LOS and PON light status

LOS and PON light status
In care we are subscribed to a broadband provider which has a fiber optic network, most of them offer to their client optical network terminals/units (ONT/ONU) manufactured by ZTE, Huawei, Fiberhome or Luster. In this article we will describe what is the status of LOS, PON and other LED lights on fiber optic terminals.

LOS red light blinking
This light is usually off when everything is working fine, if it’s on (usually it’s red and it’s blinking), that usually indicates a fiber cut which can be, obviously, solved only by the internet service provider. The only check we can do is to make sure the fiber optic cable is not bent in our location.

PON light blinking
This light needs to be on permanently, if it’s off or it blink, that indicates a problem in the ISP network and we need to raise a ticket to them so they fix this issue.

Internet LED light
This shows the WAN connection status and it blinks when internet is working fine.

LAN/GE/FE light
This light shows the link status for the local network, if it’s off then we don’t have link on this port and we need to check the cable between the fiber optic device and our computer. If it’s on, link is fine and it blinks when we have traffic on this interface.

Shows the wireless network status, if it blinks then traffic is done on this network.

CATV light
This shows the TV connection status, in case we also have television via this equipment. If light is off, television will not work.

TEL/Phone light
This one shows the phone landline status, if it’s off, then phone is not working, if it’s on then phone should be fine. If it blinks, landline is currently in use.

Power light
As you suspect, this needs to be always on as long as the device is connected to a power source and it’s turned on. If light is off but the device is turned on, then we have a power issue (either change the power outlet or the power cable).

WPS light
This is on only when we pushed WPS button and we’re using this option. Else, it stays off.

LOS and PON light status

Some of the most used fiber optic terminals are: ZTE (F660, F660RV1, F620, F625, F618, F668, F680, F663, ) and Huawei (Echolife EG8247W, HG8121H, HG8245H, HG8247H, HG865), Fiberhome or Luster. What is the device model you received for the fiber optic network?

Basically, these are the most important light indicators for fiber optic terminals, if you have any problem related to this subject or need additional info, please leave a comment below and we will try to support.


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  1. Hi I am using Airtel X stream fiber and the PON which is green usually starts blinking green rapidly and i get disconnected from the internet .It happens usually for 6-7 times a day.Can u please tell me what causes this and give me any solution?

    • Hi Zayed,
      Sorry for the delay.
      It may happen that the ONT disconnects from the provider OLT, I suggest open a complaint to your provider in order to check this, in case you still have this issue.

  2. I am using F620 model the PON light is not glowing. I have BSNL Fiber net connection. Kindly help to sort this issue. If I use a different modem instead of ZTE then PON is glowing and able to connect to network.

    • Is the ZTE F620 the device your ISP provided? I’m asking because it may happen that your operator doesn’t allow you to connect using other GPON devices.