PC)

4. What is the reason why the Fxlink lamp is not on?


1. The connection of optical fiber is wrong. The correct connection method is TX-RX, RX-TX or the mode of optical fiber is wrong.

2. The transmission distance is too long or the intermediate loss is too large to exceed the nominal loss of the product. The solution is to take measures to reduce the intermediate loss or replace it with a longer transmission distance.

3. The operating temperature of optical transceiver is too high.

5. What is the reason why the Fxlink lamp does not flicker but always lights up after the normal connection of optical fibers?

Cause: The fault is usually caused by too long transmission distance or too large intermediate loss, which exceeds the nominal loss of the product. The solution is to minimize the intermediate loss or replace it with a transmitter with longer transmission distance.

6. What if the five lights are on or the indicator is normal but cannot be transmitted? Reason: Generally, the power supply can be turned off and restarted to normal.


7. What is the ambient temperature of the transceiver?

Cause: Fiber module is greatly affected by ambient temperature. Although it has built-in automatic gain circuit, when the temperature exceeds a certain range, the transmitted optical power of the optical module will be affected and decreased, which will weaken the quality of the optical network signal, increase the packet loss rate and even disconnect the optical link. (General optical module works.) Temperature up to 70 C)

8. How compatible is the protocol with external equipment?

Reasons: Like 10/100M optical transceiver and 10/100M switch, there are certain restrictions on frame length, generally no more than 1522B or 1536B. When the switch connected at the local end supports some special protocols (such as Ciss ISL), the packet overhead increases (Ciss ISL's packet overhead is 30Bytes), thus exceeding the frame of optical transceiver. The long upper limit is discarded, which reflects the high or no packet loss rate. At this time, it is necessary to adjust the MTU of the terminal equipment (MTU maximum sending unit, the cost of IP packet is 18 bytes, MTU is 1500 bytes). Now there is an internal network protocol in the high-end communication equipment manufacturer, which will aggravate the opening of IP packet by means of separate packet. If the data is 1500 bytes, the size of IP packet after IP packet will exceed 18 and be discarded, which satisfies the limitation of frame length by network devices. The 1522 byte package is added VLAN tag.

9. Why do some cards fail to work properly after the chassis has been working normally for a period of time?

Reason: In the early stage, the power supply of chassis was relay mode. The main problems are insufficient power margin and high line loss. After a period of normal operation of the chassis, some cards can not work properly. When part of the plug-in card is pulled out, the remaining cards work normally. After long-term operation of the chassis, the oxidation of the joints results in greater joint loss. This kind of power supply falls beyond the prescribed requirements, which may cause the abnormal phenomenon of the chassis plug-in card. High-power Schottky diode is used to isolate and protect the power switching of the chassis. The form of the joint is improved to reduce the power drop caused by the control circuit and the joint. At the same time, the power redundancy of power supply should be increased to make the backup power supply convenient, safe and more suitable for the requirement of long-term uninterrupted work.

10. What are the functions of providing link alarms on transceivers?

Reasons: Transceivers have link loss function. When a certain optical fiber drops off, it will automatically feed back to the switch (that is, the indicator lights on the switch will also be extinguished), and if the switch has network management, it will immediately reflect to the switch's network management software.

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