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GS748T sfp port issue

Liamcatt
Aspirant

GS748T sfp port issue

Hi

We have recently had a fibre link installed between two buildings and I am trying to connect them up however I am having issues with the switches

Both are GS748T, and I am plugging the SFP into 48 with nothing plugged in the copper side of the combo port however I get no light on the switch to acknowledge that the sfp is even plugged in on both switches

I have tried 2 lots of different sfps (HP and Ubiquiti)

Any other suggestions or ideas?

Cheers
Model: GS748T|48-port Gigabit Smart Switch
Message 1 of 6

Accepted Solutions
Hopchen
Prodigy

Re: GS748T sfp port issue

Hi,

There can be a few reasons for the fibre connection not working. I have listed 3 common ones below.

1. How far are your buildings apart and what type of fibre are you using (multi-mode or single-mode)? Multi-mode is used for short distances and is the "cheaper" form of fibre modules. Typically, the max distance for multi-mode is 500m (but that can vary). Single-mode modules are more expensive, but have much greater greater range. Often 10-20 KMs. You need to make sure that you use Single-mode fibre modules if your buildings are far apart and you must make sure that you use the same type of module (single/multi-mode) in each end. Look at the manufacturer datasheet for those modules. Are you using the same module type in both ends and are you OK for distance?  

2. Have you checked the fibre polarity? You need to make sure that transmit in one end, goes to receive in the other end - and vice versa. Else it won't work. This is important! Try to swap the transmit with receive, in one end.
Like this: http://community.fs.com/blog/wp-content/uploads/2016/06/polarity.jpg

3. Even though fibre is a standard, sometimes certain modules won't work with certain switches. It is just hardware compatibility. This is why Netgear lists official compatible modules in the datasheet, for each switch. That being said, it often will work with different vendor modules, but not always! See here, under the "Modules" section:
http://www.downloads.netgear.com/files/GDC/GS748Tv1/GS748T_ds_03Feb05.pdf

NETGEAR AGM731F (multi-mode)
NETGEAR AGM732F (single-mode)


Cheers

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Message 2 of 6

All Replies
Hopchen
Prodigy

Re: GS748T sfp port issue

Hi,

There can be a few reasons for the fibre connection not working. I have listed 3 common ones below.

1. How far are your buildings apart and what type of fibre are you using (multi-mode or single-mode)? Multi-mode is used for short distances and is the "cheaper" form of fibre modules. Typically, the max distance for multi-mode is 500m (but that can vary). Single-mode modules are more expensive, but have much greater greater range. Often 10-20 KMs. You need to make sure that you use Single-mode fibre modules if your buildings are far apart and you must make sure that you use the same type of module (single/multi-mode) in each end. Look at the manufacturer datasheet for those modules. Are you using the same module type in both ends and are you OK for distance?  

2. Have you checked the fibre polarity? You need to make sure that transmit in one end, goes to receive in the other end - and vice versa. Else it won't work. This is important! Try to swap the transmit with receive, in one end.
Like this: http://community.fs.com/blog/wp-content/uploads/2016/06/polarity.jpg

3. Even though fibre is a standard, sometimes certain modules won't work with certain switches. It is just hardware compatibility. This is why Netgear lists official compatible modules in the datasheet, for each switch. That being said, it often will work with different vendor modules, but not always! See here, under the "Modules" section:
http://www.downloads.netgear.com/files/GDC/GS748Tv1/GS748T_ds_03Feb05.pdf

NETGEAR AGM731F (multi-mode)
NETGEAR AGM732F (single-mode)


Cheers

Message 2 of 6
Liamcatt
Aspirant

Re: GS748T sfp port issue

Thanks for the quick reply

The distance is less than 500m so shouldn't be an issue there.

Thanks for the diagram, I will give that a try when I can, does the light need to go into light or the no light?
Message 3 of 6
Hopchen
Prodigy

Re: GS748T sfp port issue

Hi,

Yes, you should see some LED activity on the ports once the link is working. Let me know how it goes with swapping the fibre polarity on one end.

I would encourage you to still check the range of the modules you use. It can vary from vendor to vendor. Also, double-check that you are using the same type of module in each end 🙂


Cheers

Message 4 of 6
Liamcatt
Aspirant

Re: GS748T sfp port issue

Should the laser from one end go in to the non-laser on the other side?
Message 5 of 6
Hopchen
Prodigy

Re: GS748T sfp port issue

Hi,

 

Yes, that is correct. The laser is the transmit and thus must connect to the non-laser (receive) on the other module.

 

However, don't look into the laser beam please. Instead just look at the module. It should be clearly indicated on the module which lane is for transmit and which is for receive.

 

 

Thanks

Message 6 of 6
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