Troubleshooting Instruction of SFP/Media Converter

User Application Requirement
Güncellendi11-11-2019 09:37:34 AM 185033
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The SFP/Media Converter are designed for easy use for optical fiber transmission. When the connection does not work as expected after we set it up according to the Installation Guide, we need to do some troubleshooting. The checking include but not limited to the following three aspects:

  1. Basic checking: LED status; the suitable fiber/Ethernet cable; the wave length and the mode (multi/single); the speed, and etc.
  2. Connection checking: the matching of the Rx & Tx; the red laser of the multi-mode devices.
  3. Hardware switches: the mode (Auto/Manual) of the Media Converter; the LFP function, and etc.


Application Scenario

With our TP-Link fiber products, we have the following three kinds of application scenarios generally:

1. SFP <----> SFP

2. SFP <----> Media Converter

3. Media Converter <----> Media Converter


Troubleshooting Instruction


1. In application scenario 1, plug the suitable SFP modules into the SFP slots and then connect them with the proper fiber, then the connection should be OK.

 Q1: Why the LED of the SFP slot isn’t on after plugging the SFP module?

 The status of the LED has no any change when we plug the SFP module only. Only when all the connection is OK can the ports’ LED lights go on.


 Q2: How can I tell the RX & TX port of the SFP module?

 On the SFP module, you can see two triangles as is noted in the picture below, the pole towards outside means Tx (Transmit) port while the pole towards inside means Rx (Receive) port. When we connect  the SFPs,we need to make sure the Tx and Rx are matched on both sides, which means Tx <--> Rx, Rx <--> Tx.


 Q3: How can I judge the SFP module is working with the switch?

 For multi-mode SFP module, since the wave length of the multi-mode in the range of visible light, we can see the red laser from the Tx port when we plug the SFP module into the SFP slot. And when we  plug the fiber, we can also see the red laser from the end of the fiber that connected to the Tx port. But for single-module devices, we cannot see such phenomenon because the wave length of the  single-  mode is out of the range of the visible light.


 Q4: What can I do if the LED is off after the connection?

 1)For multi-mode SFP module, we can check the red laser on both sides as we explained above; for single-mode SFP module, you can check by using some professional Fiber-Optical Testers.

  • If there is no red laser from the Tx port of the SFP module when it is plugged into the SFP slot, the SFP module or the SFP slot may be broken, it is advised to change a SFP module or a SFP slot to have a test.
  • If we can see the red laser from the Tx port of the SFP module, but there is no red laser from the end of the fiber that connected to the Tx port, it may be the fault of the fiber, we can try another fiber.                                                                                                                       

 2)For both multi-mode and single mode SFP module, we need to check the following points as well:

  • Check if the Tx and Rx are matched as well explained above.
  • Check if the size (9/125um, etc), mode (single/multi), length of the fiber meet the requirement of the SFP module.
  • Check if the speed of the SFP port is matched with the SFP module. For example, the Gigabit SFP module can only work with 1000Mbps SFP port.


2. In application scenario 2, connect the Ethernet port to the switch’s port or other Ethernet devices with the Ethernet cable, and then connect the fiber port to the SFP module or other fiber devices    with the proper fiber.

Q1: What can I do if the TP LINK is not on then the Ethernet port is connected?

When the Media Converter’s Ethernet port is connected, the TP LINK LED light will go on, as shown in the picture below. Here we take MC210CS for example.


If the TP LINK port is still off when Ethernet port is connected, we need to check:

  • If the speed of the Ethernet ports of the Media Converter and the device that it connects to matches. For Gigabit Ethernet Media Converter who only supports 1000BASE-T, it can only work with 1000BASE-T Ethernet port; For other Gigabit Ethernet Media Converter who supports 10/100/1000Base-TX, it's port support auto-negotiation, so it can work with 10/100/1000Base-TX for port and negotiate the speed and duplex automatically. And for Fast Ethernet Media Converter, similarly, its 10/100Base-TX port supports auto-negotiation which means it can work with 10/100Base-TX port and negotiate the speed and duplex automatically.

  • For Fast Ethernet Media Converter, we need to make sure the LFP function is off. For more information about LFP, please refer to Q5.
  • We should use Cat5 or above cable and length should be not longer than 100m.
  • It is advised to change a cable or a port to have a test. 


Q2: What can I do if the TP-Link FX light is not on after the fiber ports are connected?

After FX ports are also connected, the FX LINK LED will go on as shown in the picture below, and the TP RX light will blink when there is data transmission.

The troubleshooting in this part is the same as the application scenario 1, and you can refer to the Q3&Q4 in the application scenario 1 for help.


Q3: what is the use of the hardware switches on the Media Converter?

On the back plane of the Media Converter, there are some hardware switches. For Gigabit Ethernet Media Converter, it has only an Auto/Force switch; and for Fast Ethernet Media Converter, it has more complex switches as shown in the pictures below:


Gigabit Ethernet Media Converter                    

For Gigabit Ethernet Media Converter:

  • Force: the FX port works at force mode
  • AUTO: the FX port works as auto mode

Fast Ethernet Media Converter

For Fast Ethernet Media Converter:

  • TP_AUTO: the TP port works at Auto Negotiate Mode
  • TP_DIS: the TP port works at Manual Mode
  • TP_100M: the TP port works at 100Mbps
  • TP_10M: the TP port works at 10Mbps
  • TP_FDX: the TP port works at full duplex mode
  • TP_HDX: the TP port works at half duplex mode
  • LFP_OFF: the LFP function is off
  • LFP_ON: the LFP function is on.


Q4: how do I choose the mode of the Force or Auto?

When a Media Converter is connected to a SFP module or other fiber devices, it is Auto mode while the two Media Converter connect back to back, it is advised to use Force mode, but in troubleshooting, we can try both.

Note: the changed mode of the Media Converter takes effect after the power cycle.


Q5: what is the LFP?

The Fast Ethernet Media Converter has a function called Link Fault Pass Through,. For more information about the Link Fault Pass Through Function, please refer to the User Guide for help.


3. For application scenario 3, it has almost the same phenomenon of the LED status and troubleshooting as explained above, please refer to the steps in the application scenario 1 and 2 for help.



  1. For Media Converter, we should power on it after the connection is set up.
  2. For SFP module such as TL-SM321A/B that supports WDM (Wavelength Division Multiplex), they must work together.
  3. For TL-MC220L, it has a 1000BASE-T port and a 1000BASE-TX SFP port, its wave length, transmission distance and mode (single/multi) depend on the SFP module that is plugged into.


FAQ: Can TP-Link SFP/Media Converter/Switches work with other vendors’ devices?

  1. All the TP-Link SFP, Media Converter, Switches can work together.
  2. Our SFP/Media Converter/Switches are in line with the industry standard and have no any detection code or any other detection mechanism, but some other vendors may limit their models to only cooperate with their own devices. If you want to use our SFP/Media Converter/Switches with some other vendors' devices together, please contact with their supporter to check if there are any detection design or can cooperate with other vendors' switch.

Get to know more details of each function and configuration please go to Download Center to download the manual of your product.


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