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cusna
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Test bandwidth Optic Fiber Vs Cable Cat 6

Wed Dec 08, 2021 7:23 pm

Hi all,
I wanted to run a speed test to understand the difference between various CAT5e CAT6 and Fiber Optic cables.
For the tests I used two RB760iGS using the BTTest Server tool in the first (MK1) and the Bandwidth Test tool in the second.(MK2)
Direction: Both
Protocol: UDP
No autentication
The first test I performed by connecting ETH1 of MK1 with ETH1 of MK2 with a CAT 5e cable 5 meters long and of poor quality and the band is 400/500 Mb
if I replace the cable with one of good quality and category 6 I reach the maximum that can be obtained, that is 900/950 Mb

In the following tests I disconnected the copper cable from the ETH1 sockets of MK1 and MK2 and I inserted two SFPs in the respective ports of MK1 and MK2
I connected the two Mikrotiks via a 1m long fiber optic cable and I tested the speed again using the previous method
The speed reached was never higher than 700/750 Mb that is lower than that with a CAT6 cable, how is this possible?
I changed various SFPs of different brands and also FIBER OPTIC cables but nothing changed the speed was always lower.
Can you give me an explanation for this?
Where am I wrong?
Thanks
 
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mkx
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Re: Test bandwidth Optic Fiber Vs Cable Cat 6

Wed Dec 08, 2021 10:57 pm

When running BT, run CPU profiler. I guess you'll see one of cores running at 100% which means CPU performance is bottleneck, not port performance. When performing bandwidth tests, you should run tests through device being tested, not by device being tested. In your case that would mean connecting two computers, one to each of Mikrotiks, and run iperf test between computers.
 
cusna
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Re: Test bandwidth Optic Fiber Vs Cable Cat 6

Thu Dec 09, 2021 4:26 pm

So you think that the reason for the difference in speed between using the copper cable and the optical fiber is because the mikrotik, when using the optical fiber, has the most busy processor perhaps for the management of SFPs?
 
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mkx
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Re: Test bandwidth Optic Fiber Vs Cable Cat 6

Thu Dec 09, 2021 6:45 pm

Things slightly depend on particular hardware and how certain connections are engineered. For example, in hEX S CPU has two gigabit interconnects from CPU outwards. When SFP port is not used, both interconnects are used by switch chip (which drives all RJ45 ports). When SFP port is used, one of interconnects is dedicated to SFP, the other is used by switch chip. If both interconnects are used for switch chip, there's some magic how the interconnects are used (one might be used by ports which are not part of bridge port group, the other one for the bridged ports). All that means that in certain scenarios, the interconnects might be bottleneck.
And then there's the unknown how CPU actually handles the I/O paths ... if some tasks are bound to one particular CPU core and if there are multiple processes all competing for same CPU core cycles, it's only inevitable that performance drops. Some things are solvable in software, some are on hardware layer.

And then hEX S CPU is not really a beast: MT's official test results indicate that the real-life routing capacity of said device might be somewhere around 380 Mbps.
If you try to bridge RJ45 and SFP ports (swiching/bridging traffic), traffic still passes CPU (when one tests RJ45-RJ45, normally traffic is handled by switch chip without ever bothering CPU) and bridging capacity seems to be somewhere around 700 Mbps. So when one uses SFP port of hEX S, it's extremely hard to get near wirespeed in any use scenario, and the reason is hardware design.

So if you try to compare different options (UTP vs. fibre), you should be using appropriate equipment which doesn't create a bottleneck by itself.
 
cusna
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Re: Test bandwidth Optic Fiber Vs Cable Cat 6

Wed Dec 15, 2021 1:02 pm

Thanks !

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