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Question Slow Fibre Media Converters?

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technomagus

Nov 21, 2023
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I'm experimenting with galvanically isolating part of my house LAN using a pair of TP-Link fibre media converters (MC210CS) back to back, connected to a local Netgear gigabit switch at the isolated end and the main Netgear gigabit switch upstream. The FMCs are connected using an SC OS2 Single Mode Duplex 9/125 fibre patch. The problem is that, as soon as I put these into circuit, the speed from which the computer on the isolated section can access either the rest of the house or the wider internet drops from a reliable 900-1000Mb/s to 60-70Mb/s (upload or download).

Given that the FMCs should be operating duplex at a straight gigabit, I'd expect very little slowdown from the conversion process. Any ideas/suggestions?

thanks…
 
I assume the distance is rather short if you are running the connection inside your house.

Why are you using single mode adapters. Is it something you just happen to have laying around.

I would first check the common issue like one of the ethernet connection between the media converter and your switches is actually running at 100mbps and not 1gbit. You could have a bad ethernet cable.

Another thing that might be your issue is you are blinding your media converters. The lasers in single mode devices are very strong designed to send the distance over very long distances like 20km. When short cables are used the light is so bright the receiver has troubles. You can actually damage the receivers in some cases. What is commonly done is people use a mulitimode cable instead of single mode. This intentionally causes some signal loss. You can also get attenuates that will reduce the signal levels.
 
technomagus said:
I'm experimenting with galvanically isolating part of my house LAN using a pair of TP-Link fibre media converters (MC210CS) back to back, connected to a local Netgear gigabit switch at the isolated end and the main Netgear gigabit switch upstream. The FMCs are connected using an SC OS2 Single Mode Duplex 9/125 fibre patch. The problem is that, as soon as I put these into circuit, the speed from which the computer on the isolated section can access either the rest of the house or the wider internet drops from a reliable 900-1000Mb/s to 60-70Mb/s (upload or download).

Given that the FMCs should be operating duplex at a straight gigabit, I'd expect very little slowdown from the conversion process. Any ideas/suggestions?

thanks…
Click to expand...
Single mode fiber on VERY short connections could be overloading.
 
bill001g said:
I assume the distance is rather short if you are running the connection inside your house.

Why are you using single mode adapters. Is it something you just happen to have laying around.

I would first check the common issue like one of the ethernet connection between the media converter and your switches is actually running at 100mbps and not 1gbit. You could have a bad ethernet cable.

Another thing that might be your issue is you are blinding your media converters. The lasers in single mode devices are very strong designed to send the distance over very long distances like 20km. When short cables are used the light is so bright the receiver has troubles. You can actually damage the receivers in some cases. What is commonly done is people use a mulitimode cable instead of single mode. This intentionally causes some signal loss. You can also get attenuates that will reduce the signal levels.
Click to expand...
Correct: just running just over a 1.5m patch. Single mode as higher bandwidth and all the usual reasons for not using multimode any more - like most FMCs, the TP-Links are single mode. No issue with ethernet connection as using the same cables, just moving the patch from the FMC loop directly to the switch. Brightness should not be an issue because standards. All I can imagine is that I may have a dodgy patch cable, but that too is less than likely because of the binary nature of fibre connections - you don't usually get degraded b/w. Mystery continues…
 
technomagus said:
Correct: just running just over a 1.5m patch. Single mode as higher bandwidth and all the usual reasons for not using multimode any more - like most FMCs, the TP-Links are single mode. No issue with ethernet connection as using the same cables, just moving the patch from the FMC loop directly to the switch. Brightness should not be an issue because standards. All I can imagine is that I may have a dodgy patch cable, but that too is less than likely because of the binary nature of fibre connections - you don't usually get degraded b/w. Mystery continues…
Click to expand...
There is NO (ZERO) benefit for single mode at 1.5m. And I would say it is probably is overloading. If you must use single mode get some of these for each end -- https://www.amazon.com/Fiber-Attenuator-Singlemode-Fixed-Male-Female/dp/B0BZZLH653?th=1

Do you have a single mode (9/125) patch cable ?
 
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kanewolf said:
There is NO (ZERO) benefit for single mode at 1.5m. And I would say it is probably is overloading. If you must use single mode get some of these for each end -- https://www.amazon.com/Fiber-Attenuator-Singlemode-Fixed-Male-Female/dp/B0BZZLH653?th=1

Do you have a single mode (9/125) patch cable ?
Click to expand...
Correct, but it's much easier to get single mode devices. Interesting that it may be overloading, and i'll try a pair of attenuators - presumably 5dB would do the trick and I'm assuming that I'd just need a pair , one on each TX port? Slight conceptual difficulty as we use short single mode fibre patch cables in our WAN switches without issue and - obviously - in the FMCs in each house from the WAN feed. This is the first time I've tried just a short patch within a property, so I don't see why it would be overloading
 
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technomagus said:
Correct, but it's much easier to get single mode devices. Interesting that it may be overloading, and i'll try a pair of attenuators - presumably 5dB would do the trick and I'm assuming that I'd just need a pair , one on each TX port? Slight conceptual difficulty as we use short single mode fibre patch cables in our WAN switches without issue and - obviously - in the FMCs in each house from the WAN feed. This is the first time I've tried just a short patch within a property, so I don't see why it would be overloading
Click to expand...
There is no way to know how tolerant the HW in a media converter is.
 
bill001g said:
Note can you try a actual ethernet patch cable just to be sure it is really something with the media converters or the fiber.
Click to expand...
First thing I tried - using the same Ethernet patch cable that was connected to the FMC - immediately jumped to 900Mb/s+ both ways, so that's fairly definitive
 
bill001g said:
If you have a multimode fiber laying around you can try that. 1310 nm can go 300 meters when running at 10gbit on mulitmode fiber so it will not affect your performance.
Click to expand...
Unfortunately none around - all our stuff (we have a community ISP) is single mode and LC - I had to buy an SC patch cable for the FMCs. Attenuators should arrive tomorrow, so will give those a try.
 
Well, that didn't work: attentuators made no difference whatsoever. Nor did moving the entire sub system to another part of the LAN. Only thing left to try is a new patch cable, before deciding that at least one of the FMCs is faulty
 
I really hated media converters. They were so simple and should have just worked. Problem is there was no ability to log in and see simple stuff like what the port speed negotiated. Years ago they really liked to run at 100mbps/half duplex.

I though you had already tried new ethernet cables. The ethernet part tends to be the most common source of issues. I assume you are using quality cables but just to be sure you want pure copper cables with wire size 22-24. There are massive amounts of those fake flat cables sold on amazon.
 
Yep, and i use proper (and shielded) Ethernet patch cables - same as I use on our enterprise gear, so no issue there. I also tried repatching the same cables past the FMCs and it was working just fine. What I was referring to was the fibre patch cable, not the ethernet one
 
Can you tell on your switches if they think the ports are running 1gbit.

Generally your slowness almost has to be packet loss. It would be nice to know which link it was on. Maybe your switches will show packet error counts but if the loss is in the media converters they will not tell you.
 
bill001g said:
Can you tell on your switches if they think the ports are running 1gbit.

Generally your slowness almost has to be packet loss. It would be nice to know which link it was on. Maybe your switches will show packet error counts but if the loss is in the media converters they will not tell you.
Click to expand...
Indeed it was - but it's turned out not to be the fibre side of things, but the Ethernet patch cable I was using at the LAN (cf device) end. I'd used a patch cable that I knew to be working, tested it, then installed it, so thought that was working. But not. Just replaced it with a longer drop cable (all STP Duronic) and it's working fine. Argh etc…
 
It would be nice if ethernet cables would just stop working completely when they get out of spec. Some equipment is just more tolerant of a bad cable....that is what allows them to sell all that garbage on amazon if it didn't work at all people would get amazon to ban them.

All it takes is for the metal to expand and contract enough times in one of the cable ends to slightly loosen the connection.

Fiber it better but all it takes is a finger print on the end of the fiber to mess that up too.
 
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